Photosynthetic efficiency of maize and bean leaves in the canopy of sole and intercropping systems under water stress

Abstract

In this study the leaf water potential and the photosynthetic efficiency at different leaf levels (top, middle and the lower leaves) for dry bean (Phaseolus vulgaris) and maize (Zea mays) were measured using intercrop and sole cropping systems under rainfed and irrigated conditions. The specific ecotope in which the study was conducted is Agrometeorological experimental site at West Campus in Bloemfontein, South Africa where the annual rainfall average of 600 mm. The field experiment was only conducted for one season. The expected results are that the rainfed treatments will experience more stress than irrigated treatments, and the rate of photosynthesis would be higher under irrigated than rainfed conditions. A randomised complete block design was used, with three treatments intercrop, sole maize and sole bean (IMB, SM and SB) and three replicates. The experiment determined the most stressed plants throughout the season. Chlorophyll fluorescence kinetics provides considerable information on the organisation and function of the photosynthetic efficiency. Chlorophyll fluorescence is used to study the different functional levels o f photosynthesis. Photosynthetic efficiency (cpEo) changes with leaf water potential, irrigated sole maize (SMI) and irrigated sole bean (SBI) performed better than rainfed treatments since cpEo was higher when the leaf water potential was lower negative. Irrigated sole bean (SBI) plants improved considerable over the experimental period as rainfed sole bean (SBR) plants became severely stressed. The whole plant bean leaf water potential indicated that the irrigated plants performed better than the rainfed plants and the sole plants did better than intercrop rainfed maize, the rainfed sole maize performed the best. Photosynthesis can be a good indicator of the overall fitness ofthe plants, as unfavorable environments and competition decrease the rate of photosynthesis.