A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies
Citation:
Voelker, S., J. Renee Brooks, F. Meinzer, R. Anderson, M. Bader, G. Battipaglia, K. Beclin, D. Beerling, D. Bert, J. Betancourt, T. Dawson, J. Domec, R. Guyette, C. Korner, S. Leavitt, S. Linder, J. Marshall, M. Mildner, J. Ogee, I. Panyushkina, H. Plumpton, K. Pregitzer, M. Saurer, A. Smith, R. Siegwolf, M. Stambaugh, A. Talhelm, J. Tardif, P. Van de Water, J. Ward, AND L. Wingate. A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies. GLOBAL CHANGE BIOLOGY. Blackwell Publishing, Malden, MA, 22:889-902, (2016).
Impact/Purpose:
The impact of climate change on water availability will be strongly influenced by changes in forest transpiration, since transpiration can utilize 30-90% of incoming precipitation. The rising concentration of CO2 in the atmosphere alters the way plants use water and take up carbon (know as gas-exchange), but exactly what those changes will be is not clearly known. This study aims understand the trends in how woody plant regulate leaf gas-exchange from complied studies spanning CO2 increases from 180 ppm in paleostudies to 700 ppm in elevated CO2 studies. We found that woody plants shift their gas-exchange strategies as CO2 increases to optimize their ability to minimizing plant water loss for a given amount of carbon gained. Our results indicate that as CO2 rises, woody plants will use less water and will be more likely to avoid future drought stress.
Description:
Rising atmospheric [CO2], ca, is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water and nutrient cycling of forests. Researchers have reported that stomata regulate leaf gas-exchange around “set points” that include a constant leaf internal [CO2], ci, a constant drawdown in CO2 (ca - ci), and a constant ci/ca. Because these set points can result in drastically different consequences for leaf gas-exchange, it will be essential for the accuracy of Earth systems models that generalizable patterns in leaf gas-exchange responses to ca be identified if any do exist. We hypothesized that the concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these set point strategies, would provide a unifying framework for understanding leaf gas-exchange responses to ca. We analyzed studies reporting C stable isotope ratio (δ13C) or photosynthetic discrimination (∆13C) from woody plant taxa that grew across ca spanning at least 100 ppm for each species investigated. From these data we calculated ci, and in combination with known or estimated ca, leaf gas-exchange regulation strategies were assessed. Overall, our analyses does not support the hypothesis that trees are canalized towards any of the proposed set points, particularly so for a constant ci. Rather, the results are consistent with the hypothesis that stomatal optimization regulates leaf gas-exchange of woody plants dynamically, toward maximizing C gain at low ca by maintaining low ci/ca and ca - ci, and avoiding drought stress at high ca by maintaining greater ci/ca and ca - ci. Our results suggest that much of the ca-induced changes in ci/ca occurred in past, across the lower range of ca (i.e. 200-400 ppm). The same data project that ca - ci will keep increasing but eventually approach a constant level at high ca since assimilation rates will reach a maximum and each species should be constrained by some minimum level of stomatal conductance. Although additional research may resolve small differences in the scaling of ci/ca and ca - ci responses to ca, our analyses support the existence of a broadly conserved pattern of leaf gas-exchange response across woody angiosperms and gymnosperms.
