Warming Effects on Ecosystem Carbon Fluxes Are Modulated by Plant Functional Types
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Despite the importance of future carbon (C) pools for policy and land management decisions under various climate change scenarios, predictions of these pools under altered climate vary considerably. Chronic warming will likely impact both ecosystem C fluxes and the abundance and distribution of plant functional types (PFTs) within systems, potentially interacting to create novel patterns of C exchange. Here, we report results from a 3-year warming experiment using open top chambers (OTC) on the Tibetan Plateau meadow grassland. Warming significantly increased C uptake through gross primary productivity (GPP) but not ecosystem respiration (ER), resulting in a 31.0% reduction in net ecosystem exchange (NEE) in warmed plots. The OTC-induced changes in ecosystem C fluxes were not fully explained by the corresponding changes in soil temperature and moisture. Warming treatments significantly increased the biomass of graminoids and legumes by 12.9 and 27.6%. These functional shifts were correlated with enhanced local GPP, but not ER, resulting in more negative NEE in plots with larger increases in graminoid and legume biomass. This may be due to a link between greater legume abundance and higher levels of total inorganic nitrogen, which can potentially drive higher GPP, but not higher ER. Overall, our results indicate that C-climate feedbacks might be closely mediated by climate-induced changes in PFTs. This highlights the need to consider the impacts of changes in PFTs when predicting future responses of C pools under altered climate scenarios.
Keywordsecosystem carbon fluxes net ecosystem exchange climate change aboveground biomass plant functional types soil inorganic nitrogen experimental warming Tibetan plateau
This study was supported by the Ministry of Science & Technology (2012BAH31B03), and the State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment of Chinese Academy of Sciences (SKLLQG1303). Contributions from Dr. Luo’s Eco-lab to this study was financially supported by US Department of Energy, Terrestrial Ecosystem Sciences Grant DE SC0008270 and US National Science Foundation (NSF) Grant DBI 0850290, EPS0919466, DEB 0743778, DEB 0840964, and EF 1137293. The authors gratefully acknowledge financial support from China Scholarship Council (award for a 1-year study abroad at the University of Oklahoma).
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