Irrigation Water Source Matters: Saline Groundwater Irrigation Lowers Date Palm Root-Associated Fungal Richness and Alters Their Community Structural Patterns

Saline groundwater irrigation is commonly used in arid regions of the Middle East and North Africa for date palm (Phoenix dactylifera) cultivation, yet little is known about its impact on communities of root-associated fungi (RAF). We investigated the impact of irrigation water sources (freshwater versus saline groundwater) on date palm RAF diversity, communities, and their assembly processes. RAF richness was lower in roots under saline groundwater irrigation and was significantly related to soil and water electrical conductivity (EC), and only 25.3% of the total operational taxonomic units (OTUs) were strictly found in roots under saline groundwater irrigation. Overall, the RAF communities were distinct among irrigation water sources, wherein water pH and EC were the major structuring factors. The relative importance of drift assembly was higher for RAF distribution under saline groundwater irrigation. Saprotrophic and pathotrophic communities were also distinct between irrigation water sources and shaped by irrigation water pH. In addition, we found higher abundance of saprotrophic OTUs Acrocalymma vagum, Coprinopsis sp., and Myrothecium sp. in roots under saline groundwater irrigation. In summary, we show that saline groundwater irrigation lowers RAF richness and alters overall and guild level RAF communities (saprotroph and pathotroph), which assemble mainly through drift process, wherein overall communities are shaped by irrigation water pH and EC, while saprotrophic and pathotrophic communities are structured by water pH. The high abundance of specific saprotrophs under saline groundwater irrigation indicates their potential role in nutrient cycling and plant growth promotion in arid agroecosystems.