Long-term nitrogen application decreased mineral-associated organic carbon while increasing particulate organic carbon in purple soil in southwest China

Jun Xie; Yuanxue Chen; Rong Huang; Wencai Dai; Jie Lu; Zifang Wang; Ming Gao

doi:10.1016/j.jenvman.2024.123455

Long-term nitrogen application decreased mineral-associated organic carbon while increasing particulate organic carbon in purple soil in southwest China

J Environ Manage. 2024 Nov 25:373:123455. doi: 10.1016/j.jenvman.2024.123455. Online ahead of print.

Authors

Jun Xie¹, Yuanxue Chen², Rong Huang², Wencai Dai¹, Jie Lu¹, Zifang Wang¹, Ming Gao³

Affiliations

¹ College of Resources and Environment, Southwest University, Chongqing, 400716, China.
² College of Resources, Sichuan Agricultural University, Chengdu, 611130, China.
³ College of Resources and Environment, Southwest University, Chongqing, 400716, China. Electronic address: gaoming@swu.edu.cn.

PMID: 39603105
DOI: 10.1016/j.jenvman.2024.123455

Abstract

In recent years, anthropogenic activities have increased nitrogen (N) input into terrestrial ecosystems, profoundly impacting soil organic carbon (SOC) sequestration. However, the potential mechanisms through which N affects mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) remain unclear. To address this gap, we conducted a 12-year field trial applying continuous N application (0, 90, 180, 270, and 360 kg N·ha^-1) in a maize agro-ecosystem. We assessed plant biomass (yield, straw, and root biomass), microbial properties (enzyme activity, biomass, and diversity), soil chemistry (pH, N availability, and base ions), mineralogy (oxides and silicates), and SOC fractions to elucidate the primary control mechanisms influencing MAOC and POC. Our findings showed that N application increased SOC and POC by 6.56%-10.4% and 43.1%-54.0%, respectively, but decreased MAOC by 7.31%-17.1%. And N application increased plant biomass, but decreased soil pH (pH from 6.7 to 5.6), base ion concentrations (K⁺, Na⁺, Ca²⁺, Mg²⁺), amorphous oxides, and illite content. Partial least squares path model (PLS-PM) and correlation analyses indicated that N application enhances root biomass while increasing microbial decomposition, and ultimately their combined effect increased POC. The decline in MAOC is primarily attributed to soil acidification decreasing the C input from microbial residues, altering mineral composition and diminishing the minerals' capacity to protect SOC. Thus, our study demonstrates that N addition predominantly increases POC through enhanced root biomass, while reducing MAOC by decreasing microbial biomass and weakening mineral protection. These insights provide a deeper understanding of the mechanisms governing SOC fraction dynamics in answer to N inputs in agroecosystems.

Keywords: Mineral; Mineral associated organic carbon; Nitrogen fertilizer; Particulate organic carbon.