Plant traits, diversity, and environmental factors shape soil carbon dynamics in a restored grassland

Introduction Plant diversity and functional traits can improve ecosystem function in degraded plant communities, but there are gaps in our understanding of how to utilize plants to increase soil carbon (C) in the context of ecological restoration. Objectives This study explores how plants and environmental conditions interact to alter five soil C pools in restored grassland plots. Methods We seeded 35 grassland species in various combinations and subjected them to two precipitation and two land use history treatments. We assessed plant traits, species evenness, and five soil C pools across 2 years. We expected that acquisitive traits would increase microbial biomass (MBC), water‐extractable organic C (WEOC), and mineral‐associated organic C (MAOC) via labile tissues and root exudates, while recalcitrant tissues with opposite trait values would increase particulate organic C. Results Traits and diversity influenced several soil C pools, and relationships varied with precipitation, land use history, and year. Labile tissues had positive effects on MBC in most conditions and across multiple years, while dense roots supported MBC under wet conditions after a 1‐year delay. Plant diversity positively affected MBC and MAOC in wet conditions. Land use history was the dominant predictor for all pools except the most labile (WEOC), showing that variations in plant communities and management have enduring effects on soil C. Conclusions These results demonstrate that restored plant communities contribute to soil C through disparate pathways and on various timescales, and that environmental factors mediate the relationship between plant traits and soil C following restoration.