Combined effects of climate warming and plant diversity loss on above- and below-ground grassland productivity

Projections of global change predict both increases of the surface temperature and decreases of biodiversity, but studies on the combined impact of both on terrestrial ecosystems are lacking. We assessed the impact of these two global changes on above- and below-ground productivity of grassland communities. Experimental ecosystems containing one, three or nine grassland species were grown in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures, while the other half were warmed by 3 °C. Equal amounts of water were added to heated and unheated communities, so that any increases in evapotranspiration due to warmer conditions would result in a drier soil. Warming led to a decreased productivity of both above-ground plant parts (−18%) and roots (−23%), which coincided with a significantly lower soil water content. Complementarity in resource use and/or facilitation slightly enhanced above-ground productivity in multi-species communities, regardless of the induced warming. Interactive effects between temperature treatment and species richness level were found below-ground, however, where warming nullified the positive effect of richness on root productivity. Future warmer conditions could further increase losses of productivity associated with declining species numbers.