Low impact of Carpobrotus edulis on soil microbiome after manual removal from a climate change field experiment

Abstract

Synergic effects between climate change and invasive species may alter soil microbial diversity and functioning, as well as cause major shifts in physicochemical properties. Moreover, some of these ecological impacts may manifest even after the removal of the invasive species. We have conducted a field experiment to assess such effects on soil microbial communities (fungi and bacteria) and physicochemical properties seven months after the removal of Carpobrotus edulis (L.), an invasive plant of coastal dune ecosystems. C. edulis grew on the experimental plots for 14 months under current (“invasive species treatment”) and increased warming and drought conditions (“combined treatment”). Then, all plant parts (above and belowground biomass) were removed with a non-aggressive eradication method and soil samples were collected seven months later in the experimental and control plots (no invasive species and current climatic conditions). We predicted a general compositional shift in microbial communities in response to the presence of the invasive species. Moreover, given that water is the most limiting factor in this type of ecosystem, we also predicted a more pronounced compositional shift in the treatment combining invader presence and climate change. While species richness was similar amongst treatments, we observed some taxonomic and functional variation in soil microbial communities. Notably, fungal and bacterial communities exhibited contrasting responses. The species composition of bacteria differed significantly between the “invasive species” and “control” treatments, while, in the case of fungi, the most substantial difference occurred between the “invasive species” treatment and the combined treatment of “invasive species and climate change”. Some chemical properties, such as carbon and nitrogen content or pH, strongly differed amongst treatments, with the “invasive species” showing a different response compared to the other two treatments. Overall, our study suggests smaller short-term effects on the microbial community compared to soil chemical properties. Furthermore and contrary to our initial expectations, the potential impact on the soil microbiome seemed to be weaker in the face of rising temperatures and drought conditions predicted by climate change. This outcome highlights the remarkable complexity of the impact of invasive species and climate change on belowground microbial communities.