Investigating the compensatory effect of legume reseeding on soil organic carbon loss under tillage management in a saline-alkali grassland in the semi-arid region

Abstract

Tillage and reseeding are recognized as effective near-natural restoration practices for degraded grasslands. Despite of ecological restoration efforts of these practices on degraded saline-alkali grasslands in the semi-arid Songnen Plain, the focus on soil functions, particularly carbon (C) accumulation, remains inadequate. This study implemented four restoration measures—tillage (T), tillage combined with Astragalus adsurgens reseeding (TR), no-tillage and reseeding (NR), and no-tillage (N)—on degraded saline-alkali grasslands in 2017. We investigated changes in plant community characteristics and species diversity, soil physical and chemical properties, and soil organic carbon (SOC) pool in 2019 (third-year post-restoration) and 2022 (sixth-year post-restoration). The results indicate that TR had the highest coverage, above-ground biomass (AGB), and below-ground biomass (BGB) in both surveys. From 2019 to 2022, NR exhibited the most pronounced increase in coverage, whereas AGB and BGB of TR achieved the largest increment. In terms of soil properties, the TR and T treatments decreased soil total nitrogen (SN) content and soil bulk density (SBD), and the TR and NR treatments decreased pH and EC. Although SOC content and storage (TSOC) values were lower in T and TR treatments in 2019, a compensation effect with highest C accumulation rate in TR was observed in 2022. Regression analysis showed significant positive correlations between TSOC and plant community height, coverage, AGB, species richness, and SN and soil phosphorus (SP) content. Structural equation models (SEMs) further indicated that tillage practices negatively impacted TSOC. In contrast, legume reseeding, through adjustments in plant density, positively impacted TSOC, with SWC playing a pivotal role. This study quantifies the impact of tillage combined with reseeding on SOC sequestration and provides critical scientific evidence for managing the natural-based restored grasslands in semi-arid regions.