Climatic, Edaphic and Biotic Controls over Soil δ13C and δ15N in Temperate Grasslands

Xing Zhao,Li Zhang,Xingliang Xu,Min Liu,Rongxiao Che,Fang Wang,Isabel Greenberg,Xiaoyong Cui

doi:10.3390/f11040433

Abstract

Soils δ13C and δ15N are now regarded as useful indicators of nitrogen (N) status and dynamics of soil organic carbon (SOC). Numerous studies have explored the effects of various factors on soils δ13C and δ15N in terrestrial ecosystems on different scales, but it remains unclear how co-varying climatic, edaphic and biotic factors independently contribute to the variation in soil δ13C and δ15N in temperate grasslands on a large scale. To answer the above question, a large-scale soil collection was carried out along a vegetation transect across the temperate grasslands of Inner Mongolia. We found that mean annual precipitation (MAP) and mean annual temperature (MAT) do not correlate with soil δ15N along the transect, while soil δ13C linearly decreased with MAP and MAT. Soil δ15N logarithmically increased with concentrations of SOC, total N and total P. By comparison, soil δ13C linearly decreased with SOC, total N and total P. Soil δ15N logarithmically increased with microbial biomass C and microbial biomass N, while soil δ13C linearly decreased with microbial biomass C and microbial biomass N. Plant belowground biomass linearly increased with soil δ15N but decreased with soil δ13C. Soil δ15N decreased with soil δ13C along the transect. Multiple linear regressions showed that biotic and edaphic factors such as microbial biomass C and total N exert more effect on soil δ15N, whereas climatic and edaphic factors such as MAT and total P have more impact on soil δ13C. These findings show that soil C and N cycles in temperate grasslands are, to some extent, decoupled and dominantly controlled by different factors. Further investigations should focus on those ecological processes leading to decoupling of C and N cycles in temperate grassland soils.

Highlights

Soil organic matter (SOM) consists of a heterogeneous mixture of substances in various stages of decay, mainly including plant and animal residues, microbial necromass, and new substances synthesized and released by microbes into the soil [1,2]
Considering that δ13 C can be regarded as an indicator of soil organic carbon (SOC) dynamics, our results suggest that SOC dynamics in temperate grasslands are largely controlled by climatic and edaphic factors since mean annual precipitation (MAP) and Pt most dominantly affected soil 13 C values
Soil δ15 N was not correlated with MAP and mean annual temperature (MAT), while soil δ13 C

Summary

Introduction

Soil organic matter (SOM) consists of a heterogeneous mixture of substances in various stages of decay, mainly including plant and animal residues, microbial necromass, and new substances synthesized and released by microbes into the soil [1,2]. SOM is critical for soil quality and ecosystem dynamics [5,6]. SOM plays an important role in global climate change because soils could act as a potential sink for C [7,8]. A large number of studies have investigated the effects of various climatic, edaphic and biotic factors on the dynamics of C and N in soils to better understand their turnover and SOM destabilization as well as their role in climate change [9,10,11,12,13]. It is difficult to explore the dynamics of SOM by direct measurement of the change in C and N stocks due to their large size [14]. Older and more microbially-processed SOM is enriched in 13 C and 15 N compared to less-decomposed substrates [18,21]

Results

Discussion

Conclusion