Warming differently affects the inter- and intraspecific interactions among semi-dry grassland species

Abstract

Climate warming affects plant-plant interactions regulating species composition, productivity, structure, and dynamics in plant communities and ecosystems, which often leads to a change in biodiversity. A competition experiment was set up to investigate the effect of warming on plant-plant interactions in semi-dry grasslands. The dominant grass Festuca rupicola and the four rare forbs Biscutella laevigata, Filipendula vulgaris, Scabiosa canescens, and Veronica spicata were placed in pots as monocultures (similar densities), as mixtures (varying densities), and as single individuals. In growth chambers, ambient temperatures (20 °C by day / 10 °C by night) and warmer temperatures predicted under climate change (+3.5 °C) were simulated. After nine months, growth parameters, aboveground biomass and leaf number, and a trait of phenotypic plasticity, leaf length, were measured and plant-plant interactions calculated. Warming significantly increased the growth of the four forbs, while the growth of the grass decreased or remained unchanged. The plant-plant interactions were negative and species-specific, and affected the three parameters differently, with the strongest effect on biomass and the lowest effect on leaf length. In monocultures, the strongest intraspecific competition on biomass was found in the grass. Warming only significantly reduced intraspecific competition on biomass in B. laevigata, but significantly decreased intraspecific competition measured on leaf length for all species. In mixtures with the grass, interspecific competition was the strongest to F. vulgaris and S. canescens, and did not change by warming. Interspecific competition to B. laevigata and V. spicata was reduced by warming. The associated grass was significantly reduced in interspecific competition on biomass in the presence of F. vulgaris and S. canescens by warming. But the grass was unaffected in mixtures with B. laevigata and V. spicata. A temperature increase can led to different patterns in interspecific and intraspecific competition, which suggests that some forbs, like B. laevigata and V. spicata, can benefit from warming but that other species are unaffected. The grass exhibited different responses depending on its heterospecific neighbors. Although the effects of warming and competition are species-specific, warming generally decreased competition. This effect may shape patterns of plant performance and biodiversity in the face of warming in semi-dry grasslands.