It is well established that species mixtures could enhance ecosystem functioning in diverse ecosystem types,with these benefits increasing over time.However,the impact of tree mixtures on Collembola communities follow...It is well established that species mixtures could enhance ecosystem functioning in diverse ecosystem types,with these benefits increasing over time.However,the impact of tree mixtures on Collembola communities following stand development in natural forests remains unclear,despite the critical roles Collembola plays in litter decomposition and nutrient cycling.We investigated the effects of tree species mixtures on Collembola abundance,diversity,and community structure by sampling pure and mixed jack pine(Pinus banksiana Lamb.)and trembling aspen(Populus tremuloides Michx.)of 15-year-old and 41-year-old stands in natural boreal forest.In total,6,620 individuals of Collembola were identified as belonging to 39 species/morphospecies.Our results showed significant effects of stand types on Collembola with higher abundance and richness in conifer and mixed stands than in broadleaf stands.Additionally,with stand development,we observed increased Collembola abundance and richness.In 15-year-old stands,Collembola abundance,richness,and evenness in mixed-species stands were comparable to those in single-species stands.However,as stands developed,tree mixture effects became more pronounced,resulting in higher Collembola abundance and richness in mixed-species stands compared to the average of single-species stands in 41-year-old stands.Further,we observed positive associations between the mixture effects on Collembola abundance and richness with soil nutrient contents.We conclude that tree species mixtures can significantly enhance Collembola abundance and diversity,particularly in older stands and those with elevated soil nutrient levels.展开更多
The priming effect(PE)induced by biochar provides a basis for evaluating its carbon(C)sequestration potential in soils.A 60 days’laboratory incubation was conducted,which involved the amendment of biochar(1%of soil m...The priming effect(PE)induced by biochar provides a basis for evaluating its carbon(C)sequestration potential in soils.A 60 days’laboratory incubation was conducted,which involved the amendment of biochar(1%of soil mass)produced from rice straw at 300℃(B300)and 500℃(B500)to young(Y)and old(O)poplar plantation soils,with the aim of studying the responses of biochar-induced PEs to poplar plantation ages.This incubation included six treatments:Y+CK(control),Y+B300,Y+B500,O+CK,O+B300,and O+B500.Carbon dioxide(CO_(2))emissions were significantly increased(p<0.05)in the B300 amended soils,while it was decreased in the B500 amended soils compared to the CK.The primed CO_(2) emissions were 2.35 times higher in the Y+B300 than the O+B300 treatments,which was measured to be 18.6 and 5.56 mg C·kg^(-1) with relative PEs of 12.4%and 3.35%,respectively.However,there was little difference between the primed CO_(2) emissions in Y+B500 and O+B500 treatments,which were measured to be-24.9 and-29.6 mg·C·kg^(-1) with relative PEs of-16.6%and-17.8%,respectively.Dissolved organic carbon(DOC)was significantly lower in the young poplar plantation soil than that in the old poplar plantation soil regardless of biochar amendment throughout the incubation,indicating greater C-limit of soil microorganisms in the young poplar plantation soil.Using ^(13)C isotope tracing,neither B300 nor B500 decreased native soil-derived DOC,which indicated that the negative B500-induced PEs were not due to a reduction in the availability of native soil-derived C.In conclusion,the response of biochar-induced PEs to poplar plantation age depends on biochar types while soil available C indirectly affects biochar-induced PEs.Further studies should focus on how the interactive effects between soil C availability and microbial community impacts biochar-induced PEs.展开更多
The aboveground biomass(AGB)of shrubs and small trees is the main component for the productivity and carbon storage of understory vegetation in subtropical secondary forests.However,few allometric models exist to accu...The aboveground biomass(AGB)of shrubs and small trees is the main component for the productivity and carbon storage of understory vegetation in subtropical secondary forests.However,few allometric models exist to accurately evaluate understory biomass.To estimate the AGB of five common shrub(diameter at base<5 cm,<5 m high)and one small tree species(<8 m high,trees’s seedling),206 individuals were harvested and species-specific and multi-species allometric models developed based on four predictors,height(H),stem diameter(D),crown area(Ca),and wood density(ρ).As expected,the six species possessed greater biomass in their stems compared with branches,with the lowest biomass in the leaves.Species-specific allometric models that employed stem diameter and the combined variables of D~2H andρDH as predictors accurately estimated the components and total AGB,with R^(2) values from 0.602 and 0.971.A multi-species shrub allometric model revealed that wood density×diameter×height(ρDH)was the best predictor,with R^(2) values ranging from between 0.81 and 0.89 for the components and total AGB,respectively.These results indicated that height(H)and diameter(D)were effective predictors for the models to estimate the AGB of the six species,and the introduction of wood density(ρ)improved their accuracy.The optimal models selected in this study could be applied to estimate the biomass of shrubs and small trees in subtropical regions.展开更多
