The impact of warming on peak-season ecosystem carbon uptake is influenced by dominant species in warmer sites

Climatic warming influences ecosystem-scale carbon fluxes directly via effects on photosynthesis and respiration, and indirectly via effects on the plant community. Here, we report on a 10-year factorial warming and dominant plant species removal experiment established in both a high- and in a low-elevation montane meadow to explore how dominant plants modify the effect of warming on the carbon cycle across space and over time. At low-elevation, warming increased peak-season net carbon uptake in most years, driven by higher primary productivity, but only in plots where the dominant was left intact. Here, net carbon uptake tended to be positive, but was more likely to be negative when the dominant plant was removed, and in dry years. Surprisingly, the high-elevation site was unaffected by the warming and plant removal treatments, suggesting these sites are resistant to these disturbances. Taken together, these results demonstrate that dominant plant species can modify the impacts of warming on carbon fluxes, but show how this influence can vary spatially and temporally. These findings provide insight into when and how abiotic and biotic factors influence ecosystem carbon source/sink dynamics.