Plant responses to far-red supplementation and photosynthetically active radiation in an olive cultivar common to super high-density orchards

FEDERICO LADUX; CARINA GONZÁLEZ; EDUARDO TRENTACOSTE; PETER SEARLES; M. CECILIA ROUSSEAUX

Congreso; XXXIV Reunion de la Sociedad Argentina de Fisiologia Vegetal; 2023

Cultivation of olive trees in super high-density (SHD) hedgerows leads to a rapid increase in photosynthetic leaf area and crop yield, but also increases shading within and between trees. Such canopy shading reduces both photosynthetic active radiation (PAR) and red-to-far red ratio (R/FR). The objective of this study was to assess plant morphology, biomass, and photosynthetic pigment responses to different PAR and R/FR combinations in an olive cultivar (Arbequina) common to SHD hedgerows. The four experimental combinations were low (L) or high (H) PAR with either supplemental lateral FR (+FR) or no FR supplementation (-FR). The L and H treatments were obtained using either a 25% transmittance shade cloth or 90% transmittance netting, respectively. The lateral FR supplementation was applied to individual plants using light-emitting diodes that reduced the R/FR ratio from about 0.90 to 0.25. The internode length and main stem elongation were lower under L than H, and were higher in L+FR than L-FR. Axillary shoots were more vertically-oriented under L+FR than the other treatments, while leaf angle was more vertical with +FR at both PAR levels. Based on a principal component analysis of all the measured variables, the +FR plants did not differ from -FR under H, but they did differ from -FR under L. These findings suggest that young, cv. Arbequina olive trees do not anticipate imminent shading when PAR is still high through early low R/FR signals. However; different plant morphology, architecture and photosynthetic pigment traits were modified that could affect light absorption and penetration into the hedgerow later in orchard development when low PAR through direct shading is prominent.