Global change threatens mountainous plant communities,causing habitat displacement.Phylogenetic studies reveal evolutionary and ecological processes in community assembly.We examined taxonomic and phylogenetic diversi...Global change threatens mountainous plant communities,causing habitat displacement.Phylogenetic studies reveal evolutionary and ecological processes in community assembly.We examined taxonomic and phylogenetic diversity in Andean Páramos across altitudes.Our hypotheses were that increasing altitude is an environmental filter,as altitude is expected to be a stronger variable than soil depth.The Páramos,alpine vegetation in the Andes,range from 3,000 to 4,700 meters,with our plots spanning 3,200 to 4,100 meters.Sampling was conducted at six altitudinal levels,measuring soil depth,taxonomic,and phylogenetic diversity.Data analysis employed multiple linear regressions and mixed-effects models to assess the effects of soil depth and altitude.We sampled 110 angiosperm species from 70 genera,30 families,and 18 orders.Asterales and Poales were prominent.Species richness generally decreased with altitude but increased at the summit.Soil depth affected species richness and taxonomic diversity,while altitude did not.Phylogenetic diversity increased with soil depth and decreased with altitude.Phylogenetic turnover increased with altitude differences.The hypothesis that increasing altitude intensifies environmental filtering in the altitudeadapted Páramos resulting in lower species richness and more clustered phylogenetic structures,was rejected.Although species richness,Shannon diversity,and Simpson diversity decreased initially with increasing altitude,this trend was not linear because the summit presented intermediate species richness.The hypothesis that altitude is a stronger explanatory variable than soil depth was also rejected.Despite expectations,taxonomic results did not support altitude as an environmental filter,but soil depth.Greater altitude differences increased beta phylogenetic dissimilarity,supporting niche conservatism.展开更多
The rates of soil N mineralization at soil depths of 0-15, 15-30, 30-45 and45-60 cm and moisture regimes were measured at three sand-fixation plantations of Pinus sylvestrisvar. mongolica by laboratory aerobic incubat...The rates of soil N mineralization at soil depths of 0-15, 15-30, 30-45 and45-60 cm and moisture regimes were measured at three sand-fixation plantations of Pinus sylvestrisvar. mongolica by laboratory aerobic incubation method. The results showed that average rates ofsoil net N-mineralization across soil depth varied from 1.06 to 7.52 mg · kg^(-1)·month^(-1) atsoil depths from 0 to 60 cm. Statistical analyses indicated that the effects of different soildepths, moistures and their interactions on net N-mineralization rates were significant (P < 0.05).The net N-mineralization rates significantly decreased with increasing soil depths and at depth 0-15cm accounted for 60.52% of that at depth of 0-60 cm. There was no difference in soil netN-mineralization rates between half and fully-saturated water treatments, however these rates weresubstantially higher than that without water treatment (P < 0.05). The factors influencing Nmineralization process have to be studied further in these semiarid pine ecosystems.展开更多
Partitioning soil respiration into three components is vital to identify CO_2 sink or source and can help us better understand soil carbon dynamics. However, knowledge about the influences of soil depth and the primin...Partitioning soil respiration into three components is vital to identify CO_2 sink or source and can help us better understand soil carbon dynamics. However, knowledge about the influences of soil depth and the priming effect on soil respiration components under field has been limited. Three components of soil respiration（root respiration, rhizomicrobial respiration and basal respiration） in a plantation in the hilly area of the North China were separated by the 13 C natural abundance method. The results showed that the average proportions of rhizomicrobial respiration, root respiration and basal respiration at the 25-65 cm depths were about 14, 23 and 63 %, respectively. Three components of soil respiration varied with soil depth, and root respiration was the main component of soil respiration in deeper soil. The priming effect was obvious for the deep soil respiration, especially at the 40-50 cm depth. Thus, depth and priming effect should be taken into account to increase the accuracy of estimations of soil carbon flux.展开更多
Soil depth generally varies in mountainous regions in rather complex ways.Conventional soil survey methods for evaluating the soil depth in mountainous and hilly regions require a lot of time,effort and consequently r...Soil depth generally varies in mountainous regions in rather complex ways.Conventional soil survey methods for evaluating the soil depth in mountainous and hilly regions require a lot of time,effort and consequently relatively large budget to perform.This study was conducted to explore the relationships between soil depth and topographic attributes in a hilly region in western Iran.For this,one hundred sampling points were selected using randomly stratified methodology,and considering all geomorphic surfaces including summit,shoulder,backslope,footslope and toeslope;and soil depth was actually measured.Eleven primary and secondary topographic attributes were derived from the digital elevation model(DEM) at the study area.The result of multiple linear regression indicated that slope,wetness index,catchment area and sediment transport index,which were included in the model,could explain about 76 % of total variability in soil depth at the selected site.This proposed approach may be applicable to other hilly regions in the semi-arid areas at a larger scale.展开更多
Soil depth is critical for eco-hydrological modeling,carbon storage calculation and land evaluation.However,its spatial variation is poorly understood and rarely mapped.With a limited number of sparse samples,how to p...Soil depth is critical for eco-hydrological modeling,carbon storage calculation and land evaluation.However,its spatial variation is poorly understood and rarely mapped.With a limited number of sparse samples,how to predict soil depth in a large area of complex landscapes is still an issue.This study constructed an ensemble machine learning model,i.e.,quantile regression forest,to quantify the relationship between soil depth and environmental conditions.The model was then combined with a rich set of environmental covariates to predict spatial variation of soil depth and straightforwardly estimate the associated predictive uncertainty in the 140000 km^(2)Heihe River basin of northwestern China.A total of 275 soil depth observation points and 26 covariates were used.The results showed a model predictive accuracy with coefficient of determination(R)of 0.587 and root mean square error(RMSE)of 2.98 cm(square root scale),i.e.,almost 60% of soil depth variation explained.The resulting soil depth map clearly exhibited regional patterns as well as local details.Relatively deep soils occurred in low lying landscape positions such as valley bottoms and plains while shallow soils occurred in high and steep landscape positions such as hillslopes,ridges and terraces.The oases had much deeper soils than outside semi-desert areas,the middle of an alluvial plain had deeper soils than its margins,and the middle of a lacustrine plain had shallower soils than its margins.Large predictive uncertainty mainly occurred in areas with a lack of soil survey points.Both pedogenic and geomorphic processes contributed to the shaping of soil depth pattern of this basin but the latter was dominant.This findings may be applicable to other similar basins in cold and arid regions around the world.展开更多