Available light under forest canopies includes two components, diffuse light and direct light (sunflecks), and is characterized as low and highly dynamic. Understory habitats under different forest types experience di...Available light under forest canopies includes two components, diffuse light and direct light (sunflecks), and is characterized as low and highly dynamic. Understory habitats under different forest types experience different light conditions. Sunflecks as a critical resource for understory plants have great importance on carbon gain of understory plants. Under the light-limiting habitat, understory plants exhibit a high light utilization efficiency attributed by a post-illumination CO2 uptake. Although different species have different photosynthetic responses, shade plants appear to be acclimated to respond more quickly and efficiently to sunflecks. This acclimation includes a faster induction, relatively lower rate of induction loss, lower photosynthetic compensation point, and higher water use efficiency. The process that shade plants harvest light energy is not well known. Studies of photosynthetic responses to sunflecks in natural conditions are rare. Little is known about constraints on sunfleck utilization, which may change seasonally. Extensive field studies in conjunction with laboratory investigations will be needed to further understand potential and actual constraints on sunfleck utilization. Most studies on photosynthetic responses to fluctuating light condition were done in the level of leaves. Fluctuating light utilization on the basis of whole plants and populations presents future challenges to ecologists.展开更多
Forest canopy structure is closely related to species diversity,crown packing efficiency,and ecological processes,while influencing ecosystem functions.However,most existing structural diversity indices only consider ...Forest canopy structure is closely related to species diversity,crown packing efficiency,and ecological processes,while influencing ecosystem functions.However,most existing structural diversity indices only consider internal heterogeneity within the canopy but often neglect the heterogeneity of the external canopy.While,the external canopy heterogeneity can increase the exchange surface area between canopy and external atmosphere,capture more light,which is closely linked to tree growth and ecosystem functions.Comprehensively and accurately estimating canopy structural diversity is crucial in understanding the underlying mechanisms of productivity change.Therefore,in this study,we apply a topographic index–canopy surface rugosity(CSR)–to capture canopy external heterogeneity,and use crown complementary index(CCI)and other canopy structural variables to quantify canopy internal heterogeneity.We find that CSR varies significantly among quadrats(20 m×20 m)and it decreases with species diversity and wood net primary productivity(NPP_(wood)).Species diversity increases NPP_(wood) directly and indirectly through CSR and CCI.Functional diversity increases NPP_(wood) through CSR and CCI.Community weighted mean of light demand decreases with NPP_(wood) through CCI.The mediating effect of CSR on the relationship between species(functional)diversity and NPP_(wood) is greater than the mediating effect of CCI.We find soil fertility positive effects on NPP_(wood) mainly through species richness and CSR.Conversely,water availability affects NPP_(wood) by a direct positive effect and indirect negative effects through species richness,CSR and CCI.Overall,our CSR and CCI provide strong support for a space-based niche partitioning mechanism regulating the relationship between species diversity and NPP_(wood).Additionally,CSR is sensitive to gap dynamics,suggesting mechanistic relationships between local disturbance,species diversity,and NPP_(wood).展开更多
基金support from the National Natural Science Foundation of China(NSFC)for the Excellent Young Scientists Fund(overseas)and NSFC Grant(No.32401546)the Scientific Research Startup Fund Project of Zhejiang A&F University(Grant No.2024LFR019)the Natural Sciences and Engineering Research Council of Canada(RGPIN-2014-04181,STPGP428641,RTI-2017-00358,and STPGP506284).
