EFFICIENCY OF LIGHT ENERGY USED BY LEAVES SITUATED IN DIFFERENT LEVELS OF A SWEET PEPPER CANOPY

In order to make the most use of the available light in glasshouse crops, measurements of light penetration, leaf photosynthesis, respiration and transpiration were performed at five levels in a sweet paper canopy at two commercial farms, from July to November 2004. Light response curves of leaf photosynthesis showed that photosynthesis, transpiration respiration decreased from top to bottom in the canopy. These reductions in gas exchange lower in the canopy likely result from adaptation to lower ambient light conditions as well as leaf aging. At a low light intensity of 50 µmol m-2 s-1 above the canopy, the net photosynthesis in the top 25% of the leaves (2 m2 m-2 ) was positive, while at a higher light irradiance, 200 µmol m-2 s-1, the top 50% (4 m2 m-2) was positive. From the middle of August onwards, the net photosynthesis of the lower half of the crop was negative. Based on these measurements, the contribution of each leaf level to the net crop photosynthesis and transpiration was calculated. On an annual basis, the lower half of the crop made a 0.5% negative contribution to net photosynthesis, while making a 10% positive contribution to crop transpiration. Thus, removal of leaves from the lower levels might increase the efficiency of energy utilization. In this contribution, participation of leaves from different part of the canopy in crop photosynthesis and transpiration were quantified and discussed in relation to growth, production and energy utilization