The combined application of organic fertilizer and chemical fertilizer is an effective measure to increase nutrient content of soil plough layer, which must have a profound impact on the deep soil nutrients, especiall...The combined application of organic fertilizer and chemical fertilizer is an effective measure to increase nutrient content of soil plough layer, which must have a profound impact on the deep soil nutrients, especially the contents of nitrogen forms. The purpose of this study was to explore the characteristics of soil nitrogen forms in plough layer and along depth gradient in different fertilization treatments, so as to evaluate the soil quality in spatial dimension, further provid</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> a theoretical basis for scientific fertilization and improvement of paddy soil fertility. Here, a 34-year field experiment was conducted with three treatments: without any fertilizer (CK), pure chemical fertilizer (NPK) and chemical fertilizer combined with organic fertilizer (NPKM). We analyzed the content of nitrogen forms in 0 - 100 cm soil depth and their ratios to total nitrogen (TN), and discussed the correlation between nitrogen forms contents and pH, CEC. Results showed that, compared with CK, both NPK and NPKM significantly increased the contents of nitrogen forms in topsoil (soil layer of 0 - 20 cm), especially nitrate nitrogen (NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N) content increased by 70% (NPK) and 111% (NPKM), respectively. Although the contents of different nitrogen forms decreased gradually along soil depth gradient, NPKS slowed down the decline rate of TN and alkali-hydrolysable nitrogen (AN) in 0 - 60 cm soil layer, compared to CK. Compared to NPK, NPKM significantly increased the NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N/TN ratio in 0 - 20 cm soil layer, but also decreased the content of </span><span><span></span><span style="font-family:Verdana;">-N in 20 - 40 cm, which was beneficial to reduce the risk of nitrogen leaching caused by nitrate leaching into deep layer. The increase of soil pH in NPKM treatment obviously alleviated the problem of soil acidification caused by long-term application of chemical fertilizer. Correlation analysis showed that there was a significant positive correlation between soil nitrogen forms and cation exchange capacity (CEC), but no significant correlation with soil pH. In conclusion, NPKM ensured the nutrients of soil plough layer (0 - 20 cm), also reduced the risk of nitrogen infiltration and nitrogen loss, thus ensur</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> the fertility of soil profile.展开更多
<span style="white-space:normal;">There has been increased interest in soil organic carbon in recent times because of its role in carbon sequestration. Different parent materials affect soil properties...<span style="white-space:normal;">There has been increased interest in soil organic carbon in recent times because of its role in carbon sequestration. Different parent materials affect soil properties and hence will influence how much carbon is sequestered by soil. The study was conducted in June 2019 to investigate soil carbon stock in forest soils with respect to their parent materials in three States in South-eastern Nigeria. Sampling was aided by the location map of the area and free soil survey method was used to locate sampling points. 0ne profile was dug in each location and described using the Food and Agricultural Organization guideline. A total of twelve soil samples were collected and analyzed for selected properties. Results showed that sand content was significantly higher in soils under coastal plain sands (851.96 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) and was lowest in soils of Imo clay shale (605.60 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;">−1</sup><span style="white-space:normal;">). Clay content was higher in soils of Imo clay shale (277.34 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) and was lowest in coastal plain sand (118.80 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">). Silt and clay had moderate variation in coastal plain sand (>15 ≤ 35%) and high variations in Asu River and Imo clay shale (CV > 35%). The soils studied were generally acidic with values ranging (3.52) in soils formed from coastal plain sand, followed by forest soils of Imo clay shale (3.64) and Asu river group (3.85). Soil organic carbon decreased with increase in soil depth in all soil parent materials studied. Mean values ranged from 6.14 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;"> in soil underlain by coastal plain sand to 10.62 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) in soils of Imo clay shale. Soil carbon sequestered under the three different parent materials ranged from 1575 - 4676.41 (g<span style="white-space:nowrap;">·</span>cm</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>2</sup><span style="white-space:normal;">). Also, soil depth had a notable impact on carbon sequestration with values ranging from 1529.42 - 4374.0541 (g<span style="white-space:nowrap;">·</span>cm</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>2</sup><span style="white-space:normal;">) and the thicker the horizon, the more carbon sequestered. Hence, the study concluded that more carbon is sequestered in the subsurface horizons of the soil pedons than in the epipedons.</span>展开更多
Environmental covariates are the basis of predictive soil mapping.Their selection determines the performance of soil mapping to a great extent,especially in cases where the number of soil samples is limited but soil s...Environmental covariates are the basis of predictive soil mapping.Their selection determines the performance of soil mapping to a great extent,especially in cases where the number of soil samples is limited but soil spatial heterogeneity is high.In this study,we proposed an integrated method to select environmental covariates for predictive soil depth mapping.First,candidate variables that may influence the development of soil depth were selected based on pedogenetic knowledge.Second,three conventional methods(Pearson correlation analysis(PsCA),generalized additive models(GAMs),and Random Forest(RF))were used to generate optimal combinations of environmental covariates.Finally,three optimal combinations were integrated to produce a final combination based on the importance and occurrence frequency of each environmental covariate.We tested this method for soil depth mapping in the upper reaches of the Heihe River Basin in Northwest China.A total of 129 soil sampling sites were collected using a representative sampling strategy,and RF and support vector machine(SVM)models were used to map soil depth.The results showed that compared to the set of environmental covariates selected by the three conventional selection methods,the set of environmental covariates selected by the proposed method achieved higher mapping accuracy.The combination from the proposed method obtained a root mean square error(RMSE)of 11.88 cm,which was 2.25–7.64 cm lower than the other methods,and an R^2 value of 0.76,which was 0.08–0.26 higher than the other methods.The results suggest that our method can be used as an alternative to the conventional methods for soil depth mapping and may also be effective for mapping other soil properties.展开更多
