Global temperature has been Increased by 0.6 ℃ over the past century and is predicted to Increase by 1.4-5.8 ℃ by the end of this century. It is unclear what impacts global warming will have on tallgrass species. In...Global temperature has been Increased by 0.6 ℃ over the past century and is predicted to Increase by 1.4-5.8 ℃ by the end of this century. It is unclear what impacts global warming will have on tallgrass species. In the present study, we examined leaf net photosynthetic rate （P.） and leaf respiration rate in darkness （Rd） of Aster erlcoldes （L.） Nesom, Ambrosia psllostachya DC., Helianthus mollis Lam., and Sorghastrum nutans （L.） Nash In response to experimental warming in a tallgrass prairie ecosystem of the Great Plains, USA, in the autumn （fall） of 2000 and through 2001. Warming has been Implemented with infrared heaters since 21 November 1999. The P. increased significantly In spring, decreased in early fall, and did not change in summer and late fall in the four species under warming compared with control. The Rd of the four species increased significantly until mid-summer and then did not change under warming. Measured temperature-response curves of P. showed that warming Increased the optimum temperature of P. （Topt） by 2.32 and 4.59 ℃ for H. mollis and S. nutans, respectively, in August, whereas there were no changes in May and September, and A. ericoldes and A. psllostachya also showed no changes in any of the 3 months. However, P. at optimum temperature （Popt） showed downregulation in September and no regulation in May and August for all four species. The temperature-response curves of Rd Illustrate that the temperature sensitivity of Rd, Q10, was lower in the warmed plots compared with the control plots, except for A. ericoides in August, whereas there were no changes In May and September for all four species. The results of the present study indicate that photosynthetic and respiratory acclimation varies with species and among seasons, occurring In the mid-growing season and not in the early and late growing seasons.展开更多
Temperate grassland soils are typically a sink for carbon. However, it is estimated that up to 99% of tallgrass prairies in North America have been converted to another land use. These conversions can lead to increase...Temperate grassland soils are typically a sink for carbon. However, it is estimated that up to 99% of tallgrass prairies in North America have been converted to another land use. These conversions can lead to increased soil erosion and soil organic carbon (SOC) mineralization rates, turning a large carbon sink into a source. The purpose of this study was to compare by land use the retention of SOC, TSN, and fly ash on sloping landscapes with an emphasis on measuring the subsoil in addition to the surface soil. Eight paired plots were established on adjacent, sloping landscape profiles in western Iowa;one site a cropland and the other a remnant tallgrass prairie. The prairie landscape had a baseline SOC stock of 232 Mg-C ha-1. After roughly 150 years of agriculture the cropland had 52% less SOC, 39% less TSN, and 22% less fly ash which equates to annual losses of 0.55 Mg-C ha-1 yr-1, 0.04 Mg-N ha-1 yr-1, and 0.0002 Mg-fly ash ha-1 yr-1.展开更多
Aims In order to better understand how tornados structure the ecotone between eastern deciduous forest and tallgrass prairie,we sampled trees in a recent tornado blowdown area and in the adjacent undisturbed forest.Bo...Aims In order to better understand how tornados structure the ecotone between eastern deciduous forest and tallgrass prairie,we sampled trees in a recent tornado blowdown area and in the adjacent undisturbed forest.Both are part of the Cross Timbers ecotone of Osage County,Northeastern Oklahoma,USA.Methods We set up a 1-ha square plot in each area and sampled all tree stems at least 50 cm tall where stems were identified to species and measured for size and spatial location in both plots.For the stems in the blowdown plot,we also scored damage and resprouting.We then used the spatial location data to compute the spatial heterogeneity and degree of clumping in both areas.Important Findings Significant clumping was observed in the control forest at the small spatial scale of 1–8 m and at the medium spatial scale of 30–36 m.The blowdown area:showed domination by post oak(Quercus stellata)with small stems,branch damage and stem resprouting above 1 m most common;had no trees that either lost their leaves without branch or stem damage or lived without some sort of resprouting,had a significant negative correlation between damage and resprouting and clumped only at small spatial scales for stems of medium size,for stems with branch damage and for stems that resprouted at or below 1 m height.We conclude that in addition to largely eliminating a forest’s spatial heterogeneity,tornados may also structure this ecotone by increasing tree persistence through resprouting。展开更多
