New insights into the covariation of stomatal, mesophyll and hydraulic conductances from optimization models incorporating nonstomatal limitations to photosynthesis
التفاصيل البيبلوغرافية
العنوان:
New insights into the covariation of stomatal, mesophyll and hydraulic conductances from optimization models incorporating nonstomatal limitations to photosynthesis
Institute for Atmospheric and Earth System Research (INAR), Department of Physics, Department of Forest Sciences, Annikki Mäkelä-Carter / Principal Investigator, Viikki Plant Science Centre (ViPS), Ecosystem processes (INAR Forest Sciences), Micrometeorology and biogeochemical cycles, Forest Ecology and Management, Forest Modelling Group
Optimization models of stomatal conductance (g(s)) attempt to explain observed stomatal behaviour in terms of cost-benefit tradeoffs. While the benefit of stomatal opening through increased CO2 uptake is clear, currently the nature of the associated cost(s) remains unclear. We explored the hypothesis that g(s) maximizes leaf photosynthesis, where the cost of stomatal opening arises from nonstomatal reductions in photosynthesis induced by leaf water stress. We analytically solved two cases, CAP and MES, in which reduced leaf water potential leads to reductions in carboxylation capacity (CAP) and mesophyll conductance (g(m)) (MES). Both CAP and MES predict the same one-parameter relationship between the intercellular:atmospheric CO2 concentration ratio (c(i)/c(a)) and vapour pressure deficit (VPD, D), viz. c(i)/c(a) approximate to xi/xi (xi+D), as that obtained from previous optimization models, with the novel feature that the parameter xi is determined unambiguously as a function of a small number of photosynthetic and hydraulic variables. These include soil-to-leaf hydraulic conductance, implying a stomatal closure response to drought. MES also predicts that g(s)/g(m) is closely related to c(i)/c(a) and is similarly conservative. These results are consistent with observations, give rise to new testable predictions, and offer new insights into the covariation of stomatal, mesophyll and hydraulic conductances.