Shallow slope failure is often induced by rainfall infiltration in a soil mantle overlying a less permeable bedrock. Soil depth is an important input parameter in slope stability analysis. This paper provides the spat...Shallow slope failure is often induced by rainfall infiltration in a soil mantle overlying a less permeable bedrock. Soil depth is an important input parameter in slope stability analysis. This paper provides the spatial variation of soil depth and the occurrence of slope failure in Sangun mountains area. The spatial pattern of soil depth was simulated by proses based model using airborne laser survey data (LiDAR data) and Geographic Information System (GIS) function. As a function for soil production, we use in the study area a numerical model developed by Dietrich?et al.?(1995) to predict the local spatial variation of the depth of soil. The soil depth data measured at 20 locations that represent morphological variability are used as a sample data set to test the model results. Furthermore, the soil depth variations are compared to the slope failure distribution in the whole area. Slope failure locations in the study area are identified from interpretation of aerial photographs and field surveys. Fifty-five of slope failures are considered for slope failure hazard analysis. Therefore, the slope failures occur more frequently at soil depth intervals in the ranged from 1.01 m to 1.5 m.展开更多
Forest ecosystems can be characterized by a set of catenas arranged along the slope in mountainous areas as these affect microhabitat features,which in turn influence soil properties.Heretofore,few studies have examin...Forest ecosystems can be characterized by a set of catenas arranged along the slope in mountainous areas as these affect microhabitat features,which in turn influence soil properties.Heretofore,few studies have examined how topographic variables affect soil properties and quality in semiarid regions.This study aimed to provide important insights into how catena position and shape influence soil properties,soil quality,and their interrelationships in a semiarid protected oak forest in western Iran.Basic soil properties were measured in the laboratory.In addition,the soil quality index(SQI)was calculated at different topographic positions along both convex(Λ-shaped)and concave(V-shaped)catenas at two soil depths(0-15 and 15-30 cm).The findings indicated that soil organic carbon and total nitrogen declined in the lower depth in both V-andΛ-shaped catenas and at all catena positions.The lowest porosity was observed in the lower depth at toeslope positions(TS)of both catenas.Substrate-induced respiration(SIR),microbial biomass carbon(MBC),and basal respiration(BR)were higher in the upper depths at TS positions on V-shaped catenas than onΛ-shaped catenas.These biological indices were consistently higher in the upper depths than in the lower depths across all positions of both catenas.SQI had the highest values at TS positions on both catenas and in the upper depths across all positions.Pearson correlations between soil properties indicated that SQI was most strongly and positively correlated with biological properties in both catenas.The nutrient levels,microbial activity,and soil porosity in both catena shapes and at both soil depths displayed a relatively downward trend with increasing elevation from toeslope to summit positions.The results showed that catena topographic sequence shape and position affected most of the soil properties,providing evidence of the important role of topography in creating pedodiversity in oak forest ecosystems.展开更多
The environmental impacts of acid mine drainage(AMD)from open-pit mining are profoundly detrimental,yet knowledge about its effects on paddy soil microbial communities,especially at greater depths,remains limited.In t...The environmental impacts of acid mine drainage(AMD)from open-pit mining are profoundly detrimental,yet knowledge about its effects on paddy soil microbial communities,especially at greater depths,remains limited.In this investigation,we compared soils affected by AMD versus unaffected soil depth profiles in terms of bacterial diversity and community assembly.The profiles in AMD-polluted soils exhibited tight geochemical gradients,characterized by increased acidity,SO_(4)^(2-),NO_(3)^(-),and heavy metal content compared to unpolluted soils.Notably,AMD significantly diminished soil bacterial biodiversity.A depthwise analysis showed distinct microbial stratification,with certain bacteria like Candidatus_Solibacter and Candidatus_Koribacter predominated in polluted soils,while others like Haliangium and Nitrospira were more prevalent in control soils.Interestingly,despite variable soil conditions,predictedmetabolic pathways,particularly those involving carbon,nitrogen,and sulfur,showed relative stability.AMD pollution induced the upregulation of methylcoenzyme M reductase and sulfate reductase genes.Bacterial communities were more responsive to pH and nutrient content rather than heavy metals,with pH and SO_(4)^(2-)being the primary drivers of microbial diversity and distribution.Additionally,pHwas identified as the most significant influence on the predicted methane,sulfur,and nitrogen metabolism.Furthermore,deterministic processes played a more significant role in community assembly of polluted soils,while heterogeneous selection gained importance with increasing depth in control soils.Additionally,microbial co-occurrences,particularly positive interactions,were more prevalent in the polluted soils with reduced network modularity and keystone taxa.These findings offer insights into sustaining microbial diversity in extreme environments.展开更多
The source region of the Yellow River(SRYR),with its semi-humid to semi-arid climate,is crucial for understanding water resource dynamics.Precipitation is key for replenishing surface water and balancing the ecosystem...The source region of the Yellow River(SRYR),with its semi-humid to semi-arid climate,is crucial for understanding water resource dynamics.Precipitation is key for replenishing surface water and balancing the ecosystem’s water cycle.However,the soil moisture response to precipitation across climate zones and soil layers remains poorly understood due to limited long-term data.This study examines the response of soil moisture to precipitation at multiple time scales in the SRYR,using data from Maqu,Mado,Ngoring Lake sites,and the Maqu monitoring network(MMN),along with CN05.1 precipitation and GLEAM v3.8a soil moisture data.Results show that the semi-humid area requires more precipitation to trigger soil moisture responses compared to the semi-arid area in the SRYR.Surface soil at Maqu,MMN,Ngoring Lake,and Mado sites require at least 8.6,8.4,5.2,and 2.84 mm of precipitation,respectively,for effective replenishment.Significant responses to precipitation events were observed in soil layers at 40 cm and above in the semi-humid area,while at 20 cm and above in the semi-arid area.Precipitation volume is the primary factor influencing soil moisture,affecting both the increment and time lag to maximum moisture.Precipitation intensity and pre-rain moisture have no direct effect.In the central SRYR,accumulated precipitation has a greater impact.Root-zone soil moisture has a weaker correlation with precipitation compared to surface soil moisture but persists longer,responding for up to 10 days,while surface soil moisture responds more immediately but only lasts about 5 days.展开更多
Soil organic carbon(SOC):total nitrogen(TN):total phosphorus(TP)(C:N:P)stoichiometry can give important information about biogeochemical cycling in terrestrial ecosystems.The spatial patterns and driving mechanisms of...Soil organic carbon(SOC):total nitrogen(TN):total phosphorus(TP)(C:N:P)stoichiometry can give important information about biogeochemical cycling in terrestrial ecosystems.The spatial patterns and driving mechanisms of soil C:N:P ratios are still poorly understood on the Qinghai-Tibetan Plateau of China.In this study,we therefore combined data of the geography,climate,soil properties,and vegetation characteristics from 319 sites across the plateau to investigate their relationships with the horizontal and vertical patterns of SOC,TN,and TP concentrations and their stoichiometric ratios(C:N and N:P).We observed higher SOC(30.5–46.8 mg g^(-1)),TN(2.4–3.4 mg g^(-1)),C:N(14.7–18.0),and N:P(6.9–8.0)in alpine meadows,forests,and shrublands and higher TP(1.6 mg g^(-1))in croplands.Overall,SOC,TN,TP,C:N,and N:P showed decreasing trends(by 67%,64%,19%,12%,and 54%,respectively)along the whole soil profile(0–100 cm).Soil cation exchange capacity and bulk density were the stronger environmental drivers of SOC and TN.Soil TP showed latitudinal and longitudinal increasing trends in all soil layers.Soil properties explained most of the variations in SOC(67%–90%),TN(67%–87%),C:N(61%–89%),and N:P(64%–85%),with increasing impacts along the soil profile.Geography and climate influenced soil TP directly and indirectly through their impacts on soil properties,with geography being the predominant driver(46%–65%)along the soil profile.The variation in soil C:N was mostly driven by SOC and TN,and the direct and indirect effects of the environmental factors were relatively weak.Geography,climate,soil properties,and vegetation characteristics indirectly impacted soil N:P through their impacts on TN and TP in all the soil layers.Altogether,our findings illuminate the relative contributions of geography,climate,soil properties,and vegetation characteristics to soil C:N and N:P,thus enhancing our understanding of C,N,and P cycling across the Qinghai-Tibetan Plateau.展开更多