文摘It is well established that species mixtures could enhance ecosystem functioning in diverse ecosystem types,with these benefits increasing over time.However,the impact of tree mixtures on Collembola communities following stand development in natural forests remains unclear,despite the critical roles Collembola plays in litter decomposition and nutrient cycling.We investigated the effects of tree species mixtures on Collembola abundance,diversity,and community structure by sampling pure and mixed jack pine(Pinus banksiana Lamb.)and trembling aspen(Populus tremuloides Michx.)of 15-year-old and 41-year-old stands in natural boreal forest.In total,6,620 individuals of Collembola were identified as belonging to 39 species/morphospecies.Our results showed significant effects of stand types on Collembola with higher abundance and richness in conifer and mixed stands than in broadleaf stands.Additionally,with stand development,we observed increased Collembola abundance and richness.In 15-year-old stands,Collembola abundance,richness,and evenness in mixed-species stands were comparable to those in single-species stands.However,as stands developed,tree mixture effects became more pronounced,resulting in higher Collembola abundance and richness in mixed-species stands compared to the average of single-species stands in 41-year-old stands.Further,we observed positive associations between the mixture effects on Collembola abundance and richness with soil nutrient contents.We conclude that tree species mixtures can significantly enhance Collembola abundance and diversity,particularly in older stands and those with elevated soil nutrient levels.
基金This work was supported by National Priority Research and Development Program of China(2016YFD0600204)National Natural Science Foundation of China(41701264)+2 种基金Natural Science Foundation of Jiangsu Province,China(BK20170931)Natural Science Research Program(16KJB210005)Overseas Training Program and Priority Academic Program Development Funds(PAPD)of Jiangsu Higher Education Institutions.
文摘The priming effect(PE)induced by biochar provides a basis for evaluating its carbon(C)sequestration potential in soils.A 60 days’laboratory incubation was conducted,which involved the amendment of biochar(1%of soil mass)produced from rice straw at 300℃(B300)and 500℃(B500)to young(Y)and old(O)poplar plantation soils,with the aim of studying the responses of biochar-induced PEs to poplar plantation ages.This incubation included six treatments:Y+CK(control),Y+B300,Y+B500,O+CK,O+B300,and O+B500.Carbon dioxide(CO_(2))emissions were significantly increased(p<0.05)in the B300 amended soils,while it was decreased in the B500 amended soils compared to the CK.The primed CO_(2) emissions were 2.35 times higher in the Y+B300 than the O+B300 treatments,which was measured to be 18.6 and 5.56 mg C·kg^(-1) with relative PEs of 12.4%and 3.35%,respectively.However,there was little difference between the primed CO_(2) emissions in Y+B500 and O+B500 treatments,which were measured to be-24.9 and-29.6 mg·C·kg^(-1) with relative PEs of-16.6%and-17.8%,respectively.Dissolved organic carbon(DOC)was significantly lower in the young poplar plantation soil than that in the old poplar plantation soil regardless of biochar amendment throughout the incubation,indicating greater C-limit of soil microorganisms in the young poplar plantation soil.Using ^(13)C isotope tracing,neither B300 nor B500 decreased native soil-derived DOC,which indicated that the negative B500-induced PEs were not due to a reduction in the availability of native soil-derived C.In conclusion,the response of biochar-induced PEs to poplar plantation age depends on biochar types while soil available C indirectly affects biochar-induced PEs.Further studies should focus on how the interactive effects between soil C availability and microbial community impacts biochar-induced PEs.
