Effects of potassium supply on limitations of photosynthesis by mesophyll diffusion conductance in Carya cathayensis

Abstract

Potassium (K) influences the photosynthesis process in a number of ways; however, the mechanisms underlying the photosynthetic response to differences in K supply are not well understood. Concurrent measurements of gas exchange and chlorophyll fluorescence were made to investigate the effect of K nutrition on photosynthetic efficiency and mesophyll conductance (g m) in hickory seedlings (Carya cathayensis Sarg.) in a greenhouse. The results show that leaf K concentrations <0.7-0.8 appeared to limit the leaf net CO 2 assimilation rate (A), and that the relative limitation of photosynthesis due to g m and stomatal conductance (g s) decreased with increasing supplies of K. However, a sensitivity analysis indicated that A was most sensitive to the maximum carboxylation rate of Rubisco (V c,max) and the maximum rate of electron transport (J max). These results indicate that the photosynthetic rate is primarily limited by the biochemical processes of photosynthesis (Vc,max and J max), rather than by g m and gs in K-deficient plants. Additionally, g m was closely correlated with gs and the leaf dry mass per unit area (M A) in hickory seedlings, which indicates that decreased g m and g s may be a consequence of leaf anatomical adaptation. © The Author 2011. Published by Oxford University Press. All rights reserved.