Abstract: Aims Grassland plant roots and mycorrhizal fungi are the main sources of soil organic carbon, which play an important role in the formation and turnover of soil organic carbon and its components, and they also affect the soil nitrogen pool. Under the scenario of climate change, global drought events are frequent. How drought regulates the effects of roots and mycorrhizal fungi on soil carbon and nitrogen pools of different components is still unclear. Methods In this study, Cleistogenes squarrosa was planted in indoor pots and subjected to control and drought treatments. Root bags and mycorrhizal bags were set up to distinguish the effects of plant roots and mycorrhizal fungi on the carbon and nitrogen content of soil organic matter and its components during plant growth. After 64 days of plant growth, the plants were harvested. The soil inorganic nitrogen content, plant biomass, plant leaf carbon and nitrogen content, carbon and nitrogen content of soil organic matter and its components in root bags and mycorrhizal bags, and microbial community composition were measured. Important findings The results showed that compared with mycorrhizal bags without root participation, the soil organic carbon and particulate organic carbon content in the root bags enhanced by 17.5% and 55.8%, and the mineral-bound organic nitrogen content increased by 10.1%. Drought treatment increased soil inorganic nitrogen content, reduced plant biomass, had no significant effect on the carbon and nitrogen content of soil organic matter and its components in the root bag, but significantly reduced the content of particulate organic carbon in the mycorrhizal bag. Drought treatment did not significantly change the microbial biomass in the root bag, but increased the microbial biomass in the mycorrhizal bag. The particulate organic carbon content in the mycorrhizal bags was negatively correlated with the amount of mycorrhizal fungi and the total microbial biomass. The results showed that during plant growth, the roots mainly affected the content of particulate organic carbon in the soil, and mycorrhizal fungi mainly affected the content of mineral-bound organic nitrogen. Short-term drought would reduce the content of particulate organic carbon in the soil in which mycorrhizal fungi participated. Future research should pay more attention to how global change affects the relative contribution of grassland plant roots and mycorrhizal fungi to soil organic matter and its components and their soil organic carbon and nitrogen potential on a long-term scale.

Key words: plant roots, mycorrhizal fungi, soil organic matter, particulate organic matter, mineral-associated organic matter, drought