Gross primary production responses to warming, elevated CO2 , and irrigation:quantifying the drivers of ecosystem physiology in a semiarid grassland.

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Glob Chang Biol. 2016 Dec 19. doi: 10.1111/gcb.13602. [Epub ahead of print]

Ryan EM1, Ogle K2,3, Peltier D3, Walker AP4, De Kauwe MG5, Medlyn BE6, Williams DG7, Parton W8, Asao S8, Guenet B9, Harper A10, Lu X11, Luus KA12,13, Zaehle S12, Shu S14, Werner C15, Xia J16,17, Pendall E6,7.

Author information

• 1Lancaster Environment Centre, Lancaster, UK.
• 2School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, Arizona, USA.
• 3Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, USA.
• 4Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.
• 5Macquarie University, Department of Biological Sciences, New South Wales 2109, Australia.
• 6Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia.
• 7University of Wyoming, Department of Botany, Laramie, WY, USA.
• 8Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499, USA.
• 9Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France.
• 10College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, UK.
• 11CSIRO Ocean and Atmosphere, PBM #1, Aspendale, Victoria, 3195, Australia.
• 12Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745, Jena, Germany.
• 13Now at: Dublin Institute of Technology, Dublin, Ireland.
• 14Department of Atmospheric Sciences, University of Illinois, 105 South Gregory Street, Urbana, Illinois, 61801-3070, USA.
• 15Senckenberg Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325, Frankfurt, Germany.
• 16Department of Microbiology & Plant Biology, University of Oklahoma, Norman, OK 73019, USA.
• 17Research Center for Global Change and Ecological Forecasting, East China Normal University, Shanghai, 200062, China.

Abstract

Determining whether the terrestrial biosphere will be a source or sink of carbon (C) under a future climate of elevated CO2 (eCO2 ) and warming requires accurate quantification of gross primary production (GPP), the largest flux of C in the global C cycle. We evaluated six years (2007-2012) of flux-derived GPP data from the Prairie Heating and CO2Enrichment (PHACE) experiment, situated in a grassland in Wyoming, USA. The GPP data were used to calibrate a light response model whose basic formulation has been successfully used in a variety of ecosystems. The model was extended by modeling maximum photosynthetic rate (Amax ) and light-use efficiency (Q) as functions of soil water, air temperature, vapor pressure deficit, vegetation greenness and nitrogen at current and antecedent (past) time scales. The model fit the observed GPP well (R2 = 0.79), which was confirmed by other model performance checks that compared different variants of the model (e.g., with and without antecedent effects). Stimulation of cumulative six-year GPP by warming (29%, P=0.02) and eCO2 (26%, P=0.07) was primarily driven by enhanced C uptake during spring (129%, P=0.001) and fall (124%, P=0.001), respectively, which was consistent across years. Antecedent air temperature (Tairant ) and vapor pressure deficit (VPDant ) effects on Amax (over the past 3-4 days and 1-3 days, respectively) were the most significant predictors of temporal variability in GPP among most treatments. The importance of VPDant suggests that atmospheric drought is important for predicting GPP under current and future climate; we highlight the need for experimental studies to identify the mechanisms underlying such antecedent effects. Finally, posterior estimates of cumulative GPP under control and eCO2 treatments were tested as a benchmark against 12 terrestrial biosphere models (TBMs). The narrow uncertainties of these data-driven GPP estimates suggest that they could be useful semi-independent data streams for validating TBMs. This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

KEYWORDS:

Bayesian modelling; carbon cycle; elevated CO2; grasslands; gross primary production; multi-factor global change experiment; warming