Soil properties and climate affect arbuscular mycorrhizal fungi and soil microbial communities in Mediterranean rainfed cereal cropping systems

Soil microorganisms are generally considered sensitive indicators of soil health and fertility. Understanding the role of environmental factors in driving soil microorganisms’ distributions is vital for sustainable crop production, particularly in vulnerable agricultural systems. This study aims to investigate the effect of environmental factors on the variation of soil microbial biomass and arbuscular mycorrhizal (AM) fungi in Mediterranean rainfed cereal systems. To do so, plant roots and soil were sampled from three cereal crops: Avena sativa L., Hordeum vulgare L. and Triticum turgidum L. growing in 24 rainfed sites from three different bioclimatic zones (sub-humid, superior semi-arid and middle semi-arid) in northern Tunisia. Soil microbial phospholipid fatty acids (PLFA) fingerprints, percentage of root length colonized by AM fungi as well as AM fungal spore density were then assessed. The redundancy analysis (RDA) revealed that soil organic matter (SOM), temperature, altitude and soil sand content accounted for 22.7 % of the variation of the microbial PLFA profiles used to estimate both soil microbial biomass and their distribution across different microbial groups. These environmental factors were the most important drivers affecting bacterial PLFAs. However, no significant relationships were observed between fungal PLFAs and environmental factors. Mycorrhizal colonization differed significantly among the different host species and regions. The RDA results indicated that environmental factors, in particular mean annual precipitation (MAP), pH, available phosphorus (P) and carbon/ nitrogen ratio (C/N) explained 44.8 % of AM fungal root colonization and spore number variation. Mycorrhizal colonization was positively correlated with pH but negatively with P, C/N and MAP. Concerning AM fungal spore number, it was positively linked to P and MAP. In contrast, it was inversely related to soil pH. Highlighting the main edaphic and climatic factors disturbing soil microorganisms, especially AM fungi, helps to better understand how environmental change will influence soil microbial communities in Mediterranean rainfed cereal systems.