Litter species richness and mycorrhizal symbionts improving soil carbon and nitrogen depends on soil macroaggregates and glomalin accrual

Abstract Background: Biodiversity loss may seriously impact essential ecological functions, such as nutrient cycling. How litter diversity affects soil carbon and nitrogen cycles in high-latitude forests in northeast China remains unknown. Methods: We collected fresh litter from 8 tree species in Northeast China and incubated it with native soils for one year. This experiment included 107 treatments representing four species richness (1, 2, 4, and 8) and different arbuscular mycorrhizal (AM) abundance (0, 25%, 50%, 75%, and 100%). The soil aggregate fractions and the contents of glomalin-related soil protein (GRSP), soil organic carbon (SOC), and total nitrogen (TN) in different aggregate fractions were measured. Results: The increase in litter species richness and AM abundance promoted SOC and TN accrual in macroaggregates (0.25-2 mm). Meanwhile, the same treatment also increased the proportion of macroaggregates and decreased that of silt and clay (< 0.053 mm). The SOC and TN accrual were accompanied by the increase of easily extractable GRSP (EEG) and total GRSP (TG) in macroaggregates and their decrease in silt and clay. Structure equation modeling revealed that aggregate stability was directly increased by EEG (0.476) and TG (0.276). Litter species richness (0.182), AM (0.321), and TG (0.43) directly promoted the SOC accumulation, while litter species richness (0.338), TG (0.331), and EEG (0.203) increased the TN content in the bulk soil. Conclusion: This study has proved that macroaggregates and GRSP play vital roles in improving the SOC and TN accrual through the increase of litter species richness and AM abundance.