Long–term (25 years) continuous cotton cropping combined with residue incorporation affects the fungal communities in reclaimed saline soil

Soil fungi are essential in the degradation of crop residues in natural systems. However, how long–term continuous cropping combined with residue incorporation (CCRI) affects the fungal communities in reclaimed saline soils is still unclear. In this study, CCRI was implemented in a reclaimed salinized farmland for 0 (control group), 5, 10, 15, 20, and 25 years to explore the effects on soil properties and fungal communities. The results showed that CCRI reduced soil pH, electrical conductivity (EC), and available potassium (AK) by 2.6–8.3%, 24.0–71.4%, and 9.1–59.4%, respectively, and increased soil organ carbon (SOC), total nitrogen (TN), available phosphorus (AP), and microbial biomass carbon (MBC) by 36.0–117.2%, 84.2–173.4%, 18.5–344.8%, and 16.0–206.8%, respectively, compared with the control group (0–yr treatment). CCRI increased soil fungal species richness, but this effect decreased after 15–yr CCRI treatment; Ascomycota had the highest relative abundance (75.8–90.9%) in the CCRI soils. CCRI treatments significantly reduced the relative abundance of symbiotroph, saprotroph, and pathotroph; Especially, the relative abundance of plant pathogen fungi was significantly reduced by (25.5–36.7%), and that of arbuscular mycorrhizal fungi (AMF) was significantly increased (0.01–0.07%), compared with the control group. Besides, the main soil properties affecting soil fungal community were pH and AK. Overall, the 10 – 15 years CCRI treatment was most beneficial for soil nutrient accumulation and maintaining the richness and diversity of fungal communities. However, it also decreased the abundance of some beneficial fungi and increased soil pathogenic fungi. Therefore, the duration of CCRI can not exceed 15 years, and attention can be paid to maintaining the stability of soil fungal community by regulating soil pH and AK content to reduce the negative impact of long term CCRI. This study will have important guiding significance for soil health improvement in arid areas.