Biomass is the component of living organism and mostly obtained from plants, animals, insects and the residue of all the mentioned organisms. Biomass is the key source of energy present in the form of organic matter. ...Biomass is the component of living organism and mostly obtained from plants, animals, insects and the residue of all the mentioned organisms. Biomass is the key source of energy present in the form of organic matter. The study aimed to find out biomass and its variation in each component of Betula utilis D. Don (Birch Tree) with varying diameter at Kalam forest division Swat, Khyber Pakhtunkhwa (KPK) province, Pakistan. The biomass of different components was determined by non-destructive methods. Overall, 30 trees were selected from different diameter classes viz a viz up to 10, 11 - 20 and greater than 20 cm. Ten trees were selected from each class. The diameter of stem and large branches and their length were measured in the field. Later, the volumes of stem and branches were calculated and converted into biomass. The study revealed that stem contributes 42.65% biomass followed by large and sub branches as 39.22% and 13.54% respectively. Leaves contribute 4.59% only. The above tree biomass contribution by different components was arranged as stem was greater than large branches;these were greater than sub branches and the lowest was in leaves. The total above ground biomass of single tree was 20.59, 58.041 and 197.214 kg·tree-1 respectively for diameter up to 10, 11 - 20 and greater than 20 cm. The averaged biomass in all diameter classes was 91.95 ± 93.064 kg·tree-1. The total biomass of single tree of diameter class up to 10, 11 - 20 and greater than 20 cm was 24.71, 69.649 and 236 kg respectively. The below ground biomass of single tree of diameter class up to 10, 11 - 20 and greater than 20 cm was 4.11 ± 1.24 kg, 11.61 ± 3.56 kg and 39.44 ± 8.9 kg respectively. The biomass expansion factor was 1.34, 1.47, and 1.5 t·m-3 respectively for diameter classes up to 10 cm, 11 - 20 cm and greater than 20 cm respectively. The mean biomass expansion factor for all diameter classes was 1.44 t·m-3.展开更多
There are differing views regarding the climatic factors that limit radial growth of Qilian juniper （Juniperus przewalskii Kom.） at the upper treelines on the northeastern Tibetan Plateau. In this study, trees from ...There are differing views regarding the climatic factors that limit radial growth of Qilian juniper （Juniperus przewalskii Kom.） at the upper treelines on the northeastern Tibetan Plateau. In this study, trees from an upper tree northeastern Tibetan Plateau were selected to limits the radial growth of Qilian juniper. Using ine site in the Anyemaqen Mountains of the present new evidence that low temperature a signal-free regional curve standardization （SF-RCS） method, a ring-width chronology for Qilian juniper was developed extending from AD 1082 to 2010. The results of correlation analysis between tree-ring index and instrumental climatic variables showed that both winter （December in the previous year and January in the current year） and summer （July and August in the current year） temperatures were signifi- cantly and positively correlated with the tree-ring index. Precipitation in June was also significantly and positively correlated with the tree-ring index, but was not as important as low temperature in controlling tree growth. To test the key limiting climatic factor for tree radial growth at different altitudes, an indicator termed the ＂relative distance to upper treeline＂ （RDUT） was developed to quantify the representativeness of collected samples for the forest＇s upper treeline. The RDUT showed that the upper 20% of the forest belt may be an important boundary in terms of capturing the temperature signal from tree-ring width at the upper treelines on the northeastern Tibetan Plateau. Our findings enhance the existing understanding that temperature is the limiting factor at upper treelines on the northeastern Tibetan Plateau, and will be useful in the reconstruction of past temperature in future studies.展开更多
