Significance of mesophyll conductance for photosynthetic capacity and water-use efficiency in response to alkaline stress in Populus cathayana seedlings

Abstract

Cuttings of Populus cathayana were exposed to three different alkaline regimes (0, 75, and 150 mM Na2CO3) in a semicontrolled environment. The net photosynthesis rate (P N), mesophyll conductance (g m), the relative limitations posed by stomatal conductance (L s) and by mesophyll conductance (L m), photosynthetic nitrogen-use efficiency (PNUE), carbon isotope composition (δ13C), as well as specific leaf area (SLA) were measured. P N decreased due to alkaline stress by an average of 25% and g m decreased by an average of 57%. Alkaline stress caused an increase of L m but not L s, with average L s of 26%, and L m average of 38% under stress conditions. Our results suggested reduced assimilation rate under alkaline stress through decreased mesophyll conductance in P. cathayana. Moreover, alkaline stress increased significantly δ13C and it drew down CO2 concentration from the substomatal cavities to the sites of carboxylation (C i-C c), but decreased PNUE. Furthermore, a relationship was found between PNUE and C i-C c. Meanwhile, no correlation was found between δ13C and C i/C a, but a strong correlation was proved between δ13C and C c/C a, indicating that mesophyll conductance was also influencing the 13C/12C ratio of leaf under alkaline stress. © 2013 Springer Science+Business Media Dordrecht.