The Impact of Elevated CO2 on Plant Production Responses to Drought: A Model-Data Comparison at Four US FACE Sites.

Tuesday, 16 December 2014
Anthony P Walker1, Martin G De Kauwe2, Lynn Fenstermaker3, Belinda Elizabeth Medlyn2, Jack A Morgan4, Ram Oren5, Soenke Zaehle6 and Richard J Norby7, (1)Oak Ridge National Laboratory, Oak Ridge, TN, United States, (2)Macquarie University, Sydney, Australia, (3)Desert Research Institute, Las Vegas, NV, United States, (4)United States Department of Agriculture, Agricultural Research Service, Rangeland Resources Research Unit, CO, United States, (5)Duke University, Durham, NC, United States, (6)Max Planck Institute for Biogeochemistry, Jena, Germany, (7)Oak Ridge National Lab, Oak Ridge, TN, United States
Plants respond to increased atmospheric CO[2] (eCO2) by reducing stomatal apatures which increases plant water use efficiency. In some environments, increased WUE allows for water savings and can prolong the onset of drought effects on plants.

Ecosystem observations from four long-term free air CO[2] enrichment (FACE) experimentsthe evergreen needleleaf Duke Forest FACE experiment (NC), the deciduous broadleaf Oak Ridge FACE experiment (TN), the prairie heating and FACE experiment (WY), and the Nevada desert FACE experiment—were used to evaluate the assumptions of a suite of terrestrial ecosystem models.

All sites suffered from a drought that affected annual net primary production (NPP) in at least one year. In all cases the NPP response to drought was affected by eCO2, however the relative response was both greater and smaller under eCO2 compared with ambient CO[2] conditions depending on the climate of the site in question. Model assumptions that were important in determining the eCO2 by drought interaction on plant productivity were the soil water content at which soil water becomes limiting to plants; whether soil water limitation affects stomatal conductance, photosynthetic parameters, or both; and the shape of the soil water limitation curve.