The study on assessment of factors affecting tree husbandry and woodlots establishment was carried out between September and November 2014 in all seven districts of Kilimanjaro region, namely Hai, Siha Rombo, Mwanga, ...The study on assessment of factors affecting tree husbandry and woodlots establishment was carried out between September and November 2014 in all seven districts of Kilimanjaro region, namely Hai, Siha Rombo, Mwanga, Same, Moshi Rural and Moshi Municipal Council (MMC). A purposive sampling design was employed whereby two wards per district were selected for the study. Household questionnaire survey was used in data collection. Results show that, factors affecting tree husbandry and woodlots establishment in Kilimanjaro region are gender, livelihood activities, access and ownership/land tenure, cultural factors, legal issues and by-laws insisting people to plant trees. About 32.4%, 32.4% and 30% of all respondents own land with size of 1.0 acre and below, 1.1 - 2.0 and 2.1 - 5.0 acres respectively. Respondents from Hai (55.3%), Same (26.3%), Rombo (11%) and MMC (8%) agreed that cultural issues affect tree husbandry. About 1%, 23%, 30% and 40.8% of respondents in Siha, Same, Hai and Rombo districts respectively agreed that some of by-laws insist people to plant trees on their environments. None of the respondents from any district reported labour availability to be one of the factors affecting tree husbandry. Other factors reported to affect tree husbandry in Kilimanjaro region were capacity building in tree planting and tending, insect pests, diseases and climate change. Formulation of by-laws which insist on tree planting and limit land degradation is recommended at village level. Every piece of land should be planned and used sustainably including area for tree planting. Custom and norms which inhibit women to plant trees should be prohibited through capacity building.展开更多
In order to clarify the correlation between short-shoot Fuji apple tree structure and different factors under different trimming and pruning modes,we investigate the trunk taperingness of free-spindle short-shoot Fuji...In order to clarify the correlation between short-shoot Fuji apple tree structure and different factors under different trimming and pruning modes,we investigate the trunk taperingness of free-spindle short-shoot Fuji and slender-spindle short-shoot Fuji,respectively,as well as the total thickness,average thickness,total length and average length of small main branches in the standard demonstration apple garden in Xingtang County of Hebei Province. By SPSS analysis,we study the correlation between trunk taperingness of trees with different shapes and the growth indices of their small main branches. The results show that the trunk taperingness of free-spindle short-shoot Fuji apple is negatively correlated with the total thickness,average thickness,total length and average length of small main branches,but the correlation is not significant; the trunk taperingness of slender-spindle short-shoot Fuji apple is negatively correlated with the total thickness but positively correlated with other factors,and the correlation with average length reaches a significant level. The results of this study can provide a scientific basis for guiding the high-density dwarf rootstock short-shoot Fuji apple tree trimming technology.展开更多
Background: Geographic variation in body size is assumed to reflect adaptation to local environmental conditions. Although Bergmann's rule is usually sufficient to explain such variation in homeotherms, some excep...Background: Geographic variation in body size is assumed to reflect adaptation to local environmental conditions. Although Bergmann's rule is usually sufficient to explain such variation in homeotherms, some exceptions have been documented. The relationship between altitude, latitude and body size, has been well documented for some vertebrate taxa during the past decades. However, relatively little information is available on the effects of climate variables on body size in birds.Methods: We collected the data of 267 adult Eurasian Tree Sparrow(Passer montanus) specimens sampled at 48 localities in China's mainland, and further investigated the relationships between two response variables, body mass and wing length, as well as a suit of explanatory variables, i.e. altitude, latitude, mean annual temperature(MAT), annual precipitation(PRC), annual sunshine hours(SUN), average annual wind speed(WS), air pressure(AP) and relative humidity(RH).Results: Our study showed that(1) although the sexes did not differ significantly in body mass, males had longer wings than females;(2) body mass and wing length were positively correlated with altitude but not with latitude;(3) body mass and wing length were negatively correlated with AP and RH, but not significantly correlated with WS. Body mass was positively correlated with SUN and inversely correlated with MAT. Wing length was not correlated with MAT in either sex, but was positively correlated with SUN and negatively correlated with PRC in male sparrows;(4) variation in body mass could be best explained by AP and SUN, whereas variation in wing length could be explained by RH and AP in both sexes. In addition, variation in male sparrows can be explained by SUN, WS and PRC but not in females.Conclusions: Two different proxies of body size, body mass and wing length, correlated with same geographic factors and different climate factors. These differences may reflect selection for heat conservation in the case of body mass, and for efficient flight in the case of wing length.展开更多
