Aims Elevated anthropogenic nitrogen(N)deposition could alter N status in temperate steppe.However,threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems.R...Aims Elevated anthropogenic nitrogen(N)deposition could alter N status in temperate steppe.However,threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems.Research on the natural abundance of ^(15)N( δ^(15)N)could greatly help provide integrated information about ecosystem N status.The goal of this study was to investigate the suitability of measurements of δ^(15)N of major ecosystem N pools and several key species,plant ^(15)N fractionation,together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia.Methods We carried out a N addition experiment during 2011-14 on a Stipa krylovii steppe in Inner Mongolia,Northern China.We investigated the response of several key N transformation processes,vegetation and soil properties to N addition.Aboveground biomass and below-ground biomass(BGB) δ^(15)N,root and foliar δ^(15)N of three dominant species(Artemisia frigida,S.krylovii and Leymus chinensis), δ^(15)N of soil total N and soil KCl-extractable NO_(3)^(−)-N were determined.The responses of isotope fractionation during plant N uptake and reallo-cation to N addition were also determined.Important Findings Our results suggest that the N addition rate of 5g N m^(−2) yr^(−1) could be regarded as threshold of early N saturation in this S.krylovii steppe as indicated by an increase in plant fraction-ation and a decrease in plant δ^(15)N.When N input rate is>10 g N m^(-2) yr^(-1),increased N deposition can lead to an apparent reduction in species richness and BGB as well as an increase in NO_(3)^(−)in extractable soil pools<30-cm soil profile.With N addition,S.krylovii and A.frigida undergo earlier N status shift from N limitation toward N excess compared with L.chinen-sis,contributing to L.chinensis out-competing other species.Overall,this study provides a better understanding of N status change in temperate steppe based on isotope evidence and several other functional variables and contributes to predicting the responses of temperate steppe to future global N deposition scenario.展开更多
基金This study was funded by the projects of the National Natural Science Foundation of China(No.41371069).Conflict of interest statement.None declared.
文摘Aims Elevated anthropogenic nitrogen(N)deposition could alter N status in temperate steppe.However,threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems.Research on the natural abundance of ^(15)N( δ^(15)N)could greatly help provide integrated information about ecosystem N status.The goal of this study was to investigate the suitability of measurements of δ^(15)N of major ecosystem N pools and several key species,plant ^(15)N fractionation,together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia.Methods We carried out a N addition experiment during 2011-14 on a Stipa krylovii steppe in Inner Mongolia,Northern China.We investigated the response of several key N transformation processes,vegetation and soil properties to N addition.Aboveground biomass and below-ground biomass(BGB) δ^(15)N,root and foliar δ^(15)N of three dominant species(Artemisia frigida,S.krylovii and Leymus chinensis), δ^(15)N of soil total N and soil KCl-extractable NO_(3)^(−)-N were determined.The responses of isotope fractionation during plant N uptake and reallo-cation to N addition were also determined.Important Findings Our results suggest that the N addition rate of 5g N m^(−2) yr^(−1) could be regarded as threshold of early N saturation in this S.krylovii steppe as indicated by an increase in plant fraction-ation and a decrease in plant δ^(15)N.When N input rate is>10 g N m^(-2) yr^(-1),increased N deposition can lead to an apparent reduction in species richness and BGB as well as an increase in NO_(3)^(−)in extractable soil pools<30-cm soil profile.With N addition,S.krylovii and A.frigida undergo earlier N status shift from N limitation toward N excess compared with L.chinen-sis,contributing to L.chinensis out-competing other species.Overall,this study provides a better understanding of N status change in temperate steppe based on isotope evidence and several other functional variables and contributes to predicting the responses of temperate steppe to future global N deposition scenario.
