Relative importance of climatic and edaphic factors as drivers of plantδ^(15)N along a longitudinal transect

Many studies have shown that climatic and edaphic factors influence the variations in nitrogen isotopes(δ^(15)N)in terrestrial ecosystems.However,the relative importance of co-varying climatic and edaphic controls on plantδ^(15)N remains somewhat unclear.To address this issue,regional-scale plant(L.chinensis)and soil samples were collected along a longitudinal transect across the temperate grasslands in northern China.The influences of climatic and edaphic factors on the plantδ^(15)N were disentangled using the variable importance in projection(VIP)approach.We found that the climatic and edaphic variables explained 52.4%and 31.2%,respectively,of the variation in plantδ^(15)N.The mean annual precipitation(MAP),soil N,and mean annual temperature(MAT)were the most important variables,but the soil water content(SWC),aridity index(AI),and soil clay content were also important variables.The soil pH and soil C:N ratios were identified as unimportant variables.Furthermore,a high-performance model for simulating plantδ^(15)N values was constructed based on the important variables(VIP>0.8).Further investigations should focus on the effects of the interaction between the climatic and edaphic variables on the N cycles in the temperate grasslands to provide more reliable predictions of plantδ^(15)N.