Ro-Ro vessels for cargo and passengers （RoPax） are a relatively new concept that has proven to be popular in the Mediterranean region and is becoming more widespread in Northern Europe. Due to its design characteris...Ro-Ro vessels for cargo and passengers （RoPax） are a relatively new concept that has proven to be popular in the Mediterranean region and is becoming more widespread in Northern Europe. Due to its design characteristics and amount of passengers, although less than a regular passenger liner, accidents with RoPax vessels have far reaching consequences both for economical and for human life. The objective of this paper is to identify hazards related to casualties of RoPax vessels. The terminal casualty events chosen are related to accident and incident statistics for this type of vessel. This paper focuses on the identification of the basic events that can lead to an accident and the performance requirements. The hazard identification is carried out as the first step of a Formal Safety Assessment （FSA） and the modelling of the relation between the relevant events is made using Fault Tree Analysis （FTA）. The conclusions of this study are recommendations to the later steps of FSA rather than for decision making （Step 5 of FSA）. These recommendations will be focused on the possible design shortcomings identified during the analysis by fault trees throughout cut sets. Also the role that human factors have is analysed through a sensitivity analysis where it is shown that their influence is higher for groundings and collisions where an increase of the initial probability leads to the change of almost 90% of the accident occurrence.展开更多
On the basis of Hardy-Weinberg law the distinction in the philosophy of the description of a family tree and a population is considered. With the help of introduction of the equivalent constant mutagen factor both in ...On the basis of Hardy-Weinberg law the distinction in the philosophy of the description of a family tree and a population is considered. With the help of introduction of the equivalent constant mutagen factor both in a family tree and in a population, the analysis of hemophilia is led. Influence of selection at presence of hemophilia is considered. On the basis of idea of Danforth and Haldane about the balance mutagenesis and selection at presence of hemophilia, the inter-relation of selection parameter and the equivalent constant mutagen factor is found. It is shown, that dynamics of development of hemophilia in a family tree and in population are similar.展开更多
【目的】探讨梵净山典型优势树种根系土壤细菌群落结构、多样性、生态系统功能及其不同树种间差异的环境驱动因子。【方法】以梵净山世界自然遗产地的丝栗栲、西南米槠、厚皮栲、长柄水青冈、云山青冈和亮叶水青冈6种优势树种为研究对象...【目的】探讨梵净山典型优势树种根系土壤细菌群落结构、多样性、生态系统功能及其不同树种间差异的环境驱动因子。【方法】以梵净山世界自然遗产地的丝栗栲、西南米槠、厚皮栲、长柄水青冈、云山青冈和亮叶水青冈6种优势树种为研究对象,通过高通量测序技术分析根系土壤细菌群落组成及其在树种间的多样性差异,并应用PICRUSt(phylogenetic investigation of communities by reconstruction of unobserved states)对功能基因进行预测,基于冗余分析或相关性分析揭示土壤细菌群落、功能基因及环境因子(气候因素和土壤化学性质)间的相互关系。【结果】土壤化学性质因树种不同而存在一定差异,梵净山6种优势树种根系土壤碱解氮(AN)、有效磷(AP)和速效钾(AK)含量分别为4.09~12.98,5.64~9.91和29.38~68.33 mg/kg;全氮(TN)、全磷(TP)和全碳(TC)含量分别为1.85~3.41,0.29~0.50和33.01~85.77 g/kg;pH和C/N分别为4.45~4.82和17.19~27.58。高通量测序结果表明,从72份土壤样品中共鉴定出851个属的细菌,分属38个门、99个纲、238个目、394个科。在不同树种间,细菌群落组成存在一定差异,其中酸杆菌门、变形菌门和放线菌门是根系土壤细菌的主要优势门类,三者相对丰度之和的均值为88.27%。多样性分析表明,虽然不同树种根系土壤中的细菌群落在丰富度和多样性上表现出很高的相似性,但也存在一定差异,其中厚皮栲根系土壤的Chao1指数最高,为5284.8;亮叶水青冈的Shannon指数最高,为9.1;而长柄水青冈的Chao1指数和Shannon指数均为最低,分别为4469.8和8.5。PICRUSt功能预测表明,不同树种根系土壤细菌主要参与5类一级代谢通路及其下属的33个子功能代谢通路,其中厚皮栲和长柄水青冈的KEGG功能基因相对丰度明显高于其他树种。冗余分析显示,海拔(Alt)和土壤AN含量是驱动土壤细菌群落结构变化的关键影响因素。相关性分析表明,细菌多样性指数与年平均温度(MAT)、年均大气湿度(AAH)呈显著负相关,而与土壤全碳(TC)呈显著正相关;KEGG功能基因相对丰度与环境因子的相关性较弱,而与细菌门水平的相对丰度存在较强相关性。【结论】梵净山6种优势树种根系土壤的化学性质、细菌群落组成、多样性及KEGG功能基因相对丰度存在一定差异。Alt和土壤AN含量是不同树种根系土壤细菌群落结构产生差异的关键环境驱动因子,而KEGG功能基因相对丰度主要与细菌群落结构变化相关。展开更多
LDL-factorization is an efficient way of solving Ax = b for a large symmetric positive definite sparse matrix A. This paper presents a new method that further improves the efficiency of LDL-factorization. It is based ...LDL-factorization is an efficient way of solving Ax = b for a large symmetric positive definite sparse matrix A. This paper presents a new method that further improves the efficiency of LDL-factorization. It is based on the theory of elimination trees for the factorization factor. It breaks the computations involved in LDL-factorization down into two stages： 1） the pattern of nonzero entries of the factor is predicted, and 2） the numerical values of the nonzero entries of the factor are computed. The factor is stored using the form of an elimination tree so as to reduce memory usage and avoid unnecessary numerical operations. The calculation results for some typical numerical examples demonstrate that this method provides a significantly higher calculation efficiency for the one-to-one marketing optimization algorithm.展开更多