The effect of long-term fertilization on soil denitrifying communities was analysed by measuring the abundance and diversity of the nitrous oxide （N2O） reductase gene, nosZ. Soil samples were collected from plots of...The effect of long-term fertilization on soil denitrifying communities was analysed by measuring the abundance and diversity of the nitrous oxide （N2O） reductase gene, nosZ. Soil samples were collected from plots of a long-term fertilization experiment established in 1982 in Suining City, China. The fertilizer treatments were no fertilizer （CK）, three chemical fertilizer （CF） treatments （N, NP, NPK）, manure （M） alone, and manure with chemical fertilizers （NM, NPM, NPKM）. The abundance and diversity of the denitrifying bacteria were assessed by real-time quantitative PCR, terminal restriction fragment length polymorphism （T-RFLP）, and cloning and sequencing of nosZ genes. The diversity and abundance of nosZ-denitrifiers was higher in soil amended with manure and chemical fertilizers （CFM） than in soil amended with CF alone, and the highest in topsoil （0-20 cm）. The nosZ-denitrifier community composition was more complex in CFM soil than in CF soil： Specific species were detected only in the CFM soil. The abundance of nosZ-denitrifier in the NPKM treatment was approximately two times higher than that in the CK, N, and NPK treatments. Most of the cloned nosZ sequences were closely related to nosZ sequences from Bradyrhizobiaceae and Rhodospirillaceae in Alphaproteobacteria. Of the measured abiotic factors, soil organic matter correlated significantly with the abundance （P〈0.01）; available phosphorus correlated significantly with the topsoil community composition （P〈0.01）, whereas soil organic matter correlated significantly with the subsoil （20-90 cm） community composition （P〈0.01）. This study demonstrated that long-term CFM fertilization affected both the abundance and composition of the nosZ-denitrifier community.展开更多
This study was conducted to assess the current stock of soil organic carbon under different agricultural land uses, soil types and soil depths in the Noun plain in western Cameroon. Three sites were selected for the s...This study was conducted to assess the current stock of soil organic carbon under different agricultural land uses, soil types and soil depths in the Noun plain in western Cameroon. Three sites were selected for the study, namely Mangoum, Makeka and Fossang, representative of the three dominant soil types of the noun plain (Andosols, Acrisols and Ferralsols). Three land uses were selected per site including natural vegetation, agroforest and crop field. Soil was sampled at three depths;0 - 20 cm, 20 - 40 cm, and 40 - 60 cm. Analysis of variance showed that soil type did not significantly influence carbon storage, but rather land uses and soil depth. SOCS decreased significantly with depth in all the sites, with an average stock of 66.3 ± 15.8 tC/ha at 0 - 20 cm, compared to an average stock of 33.3 ± 7.4 tC/ha at 40 - 60 cm. SOCS was significantly highest in the natural formation with 57.2 ± 19.7 tC/ha, and lowest in cultivated fields, at 37.7 ± 10.6 tC/ha. Andosols, with their high content of coarse fragments, stored less organic carbon than Ferralsols and Acrisols.展开更多
Analyses of 114 soil samples in Ningbo City show that,in general,there are statistical differences of 137Cs and 40K contents between every layers,the other kinds of natural radionuclides present an increasing tendency...Analyses of 114 soil samples in Ningbo City show that,in general,there are statistical differences of 137Cs and 40K contents between every layers,the other kinds of natural radionuclides present an increasing tendency with depth.When the γ radiation dose rate is estimated by Beck Formula,owing to the effect of those nonuniform distributions is less than 1% and can be ignored.'展开更多
To better understand soil moisture dynamics in the Yangtze River Estuary （YRE） and predict its variation in a simple way, a field monitoring experiment was carried out along the north branch of the Yangtze River, wh...To better understand soil moisture dynamics in the Yangtze River Estuary （YRE） and predict its variation in a simple way, a field monitoring experiment was carried out along the north branch of the Yangtze River, where seawater intrusion was strong and salt-water variation is one of the limiting factors of local agriculture. In present paper, relation between antecedent precipitation index （API） and soil water content is studied, and effects of groundwater depth on soil water content was analyzed. A relatively accurate prediction result of soil water content was reached using a neural network model. The impact analysis result showed that the variation of the API was consistent with soil water content and it displayed significant correlations with soil water content in both 20 and 50 cm soil layer, and higher correlation was observed in the layer of 20 cm. Groundwater impact analysis suggested that soil moisture was affected by the depth of groundwater, and was affected more greatly by groundwater at depth of 50 cm than that at 20 cm layer. By introducing API, groundwater depth and temperature together, a BP artificial network model was established to predict soil water content and an acceptable agreement was achieved. The model can be used for supplementing monitoring data of soil water content and predicting soil water content in shallow groundwater areas, and can provide favorable support for the research of water and salt transport in estuary area.展开更多
The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered ...The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties(the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed.Finally, a sensitivity analysis on the parameters in the formula was performed.展开更多
This paper conducts laboratory tests to investigate detailedly the soil deformation law around the pipeline and its penetration depth under self-gravity. The seabed model is prepared by consolidating saturated soil us...This paper conducts laboratory tests to investigate detailedly the soil deformation law around the pipeline and its penetration depth under self-gravity. The seabed model is prepared by consolidating saturated soil using vacuum pressure technology, and the pipeline models are specifically designed to possess different radii. Based on the experimental results and digital images, the soil deformation process is analyzed and summarized, a kinematic admissible velocity field is given and an upper bound solution of pipeline penetration depth and soil reaction force is derived and proposed in this paper. In order to verify the accuracy of the upper bound solution deduced in this paper,a comparison is made among some published results and the solution suggested in this paper, the comparison results confirm that the upper bound solution and the soil failure mode are reasonable. Finally two empirical formulas are given in this paper to estimate the soil reaction force of seabed and the penetration depth of pipeline. The empirical formulas are in agreement with the upper bound solution derived in this paper, and the conclusion of this paper could provide some theoretical reference for the further study of the interaction between the pipeline and the soil.展开更多
