Climate change largely impacts ecosystem carbon and water cycles by changing plant gas exchange, which may further cause positive or negative feedback to global climate change. However, long-term global change manipulative experiments are seldom conducted to reveal plant ecophysiological responses to climatic warming and altered precipitation regimes.Methods
An 8-year field experiment with both warming and increased precipitation was conducted in a temperate grassland in northern China. We measured leaf gas exchange rates (including plant photosynthesis, transpiration and instantaneous water use efficiency [WUE]) of two dominant plant species (Stipa sareptana var. krylovii and Agropyron cristatum) from 2005 to 2012 (except 2006 and 2010) and those of other six species from 2011 to 2012.Important Findings
Increased precipitation significantly stimulated plant photosynthetic rates (A) by 29.5% and 19.9% and transpiration rates (E) by 42.2% and 51.2% for both dominant species S. sareptana var. krylovii and A. cristatum, respectively, across the 8 years. Similarly, A and E of the six plant functional types were all stimulated by increased precipitation in 2011 and 2012. As the balance of A and E, the instantaneous WUEs of different plant species had species-specific responses to increased precipitation. In contrast, neither warming nor its interaction with increased precipitation significantly affected plant leaf gas exchange rates. Furthermore, A and E of the two dominant species and their response magnitudes to water treatments positively correlated with rainfall amount in July across years. We did not find any significant difference between the short-term versus long-term responses of plant photosynthesis, suggesting the flexibility of leaf gas exchange under climate change. The results suggest that changing precipitation rather than global warming plays a prominent role in determining production of this grassland in the context of climate change.