Differential contributions of plant- and microbial-derived carbon to soil organic carbon under perennial and annual herbaceous species in a temperate desert grassland, Northwest China

Desert grasslands are critical carbon sinks in arid regions, where herbaceous species selection plays a vital role in ecosystem restoration. While plant life cycle (annual vs. perennial) is known to affect soil organic carbon (SOC) stocks, its influence on SOC molecular composition remains poorly understood. This study examined the accumulation and environmental drivers of plant- and microbial-derived carbon biomarkers (lignin phenols and amino sugars) across the 0-40 cm soil profile under four desert herbaceous species: perennial Karelinia caspica (Pall.) Less. and Glycyrrhiza inflata Batalin., annual Chenopodium glaucum L. and Salsola lanata (Pall.) Botsch. Plant-derived C contributed more to SOC (9-15%) than microbial-derived C (3-8%), with contributions differing significantly between plant life cycles. These differences were shaped primarily by edaphic factors: plant-derived C accumulation was mainly regulated by pH, whereas microbial-derived C was affected by labile organic carbon (LOC), elemental stoichiometry (C/N, C/P), electrical conductivity, and pH. Our results indicate that herbaceous species influence SOC sequestration through divergent plant and microbial pathways. Perennial species, especially K. caspica and G. inflata, enhance SOC storage more effectively and should be prioritised in desert grassland restoration.