基金the Botany Graduate Program of Universidade Federal de Vicosa - PPGBot-UFV for the infrastructure and scholarshipsprovided by FAPEMIG (FORTIS/PPGBot-UFV, PPM00584-16, APQ-01309-16)+1 种基金CAPES (PROAP and Pr Int/PPGBot-UFV)CNPq (307591/2016-6, 306335/2020-4)
文摘Global change threatens mountainous plant communities,causing habitat displacement.Phylogenetic studies reveal evolutionary and ecological processes in community assembly.We examined taxonomic and phylogenetic diversity in Andean Páramos across altitudes.Our hypotheses were that increasing altitude is an environmental filter,as altitude is expected to be a stronger variable than soil depth.The Páramos,alpine vegetation in the Andes,range from 3,000 to 4,700 meters,with our plots spanning 3,200 to 4,100 meters.Sampling was conducted at six altitudinal levels,measuring soil depth,taxonomic,and phylogenetic diversity.Data analysis employed multiple linear regressions and mixed-effects models to assess the effects of soil depth and altitude.We sampled 110 angiosperm species from 70 genera,30 families,and 18 orders.Asterales and Poales were prominent.Species richness generally decreased with altitude but increased at the summit.Soil depth affected species richness and taxonomic diversity,while altitude did not.Phylogenetic diversity increased with soil depth and decreased with altitude.Phylogenetic turnover increased with altitude differences.The hypothesis that increasing altitude intensifies environmental filtering in the altitudeadapted Páramos resulting in lower species richness and more clustered phylogenetic structures,was rejected.Although species richness,Shannon diversity,and Simpson diversity decreased initially with increasing altitude,this trend was not linear because the summit presented intermediate species richness.The hypothesis that altitude is a stronger explanatory variable than soil depth was also rejected.Despite expectations,taxonomic results did not support altitude as an environmental filter,but soil depth.Greater altitude differences increased beta phylogenetic dissimilarity,supporting niche conservatism.
基金This paper was supported by National Natural Science Foundation of China (30471377), the Chinese Academy of Sciences (Knowledge Innovation Project KZCX3-SW-418), and the Institute of Applied Ecology of Chinese Academy of Sciences (SLYQY0409).
文摘The rates of soil N mineralization at soil depths of 0-15, 15-30, 30-45 and45-60 cm and moisture regimes were measured at three sand-fixation plantations of Pinus sylvestrisvar. mongolica by laboratory aerobic incubation method. The results showed that average rates ofsoil net N-mineralization across soil depth varied from 1.06 to 7.52 mg · kg^(-1)·month^(-1) atsoil depths from 0 to 60 cm. Statistical analyses indicated that the effects of different soildepths, moistures and their interactions on net N-mineralization rates were significant (P < 0.05).The net N-mineralization rates significantly decreased with increasing soil depths and at depth 0-15cm accounted for 60.52% of that at depth of 0-60 cm. There was no difference in soil netN-mineralization rates between half and fully-saturated water treatments, however these rates weresubstantially higher than that without water treatment (P < 0.05). The factors influencing Nmineralization process have to be studied further in these semiarid pine ecosystems.
基金supported by the National Natural Science Foundation of China(3157061731100322)+2 种基金Special Public Sector Research(GYHY20110400904)the Fundamental Research Funds for the Central Universities(NO.YX2011-19TD2011-07)
文摘Partitioning soil respiration into three components is vital to identify CO_2 sink or source and can help us better understand soil carbon dynamics. However, knowledge about the influences of soil depth and the priming effect on soil respiration components under field has been limited. Three components of soil respiration（root respiration, rhizomicrobial respiration and basal respiration） in a plantation in the hilly area of the North China were separated by the 13 C natural abundance method. The results showed that the average proportions of rhizomicrobial respiration, root respiration and basal respiration at the 25-65 cm depths were about 14, 23 and 63 %, respectively. Three components of soil respiration varied with soil depth, and root respiration was the main component of soil respiration in deeper soil. The priming effect was obvious for the deep soil respiration, especially at the 40-50 cm depth. Thus, depth and priming effect should be taken into account to increase the accuracy of estimations of soil carbon flux.
文摘Soil depth generally varies in mountainous regions in rather complex ways.Conventional soil survey methods for evaluating the soil depth in mountainous and hilly regions require a lot of time,effort and consequently relatively large budget to perform.This study was conducted to explore the relationships between soil depth and topographic attributes in a hilly region in western Iran.For this,one hundred sampling points were selected using randomly stratified methodology,and considering all geomorphic surfaces including summit,shoulder,backslope,footslope and toeslope;and soil depth was actually measured.Eleven primary and secondary topographic attributes were derived from the digital elevation model(DEM) at the study area.The result of multiple linear regression indicated that slope,wetness index,catchment area and sediment transport index,which were included in the model,could explain about 76 % of total variability in soil depth at the selected site.This proposed approach may be applicable to other hilly regions in the semi-arid areas at a larger scale.
基金supported by the National Natural Science Foundation of China(41130530,91325301 and 42071072)。
文摘Soil depth is critical for eco-hydrological modeling,carbon storage calculation and land evaluation.However,its spatial variation is poorly understood and rarely mapped.With a limited number of sparse samples,how to predict soil depth in a large area of complex landscapes is still an issue.This study constructed an ensemble machine learning model,i.e.,quantile regression forest,to quantify the relationship between soil depth and environmental conditions.The model was then combined with a rich set of environmental covariates to predict spatial variation of soil depth and straightforwardly estimate the associated predictive uncertainty in the 140000 km^(2)Heihe River basin of northwestern China.A total of 275 soil depth observation points and 26 covariates were used.The results showed a model predictive accuracy with coefficient of determination(R)of 0.587 and root mean square error(RMSE)of 2.98 cm(square root scale),i.e.,almost 60% of soil depth variation explained.The resulting soil depth map clearly exhibited regional patterns as well as local details.Relatively deep soils occurred in low lying landscape positions such as valley bottoms and plains while shallow soils occurred in high and steep landscape positions such as hillslopes,ridges and terraces.The oases had much deeper soils than outside semi-desert areas,the middle of an alluvial plain had deeper soils than its margins,and the middle of a lacustrine plain had shallower soils than its margins.Large predictive uncertainty mainly occurred in areas with a lack of soil survey points.Both pedogenic and geomorphic processes contributed to the shaping of soil depth pattern of this basin but the latter was dominant.This findings may be applicable to other similar basins in cold and arid regions around the world.
