Influence of pruning intensity on light penetration and leaf physiology in high-density orchards of mango trees.

摘要

High-density orchards of 'Amrapali' mango trees become overcrowded and show progressive decline in yield after 14-15 years of planting; hence, trees require pruning for sustainable production. Reduction in yield in such orchards is due to poor light interception and a low photosynthetic rate, which influence vegetative growth, flower initiation, fruit set and, thereby, the fruit yield. Hence, to help design a tree canopy for optimum plant growth and yield, we studied the effect of pruning on light interception and on different leaf physiological parameters of 'Amrapali' mango trees under high density. Sixteen-year-old trees of an 'Amrapali' mango high-density orchard in New Delhi, India, were subjected to tipping and light, moderate and heavy pruning; unpruned trees were used as the control. The available photosynthetic photon flux (PPF) and leaf physiological parameters such as rate of photosynthesis, specific leaf weight (SLW) and leaf chlorophyll (Chl) content were measured in pruned and unpruned tree canopies, following standard procedures. The percent available PPF was greater in all pruned tree canopies than in unpruned tree canopies; this could be due to tree openness caused by pruning. The light interception was lower at the lowest height of the tree canopy, probably because the centre of the tree canopy was partially blocked by new growth or criss-cross branches. The rate of photosynthesis was greater in leaves that developed in pruned tree canopies than in those developed in unpruned tree canopies, although there was no difference in SLW; this could be due to better light interception in pruned trees. In contrast, total leaf chlorophyll content was the highest in leaves that developed in unpruned and tipped tree canopies; this may be due to increased shade owing to overlapping or crowding of tree canopies in these trees, indicating that mango leaves that developed in shade appeared to be more physiologically efficient at synthesizing chlorophyll than leaves that grew in the sun or on the sunny side. The studies indicated that pruning 'Amrapali' mango trees by removing approximately 10-15 cm of the top from old branches improves light penetration, which influences the leaf physiology considerably. Hence, it would be useful to design high-density 'Amrapali' mango orchards maximizing productivity, although it requires additional studies to recommend a particular pruning intensity..