Effects of elevated CO2, warming and precipitation change on plant growth, photosynthesis and peroxidation in dominant species from North China grassland

Warming, watering and elevated atmospheric CO2-concentration effects have been extensively studied separately; however, their combined impact on plants is not well understood. In the current research, we examined plant growth and physiological responses of three dominant species from the Eurasian Steppe with different functional traits to a combination of elevated CO2, high temperature, and four simulated precipitation patterns. Elevated CO2 stimulated plant growth by 10.8-41.7 % for a C-3 leguminous shrub, Caragana microphylla, and by 33.2-52.3 % for a C-3 grass, Stipa grandis, across all temperature and watering treatments. Elevated CO2, however, did not affect plant biomass of a C-4 grass, Cleistogenes squarrosa, under normal or increased precipitation, whereas a 20.0-69.7 % stimulation of growth occurred with elevated CO2 under drought conditions. Plant growth was enhanced in the C-3 shrub and the C-4 grass by warming under normal precipitation, but declined drastically with severe drought. The effects of elevated CO2 on leaf traits, biomass allocation and photosynthetic potential were remarkably species-dependent. Suppression of photosynthetic activity, and enhancement of cell peroxidation by a combination of warming and severe drought, were partly alleviated by elevated CO2. The relationships between plant functional traits and physiological activities and their responses to climate change were discussed. The present results suggested that the response to CO2 enrichment may strongly depend on the response of specific species under varying patterns of precipitation, with or without warming, highlighting that individual species and multifactor dependencies must be considered in a projection of terrestrial ecosystem response to climatic change.