文摘The combined application of organic fertilizer and chemical fertilizer is an effective measure to increase nutrient content of soil plough layer, which must have a profound impact on the deep soil nutrients, especially the contents of nitrogen forms. The purpose of this study was to explore the characteristics of soil nitrogen forms in plough layer and along depth gradient in different fertilization treatments, so as to evaluate the soil quality in spatial dimension, further provid</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> a theoretical basis for scientific fertilization and improvement of paddy soil fertility. Here, a 34-year field experiment was conducted with three treatments: without any fertilizer (CK), pure chemical fertilizer (NPK) and chemical fertilizer combined with organic fertilizer (NPKM). We analyzed the content of nitrogen forms in 0 - 100 cm soil depth and their ratios to total nitrogen (TN), and discussed the correlation between nitrogen forms contents and pH, CEC. Results showed that, compared with CK, both NPK and NPKM significantly increased the contents of nitrogen forms in topsoil (soil layer of 0 - 20 cm), especially nitrate nitrogen (NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N) content increased by 70% (NPK) and 111% (NPKM), respectively. Although the contents of different nitrogen forms decreased gradually along soil depth gradient, NPKS slowed down the decline rate of TN and alkali-hydrolysable nitrogen (AN) in 0 - 60 cm soil layer, compared to CK. Compared to NPK, NPKM significantly increased the NO<sub>3</sub><sup style="margin-left:-6px;">-</sup>-N/TN ratio in 0 - 20 cm soil layer, but also decreased the content of </span><span><span></span><span style="font-family:Verdana;">-N in 20 - 40 cm, which was beneficial to reduce the risk of nitrogen leaching caused by nitrate leaching into deep layer. The increase of soil pH in NPKM treatment obviously alleviated the problem of soil acidification caused by long-term application of chemical fertilizer. Correlation analysis showed that there was a significant positive correlation between soil nitrogen forms and cation exchange capacity (CEC), but no significant correlation with soil pH. In conclusion, NPKM ensured the nutrients of soil plough layer (0 - 20 cm), also reduced the risk of nitrogen infiltration and nitrogen loss, thus ensur</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> the fertility of soil profile.
文摘<span style="white-space:normal;">There has been increased interest in soil organic carbon in recent times because of its role in carbon sequestration. Different parent materials affect soil properties and hence will influence how much carbon is sequestered by soil. The study was conducted in June 2019 to investigate soil carbon stock in forest soils with respect to their parent materials in three States in South-eastern Nigeria. Sampling was aided by the location map of the area and free soil survey method was used to locate sampling points. 0ne profile was dug in each location and described using the Food and Agricultural Organization guideline. A total of twelve soil samples were collected and analyzed for selected properties. Results showed that sand content was significantly higher in soils under coastal plain sands (851.96 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) and was lowest in soils of Imo clay shale (605.60 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;">−1</sup><span style="white-space:normal;">). Clay content was higher in soils of Imo clay shale (277.34 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) and was lowest in coastal plain sand (118.80 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">). Silt and clay had moderate variation in coastal plain sand (>15 ≤ 35%) and high variations in Asu River and Imo clay shale (CV > 35%). The soils studied were generally acidic with values ranging (3.52) in soils formed from coastal plain sand, followed by forest soils of Imo clay shale (3.64) and Asu river group (3.85). Soil organic carbon decreased with increase in soil depth in all soil parent materials studied. Mean values ranged from 6.14 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;"> in soil underlain by coastal plain sand to 10.62 g<span style="white-space:nowrap;">·</span>kg</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) in soils of Imo clay shale. Soil carbon sequestered under the three different parent materials ranged from 1575 - 4676.41 (g<span style="white-space:nowrap;">·</span>cm</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>2</sup><span style="white-space:normal;">). Also, soil depth had a notable impact on carbon sequestration with values ranging from 1529.42 - 4374.0541 (g<span style="white-space:nowrap;">·</span>cm</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>2</sup><span style="white-space:normal;">) and the thicker the horizon, the more carbon sequestered. Hence, the study concluded that more carbon is sequestered in the subsurface horizons of the soil pedons than in the epipedons.</span>
基金supported financially by the National Natural Science Foundation of China (91325301, 41571212 and 41137224)the Project of "One-Three-Five" Strategic Planning & Frontier Sciences of the Institute of Soil Science, Chinese Academy of Sciences (ISSASIP1622)the National Key Basic Research Special Foundation of China (2012FY112100)
文摘Environmental covariates are the basis of predictive soil mapping.Their selection determines the performance of soil mapping to a great extent,especially in cases where the number of soil samples is limited but soil spatial heterogeneity is high.In this study,we proposed an integrated method to select environmental covariates for predictive soil depth mapping.First,candidate variables that may influence the development of soil depth were selected based on pedogenetic knowledge.Second,three conventional methods(Pearson correlation analysis(PsCA),generalized additive models(GAMs),and Random Forest(RF))were used to generate optimal combinations of environmental covariates.Finally,three optimal combinations were integrated to produce a final combination based on the importance and occurrence frequency of each environmental covariate.We tested this method for soil depth mapping in the upper reaches of the Heihe River Basin in Northwest China.A total of 129 soil sampling sites were collected using a representative sampling strategy,and RF and support vector machine(SVM)models were used to map soil depth.The results showed that compared to the set of environmental covariates selected by the three conventional selection methods,the set of environmental covariates selected by the proposed method achieved higher mapping accuracy.The combination from the proposed method obtained a root mean square error(RMSE)of 11.88 cm,which was 2.25–7.64 cm lower than the other methods,and an R^2 value of 0.76,which was 0.08–0.26 higher than the other methods.The results suggest that our method can be used as an alternative to the conventional methods for soil depth mapping and may also be effective for mapping other soil properties.
文摘Shallow slope failure is often induced by rainfall infiltration in a soil mantle overlying a less permeable bedrock. Soil depth is an important input parameter in slope stability analysis. This paper provides the spatial variation of soil depth and the occurrence of slope failure in Sangun mountains area. The spatial pattern of soil depth was simulated by proses based model using airborne laser survey data (LiDAR data) and Geographic Information System (GIS) function. As a function for soil production, we use in the study area a numerical model developed by Dietrich?et al.?(1995) to predict the local spatial variation of the depth of soil. The soil depth data measured at 20 locations that represent morphological variability are used as a sample data set to test the model results. Furthermore, the soil depth variations are compared to the slope failure distribution in the whole area. Slope failure locations in the study area are identified from interpretation of aerial photographs and field surveys. Fifty-five of slope failures are considered for slope failure hazard analysis. Therefore, the slope failures occur more frequently at soil depth intervals in the ranged from 1.01 m to 1.5 m.
