Light quality environment and photomorphological responses of young olive trees

Abstract

Plant proximity in super high density (SHD) olive orchards leads to high levels of leaf area index (LAI). Horizontal light reflection by leaves of neighboring plants often reduces R/FR and B/G ratios and can trigger different photomorphological plant responses even before direct shading occurs in many annual crop plants. The objectives were to characterize whether LAI modifies R/FR and B/G ratios in olive trees; and to assess the morphological responses of three olive cultivars to light quality. For the light characterization, different spatial arrangements of olive trees growing in pots were used to obtain different LAI. Plants of Arbequina, Arauco and Coratina cvs were subject to different light quality treatments including a laterally positioned FR-mirror that reduced horizontal R/FR and a green vegetation fence that reduced both horizontal R/FR and B/G. Both treatments had their own control. Increasing LAI led to decreases in R/FR from 0.84 to 0.56 and B/G from 0.81 to 0.76. The individual leaf area was reduced 26% by the FR-mirrors in Arbequina, and increased 18% in Arauco. The above/below ground biomass ratio were lower with the FRmirrors in Arbequina and Coratina. The green-fence treatment and its control did not show any statistically significant morphological differences for the cultivars evaluated, but a cluster analysis grouped together the overall morphological responses to FR mirrors and green fences. These first 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 for them.