High-resolution observations of cambial phenology and intra-annual growth dynamics are useful approaches for understanding the response of tree growth to climate and environmental change. During the past two decades, ...High-resolution observations of cambial phenology and intra-annual growth dynamics are useful approaches for understanding the response of tree growth to climate and environmental change. During the past two decades, rapid socioeconomic development has increased the demand for water resources in the oases of the middle reaches of the Heihe River in northwestern China, and the lower reaches of the Heihe River have changed from a perennial river to an ephemeral stream with a decreased and degraded riparian zone. Tamarisk（Tamarix ramosissima） is the dominant shrub species of the desert riparian forest. In this study, the daily and seasonal patterns of tamarisk stem diameter growth, including the main period of tree ring formation, were examined. Observations concerning the driving forces of growth changes, along with implications for the ecology of the dendrohydrological area and management of desert riparian forests in similar arid regions, are also presented. The diurnal-seasonal activity of stem diameter and the dynamics of growth ring formation were studied using a point dendrometer and micro-coring methods during the 2012 growing season in shrub tamarisk in a desert riparian forest stand in the lower reaches of the Heihe River in Ejin Banner, Inner Mongolia of northwestern China. Generally, the variation in diurnal diameter of tamarisk was characterized by an unstable multi-peak pattern, with the cumulative stem diameter growth over the growing season following an S-shaped curve. The period from late May to early August was the main period of stem diameter growth and growth-ring formation. Among all of the hydroclimatic factors considered in this study, only groundwater depth was significantly correlated with stem diameter increment during this period. Therefore, for the dendrochronological study, the annual rings of the tamarisk can be used to reconstruct processes that determine the regional water regime, such as river runoff and fluctuations in groundwater depth. For the management of desert riparian forests, suitable groundwater depths must be maintained in the spring and summer to sustain tree health and a suitable stand structure.展开更多
文摘Biomass is the component of living organism and mostly obtained from plants, animals, insects and the residue of all the mentioned organisms. Biomass is the key source of energy present in the form of organic matter. The study aimed to find out biomass and its variation in each component of Betula utilis D. Don (Birch Tree) with varying diameter at Kalam forest division Swat, Khyber Pakhtunkhwa (KPK) province, Pakistan. The biomass of different components was determined by non-destructive methods. Overall, 30 trees were selected from different diameter classes viz a viz up to 10, 11 - 20 and greater than 20 cm. Ten trees were selected from each class. The diameter of stem and large branches and their length were measured in the field. Later, the volumes of stem and branches were calculated and converted into biomass. The study revealed that stem contributes 42.65% biomass followed by large and sub branches as 39.22% and 13.54% respectively. Leaves contribute 4.59% only. The above tree biomass contribution by different components was arranged as stem was greater than large branches;these were greater than sub branches and the lowest was in leaves. The total above ground biomass of single tree was 20.59, 58.041 and 197.214 kg·tree-1 respectively for diameter up to 10, 11 - 20 and greater than 20 cm. The averaged biomass in all diameter classes was 91.95 ± 93.064 kg·tree-1. The total biomass of single tree of diameter class up to 10, 11 - 20 and greater than 20 cm was 24.71, 69.649 and 236 kg respectively. The below ground biomass of single tree of diameter class up to 10, 11 - 20 and greater than 20 cm was 4.11 ± 1.24 kg, 11.61 ± 3.56 kg and 39.44 ± 8.9 kg respectively. The biomass expansion factor was 1.34, 1.47, and 1.5 t·m-3 respectively for diameter classes up to 10 cm, 11 - 20 cm and greater than 20 cm respectively. The mean biomass expansion factor for all diameter classes was 1.44 t·m-3.
