Given that plant growth is often water-limited in grasslands, it has been proposed that projected increases in precipitation could increase plant productivity and carbon sequestration. However, the existing evidence for this hypothesis comes primarily from observational studies along natural precipitation gradients or from short-term manipulative experiments. It remains unclear whether long-term increased precipitation persistently stimulates grassland productivity. In the world's largest remaining temperate grassland, we found that experimentally increased precipitation enhanced net primary production, soil-available nitrogen and foliar nitrogen concentrations during the first six years, but it ceased to do so in the following four years, unless nitrogen was simultaneously added with water. The 15N enrichment of plant and soil nitrogen pools in later years indicates increased nitrogen losses, which exacerbated nitrogen limitation and ended the stimulation of productivity by increased precipitation. Changes in species abundance might have contributed little to the changes in water treatment effects. Our study demonstrates that the long-term response of grassland ecosystems to increased precipitation will be mediated by nitrogen availability. Our results also point to a shift from co-limitation by water and nitrogen early to perhaps limitation by nitrogen only later in this temperate grassland, highlighting significant variations in the type of resource limitation induced by climate change.
Bibliographical noteFunding Information:
We thank Weixing Zhu, two anonymous reviewers, and the editor (Sara Vicca) for the comments that greatly improved the manuscript. We are grateful to Shibo Fang for providing water deficit data. We thank the large number of individuals who have helped with field sampling and laboratory analysis. We also appreciate the Duolun Restoration Ecology Research Station for access permission to the study site. This research was financially supported by the National Key Research and Development Program of China (2016YFA0600800 and 2016YFC0500707), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB15020200), the National Natural Science Foundation of China (31300387, 31370009, 31422009, and 41073056), and the China Postdoctoral Science Foundation (2012M510847).
© 2017 by the Ecological Society of America
- increased precipitation
- nitrogen deposition
- nitrogen losses
- nitrogen stable isotopes
- plant productivity
- plant species abundance