Abstract
Tree densities have increased greatly in olive orchards over the last few decades. In many annual crop species, increased density reduces the horizontal red/far-red (R/FR) and blue/green (B/G) ratios during canopy development even before direct shading occurs, and such changes are known to alter plant morphology. This study with olive trees evaluated: (1) whether the leaf area index (LAI) of neighboring trees modifies the light quality environment prior to a tree being directly shaded and (2) the potential morphological responses of three olive cultivars to changes in light quality. Increasing LAI using different spatial arrangements of potted, three-year-old trees reduced the horizontal R/FR ratio more than that of the B/G ratio. Cultivar-specific responses to low R/FR ratio were observed for individual leaf area and aboveground/belowground biomass ratio using laterally positioned FR mirrors or green fences. No statistically significant responses were detected in response to green vegetation fences that reduced both horizontal R/FR and B/G ratios, but a cluster analysis grouped together the overall morphological responses to both FR mirrors and green fences. These results in olive trees suggest that cultivar differences in response to light quality may be relevant for understanding adaptation to dense orchards and identifying cultivars best suited to them.
Highlights
The R/FR and B/G ratios varied over the course of the day by azimuth orientation for the intermediate leaf area index (LAI) evaluated (1.1 m2 m−2 ; Figure 4)
The results of The our study the show opticalthat properties of olive leavesofcan modify the light quality reflected by the tree crown even before direct shading modify the light quality reflected by the tree crown even before direct shading between between trees occurs (Figures and 4)
Different spatial arrangements of potted olive trees showed that increasing LAI modifies the light quality environment by lowering horizontal R/FR and B/G ratios even before direct shading between neighboring trees occurs
Summary
The super high density production model (SHD; 1000 to 2500 trees ha−1 ) leads to high yields in only a few years after planting and is designed for mechanical harvesting with efficient straddle harvesters [2]. Due to less intra- and inter-row spacing, SHD orchards reach high levels of leaf area index (i.e., m2 of leaf area per m2 of soil surface) before individual trees cover their allotted space. This leads to a greater interception of photosynthetically active radiation (PAR) early in hedgerow formation [3], and oil yield is maximized when trees have grown enough to intercept about 65% of incident PAR [4,5]
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