Baseline Light Distribution in Kensington Pride Mango (Mangifera indica L.) tree canopies in North Queensland

Abstract

Future mango orchards systems will have canopies optimally designed for tree size, density, light and crop load relationships. Poor distribution of light within mango canopies is one of the reasons for current low orchard efficiency. Light (radiation), plays an important role in driving the photosynthesis, the developmental tree morphology, crop load and fruit quality. This study established a baseline for light transmission through the canopy (distribution) in four different ages of 'Kensington Pride' trees in Queensland commercial mango orchards. Light distribution patterns were established by measuring photosynthetically active radiation (PAR) (µmol m-2
s-1) distribution in three dimensional matrix inside the canopy, at seven equally separated transects across the canopy from north to south and 4 sectors (west, middle-west, middle-east and east) on each transect at 5 heights above the ground. Mean light transmission within the canopy increased with tree age and canopy volume, and was related to pruning and training method. Highest light transmission was recorded 73.91 µmol m-2 s-1 at 75% of tree height. Light transmission was 60.90 µmol m-2 s-1 at 50% tree height, 58.23 µmol m-2 s-1 at 25% tree height and 62.81 µmol m-2 s-1 on the ground. In the horizontal plains, light distribution was lower in the middle parts of the canopy compared to the edges. There was a significant (p<0.05) relationship between light transmission and tree height, indicating large variation in light distribution within the canopy, with many leaves in shade where photosynthesis efficiency may be low. Some of the outer canopy may be receiving too much light and possible photo-inhibition as indicted by sun burn on leaves and fruit. This baseline understanding of light distribution will assist research in to improved light distribution in mango canopies and in the development of high density mango orchard systems.Future mango orchards systems will have canopies optimally designed for tree size, density, light and crop load relationships. Poor distribution of light within mango canopies is one of the reasons for current low orchard efficiency. Light (radiation), plays an important role in driving the photosynthesis, the developmental tree morphology, crop load and fruit quality. This study established a baseline for light transmission through the canopy (distribution) in four different ages of 'Kensington Pride' trees in Queensland commercial mango orchards. Light distribution patterns were established by measuring photosynthetically active radiation (PAR) (µmol m-2
s-1) distribution in three dimensional matrix inside the canopy, at seven equally separated transects across the canopy from north to south and 4 sectors (west, middle-west, middle-east and east) on each transect at 5 heights above the ground. Mean light transmission within the canopy increased with tree age and canopy volume, and was related to pruning and training method. Highest light transmission was recorded 73.91 µmol m-2 s-1 at 75% of tree height. Light transmission was 60.90 µmol m-2 s-1 at 50% tree height, 58.23 µmol m-2 s-1 at 25% tree height and 62.81 µmol m-2 s-1 on the ground. In the horizontal plains, light distribution was lower in the middle parts of the canopy compared to the edges. There was a significant (p<0.05) relationship between light transmission and tree height, indicating large variation in light distribution within the canopy, with many leaves in shade where photosynthesis efficiency may be low. Some of the outer canopy may be receiving too much light and possible photo-inhibition as indicted by sun burn on leaves and fruit. This baseline understanding of light distribution will assist research in to improved light distribution in mango canopies and in the development of high density mango orchard systems.