文摘Forest ecosystems can be characterized by a set of catenas arranged along the slope in mountainous areas as these affect microhabitat features,which in turn influence soil properties.Heretofore,few studies have examined how topographic variables affect soil properties and quality in semiarid regions.This study aimed to provide important insights into how catena position and shape influence soil properties,soil quality,and their interrelationships in a semiarid protected oak forest in western Iran.Basic soil properties were measured in the laboratory.In addition,the soil quality index(SQI)was calculated at different topographic positions along both convex(Λ-shaped)and concave(V-shaped)catenas at two soil depths(0-15 and 15-30 cm).The findings indicated that soil organic carbon and total nitrogen declined in the lower depth in both V-andΛ-shaped catenas and at all catena positions.The lowest porosity was observed in the lower depth at toeslope positions(TS)of both catenas.Substrate-induced respiration(SIR),microbial biomass carbon(MBC),and basal respiration(BR)were higher in the upper depths at TS positions on V-shaped catenas than onΛ-shaped catenas.These biological indices were consistently higher in the upper depths than in the lower depths across all positions of both catenas.SQI had the highest values at TS positions on both catenas and in the upper depths across all positions.Pearson correlations between soil properties indicated that SQI was most strongly and positively correlated with biological properties in both catenas.The nutrient levels,microbial activity,and soil porosity in both catena shapes and at both soil depths displayed a relatively downward trend with increasing elevation from toeslope to summit positions.The results showed that catena topographic sequence shape and position affected most of the soil properties,providing evidence of the important role of topography in creating pedodiversity in oak forest ecosystems.
基金supported by the Educational Commission of Anhui Province of China(No.KJ2021A0168)the Research Fund of Anhui Agricultural University(No.rc422112).
文摘The environmental impacts of acid mine drainage(AMD)from open-pit mining are profoundly detrimental,yet knowledge about its effects on paddy soil microbial communities,especially at greater depths,remains limited.In this investigation,we compared soils affected by AMD versus unaffected soil depth profiles in terms of bacterial diversity and community assembly.The profiles in AMD-polluted soils exhibited tight geochemical gradients,characterized by increased acidity,SO_(4)^(2-),NO_(3)^(-),and heavy metal content compared to unpolluted soils.Notably,AMD significantly diminished soil bacterial biodiversity.A depthwise analysis showed distinct microbial stratification,with certain bacteria like Candidatus_Solibacter and Candidatus_Koribacter predominated in polluted soils,while others like Haliangium and Nitrospira were more prevalent in control soils.Interestingly,despite variable soil conditions,predictedmetabolic pathways,particularly those involving carbon,nitrogen,and sulfur,showed relative stability.AMD pollution induced the upregulation of methylcoenzyme M reductase and sulfate reductase genes.Bacterial communities were more responsive to pH and nutrient content rather than heavy metals,with pH and SO_(4)^(2-)being the primary drivers of microbial diversity and distribution.Additionally,pHwas identified as the most significant influence on the predicted methane,sulfur,and nitrogen metabolism.Furthermore,deterministic processes played a more significant role in community assembly of polluted soils,while heterogeneous selection gained importance with increasing depth in control soils.Additionally,microbial co-occurrences,particularly positive interactions,were more prevalent in the polluted soils with reduced network modularity and keystone taxa.These findings offer insights into sustaining microbial diversity in extreme environments.
基金supported by the National Natural Science Foundation of China(Grant No.42325502,and 42275045)the West Light Foundation of the Chi-nese Academy of Sciences(Grant No.xbzg-zdsys-202215)+1 种基金the Sci-ence and Technology Research Plan of Gansu Province(Grant Nos.23JRRA654 and 20JR10RA070)iLEAPs(Integrated Land Ecosystem-Atmosphere Processes Study).
文摘The source region of the Yellow River(SRYR),with its semi-humid to semi-arid climate,is crucial for understanding water resource dynamics.Precipitation is key for replenishing surface water and balancing the ecosystem’s water cycle.However,the soil moisture response to precipitation across climate zones and soil layers remains poorly understood due to limited long-term data.This study examines the response of soil moisture to precipitation at multiple time scales in the SRYR,using data from Maqu,Mado,Ngoring Lake sites,and the Maqu monitoring network(MMN),along with CN05.1 precipitation and GLEAM v3.8a soil moisture data.Results show that the semi-humid area requires more precipitation to trigger soil moisture responses compared to the semi-arid area in the SRYR.Surface soil at Maqu,MMN,Ngoring Lake,and Mado sites require at least 8.6,8.4,5.2,and 2.84 mm of precipitation,respectively,for effective replenishment.Significant responses to precipitation events were observed in soil layers at 40 cm and above in the semi-humid area,while at 20 cm and above in the semi-arid area.Precipitation volume is the primary factor influencing soil moisture,affecting both the increment and time lag to maximum moisture.Precipitation intensity and pre-rain moisture have no direct effect.In the central SRYR,accumulated precipitation has a greater impact.Root-zone soil moisture has a weaker correlation with precipitation compared to surface soil moisture but persists longer,responding for up to 10 days,while surface soil moisture responds more immediately but only lasts about 5 days.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program of China(No.2019QZKK0306-02)the National Natural Science Foundation of China(Nos.42322102 and 42271058)+1 种基金the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2021310)the Science&Technology Fundamental Resources Investigation Program of China(No.2022FY100202)
文摘Soil organic carbon(SOC):total nitrogen(TN):total phosphorus(TP)(C:N:P)stoichiometry can give important information about biogeochemical cycling in terrestrial ecosystems.The spatial patterns and driving mechanisms of soil C:N:P ratios are still poorly understood on the Qinghai-Tibetan Plateau of China.In this study,we therefore combined data of the geography,climate,soil properties,and vegetation characteristics from 319 sites across the plateau to investigate their relationships with the horizontal and vertical patterns of SOC,TN,and TP concentrations and their stoichiometric ratios(C:N and N:P).We observed higher SOC(30.5–46.8 mg g^(-1)),TN(2.4–3.4 mg g^(-1)),C:N(14.7–18.0),and N:P(6.9–8.0)in alpine meadows,forests,and shrublands and higher TP(1.6 mg g^(-1))in croplands.Overall,SOC,TN,TP,C:N,and N:P showed decreasing trends(by 67%,64%,19%,12%,and 54%,respectively)along the whole soil profile(0–100 cm).Soil cation exchange capacity and bulk density were the stronger environmental drivers of SOC and TN.Soil TP showed latitudinal and longitudinal increasing trends in all soil layers.Soil properties explained most of the variations in SOC(67%–90%),TN(67%–87%),C:N(61%–89%),and N:P(64%–85%),with increasing impacts along the soil profile.Geography and climate influenced soil TP directly and indirectly through their impacts on soil properties,with geography being the predominant driver(46%–65%)along the soil profile.The variation in soil C:N was mostly driven by SOC and TN,and the direct and indirect effects of the environmental factors were relatively weak.Geography,climate,soil properties,and vegetation characteristics indirectly impacted soil N:P through their impacts on TN and TP in all the soil layers.Altogether,our findings illuminate the relative contributions of geography,climate,soil properties,and vegetation characteristics to soil C:N and N:P,thus enhancing our understanding of C,N,and P cycling across the Qinghai-Tibetan Plateau.