Aims and Methods Diversity-disturbance research has focused on community diversity,but disturbance frequency could impact diversity within species as well,with important consequences for community diversity and ecosys...Aims and Methods Diversity-disturbance research has focused on community diversity,but disturbance frequency could impact diversity within species as well,with important consequences for community diversity and ecosystem function.We examined patterns of genetic diversity of a dominant grass species,Andropogon gerardii,in native North American tallgrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments(burned every 1,2,4 or 20 years)since the 1970s.In addition,we were able to assess the relationships between genetic diversity of A.gerardii,species diversity and productivity across this range of fire frequencies.Important Findings We found no significant relationships between genetic diversity of A.gerardii at the local scale(1 m^(2) plot level)and disturbance frequency(burned 2 to 32 times over a 38-year period).However,at the site level(i.e.across all plots sampled within a site,~100 m^(2))there were differences in genotype richness and composition,as well as genomic dissimilarity among individuals of A.gerardii.Genotype richness was greatest for the site burned at an intermediate(4-year)frequency and lowest for the infrequently(20-year)burned site.In addition,genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites.Genotype composition of A.gerardii was not significantly different between the frequently burned sites(annual vs.2 year)but did differ between frequently burned and infrequently burned sites(1 and 2 year vs.4 and 20 year,etc.).Together,these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies,likely driven by alterations in environmental conditions.Frequent fire promotes the abundance of dominant grass species,reduces plant community diversity and impacts ecosystem processes such as productivity.Our study suggests that genetic diversity within dominant grass species also may be affected by disturbance frequency,which could have important implications for how species are able to respond to disturbance.展开更多
基金Supported by US National Science Foundation （NSF） （DEB 0078325, DEB 0092642, and DEB 0444518）, and US Department of Energy （DE-FG03- 99ER62800）. Publication of this paper is supported by the National Natural Science Foundation of China （30624808） and Science Publication Foundation of the Chinese Academy of Sciences.Acknowledgements The authors thank Dr Edwin Kessler for the donation of his farm to the University of 0klahoma for the research.
文摘Global temperature has been Increased by 0.6 ℃ over the past century and is predicted to Increase by 1.4-5.8 ℃ by the end of this century. It is unclear what impacts global warming will have on tallgrass species. In the present study, we examined leaf net photosynthetic rate （P.） and leaf respiration rate in darkness （Rd） of Aster erlcoldes （L.） Nesom, Ambrosia psllostachya DC., Helianthus mollis Lam., and Sorghastrum nutans （L.） Nash In response to experimental warming in a tallgrass prairie ecosystem of the Great Plains, USA, in the autumn （fall） of 2000 and through 2001. Warming has been Implemented with infrared heaters since 21 November 1999. The P. increased significantly In spring, decreased in early fall, and did not change in summer and late fall in the four species under warming compared with control. The Rd of the four species increased significantly until mid-summer and then did not change under warming. Measured temperature-response curves of P. showed that warming Increased the optimum temperature of P. （Topt） by 2.32 and 4.59 ℃ for H. mollis and S. nutans, respectively, in August, whereas there were no changes in May and September, and A. ericoldes and A. psllostachya also showed no changes in any of the 3 months. However, P. at optimum temperature （Popt） showed downregulation in September and no regulation in May and August for all four species. The temperature-response curves of Rd Illustrate that the temperature sensitivity of Rd, Q10, was lower in the warmed plots compared with the control plots, except for A. ericoides in August, whereas there were no changes In May and September for all four species. The results of the present study indicate that photosynthetic and respiratory acclimation varies with species and among seasons, occurring In the mid-growing season and not in the early and late growing seasons.
