Linking stand age and straw management to carbon stocks and microbial communities in tall fescue seed fields

Abstract Background and aims Perennial grass seed systems may promote soil organic carbon (SOC) storage through continuous plant cover, reduced tillage, and straw residue retention, yet few studies have explored the effects of field management practices on SOC stocks. Methods We measured SOC stocks (0–30 and 30–100 cm depth), particulate and mineral-associated organic carbon (POM and MAOM), microbial community structure, and plant biomass across 24 tall fescue seed fields of varying stand ages (2–20 years) and straw management practices (straw retention vs removal) in Oregon, USA. Results While SOC stocks did not differ among treatments at either depth, stand age and straw retention altered plant and biomass, and SOC partitioning. Specifically, older stands exhibited higher total field-level C (SOC + plant biomass) due to greater root inputs, while straw retention increased the proportion of POM in the topsoil. Together, stand age and straw retention shifted community composition and increased microbial biomass. Total PLFAs were positively correlated with %POM and soil respiration, indicating that straw retention can drive rapid C turnover. When compared to nearby land uses, tall fescue seed fields had lower topsoil C stocks than natural grasslands but higher than arable crops, underscoring the C storage potential of these systems. Conclusions Our results indicate that stand age and straw management altered SOC dynamics primarily through changes in microbial biomass and labile SOC inputs. Maintaining older perennial stands with straw retention can support higher belowground inputs and foster a larger microbial community, potentially enhancing aspects of soil health beyond SOC accumulation.