Climate change and biocrust disturbance synergistically decreased taxonomic, functional and phylogenetic diversity in annual communities on gypsiferous soils

Abstract

Rainfall and biocrusts are important sources of temporal and spatial environmental heterogeneity and niche differentiation for annual plants, a major component of diversity in drylands. Therefore, global change processes comprising shifts in rainfall timing and drought exacerbation, together with biocrust disturbance may affect species coexistence and result in disrupted diversity patterns. In this study, we experimentally evaluated the effects of the rainfall amount and timing as well as physical biocrust disturbance and their interaction on the taxonomic, phylogenetic and functional diversity of annual plant communities on gypsum soil drylands. All diversity estimates were determined at different times during community development in each experimental unit (α), as the contribution of each experimental unit to the total diversity in each treatment (β) and as the total diversity in each treatment (γ). Rainfall timings led to changes in all diversity dimensions, with higher diversity under the typical timing. The community was quite resilient to moderate reductions in rainfall, but extreme droughts decreased the alpha and beta taxonomic, functional and phylogenetic diversities. In addition, the simultaneous occurrence of biocrust disturbance and extreme drought led to consistent collapses in all diversity dimensions, probably because the effects of water shortage were exacerbated. Observations of the community at different times during its development highlighted the importance of regenerative strategies for niche differentiation and species coexistence, and their strong dependence on global change drivers. Indeed, our experimental study demonstrated that rainfall patterns and biocrusts are key factors related to the maintenance of diversity in semiarid annual plant communities. In particular, our results highlight the key role of biocrusts in modulating the effects of drought on plant diversity and the need for integrative approaches that consider both plants and biocrusts in order to elucidate the influence of climate change on the diversity of drylands.