A laboratory simulated freeze-thaw was conducted to determine the effects of freeze-thaw on soil nutrient availability in temperate semi-arid regions. Soil samples were collected from sandy soils （0-20 cm） of three ...A laboratory simulated freeze-thaw was conducted to determine the effects of freeze-thaw on soil nutrient availability in temperate semi-arid regions. Soil samples were collected from sandy soils （0-20 cm） of three typical ecosystems （grassland, Mongolian pine plantation and poplar plantation） in southeastern Keerqin Sandy Lands of China and subjected to freeze-thaw treatment （-12℃ for 10 days, then r 20℃ for 10 days） or incubated at constant temperature （20℃ for 20 days）. Concentrations of the soil NO3^--N, NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P （MBP） were determined on three occasions： at the start of the incubation, immediate post-thawing and at the 10th day post-thawing. The results showed that soil net nitrification and N mineralization rates at three sites were negatively affected by freeze-thaw treatment, and decreased by 50%-85% as compared to the control, of which the greatest decline occurred in the soil collected from poplar plantation. In contrast, the concentration of soil NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P were insignificantly influenced by freeze-thaw except that LPi and NH4^＋-N showed a slight increase immediate post-thawing. The effects of freeze-thaw on soil N transformation were related to soil biological processes and the relatively constant available P was ascribed to severe soil aridity.展开更多
Background:Scaling sap flux measurements to whole-tree water use or stand-level transpiration is often done using measurements conducted at a single point in the sapwood of the tree and has the potential to cause sign...Background:Scaling sap flux measurements to whole-tree water use or stand-level transpiration is often done using measurements conducted at a single point in the sapwood of the tree and has the potential to cause significant errors.Previous studies have shown that much of this uncertainty is related to(i)measurement of sapwood area and(ii)variations in sap flow at different depths within the tree sapwood.Results:This study measured sap flux density at three depth intervals in the sapwood of 88-year-old red pine(Pinus resinosa)trees to more accurately estimate water-use at the tree-and stand-level in a plantation forest near Lake Erie in Southern Ontario,Canada.Results showed that most of the water transport(65%)occurred in the outermost sapwood,while only 26%and 9%of water was transported in the middle and innermost depths of sapwood,respectively.Conclusions:These results suggest that failing to consider radial variations in sap flux density within trees can lead to an overestimation of transpiration by as much as 81%,which may cause large uncertainties in water budgets at the ecosystem and catchment scale.This study will help to improve our understanding of water use dynamics and reduce uncertainties in sap flow measurements in the temperate pine forest ecosystems in the Great Lakes region and help in protecting these forests in the face of climate change.展开更多
Parasites are globally widespread pathogenic organisms,which impose im portant selective forces upon their hosts.Thus,in accordance with the A djustm ent to parasite pressure hypothesis,it is expected that defenses am...Parasites are globally widespread pathogenic organisms,which impose im portant selective forces upon their hosts.Thus,in accordance with the A djustm ent to parasite pressure hypothesis,it is expected that defenses among hosts vary relative to the selective pressure imposed by parasites.According to the latitudinal gradient in diversity,species richness and abundance of parasites peak near the equator.The uropygial gland is an im portant defensive exocrine gland against pathogens in birds.Size of the uropygial gland has been proposed to vary among species of birds because of divergent selection by pathogens on their hosts.Therefore,we should expect that bird species from the tropics should have relatively larger uropygial glands for their body size than species from higher latitudes.However,this hypothesis has not yet been explored.Here,we analyze the size of the uropygial gland of 1719 individual birds belonging to 36 bird species from 3 Neotropical(Peru)and 3 temperate areas(Spain).Relative uropygial gland volum e was 12.52%larger in bird species from the tropics than from temperate areas.This finding is consistent w ith the relative size of this defensive organ being driven by selective pressures imposed by parasites.We also explored the potential role of this gland as a means of avoiding haemosporidian infection,showing that species with large uropygial glands for their body size tend to have lower mean prevalence of haemosporidian infection,regardless o f their geographical origin.This result provides additional support for the assum ption that secretions from the uropygial gland reduce the likelihood of becoming infected with haemosporidians.展开更多
In the reconstruction of past climate using stable carbon isotope composition (δ13C) in tree ring,the responses of the stable carbon composition (δ13C) of multiple tree species to environmental factors must be known...In the reconstruction of past climate using stable carbon isotope composition (δ13C) in tree ring,the responses of the stable carbon composition (δ13C) of multiple tree species to environmental factors must be known detailedly. This study presented two δ13C series in annual tree rings for Chinese hem-lock (Tsuga chinensis Pritz) and alpine pine (Pinus densata Mast),and investigated the relationships between climatic parameters and stable carbon discrimination (△13C) series,and evaluated the poten-tial of climatic reconstruction using △13C in both species,in a temperate-moist region of Chuanxi Pla-teau,China. The raw δ13C series of the two species was inconsistent,which may be a result of different responses caused by tree's inherent physiological differences. After removing the low-frequency ef-fects of CO2 concentration,the high-frequency (year-to-year) inter-series correlation of △13C was strong,indicating that △13C of the two tree species were controlled by common environmental conditions. The △13C series of the species were most significantly correlated with temperature and moisture stress,but in different periods and intensity between the species. During the physiological year,the impacts of temperature and moisture stress on △13C occur earlier for Chinese hemlock (previous December to February for moisture stress and February to April for temperature,respectively) than for alpine pine (March to May for moisture stress and April to July for temperature,respectively). In addition,in temperate-moist regions,the control on △13C of single climatic parameter was not strongly dominant and the op-timal multiple regressions functions just explained the 38.5% variance of the total. Therefore,there is limited potential for using δ13C alone to identify clear,reliable climatic signals from two species.展开更多
Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures,function realization,and community succession.However,little is known about how abiotic and bi...Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures,function realization,and community succession.However,little is known about how abiotic and biotic drivers affect the diversity of understory species in cold temperate coniferous forests in the semiarid climate region of North China.We hypothesized that(1)topographic factors are important environmental factors affecting the distribution and variation of understory strata,and(2)different understory strata respond differently to environmental factors;shrubs may be significantly affected by the overstory stratum,and herbs may be more affected by surface soil conditions.To test these hypotheses,we used the boosted regression tree method to analyze abiotic and biotic environmental factors that influence understory species diversity,using data from 280 subplots across 56 sites in cold temperate coniferous forests of North China.Elevation and slope aspect were the dominant and indirect abiotic drivers affecting understory species diversity,and individual tree size inequality(DBH variation)was the dominant biotic driver of understory species diversity;soil water content was the main edaphic factors affecting herb layers.Elevation,slope aspect,and DBH variation accounted for 36.4,14.5,and 12.1%,respectively,of shrub stratum diversity.Shrub diversity decreased with elevation within the range of altitude of this study,but increased with DBH variation;shrub diversity was highest on north-oriented slopes.The strongest factor affecting herb stratum species diversity was slope aspect,accounting for 25.9%of the diversity,followed by elevation(15.7%),slope(12.2%),and soil water content(10.3%).The highest herb diversity was found on southeast-oriented slopes and the lowest on northeast-oriented slopes;herb diversity decreased with elevation and soil water content,but increased with slope.The results of the study provide a reference for scientific management and biodiversity protection in cold temperate conifer展开更多
基金the grants from the National Natural Science Foundation of China (No. 30471377)the National Key Basic Research Program of China (No. 2007CB106803)the National Key Technologies R & D Program of China (No. 2006BAD26B0201-1)
文摘A laboratory simulated freeze-thaw was conducted to determine the effects of freeze-thaw on soil nutrient availability in temperate semi-arid regions. Soil samples were collected from sandy soils （0-20 cm） of three typical ecosystems （grassland, Mongolian pine plantation and poplar plantation） in southeastern Keerqin Sandy Lands of China and subjected to freeze-thaw treatment （-12℃ for 10 days, then r 20℃ for 10 days） or incubated at constant temperature （20℃ for 20 days）. Concentrations of the soil NO3^--N, NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P （MBP） were determined on three occasions： at the start of the incubation, immediate post-thawing and at the 10th day post-thawing. The results showed that soil net nitrification and N mineralization rates at three sites were negatively affected by freeze-thaw treatment, and decreased by 50%-85% as compared to the control, of which the greatest decline occurred in the soil collected from poplar plantation. In contrast, the concentration of soil NH4^＋-N, NaHCO3 extractable inorganic P （LPi） and microbial biomass P were insignificantly influenced by freeze-thaw except that LPi and NH4^＋-N showed a slight increase immediate post-thawing. The effects of freeze-thaw on soil N transformation were related to soil biological processes and the relatively constant available P was ascribed to severe soil aridity.
基金funded by the Natural Sciences and Engineering Research Council(NSREC)the Global Water Futures Program(GWF)the Ontario Ministry of Environment,Conservation and Parks(MOECP).
文摘Background:Scaling sap flux measurements to whole-tree water use or stand-level transpiration is often done using measurements conducted at a single point in the sapwood of the tree and has the potential to cause significant errors.Previous studies have shown that much of this uncertainty is related to(i)measurement of sapwood area and(ii)variations in sap flow at different depths within the tree sapwood.Results:This study measured sap flux density at three depth intervals in the sapwood of 88-year-old red pine(Pinus resinosa)trees to more accurately estimate water-use at the tree-and stand-level in a plantation forest near Lake Erie in Southern Ontario,Canada.Results showed that most of the water transport(65%)occurred in the outermost sapwood,while only 26%and 9%of water was transported in the middle and innermost depths of sapwood,respectively.Conclusions:These results suggest that failing to consider radial variations in sap flux density within trees can lead to an overestimation of transpiration by as much as 81%,which may cause large uncertainties in water budgets at the ecosystem and catchment scale.This study will help to improve our understanding of water use dynamics and reduce uncertainties in sap flow measurements in the temperate pine forest ecosystems in the Great Lakes region and help in protecting these forests in the face of climate change.
