Relationship between soil microbial communities and nutrient parameters
In the present study, the most important variables explaining bacterial community composition was TOC in invaded plots and SAL in uninvaded plots (Table 2). It has been reported that soil nutrients provide ample substrates to stimulate the growth of bacteria and serve as drivers of bacterial diversity and abundance (Santonja et al., 2017; Yu et al., 2019). The significantly increased soil bacterial abundance and diversity following L.vulgare invasion can be possibly a result of the TOC levels, which provides enriched substrates for the proliferation of bacteria (Yu et al., 2019). Higher values of soil salinity were observed in the invaded plots (Table 1), but showed a significantly negative correlation with uninvaded plots (Table 2). By altering the osmotic potential of soils, high salinity can lead to alterations in microbial community structure with reduced microbial biomass and can restrict the growth of heterotrophic bacteria (Kamble et al., 2014; Xi et al., 2014). Among other variable examined, WC in plots were most significantly and closely correlated with fungal community structures (Table 2 ). Canini et al., (2019) has reported that water content and pH has a strong effect on fungal community composition and found a positive relationship between the fungal richness and the vegetation cover. Similarly, invasion of Impatiens glanduliferahas been reported to effectively change soil characteristics particularly soil moisture and soil pH in invaded areas (Ruckli et al., 2014; Gaggini et al., 2018). Therefore, fungal communities can be influenced by soil moisture and soil pH and thus can be viewed as an indirect effect of the plant invasion.
Additionally, according to Canonical Correspondence analysis, significant correlation were observed between soil physicochemical properties and altitude, which indicates that sites with distinct soil properties possess different microbial abundances and the plot-wise distribution of both soil physicochemical properties and microbial abundances are strongly influenced by temperature, K, pH, EC and Fe (Fig.6). The present study, therefore, enhances our understanding of the altitudinal patterns of variation in soil physicochemical properties and the impact of these factors on belowground soil microbial communities to drive plant invasions in the study region.