摘要
Background:Nitrogen(N)saturation theory proposes that an ecosystem might switch from N limitation to carbon(C),phosphorus(P),or other nutrient limitations if it receives continuous N input.Yet,after N limitation is removed,which nutrient is the most limited and whether topography modulates such change is rarely tested at a microbial level.Here,we conducted a two-year N addition experiment under two different topography positions(i.e.a slope and a valley)in a N-saturated subtropical forest.Soil enzyme activity was measured,and ecoenzymatic stoichiometry indexes were calculated as indicators of microbial resource limitation.Results:In the valley,two-year N addition changed the activity of all studied enzymes to various degrees.As a result,microbial C limitation was aggravated in the valley,and consequently microbial decomposition of soil labile organic C increased,but microbial P limitation was alleviated due to the stoichiometry balance.On the slope,however,N addition did not significantly change the activity of the studied enzymes,and did not alter the status of microbial resource limitation.Conclusions:These results indicate that C is a more limited element for microbial growth than P after removing N limitation,but we also highlight that topography can regulate the effect of N deposition on soil microbial resource limitation in subtropical forests.These findings provide useful supplements to the N saturation theory.
基金
funded by the Strategic Priority Research Program of Chinese Academy of Sciences(XDA13010302)
the National Natural Science Foundation of China(Nos.31872691,41877094,and 31760153)
Guangxi Bagui Scholarship Program to Dejun Li
National High-Level Talents Special Support Program to Dejun Li.