Stomatal conductance bears no correlation with transpiration rate in wheat during their diurnal variation under high air humidity

Abstract

A good understanding of the response of photosynthesis rate (PN) and transpiration rate (Tr) to stomatal alteration during the diurnal variations is important to cumulative photosynthetic production and water loss of crops. Six wheat genotypes were studied for 2 years with pot cultivation in rain-shelter. Among different genotypes, stomatal conductance (gs) was significantly correlated with both PN and Tr. But for each genotype, though gs was significantly correlated with PN regardless of relative air humidity (RH) status and it was also significantly correlated with Tr under lower RH (LRH, 15.4%) and moderate RH (MRH, 28.3%), it was not correlated with Tr under higher RH (HRH, 36.7%) during the diurnal changes. The conditional correlation between gs and Tr of wheat evoked new thinking on the relationships among gs, PN and Tr. Path analysis was further carried out to clarify the correlations of gs with the four atmospheric factors, that of Tr with gs and the four factors and the direct and indirect effects of the factors, during their diurnal dynamic variation. The effects of these factors on gs or Tr were related to RH. All the four factors had a much higher correlation with gs under HRH than that under LRH and MRH. Air temperature (T) had a rather higher direct effect than RH and photosynthetically active radiation (PAR). Also, the other factors had a much higher indirect effect on gs through vapor pressure deficit (VPD) and T. Transpiration rate was highly correlated with gs under LRH and MRH, with gs having a higher direct effect on it. In comparison, Tr was not correlated with gs under HRH but highly correlated with the atmospheric factors, with T, RH, and PAR having a higher indirect effect through VPD.

Keywords

• Stomatal conductance
• Net photosynthesis rate
• Transpiration rate
• Wheat genotypes
• Relative air humidity