Protocol for an assessment of how species richness promotes plant productivity via suppressing plant antagonists.

This protocol is intended to provide a pre-registration of the approach used for deriving literature following PRIMSMA-P protocols and subsequent planned analysis in an assessment of how plant species richness suppresses plant antagonists.   In the context of this protocol antagonists refer to invertebrate herbivores, plant diseases, weeds, plant-feeding nematodes and plant-consuming rodents that may negatively impact on plant productivity. The diversity-productivity hypothesis assumes that increasing plant species richness can attain greater productivity. However, the exact mechanisms that underpin this relationship remain unclear or potentially context specific.  One important mechanism that may underpin this effect is the role of increasing plant species richness facilitating the suppressing of plant antagonists positively affecting the overall productivity of the system.   The positive effects of plant species richness on plant productivity resulting from the suppressing of such plant antagonists remains unknown on a global scale.  A generalized synthesis is therefore urgently required to identify the research gaps and to shed light on broad trends according to the existing literature. The goals of this protocol are to outline approaches to undertake a global meta-analysis to assess the impact of increasing plant species richness in suppressing plant antagonists that have resulting impacts on the growth, reproduction and quality resulting in direct damage to tissues of plants.