PHOTOSYNTHETIC PERFORMANCE OF BANANA ('GROS MICHEL', AAA) UNDER A NATURAL SHADE GRADIENT
Bananas are frequently grown in coffee and cacao agroforestry systems. We asked whether tree shade affects leaf photosynthesis beyond simply the effects of the reduction in light availability. Does the leaf compensate for lower light availability to achieve greater than expected leaf photosynthesis? In this study, the photosynthetic performance at leaf level of banana (Musa, AAA, Gros Michel) under three levels of natural shade (25, 50 and 75% of full solar irradiance) was compared with a full sun control. Gas exchange measurements of light and CO2 response curves on the third youngest leaf were conducted to estimate the parameters of a biochemical model of leaf photosynthesis. The estimated parameters were potential light-saturated electron transport rate (Jmax), maximum carboxylation rate (Vcmax) and day respiration (Rd) standardized at 25°C. The mean parameters of photosynthesis varied under the different levels of shade. Jmax decreased with increasing shade, falling from 163 for full sun to 134, 124 and 95 μmol m-2 s-1 for 75, 50 and 25%, respectively. Vcmax was reduced only with the heaviest shade from 104 μmol m-2 s-1 in full sun to 69 at 25% light, while no significant differences were found for Rd. Light response curves showed a reduction of maximal leaf photosynthesis only at 50 and 25% full solar irradiance. No saturation value for the photosynthetic photon flux density was apparent in full sun or the 75% treatment, while the saturating photon flux density varied from 1,200 to 1,500 μmol m-2 s-1 in the 50 and 25% treatments. The results in conjunction with whole plant performance and indirect effects of shade on disease levels and nutrient cycles provide insight into improving the productivity and ecological services of bananas in multi-strata agroforestry systems.
Siles, P., Bustamante, O., Valdivia, E., Burkhardt, J. and Staver, C. (2013). PHOTOSYNTHETIC PERFORMANCE OF BANANA ('GROS MICHEL', AAA) UNDER A NATURAL SHADE GRADIENT. Acta Hortic. 986, 71-77
agroforestry systems, banana leaf, light, photosynthesis model, shade acclimation