Plant Trait‐ and Soil‐Mediated Responses of Herbaceous Aboveground Biomass Across Community Types Along a Degradation Gradient in the Desert Steppe

ABSTRACT

Grassland degradation profoundly alters the structure and function of desert steppe ecosystems. However, the responses of herbaceous aboveground biomass (Herb‐AGB) to degradation across different plant community types and the underlying mechanisms remain poorly understood. Here, we quantified changes in Herb‐AGB, species richness, plant density, community‐weighted mean (CWM) traits, functional diversity, and soil properties along a degradation gradient (based on ≥ 40%, 60%–90%, > 90% reduction in Herb‐AGB relative to nondegraded (ND) for moderately, severely, and extremely degraded, respectively) in herb‐dominated and shrub‐dominated communities of the Urat desert steppe in Inner Mongolia, China. We aimed to reveal the contrasting mechanisms regulating Herb‐AGB between the community types. We found that the degradation significantly reduced perennial grasses AGB (PG‐AGB) and total Herb‐AGB (total effect: −0.915 for herb‐dominated and −0.859 for shrub‐dominated communities), whereas AGB of annual and biennial species remained largely unchanged. Importantly, the dominant drivers of Herb‐AGB differed between community types, with CWM traits (plant height, R ²  = 0.43, p  < 0.001) primarily governing herb‐dominated communities, whereas soil available inorganic nitrogen (AIN, R ²  = 0.14, p  < 0.001) served as the primary limiting factor for biomass production in shrub‐dominated communities. Across both community types, soil pH and PG‐AGB acted as key mediators: degradation reduced Herb‐AGB not only directly but also indirectly by increasing soil alkalinity (pH effect increasing from −0.181 to −0.276, PG‐AGB effect increasing from 0.684 to 0.786). Compared with herb‐dominated communities, soil properties exerted stronger regulatory effects on biomass production in shrub‐dominated communities. These results demonstrate that degradation modifies both the magnitude and the mechanisms of biomass regulation depending on community type in desert steppe. Effective grassland restoration should therefore adopt community‐specific strategies, emphasizing the recovery of dominant plant functional traits in degraded herb‐dominated communities, while integrating shrub removal or density control with soil improvement measures in shrub‐dominated stages. Our findings provide a mechanistic basis for developing targeted management practices to sustain productivity and ecosystem functioning in degraded arid grasslands.