基金supported by the Special Major Science and Technology Project of Anhui Province(S202103b06020066)the 2020 Annual Graduate Innovation Fund of Anhui Agricultural University(2020YSJ-21)。
文摘The aboveground biomass(AGB)of shrubs and small trees is the main component for the productivity and carbon storage of understory vegetation in subtropical secondary forests.However,few allometric models exist to accurately evaluate understory biomass.To estimate the AGB of five common shrub(diameter at base<5 cm,<5 m high)and one small tree species(<8 m high,trees’s seedling),206 individuals were harvested and species-specific and multi-species allometric models developed based on four predictors,height(H),stem diameter(D),crown area(Ca),and wood density(ρ).As expected,the six species possessed greater biomass in their stems compared with branches,with the lowest biomass in the leaves.Species-specific allometric models that employed stem diameter and the combined variables of D~2H andρDH as predictors accurately estimated the components and total AGB,with R^(2) values from 0.602 and 0.971.A multi-species shrub allometric model revealed that wood density×diameter×height(ρDH)was the best predictor,with R^(2) values ranging from between 0.81 and 0.89 for the components and total AGB,respectively.These results indicated that height(H)and diameter(D)were effective predictors for the models to estimate the AGB of the six species,and the introduction of wood density(ρ)improved their accuracy.The optimal models selected in this study could be applied to estimate the biomass of shrubs and small trees in subtropical regions.
文摘Available light under forest canopies includes two components, diffuse light and direct light (sunflecks), and is characterized as low and highly dynamic. Understory habitats under different forest types experience different light conditions. Sunflecks as a critical resource for understory plants have great importance on carbon gain of understory plants. Under the light-limiting habitat, understory plants exhibit a high light utilization efficiency attributed by a post-illumination CO2 uptake. Although different species have different photosynthetic responses, shade plants appear to be acclimated to respond more quickly and efficiently to sunflecks. This acclimation includes a faster induction, relatively lower rate of induction loss, lower photosynthetic compensation point, and higher water use efficiency. The process that shade plants harvest light energy is not well known. Studies of photosynthetic responses to sunflecks in natural conditions are rare. Little is known about constraints on sunfleck utilization, which may change seasonally. Extensive field studies in conjunction with laboratory investigations will be needed to further understand potential and actual constraints on sunfleck utilization. Most studies on photosynthetic responses to fluctuating light condition were done in the level of leaves. Fluctuating light utilization on the basis of whole plants and populations presents future challenges to ecologists.
基金funded by the National Natural Science Foundation of China(No.31700356)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB31000000).
文摘Forest canopy structure is closely related to species diversity,crown packing efficiency,and ecological processes,while influencing ecosystem functions.However,most existing structural diversity indices only consider internal heterogeneity within the canopy but often neglect the heterogeneity of the external canopy.While,the external canopy heterogeneity can increase the exchange surface area between canopy and external atmosphere,capture more light,which is closely linked to tree growth and ecosystem functions.Comprehensively and accurately estimating canopy structural diversity is crucial in understanding the underlying mechanisms of productivity change.Therefore,in this study,we apply a topographic index–canopy surface rugosity(CSR)–to capture canopy external heterogeneity,and use crown complementary index(CCI)and other canopy structural variables to quantify canopy internal heterogeneity.We find that CSR varies significantly among quadrats(20 m×20 m)and it decreases with species diversity and wood net primary productivity(NPP_(wood)).Species diversity increases NPP_(wood) directly and indirectly through CSR and CCI.Functional diversity increases NPP_(wood) through CSR and CCI.Community weighted mean of light demand decreases with NPP_(wood) through CCI.The mediating effect of CSR on the relationship between species(functional)diversity and NPP_(wood) is greater than the mediating effect of CCI.We find soil fertility positive effects on NPP_(wood) mainly through species richness and CSR.Conversely,water availability affects NPP_(wood) by a direct positive effect and indirect negative effects through species richness,CSR and CCI.Overall,our CSR and CCI provide strong support for a space-based niche partitioning mechanism regulating the relationship between species diversity and NPP_(wood).Additionally,CSR is sensitive to gap dynamics,suggesting mechanistic relationships between local disturbance,species diversity,and NPP_(wood).
