Microbial- rather than plant-derived carbon contributes more to organic carbon accumulation in grassland soils of northern China

Abstract

Microbial and plant residues are primary sources of soil organic carbon (SOC). However, limited research is available on their differential contributions and influencing factors to SOC accumulation in grassland soils. Here, we collected soil samples from meadow steppe (MS), typical steppe (TS), and desert steppe (DS) across the Qinghai-Xizang Plateau, Loess Plateau, and Inner Mongolia Plateau. The distributions of microbial- and plant-derived carbon and their contributions to SOC were analyzed using amino sugars and lignin phenols (LPs) biomarkers. The relationships between microbial- and plant-derived carbon with climate, vegetations, and soil properties were explored. The results showed that microbial necromass carbon (MNC) and LPs contents were higher in MS and TS than in DS. The ratio of MNC to SOC (39.0%–54.2%) was higher whereas the ratio of LPs to SOC (1.49%–4.44%) was lower in MS and TS than in DS. Furthermore, fungal necromass carbon (FNC) accounted for larger proportion (35.1%–50.3%) than bacterial necromass carbon (BNC) (3.61%–5.87%) in SOC. Redundancy analysis identified complexed iron and aluminum oxides as the most significant factor impacting MNC and LP contents. Structural equation modeling demonstrated that mean annual precipitation and temperature influenced MNC and LPs contents by affecting vegetation biomass and soil properties (pH, silt and clay, and iron and aluminum oxides), which subsequently affected SOC accumulation. The findings suggested that MNC was the dominant source of SOC in grassland soils, with FNC contributing more to SOC accumulation. Complexed iron and aluminum oxides promoted accumulation of MNC and LPs through chemical protection.

Graphical abstract

Keywords

soil organic carbon / microbial necromass / lignin phenols / grassland types / plateau transects

Highlight

	● MNC and LPs contents were higher in meadow and typical steppes than in desert steppe.
	● MNC exhibited larger contribution to SOC accumulation than LPs in grassland soils.
	● Fungal necromass contributed more to SOC accumulation than bacterial necromass.
	● Fe and Al oxides were the most key factors regulating MNC and LPs distributions.

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