Climate and management affect grassland plant diversity but studies vary regarding the magnitude of changes in plant species richness. Here we develop a comprehensive understanding of species richness modification due to management (mowing) and climate (warming) variation worldwide, and present the results of two meta-analyses from 999 and 1793 records (articles). Recorded articles had at least one experiment with a case-control design. The results show that both mowing (43 articles) and warming (34 articles) modify species richness, which on average increased by c. 32% with once-a-year mowing (against no mowing) and reduced by c. 13% with warming (against ambient temperature). Our meta-analysis on the mowing regime supports the humped-back model, with one or two cuts per year being the level of disturbance optimising species richness. We also observed that warming-induced reduction in species richness is lower in dry climates (< 300 mm yr-1) and at low-elevations (< 1000 m a.s.l.). We also took into account, where available, a concomitant variable, harvested biomass (determined experimentally in both mown and unmown plots), and found that it overall decreased by c. 21% (mowing) and increased by c. 11% (warming). The evidence provided of an opposite response of species richness and harvested biomass to disturbance is consistent with the competitive-exclusion hypothesis of negatively correlated patterns between the two outcomes (high taxonomic diversity with low biomass production, and vice versa). Study results thus help develop a more complete picture of the role of increasing temperature and cutting regime on grassland species richness and add insights to published meta-analyses examining the outcomes of terrestrial ecosystems. The reported difficulties to retrieve representative studies in previous and the present meta-analyses highlight the need to focus on dedicated research for robust inference about environmental and management constraints on grassland performances.