Divergent Effects of Nitrogen Addition on Soil Respiration in a Semiarid Grassland.

Cheng Zhu,Honghui Wu,Zewei Sun,Qiang Yu,Tao Sun,Yiping Ma,Kimberly J La Pierre

doi:10.1038/srep33541

Abstract

Nitrogen (N) deposition has been steadily increasing for decades, with consequences for soil respiration. However, we have a limited understanding of how soil respiration responds to N availability. Here, we investigated the soil respiration responses to low and high levels of N addition (0.4 mol N m−2 yr−1 vs 1.6 mol N m−2 yr−1) over a two-year period in a semiarid Leymus chinensis grassland in Inner Mongolia, China. Our results show that low-level N addition increased soil respiration, plant belowground biomass and soil microbial biomass carbon (MBC), while high-level N additions decreased them. Soil respiration was positively correlated with plant belowground biomass, MBC, soil temperature and soil moisture. Together plant belowground biomass and MBC explained 99.4% of variation in mean soil respiration, with plant belowground biomass explaining 63.4% of the variation and soil MBC explaining the remaining 36%. Finally, the temperature sensitivity of soil respiration was not influenced by N additions. Overall, our results suggest that low levels of N deposition may stimulate soil respiration, but large increases in N availability may decrease soil respiration, and that these responses are driven by the dissimilar responses of both plant belowground biomass and soil MBC.

Highlights

Human activities such as fossil fuel combustion, land use change, and fertilizer production have significantly increased nitrogen (N) input to the biosphere[1], which has greatly altered ecosystem structure and functions[2], including the terrestrial carbon (C) cycle
N-saturated tropical forest in southern China, low-level N additions showed no significant effect on soil respiration, while high-level N additions significantly reduced soil respiration[16]
In no-till, corn-based midwestern U.S cropping systems, soil respiration was significantly reduced with high levels of N addition (29.1 g N m−2)[27]

Summary

Introduction

Human activities such as fossil fuel combustion, land use change, and fertilizer production have significantly increased nitrogen (N) input to the biosphere[1], which has greatly altered ecosystem structure and functions[2], including the terrestrial carbon (C) cycle. Previous studies have shown that N addition impacts soil respiration by altering plant above- and belowground biomass[7] and their ratios[8], water availability[9], litter quantity and quality[10], soil microbial biomass[11,12], and temperature sensitivity[13]. Investigating plant belowground biomass and microbial biomass C (MBC) may be very helpful in explaining the underlying mechanisms of how N addition affects soil respiration. This better understanding of the underlying mechanisms driving the soil respiration response to increased N availability could help improve predictions of how soil C cycling may respond to N increases in the future and aid optimization of carbon-nitrogen-climate interaction models. We hypothesize that 1) low-level N additions should increase soil respiration, while high-level of N additions should decrease soil respiration and 2) the response of belowground biomass and MBC to N addition should highly related with soil respiration

Methods

Results

Conclusion