Legume intercropping improves soil organic carbon stability in drylands: A 7-year experimental validation

Abstract

Improving soil organic carbon (SOC) stability is crucial for mitigating climate change and building resilient agroecosystems, and the legume-based crop diversification is accepted as an important initiative to improve SOC stock. We hypothesize that legume-based intercropping stabilizes SOC by modifying microbial communities and enzyme stoichiometry. However, experimental validation in this area remains limited. Over seven consecutive years, we established potato–soybean intercropping and corresponding monoculture trials to investigate the formation and transformation of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), microbial necromass, and SOC stability in relation to microbial and enzyme stoichiometry. Compared to potato monoculture, intercropping significantly decreased free POC content by 12.9 % (from 1.98 g kg⁻¹ to 1.72 g kg⁻¹), and increased MAOC content by 17.8 % (from 6.09 g kg⁻¹ to 7.18 g kg⁻¹). Intercropping also increased SOC content by 7.8 % (from 11.37 g kg⁻¹ to 12.27 g kg⁻¹) and improved SOC stability by 22.8 % (p < 0.05). High nitrogen legacy in intercropping systems intensified microbial stoichiometric demand for carbon and phosphorus. This trend further shifted microbial community composition and diversity to favor POC transformation. Simultaneously, fungal community proliferation accelerated fungal necromass accumulation and MAOC formation, thereby enhancing SOC stability. These findings reveal that SOC stability is regulated by a trade-off between microbial community characteristics and enzyme stoichiometry. These insights highlight the functional role of legume-based intercropping in stabilizing SOC pools and its potential contribution to enhancing the resilience of dryland agroecosystems to climate change.