AM fungi and pathogen dissimilarity predicting plant-microbial interactions strength in graminoids and forbs

Plant-microbial interactions (PMI) play a crucial role in plant growth, fitness and productivity, primarily through the mutualism and antagonism interactions between plants and soil microorganisms. The colonization of arbuscular mycorrhizal (AM) fungi and pathogen are often used to speculate on the effects of microorganisms on plant growth, i.e. plant-microbial interactions (PMI). However, empirical studies demonstrate the relationship between AM fungi or pathogen and PMI effects remains limited, especially under different biotic and abiotic conditions. Here, we evaluated the colonization rates of AM fungi and pathogen across 13 grassland species under individual or communal conditions, in both overgrazed and restored soil. Furthermore, we investigated the relationship between AM fungi or pathogen and PMI. Our results showed that forbs exhibited significantly higher rates of AM fungal colonization compared to graminoids in community condition and overgrazed soil while graminoid roots showed higher pathogen infestation compared to forbs in individual condition and overgrazed soil. Generally, there was a positive correlation between PMI and AM fungal colonization but a negative correlation between PMI and pathogen disease. The PMI of graminoids exhibited a negative correlation with pathogen disease in individual condition and overgrazed soil, but showed no correlation with AM fungal colonization. On the other hand, the PMI of forbs showed a positive correlation with AM colonization in both restored and overgrazed soil, as well as in both individual and community experiments. However, there was no correlation between PMI of forbs and pathogen disease. The PMI of graminoids and forbs in grassland ecosystems can be driven by distinct soil microorganisms. These insights enable us to better understand how soil mutualists and pathogen mediate PMI effects on plant growth, with implications for grassland management and restoration.