基金The Strategic Priority Research Program from the Chinese Academy of Sciences No.XDA05080201 National Natural Science Foundation of China, No.41071061
文摘There are differing views regarding the climatic factors that limit radial growth of Qilian juniper （Juniperus przewalskii Kom.） at the upper treelines on the northeastern Tibetan Plateau. In this study, trees from an upper tree northeastern Tibetan Plateau were selected to limits the radial growth of Qilian juniper. Using ine site in the Anyemaqen Mountains of the present new evidence that low temperature a signal-free regional curve standardization （SF-RCS） method, a ring-width chronology for Qilian juniper was developed extending from AD 1082 to 2010. The results of correlation analysis between tree-ring index and instrumental climatic variables showed that both winter （December in the previous year and January in the current year） and summer （July and August in the current year） temperatures were signifi- cantly and positively correlated with the tree-ring index. Precipitation in June was also significantly and positively correlated with the tree-ring index, but was not as important as low temperature in controlling tree growth. To test the key limiting climatic factor for tree radial growth at different altitudes, an indicator termed the ＂relative distance to upper treeline＂ （RDUT） was developed to quantify the representativeness of collected samples for the forest＇s upper treeline. The RDUT showed that the upper 20% of the forest belt may be an important boundary in terms of capturing the temperature signal from tree-ring width at the upper treelines on the northeastern Tibetan Plateau. Our findings enhance the existing understanding that temperature is the limiting factor at upper treelines on the northeastern Tibetan Plateau, and will be useful in the reconstruction of past temperature in future studies.
文摘The study on assessment of factors affecting tree husbandry and woodlots establishment was carried out between September and November 2014 in all seven districts of Kilimanjaro region, namely Hai, Siha Rombo, Mwanga, Same, Moshi Rural and Moshi Municipal Council (MMC). A purposive sampling design was employed whereby two wards per district were selected for the study. Household questionnaire survey was used in data collection. Results show that, factors affecting tree husbandry and woodlots establishment in Kilimanjaro region are gender, livelihood activities, access and ownership/land tenure, cultural factors, legal issues and by-laws insisting people to plant trees. About 32.4%, 32.4% and 30% of all respondents own land with size of 1.0 acre and below, 1.1 - 2.0 and 2.1 - 5.0 acres respectively. Respondents from Hai (55.3%), Same (26.3%), Rombo (11%) and MMC (8%) agreed that cultural issues affect tree husbandry. About 1%, 23%, 30% and 40.8% of respondents in Siha, Same, Hai and Rombo districts respectively agreed that some of by-laws insist people to plant trees on their environments. None of the respondents from any district reported labour availability to be one of the factors affecting tree husbandry. Other factors reported to affect tree husbandry in Kilimanjaro region were capacity building in tree planting and tending, insect pests, diseases and climate change. Formulation of by-laws which insist on tree planting and limit land degradation is recommended at village level. Every piece of land should be planned and used sustainably including area for tree planting. Custom and norms which inhibit women to plant trees should be prohibited through capacity building.
基金Supported by Modern Agricultural Industry Technology System Construction Project(CARS-28)Project of Hebei Provincial Department of Science and Technology(11220104D-1)
文摘In order to clarify the correlation between short-shoot Fuji apple tree structure and different factors under different trimming and pruning modes,we investigate the trunk taperingness of free-spindle short-shoot Fuji and slender-spindle short-shoot Fuji,respectively,as well as the total thickness,average thickness,total length and average length of small main branches in the standard demonstration apple garden in Xingtang County of Hebei Province. By SPSS analysis,we study the correlation between trunk taperingness of trees with different shapes and the growth indices of their small main branches. The results show that the trunk taperingness of free-spindle short-shoot Fuji apple is negatively correlated with the total thickness,average thickness,total length and average length of small main branches,but the correlation is not significant; the trunk taperingness of slender-spindle short-shoot Fuji apple is negatively correlated with the total thickness but positively correlated with other factors,and the correlation with average length reaches a significant level. The results of this study can provide a scientific basis for guiding the high-density dwarf rootstock short-shoot Fuji apple tree trimming technology.
