Plant invasion-induced shifts in the soil microbial community along altitudinal gradient
To understand the underlying mechanisms of interactions between plant invasion and soil microbes, the facilitation of nutrient pools by soil microbial communities for plant performance has recently attracted research attention (Dawson & Schrama 2016; Dawkins & Esiobu 2018). In this regard, the role of soil microbial community in determining invasion success along the altitudinal gradient in mountain landscapes has been little explored yet. Towards this end, our study examines the effect of invasive L.vulgare on soil microbial communities’ composition, richness and diversity by disentangling the differences between invaded and uninvaded plots across multiple sites along an altitudinal gradient in Kashmir Himalaya.
The drivers of global environmental change have the potential to disrupt ecological interactions between plants and microbes, thereby influencing the community structure and ecosystem functioning from local to global scales (Cavicchioli et al., 2019; Rudgers et al., 2020). The importance of microbial responses to drivers of change creates the context-dependent plant-microbe pairs in terms of temporal or spatial mismatches that accompany species’invasions and climate change-driven range shifts (Rudgers et al., 2020). In this regard, the microbes may respond differently to the drivers of change varying across spatial scales. In the present study, the abundance patterns of soil microbial communities in plots as well as among sites were significantly altered along the altitudinal gradient. Generally, an increase in altitude changes the environmental conditions in mountains, and a decrease in microbial abundance along altitudinal gradients is expected (Slater et al., 2008). However, our results have shown that microbial community composition shows an increasing trend with increase in altitude, which is similar to results of some recent studies (Siles et al., 2016, Siles & Margesin 2016). Higher nutrient availability and less immobilization rates at higher altitudes may lead to enhanced microbial growth, which in turn could explain the higher bacterial and fungal abundance at high altitudes (Doolittle et al., 2006). We also observed increased microbial abundance in all the invaded plots as compared to uninvaded ones at all altitudes except the highest altitude KD site. Some recent studies (Yang et al. 2020, Wang et al.2020) have also shown that invasion bySpartina alterniflora and Bidens alba greatly enhanced the abundance and diversity of soil bacterial communities. Likewise, an increase in soil fungal diversity has been reported in case of invasion by Erigeron annuus , Solidago canadensis and Wedelia trilobata (Schroeder et al., 2013, Wang et al., 2018).
We observed an increased abundance of several bacterial and fungal phyla in the L.vulgare invaded plots (Fig. 2a, b). Abundance of specific bacterial and fungal taxa belonging to the Acidobacteria and Ascomycota have been reported to increase with the increasing invasion levels (Rodrigues et al., 2015; Kong et al., 2017), while as opposite trend for Actinobacteria. The higher abundance of Chloroflexi has been found to contribute to soil fertilization and promote plant growth (Hug et al., 2013). The phylum Glomeromycota, which includes many arbuscular mycorrhizal (AM) fungi forming symbiotic association with plants (Rodriguez et al., 2004), were found at relatively higher abundance in the plots invaded by L.vulgare . This indicates that the symbiotic interaction possibly facilitates invasion by L.vulgare , a finding which has been previously reported for the Conyza canadensis andThismia sp. as well (Zhang et al., 2020; Merckx et al., 2017). Our results clearly indicate that the increasing relative abundance of various taxa in the invaded plots facilitated L. vulgare growth compared to uninvaded plots along the altitudinal gradient.