Does plant size affect growth responses to water availability at glacial, modern and future CO2 concentrations?
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Plant responses to carbon (C) and water availability are strongly connected. Thus, we can learn much about the responses of modern plants to rising atmospheric carbon dioxide (CO2) by studying their performance under a range of carbon and water availabilities, including very low CO2 as in past glacial periods. We hypothesized that, especially in shallow soils, the positive effects of high CO2 and the negative effects of low CO2 on growth response to drought are moderated by plant size-driven feedbacks through transpiration and soil water depletion. We grew two temperate annual C3 species, Avena sativa and Chenopodium album, in glacial (180 ppm), modern (400 ppm) and future (700 ppm) CO2 levels and five soil water regimes in climate chambers. In both species, low CO2 resulted in a much lower relative growth rate, biomass and total leaf area than at ambient CO2 with higher water availability, but this difference disappeared steadily towards severe drought conditions. Elevated CO2 increased relative growth rate, plant biomass and total leaf area of both species slightly compared with ambient CO2. These results were especially pronounced under drought. Our results support the hypothesis that, in annuals, plant size modulates the negative drought effect at low CO2. However, plant size-mediated effects of high CO2 on growth response to drought were inconclusive. Further experiments should reveal the interactive effects of CO2 and water regimes in environments closer to a field setting, both in shallow and in deep soils with unconstrained rooting, as well as in mixed communities.
KeywordsBiomass accumulation Drought CO2 concentration Relative growth rate Water use efficiency
We would like to thank our colleagues at Utrecht University, specifically R. Welschen, B. Robroeck, R. Wagner and M. Hefting, for hosting this research at the experimental CO2 manipulation facility. Feng Lin kindly provided the seeds for this study. This study was financially supported by Grant 142.16.3032 of the Darwin Center for Biogeosciences to R. Aerts; Grant CEP-12CDP007 by the Royal Netherlands Academy of Arts and Sciences to J.H.C. Cornelissen; the National Natural Science Foundation of China (31500399) and the Fundamental Research Funds for the Central Universities (XDJK2014C158) to J.C. Liu. J.C. Liu also gratefully acknowledges the Chinese Scholarship Council and the School of Life Science, SW China University for financially supporting her 1 year research visit to VU University.
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