Conditional variations in temperature response of photosynthesis, mesophyll and stomatal control of water use in rice and winter wheat

Environmental responses of photosynthesis and CO2 diffusive conductance as fundamental information for photosynthesis-transpiration coupled model have been increasingly concerned while are still research areas with unanswered questions in cereal crops. Photosynthesis (A), light utilization efficiency (α), mesophyll conductance (gm) and stomatal coefficient (gfac) in temperate rice and winter wheat were investigated. There were no seasonal trend, no inter- and intra-species differences in relative temperature responses (activation energy ΔHa) of Vcmax or Jmax. A phenomenon that grain-filling plants generally decreased gm and had a lower Q10 as compared to that at early growth stage existed, particularly in rice. Analyses of environmental influences indicated that optimal temperatures (Topt) in Vcmax/Jmax depended on the prevailing temperature environment. Although prevailing temperature dependence in Topt of gm was not as profound as that of Vcmax or Jmax, Topt of gm in winter wheat was significantly lower than rice. Temperature response of Rdark in all sampled leaves shared a common trajectory. α were almost invariant, while, high sensitivity to soil desiccation was observed. gfac in sunlit leaves was conservative during wet soil conditions. Shaded leaves with lower Na had higher gfac, resulting in a negative correlation between Na and gfac in canopy profiles. gfac was susceptible to fluctuations in soil water potential (ψs), rapidly declined at a threshold of top-layer ψs approx. −0.1 MPa. Numerical analyses regarding gm/Vcmax/Jmax effects on photosynthetic performance in rice and between rice and winter wheat documented that in context of climate change, consider growth environment-induced differences in temperature responses of photosynthetic parameters among cereal crops is indispensable to better predict interactions among soil-plant-atmosphere consortium.