基金funded by the National Natural Science Foundation of China(41201256)
文摘The effect of long-term fertilization on soil denitrifying communities was analysed by measuring the abundance and diversity of the nitrous oxide （N2O） reductase gene, nosZ. Soil samples were collected from plots of a long-term fertilization experiment established in 1982 in Suining City, China. The fertilizer treatments were no fertilizer （CK）, three chemical fertilizer （CF） treatments （N, NP, NPK）, manure （M） alone, and manure with chemical fertilizers （NM, NPM, NPKM）. The abundance and diversity of the denitrifying bacteria were assessed by real-time quantitative PCR, terminal restriction fragment length polymorphism （T-RFLP）, and cloning and sequencing of nosZ genes. The diversity and abundance of nosZ-denitrifiers was higher in soil amended with manure and chemical fertilizers （CFM） than in soil amended with CF alone, and the highest in topsoil （0-20 cm）. The nosZ-denitrifier community composition was more complex in CFM soil than in CF soil： Specific species were detected only in the CFM soil. The abundance of nosZ-denitrifier in the NPKM treatment was approximately two times higher than that in the CK, N, and NPK treatments. Most of the cloned nosZ sequences were closely related to nosZ sequences from Bradyrhizobiaceae and Rhodospirillaceae in Alphaproteobacteria. Of the measured abiotic factors, soil organic matter correlated significantly with the abundance （P〈0.01）; available phosphorus correlated significantly with the topsoil community composition （P〈0.01）, whereas soil organic matter correlated significantly with the subsoil （20-90 cm） community composition （P〈0.01）. This study demonstrated that long-term CFM fertilization affected both the abundance and composition of the nosZ-denitrifier community.
文摘This study was conducted to assess the current stock of soil organic carbon under different agricultural land uses, soil types and soil depths in the Noun plain in western Cameroon. Three sites were selected for the study, namely Mangoum, Makeka and Fossang, representative of the three dominant soil types of the noun plain (Andosols, Acrisols and Ferralsols). Three land uses were selected per site including natural vegetation, agroforest and crop field. Soil was sampled at three depths;0 - 20 cm, 20 - 40 cm, and 40 - 60 cm. Analysis of variance showed that soil type did not significantly influence carbon storage, but rather land uses and soil depth. SOCS decreased significantly with depth in all the sites, with an average stock of 66.3 ± 15.8 tC/ha at 0 - 20 cm, compared to an average stock of 33.3 ± 7.4 tC/ha at 40 - 60 cm. SOCS was significantly highest in the natural formation with 57.2 ± 19.7 tC/ha, and lowest in cultivated fields, at 37.7 ± 10.6 tC/ha. Andosols, with their high content of coarse fragments, stored less organic carbon than Ferralsols and Acrisols.
文摘Analyses of 114 soil samples in Ningbo City show that,in general,there are statistical differences of 137Cs and 40K contents between every layers,the other kinds of natural radionuclides present an increasing tendency with depth.When the γ radiation dose rate is estimated by Beck Formula,owing to the effect of those nonuniform distributions is less than 1% and can be ignored.'
基金financially supported by the Ecological and Environmental Monitoring Project (JJ[2011]-017)funded by the Executive Office of the Three Gorges Project Construction Committee of the State Council of China+1 种基金the National Non-Profit Research Program of China (200903001)the National Basic Research Program of China(2010CB429001)
文摘To better understand soil moisture dynamics in the Yangtze River Estuary （YRE） and predict its variation in a simple way, a field monitoring experiment was carried out along the north branch of the Yangtze River, where seawater intrusion was strong and salt-water variation is one of the limiting factors of local agriculture. In present paper, relation between antecedent precipitation index （API） and soil water content is studied, and effects of groundwater depth on soil water content was analyzed. A relatively accurate prediction result of soil water content was reached using a neural network model. The impact analysis result showed that the variation of the API was consistent with soil water content and it displayed significant correlations with soil water content in both 20 and 50 cm soil layer, and higher correlation was observed in the layer of 20 cm. Groundwater impact analysis suggested that soil moisture was affected by the depth of groundwater, and was affected more greatly by groundwater at depth of 50 cm than that at 20 cm layer. By introducing API, groundwater depth and temperature together, a BP artificial network model was established to predict soil water content and an acceptable agreement was achieved. The model can be used for supplementing monitoring data of soil water content and predicting soil water content in shallow groundwater areas, and can provide favorable support for the research of water and salt transport in estuary area.
基金financially supported by the Ministry of Education of China(Grant No.6141A02022337)
文摘The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties(the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed.Finally, a sensitivity analysis on the parameters in the formula was performed.
基金financially supported by the National Natural Science Foundation of China(Grant No.51679224)
文摘This paper conducts laboratory tests to investigate detailedly the soil deformation law around the pipeline and its penetration depth under self-gravity. The seabed model is prepared by consolidating saturated soil using vacuum pressure technology, and the pipeline models are specifically designed to possess different radii. Based on the experimental results and digital images, the soil deformation process is analyzed and summarized, a kinematic admissible velocity field is given and an upper bound solution of pipeline penetration depth and soil reaction force is derived and proposed in this paper. In order to verify the accuracy of the upper bound solution deduced in this paper,a comparison is made among some published results and the solution suggested in this paper, the comparison results confirm that the upper bound solution and the soil failure mode are reasonable. Finally two empirical formulas are given in this paper to estimate the soil reaction force of seabed and the penetration depth of pipeline. The empirical formulas are in agreement with the upper bound solution derived in this paper, and the conclusion of this paper could provide some theoretical reference for the further study of the interaction between the pipeline and the soil.
