Responses of soil organic carbon and nitrogen to land-use changes in a semiarid region of northwest China

Abstract

Currently, we lack a clear understanding of how climate influences the responses of soil organic carbon (OC) and nitrogen (N) to land-use changes in semiarid regions. Thus, to clarify the mechanisms involved, we measured the soil OC and total N (TN) concentrations and stocks in the 0–100 cm soil layer in adjacent grassland, farmland, and woodland at five sites on the Loess Plateau in China, which varied in terms of the mean annual precipitation (MAP) and mean annual temperature (MAT). The farmland or woodland was converted from grassland at each site. Conversion of grassland to farmland significantly reduced the soil OC and TN, with greater decreases in sites with relatively lower MAP and MAT (–0.60 Mg OC ha⁻¹yr⁻¹ and –0.22 Mg TN ha⁻¹yr⁻¹, respectively) than sites with relatively higher MAP and MAT (–0.35 Mg OC ha⁻¹yr⁻¹ and –0.04 Mg TN ha⁻¹yr⁻¹). Conversion of grassland to woodland increased OC and TN at sites with higher MAP and MAT, but decreased them at sites with lower MAP and MAT. OC and TN increased to a depth of 100 cm with MAP and MAT after this land-use change. OC and TN decreased at relatively drier and colder sites, but increased at relatively wetter and warmer sites. These findings provide insights into the effects of land-use changes on the soil OC and TN under different climate conditions, thereby facilitating the sustainable management of grasslands in semiarid regions.

Keywords:

• Farmland
• grassland
• the Loess plateau
• pine forest
• shrub land

Acknowledgments

We thank Cheng J, Li S, Feng C, Hua J, Yao Z, Ma B, and Cong H for their help in field and laboratory experiments. We also thank the editor and three reviewers for their comments that improved the quality of this paper. We would like to thank Professor Simon Queenborough at the Yale University and Dr. Duncan E. Jackson for assistance with English language editing of the manuscript.

Additional information

Funding

This study was supported by the National Key Research and Development Program [No. 2016YFC0500704], the National Natural Science Foundation of China [41471244 and 41622105], the Youth Innovation Team of Shaanxi Universities, the Programs from Shaanxi Province [2015JQ4103] and Chinese Academy of Sciences [QYZDB-SSW-DQC039].