The effects of global change factors on the stoichiometric composition of green and senesced plant tissues are critical determinants of ecosystem feedbacks to anthropogenic-driven global change. So far, little is known about species stoichiometric responses to these changes. We conducted a manipulative field experiment with nitrogen (N; 17.5 gm -2 year -1) and water addition (180mm per growing season) in a temperate steppe of northern China that is potentially highly vulnerable to global change. A unique and important outcome of our study is that water availability modulated plant nutritional and stoichiometric responses to increased N availability. N addition significantly reduced C:N ratios and increased N:P ratios but only under ambient water conditions. Under increased water supply, N addition had no effect on C:N ratios in green and senesced leaves and N:P ratios in senesced leaves, and significantly decreased C:P ratios in both green and senesced leaves and N:P ratios in green leaves. Stoichiometric ratios varied greatly among species. Our results suggest that N and water addition and species identity can affect stoichiometric ratios of both green and senesced tissues through direct and interactive means. Our findings highlight the importance of water availability in modulating stoichiometric responses of plants to potentially increased N availability in semi-arid grasslands.
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Acknowledgments We thank the staV of the Inner Mongolia Grassland Ecosystem Research Station (IMGERS) for facilitating this study. We gratefully acknowledge Weijun Wu, Yongsheng Jin and Qiang Li for Weld and laboratory assistance. We also wish to thank Andrea Polle and three anonymous reviewers who provided valuable comments and suggestions. This work was supported by The Knowledge Innovation Project of CAS (No. KZCX2-YW-T06), the Ministry of Science and Technology (2007CB106801), and the National Natural Science Foundation of China (30830026 and 30821062).
- Precipitation regime
- Senesced leaves
- Stoichiometric ratios