Regulation of Photosynthesis and Water Use Efficiency in Relation to Stomatal Frequency and Interveinal Distance in C3- and C4-Grass Species.

Abstract

The gas exchange rates of C3- and C4-grass leaves at low and high vapor pressure difference (VPD) conditions were measured and demonstrated the effects of anatomical and morphological features of the leaves, i.e. stomatal frequency and size and interveinal distance (IVD), on gas exchange characteristics. When the photosynthesis type was ignored, there was a positive correlation between stomatal frequency and stomatal conductance. However, there was less significant correlation between stomatal frequency and transpiration rate when plotted species within the same photosynthetic pathway. There was a negative correlation between stomatal frequency and net photosynthetic rate, suggesting that CO2 diffusion process from ambient to intercellular space was not much affected by the stomatal morphology, instead that a consequence of biochemical differences in photosynthetic characteristics of the mesophyll was more important. An increase in IVD significantly decreased net photosynthetic rate and water use efficiency (WUE) . In addition to the regulation of CO2 concentrating mechanism in Kranz cells of the C4 subtypes, a rapid translocation of photosynthate from bundle sheath cells to the phloem in grasses with C4-MS type (NADP-ME) may contribute to maintain their high performances in photosynthesis and WUE through shorter IVD.