Lycium barbarum L. (goji berry) monocropping causes microbial diversity loss and induces Fusarium spp. enrichment at distinct soil layers

Abstract

Abstract The high salt- and drought-tolerance of Lycium barbarum L. (goji berry) makes the plant suitable for cultivation in the arid and semi-arid regions of northwest China. However, monocropping of L. barbarum has caused severe issues, including increasing plant disease incidents and declining goji berry productivity. The negative impacts of L. barbarum monocropping on the soil health over time remain unclear. We investigated the temporal shifts in soil properties and microbial community diversity in the top (0–20\xa0cm) and subsoils (20–40\xa0cm) of L. barbarum fields across a 20-year age sequence and the adjacent control fields at two independent research sites in Ningxia, China. Our results show that L. barbarum monocropping leads to accumulation of total organic C, N, P, and available N stocks, but simultaneously caused secondary soil salinization and soil pH declination. The community α-diversity indices and the dissimilarities in community compositions of bacteria and fungi generally decline with the increase in stand age at both soil depths. Co-occurrence analysis found a decreased complexity of network structure with stand development, indicating that monocropping would profoundly disrupt the potential interactions among soil microbes. The phytopathogenic fungi Fusarium spp. progressively prevailed in soils of L. barbarum fields. The structural equation modeling further demonstrates that the variation in bacterial community composition directly explained the increase in the absolute abundance of Fusarium spp. The results infer an essential role of soil bacterial assemblages in the biocontrol of Fusarium wilt of L. barbarum under monocropping. Together, our results suggest that secondary soil salinization, loss of soil microbial diversity, and build-up of fungal phytopathogens, particularly in subsoils, are major threats to the soil health of L. barbarum field. An in-depth understanding of these threats to soil quality could help develop sustainable cropping management for L. barbarum.