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.