基金supported by grants from the National Natural Science Foundation of China (NSFC, 31330073, 31672292)the Natural Science Foundation of the Department of Education, Hebei Province (YQ2014024)
文摘Background: Geographic variation in body size is assumed to reflect adaptation to local environmental conditions. Although Bergmann's rule is usually sufficient to explain such variation in homeotherms, some exceptions have been documented. The relationship between altitude, latitude and body size, has been well documented for some vertebrate taxa during the past decades. However, relatively little information is available on the effects of climate variables on body size in birds.Methods: We collected the data of 267 adult Eurasian Tree Sparrow(Passer montanus) specimens sampled at 48 localities in China's mainland, and further investigated the relationships between two response variables, body mass and wing length, as well as a suit of explanatory variables, i.e. altitude, latitude, mean annual temperature(MAT), annual precipitation(PRC), annual sunshine hours(SUN), average annual wind speed(WS), air pressure(AP) and relative humidity(RH).Results: Our study showed that(1) although the sexes did not differ significantly in body mass, males had longer wings than females;(2) body mass and wing length were positively correlated with altitude but not with latitude;(3) body mass and wing length were negatively correlated with AP and RH, but not significantly correlated with WS. Body mass was positively correlated with SUN and inversely correlated with MAT. Wing length was not correlated with MAT in either sex, but was positively correlated with SUN and negatively correlated with PRC in male sparrows;(4) variation in body mass could be best explained by AP and SUN, whereas variation in wing length could be explained by RH and AP in both sexes. In addition, variation in male sparrows can be explained by SUN, WS and PRC but not in females.Conclusions: Two different proxies of body size, body mass and wing length, correlated with same geographic factors and different climate factors. These differences may reflect selection for heat conservation in the case of body mass, and for efficient flight in the case of wing length.
文摘Ro-Ro vessels for cargo and passengers （RoPax） are a relatively new concept that has proven to be popular in the Mediterranean region and is becoming more widespread in Northern Europe. Due to its design characteristics and amount of passengers, although less than a regular passenger liner, accidents with RoPax vessels have far reaching consequences both for economical and for human life. The objective of this paper is to identify hazards related to casualties of RoPax vessels. The terminal casualty events chosen are related to accident and incident statistics for this type of vessel. This paper focuses on the identification of the basic events that can lead to an accident and the performance requirements. The hazard identification is carried out as the first step of a Formal Safety Assessment （FSA） and the modelling of the relation between the relevant events is made using Fault Tree Analysis （FTA）. The conclusions of this study are recommendations to the later steps of FSA rather than for decision making （Step 5 of FSA）. These recommendations will be focused on the possible design shortcomings identified during the analysis by fault trees throughout cut sets. Also the role that human factors have is analysed through a sensitivity analysis where it is shown that their influence is higher for groundings and collisions where an increase of the initial probability leads to the change of almost 90% of the accident occurrence.
文摘On the basis of Hardy-Weinberg law the distinction in the philosophy of the description of a family tree and a population is considered. With the help of introduction of the equivalent constant mutagen factor both in a family tree and in a population, the analysis of hemophilia is led. Influence of selection at presence of hemophilia is considered. On the basis of idea of Danforth and Haldane about the balance mutagenesis and selection at presence of hemophilia, the inter-relation of selection parameter and the equivalent constant mutagen factor is found. It is shown, that dynamics of development of hemophilia in a family tree and in population are similar.