文摘Temperate grassland soils are typically a sink for carbon. However, it is estimated that up to 99% of tallgrass prairies in North America have been converted to another land use. These conversions can lead to increased soil erosion and soil organic carbon (SOC) mineralization rates, turning a large carbon sink into a source. The purpose of this study was to compare by land use the retention of SOC, TSN, and fly ash on sloping landscapes with an emphasis on measuring the subsoil in addition to the surface soil. Eight paired plots were established on adjacent, sloping landscape profiles in western Iowa;one site a cropland and the other a remnant tallgrass prairie. The prairie landscape had a baseline SOC stock of 232 Mg-C ha-1. After roughly 150 years of agriculture the cropland had 52% less SOC, 39% less TSN, and 22% less fly ash which equates to annual losses of 0.55 Mg-C ha-1 yr-1, 0.04 Mg-N ha-1 yr-1, and 0.0002 Mg-fly ash ha-1 yr-1.
文摘Aims In order to better understand how tornados structure the ecotone between eastern deciduous forest and tallgrass prairie,we sampled trees in a recent tornado blowdown area and in the adjacent undisturbed forest.Both are part of the Cross Timbers ecotone of Osage County,Northeastern Oklahoma,USA.Methods We set up a 1-ha square plot in each area and sampled all tree stems at least 50 cm tall where stems were identified to species and measured for size and spatial location in both plots.For the stems in the blowdown plot,we also scored damage and resprouting.We then used the spatial location data to compute the spatial heterogeneity and degree of clumping in both areas.Important Findings Significant clumping was observed in the control forest at the small spatial scale of 1–8 m and at the medium spatial scale of 30–36 m.The blowdown area:showed domination by post oak(Quercus stellata)with small stems,branch damage and stem resprouting above 1 m most common;had no trees that either lost their leaves without branch or stem damage or lived without some sort of resprouting,had a significant negative correlation between damage and resprouting and clumped only at small spatial scales for stems of medium size,for stems with branch damage and for stems that resprouted at or below 1 m height.We conclude that in addition to largely eliminating a forest’s spatial heterogeneity,tornados may also structure this ecotone by increasing tree persistence through resprouting。
基金National Science Foundation:Doctoral Dissertation Improvement Grant(NSF-DDIG),(DEB-1011371)Yale Institute for Biospheric Studies-Field Ecology Grant(YIBS)to CCC.
文摘Aims and Methods Diversity-disturbance research has focused on community diversity,but disturbance frequency could impact diversity within species as well,with important consequences for community diversity and ecosystem function.We examined patterns of genetic diversity of a dominant grass species,Andropogon gerardii,in native North American tallgrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments(burned every 1,2,4 or 20 years)since the 1970s.In addition,we were able to assess the relationships between genetic diversity of A.gerardii,species diversity and productivity across this range of fire frequencies.Important Findings We found no significant relationships between genetic diversity of A.gerardii at the local scale(1 m^(2) plot level)and disturbance frequency(burned 2 to 32 times over a 38-year period).However,at the site level(i.e.across all plots sampled within a site,~100 m^(2))there were differences in genotype richness and composition,as well as genomic dissimilarity among individuals of A.gerardii.Genotype richness was greatest for the site burned at an intermediate(4-year)frequency and lowest for the infrequently(20-year)burned site.In addition,genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites.Genotype composition of A.gerardii was not significantly different between the frequently burned sites(annual vs.2 year)but did differ between frequently burned and infrequently burned sites(1 and 2 year vs.4 and 20 year,etc.).Together,these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies,likely driven by alterations in environmental conditions.Frequent fire promotes the abundance of dominant grass species,reduces plant community diversity and impacts ecosystem processes such as productivity.Our study suggests that genetic diversity within dominant grass species also may be affected by disturbance frequency,which could have important implications for how species are able to respond to disturbance.
