Plant phylodiversity enhances soil microbial productivity in facilitation-driven communities

The classical relationship between biodiversity and ecosystem functioning can be better understood when the phylogenetic component of biodiversity is considered. We linked plant phylodiversity and ecosystem functioning in a water-limited gypsum ecosystem driven by plant facilitation. We tested whether (1) plant facilitation relaxes the abiotic filter imposed by gypsum, allowing the establishment of non-gypsophyte plant species, and consequently increasing plant phylodiversity, and (2) plant phylodiversity influences soil microbial productivity. Our data revealed that the gypsophyte Ononis tridentata spatially determines a macrophytic mosaic, ameliorates the microenvironment, and maximizes plant richness and phylodiversity through facilitating non-gypsophyte species. Beyond the direct effect of the nurse plant on soil microbial biomass, activity, and respiration, the analyses suggest a direct effect of plant phylodiversity (MPD) on these general indicators of soil microbial productivity. Plant diversity (Shannon index) neither correlated with the mentioned parameters nor with specific indicators of C, N and P cycling. This is the first report of a relationship between producer phylodiversity and decomposer productivity, which supports phylogenetic diversity as a relevant player of the ecosystem functioning.