基金This work was supported by the Spanish Ministry of Economy and Competitiveness research projects[grant CGL2015-64650P]Junta de Extremadura[grant IB16121]S.M.and A.M.were supported by a Ph.D.grant from the Ministry of Economy and Competition of Spain and a mobility grant of Junta de Extremadura(129/2015),respectively.L.G.-L.was supported by the Junta de Extremadura[PO17024,Post-Doc grant].
文摘Parasites are globally widespread pathogenic organisms,which impose im portant selective forces upon their hosts.Thus,in accordance with the A djustm ent to parasite pressure hypothesis,it is expected that defenses among hosts vary relative to the selective pressure imposed by parasites.According to the latitudinal gradient in diversity,species richness and abundance of parasites peak near the equator.The uropygial gland is an im portant defensive exocrine gland against pathogens in birds.Size of the uropygial gland has been proposed to vary among species of birds because of divergent selection by pathogens on their hosts.Therefore,we should expect that bird species from the tropics should have relatively larger uropygial glands for their body size than species from higher latitudes.However,this hypothesis has not yet been explored.Here,we analyze the size of the uropygial gland of 1719 individual birds belonging to 36 bird species from 3 Neotropical(Peru)and 3 temperate areas(Spain).Relative uropygial gland volum e was 12.52%larger in bird species from the tropics than from temperate areas.This finding is consistent w ith the relative size of this defensive organ being driven by selective pressures imposed by parasites.We also explored the potential role of this gland as a means of avoiding haemosporidian infection,showing that species with large uropygial glands for their body size tend to have lower mean prevalence of haemosporidian infection,regardless o f their geographical origin.This result provides additional support for the assum ption that secretions from the uropygial gland reduce the likelihood of becoming infected with haemosporidians.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 90211018, 40501076 and 40371118)the International Partnership Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-2)the Innovation Project of the Key Laboratory of Cryosphere and Environment, Cold and Arid Re-gions Environmental and Engineering Research Institute, Chinese Academy of Sciences
文摘In the reconstruction of past climate using stable carbon isotope composition (δ13C) in tree ring,the responses of the stable carbon composition (δ13C) of multiple tree species to environmental factors must be known detailedly. This study presented two δ13C series in annual tree rings for Chinese hem-lock (Tsuga chinensis Pritz) and alpine pine (Pinus densata Mast),and investigated the relationships between climatic parameters and stable carbon discrimination (△13C) series,and evaluated the poten-tial of climatic reconstruction using △13C in both species,in a temperate-moist region of Chuanxi Pla-teau,China. The raw δ13C series of the two species was inconsistent,which may be a result of different responses caused by tree's inherent physiological differences. After removing the low-frequency ef-fects of CO2 concentration,the high-frequency (year-to-year) inter-series correlation of △13C was strong,indicating that △13C of the two tree species were controlled by common environmental conditions. The △13C series of the species were most significantly correlated with temperature and moisture stress,but in different periods and intensity between the species. During the physiological year,the impacts of temperature and moisture stress on △13C occur earlier for Chinese hemlock (previous December to February for moisture stress and February to April for temperature,respectively) than for alpine pine (March to May for moisture stress and April to July for temperature,respectively). In addition,in temperate-moist regions,the control on △13C of single climatic parameter was not strongly dominant and the op-timal multiple regressions functions just explained the 38.5% variance of the total. Therefore,there is limited potential for using δ13C alone to identify clear,reliable climatic signals from two species.
基金supported by the National Natural Science Foundation of China(Grant No.31470630)Shanxi Forestry Science and Technology Innovation Project
文摘Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures,function realization,and community succession.However,little is known about how abiotic and biotic drivers affect the diversity of understory species in cold temperate coniferous forests in the semiarid climate region of North China.We hypothesized that(1)topographic factors are important environmental factors affecting the distribution and variation of understory strata,and(2)different understory strata respond differently to environmental factors;shrubs may be significantly affected by the overstory stratum,and herbs may be more affected by surface soil conditions.To test these hypotheses,we used the boosted regression tree method to analyze abiotic and biotic environmental factors that influence understory species diversity,using data from 280 subplots across 56 sites in cold temperate coniferous forests of North China.Elevation and slope aspect were the dominant and indirect abiotic drivers affecting understory species diversity,and individual tree size inequality(DBH variation)was the dominant biotic driver of understory species diversity;soil water content was the main edaphic factors affecting herb layers.Elevation,slope aspect,and DBH variation accounted for 36.4,14.5,and 12.1%,respectively,of shrub stratum diversity.Shrub diversity decreased with elevation within the range of altitude of this study,but increased with DBH variation;shrub diversity was highest on north-oriented slopes.The strongest factor affecting herb stratum species diversity was slope aspect,accounting for 25.9%of the diversity,followed by elevation(15.7%),slope(12.2%),and soil water content(10.3%).The highest herb diversity was found on southeast-oriented slopes and the lowest on northeast-oriented slopes;herb diversity decreased with elevation and soil water content,but increased with slope.The results of the study provide a reference for scientific management and biodiversity protection in cold temperate conifer
