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

Abstract

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 and agricultural management under no fertilization, chemical fertilization, and chemical fertilization plus cow manure or crop straw. The fallowed soil had more diverse fungi and maintained 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 addition significantly upregulated the genes for T. uniseriatum melanogenesis, resulting in recalcitrant necromass formation. A remarkable carbon dioxide (CO₂) assimilation capacity of T. uniseriatum was revealed using 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. Inoculation of T. uniseriatum promoted crop growth, facilitating carbon absorption from the roots. This study highlights that the valuable microbial species resources preserved in fallowed soils can improve farmland ecosystems.