文摘【目的】探讨梵净山典型优势树种根系土壤细菌群落结构、多样性、生态系统功能及其不同树种间差异的环境驱动因子。【方法】以梵净山世界自然遗产地的丝栗栲、西南米槠、厚皮栲、长柄水青冈、云山青冈和亮叶水青冈6种优势树种为研究对象,通过高通量测序技术分析根系土壤细菌群落组成及其在树种间的多样性差异,并应用PICRUSt(phylogenetic investigation of communities by reconstruction of unobserved states)对功能基因进行预测,基于冗余分析或相关性分析揭示土壤细菌群落、功能基因及环境因子(气候因素和土壤化学性质)间的相互关系。【结果】土壤化学性质因树种不同而存在一定差异,梵净山6种优势树种根系土壤碱解氮(AN)、有效磷(AP)和速效钾(AK)含量分别为4.09~12.98,5.64~9.91和29.38~68.33 mg/kg;全氮(TN)、全磷(TP)和全碳(TC)含量分别为1.85~3.41,0.29~0.50和33.01~85.77 g/kg;pH和C/N分别为4.45~4.82和17.19~27.58。高通量测序结果表明,从72份土壤样品中共鉴定出851个属的细菌,分属38个门、99个纲、238个目、394个科。在不同树种间,细菌群落组成存在一定差异,其中酸杆菌门、变形菌门和放线菌门是根系土壤细菌的主要优势门类,三者相对丰度之和的均值为88.27%。多样性分析表明,虽然不同树种根系土壤中的细菌群落在丰富度和多样性上表现出很高的相似性,但也存在一定差异,其中厚皮栲根系土壤的Chao1指数最高,为5284.8;亮叶水青冈的Shannon指数最高,为9.1;而长柄水青冈的Chao1指数和Shannon指数均为最低,分别为4469.8和8.5。PICRUSt功能预测表明,不同树种根系土壤细菌主要参与5类一级代谢通路及其下属的33个子功能代谢通路,其中厚皮栲和长柄水青冈的KEGG功能基因相对丰度明显高于其他树种。冗余分析显示,海拔(Alt)和土壤AN含量是驱动土壤细菌群落结构变化的关键影响因素。相关性分析表明,细菌多样性指数与年平均温度(MAT)、年均大气湿度(AAH)呈显著负相关,而与土壤全碳(TC)呈显著正相关;KEGG功能基因相对丰度与环境因子的相关性较弱,而与细菌门水平的相对丰度存在较强相关性。【结论】梵净山6种优势树种根系土壤的化学性质、细菌群落组成、多样性及KEGG功能基因相对丰度存在一定差异。Alt和土壤AN含量是不同树种根系土壤细菌群落结构产生差异的关键环境驱动因子,而KEGG功能基因相对丰度主要与细菌群落结构变化相关。
基金This work was supported in part by the National Natural Science Foundation of PRC (No.60425310)the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE,PRC.
文摘LDL-factorization is an efficient way of solving Ax = b for a large symmetric positive definite sparse matrix A. This paper presents a new method that further improves the efficiency of LDL-factorization. It is based on the theory of elimination trees for the factorization factor. It breaks the computations involved in LDL-factorization down into two stages： 1） the pattern of nonzero entries of the factor is predicted, and 2） the numerical values of the nonzero entries of the factor are computed. The factor is stored using the form of an elimination tree so as to reduce memory usage and avoid unnecessary numerical operations. The calculation results for some typical numerical examples demonstrate that this method provides a significantly higher calculation efficiency for the one-to-one marketing optimization algorithm.
基金funded by the National Natural Science Foundation of China (40971032, 91125026)
文摘High-resolution observations of cambial phenology and intra-annual growth dynamics are useful approaches for understanding the response of tree growth to climate and environmental change. During the past two decades, rapid socioeconomic development has increased the demand for water resources in the oases of the middle reaches of the Heihe River in northwestern China, and the lower reaches of the Heihe River have changed from a perennial river to an ephemeral stream with a decreased and degraded riparian zone. Tamarisk（Tamarix ramosissima） is the dominant shrub species of the desert riparian forest. In this study, the daily and seasonal patterns of tamarisk stem diameter growth, including the main period of tree ring formation, were examined. Observations concerning the driving forces of growth changes, along with implications for the ecology of the dendrohydrological area and management of desert riparian forests in similar arid regions, are also presented. The diurnal-seasonal activity of stem diameter and the dynamics of growth ring formation were studied using a point dendrometer and micro-coring methods during the 2012 growing season in shrub tamarisk in a desert riparian forest stand in the lower reaches of the Heihe River in Ejin Banner, Inner Mongolia of northwestern China. Generally, the variation in diurnal diameter of tamarisk was characterized by an unstable multi-peak pattern, with the cumulative stem diameter growth over the growing season following an S-shaped curve. The period from late May to early August was the main period of stem diameter growth and growth-ring formation. Among all of the hydroclimatic factors considered in this study, only groundwater depth was significantly correlated with stem diameter increment during this period. Therefore, for the dendrochronological study, the annual rings of the tamarisk can be used to reconstruct processes that determine the regional water regime, such as river runoff and fluctuations in groundwater depth. For the management of desert riparian forests, suitable groundwater depths must be maintained in the spring and summer to sustain tree health and a suitable stand structure.
