A role for soil microbial communities in plant-plant facilitation
Results/Conclusions Under greenhouse conditions, soil biota from Retama shrubs had a significant positive effect on the abundance, growth, functional traits and reproductive output of beneficiary plant species through processes that were independent of the direct influence of the benefactor species. This was also the case under field conditions, although some results were plant species-specific, i.e., Retama soil biota mainly affected seed germination either positively or negatively depending on plant identity. Preliminary analysis of the composition of soil communities across all samples and experiments reveals that, compared to those from gaps, soils from under Retama shrubs had greater relative abundance of Bacteroidetes, Acidobacteria and main Proteobacteria classes (Alpha-, Beta- and Gamma-proteobacteria); members of these groups include species that may promote plant growth and organic matter decomposition. Instead, gap soils had greater abundance of Firmicutes and Actinobacteria. Overall, our results showed that soil characteristics and microorganisms played a fundamental role in positive interactions between plant species, and were more decisive than canopy effects on plant growth. Plant-soil interactions are major drivers of facilitation contributing to the preservation of diversity of plant communities.