Long-term fallowing produces specific fungal taxa associated with soil carbon storage

Cropland expansion has caused the loss of soil organic carbon (SOC) and the degradation of microbial communities. Fallowing is an important strategy for soil restoration, and fungi are critical in soil fertilization. This study compared the soil properties and fungal assemblage in two adjacent environments (farmland vs. fallowing) using a 30-year field experiment composed of five treatments: fallowing or agricultural management plus no fertilization, chemical fertilization, and chemical fertilization plus cow manure or crop straw amendments. The fallowed soil had more diverse fungi and maintained a higher SOC than the artificially managed treatments. Importantly, the relative abundance of Chaetomiaceae was positively correlated with all the carbon components (SOC, dissolved organic carbon, and microbial biomass carbon) simultaneously. An RNA-Seq of Trichocladium uniseriatum, the key fungus affiliated with Chaetomiaceae, showed that straw amendment significantly upregulated the genes for T. uniseriatum melanogenesis, resulting in recalcitrant necromass formation. A remarkable CO2 assimilation capacity of T. uniseriatum was revealed by 13C-labelling assay. Therefore, T. uniseriatum improved SOC storage directly by CO2 fixation and indirectly by melanogenesis. Fertilization of agricultural systems can stimulate the growth of T. uniseriatum. T. uniseriatum inoculation promoted crop growth, facilitating C absorption from the roots. This study highlighted that the valuable microbial species resources preserved in fallowed soils can improve farmland ecosystems.