Life form-specific facilitative interactions determine plant biodiversity in global drylands.

Nurse plants play a crucial role on plant biodiversity in drylands. While the nurse's impacts in biodiversity are documented, we know little about such impacts of different nurse's life forms; and how these impacts associate to climatic gradients. In this regard, we re-analyzed a dataset of 72 dryland sites, established across climatic gradients in 10 countries, and assessed changes of plant taxonomic, functional and phylogenetic diversity with respect to presence of nurse plants from different plant life forms (i.e., grasses, shrubs and trees) and their absences (i.e., open communities). We observed a more substantial increase in functional and phylogenetic diversity associated to nurse grasses communities than their open pairs, with greater functional and phylogenetic dissimilarity between the communities under moderate climatic gradients. Such findings were consistent with an increase in the strength of correlations between these biodiversity facets. In communities including nurse shrubs, taxonomic and functional diversity were positively changed especially at the middle of climatic conditions, with stronger dissimilarities and relationships for taxonomic than for functional diversity. In contrast, nurse trees promoted negative impacts on all biodiversity facets under moderate climatic conditions, while the contrary pattern (except in functional diversity) was observed in their paired open communities, showing an increase with strength of correlations between biodiversity facets. Therefore, our results suggested different facilitatory mechanisms of nurse plants depending on their life forms to affect plant biodiversity. Such specific mechanisms might partly be explained by controlling beneficiary relatedness that may be significantly related to climatic conditions. [ABSTRACT FROM AUTHOR]