Banana (Musa sp.) leaf gas exchange and chlorophyll fluorescence in response to soil drought, shading and lamina folding

Reductions in net photosynthesis of banana (Musa sp.) leaves may be due to both stomatal and non-stomatal limitations. To evaluate the significance of photochemical damage, we measured chlorophyll fluorescence in conjunction with net photosynthesis. Photochemical damage was reflected in either an in crease in original fluorescence (F-O), or decreases in maximum fluorescence (F-M) or in the ratio of variable (F-V = F-M - F-O) to maximal fluorescenc e (F-V/F-M). The leaf surface receiving direct sunlight (adaxial) was more photochemically damaged, as measured by declines in chlorophyll fluorescenc e parameters than the abaxial leaf surface that received transmitted and in direct light. Damage increased over a diurnal period and was greater in dro ughted compared with irrigated plants. F-V/F-M ratio declined significantly as plant water status, measured as relative leaf water content or leaf wat er potential, declined. The decrease in the F-V/F-M ratio was due more to a decline in F-M than an increase in F-O. Shading of plants decreased photoc hemical damage in leaves but net photosynthesis (P-n) was lower than in sun lit plants because of the limitation of P-n by low photosynthetic photon fl ux density. A combination of stomatal and non-stomatal factors reduced P-n in droughted or shaded plants. Excessive sunlight can cause photochemical d amage to banana leaves but this damage does not appear to be a limitation o f P-n in well-irrigated plants. The natural folding of banana laminae (not caused by wilting) reduces photochemical damage by reducing the flux densit y of radiation intercepted by the lamina surface. (C) 2001 Elsevier Science B.V All rights reserved.