A reduction in photosynthesis results in a reduced CO2 assimilation rate and availability of carbohydrates essential for fruit growth and development. This study determined photosynthetic efficiency and photoprotection mechanisms within and outside leaf canopy positions in 'Gem' avocado orchards and their relationship with avocado fruit maturity. The study was conducted in a commercial orchard at Everdon Estate in KwaZulu-Natal, South Africa. A total of 15 eight-year-old avocado trees (cv. Gem) were selected in a completely randomised design with three replicates, with each replicate consisting of five trees. Data were collected bi-weekly on photosynthetic rate (A), effective quantum efficiency of photosystem II (ϕPSII), stomatal conductance (gs), transpiration rate (T), electron transport rate (ETR), minimum fluorescence (Fo'), maximum fluorescence (Fm'), variable fluorescence (Fv'), intrinsic water use efficiency (WUEi), instantaneous water use efficiency (WUEins), intercellular CO2 concentration (Ci) and photochemical quenching (qP) from full bloom to fruit physiological maturity (∼25 % dry matter content (DM)). The results showed that leaves from the outside position had higher A (29.46 mol CO2 m-2s-1); gs (0.078 mol CO2 m-2s-1); ΦPS II (0.32); and qP (0.52) compared to those within the canopy position with lower A (19.27 mol CO2 m-2s-1); gs (0.0037 mol CO2 m-2s-1); ΦPS II (0.044) and qP (0.075), respectively. Contrastingly, chlorophyll fluorescence and photoprotection parameters were higher within the canopy than on the outside, suggesting that the greater proportion of energy accumulated within the canopy was used for photoprotection other than photochemistry. Photosynthetic rate (A), gs, Ci, T, WUEi and WUEins, correlated significantly with mesocarp dry matter (DM), while all other parameters correlated poorly. The high photosynthetic efficiency of leaves from outside the canopy resulted in an average DM of 28.9 % compared to 26.9 % of fruit within the canopy. The present findings suggest that reduced photosynthetic efficiency of 'Gem' avocado within the canopy position does not compromise fruit DM by reserving more energy for photoprotection; however, it delays maturity by about two weeks.

中文翻译：

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“宝石”鳄梨 (Persea americana Mill.) 叶在冠层内外的光化学和光保护以及与果实成熟度的关系

光合作用的减少导致 CO2 同化率和水果生长发育所必需的碳水化合物的可用性降低。本研究确定了“宝石”鳄梨果园中叶冠位置内外的光合效率和光保护机制，以及它们与鳄梨果实成熟度的关系。该研究是在南非夸祖鲁-纳塔尔省 Everdon Estate 的一个商业果园中进行的。总共 15 棵八年生鳄梨树 (cv. Gem) 以完全随机的设计进行了三个重复，每个重复由五棵树组成。每两周收集一次光合速率 (A)、光系统 II 的有效量子效率 (φPSII)、气孔导度 (gs)、蒸腾速率 (T)、电子传输速率 (ETR)、最小荧光 (Fo')、从盛开到果实生理成熟的最大荧光（Fm'）、可变荧光（Fv'）、内在水分利用效率（WUEi）、瞬时水分利用效率（WUEins）、细胞间二氧化碳浓度（Ci）和光化学猝灭（qP）（ ∼25 % 干物质含量 (DM))。结果表明，外侧位置的叶子具有较高的A（29.46 mol CO2 m-2s-1）；gs (0.078 mol CO2 m-2s-1)；ΦPS II (0.32)；和 qP (0.52) 与冠层位置内具有较低 A (19.27 mol CO2 m-2s-1) 的那些相比；gs (0.0037 mol CO2 m-2s-1)；分别为 ΦPS II (0.044) 和 qP (0.075)。相比之下，冠层内的叶绿素荧光和光保护参数高于外部，表明树冠内积累的更大比例的能量用于光化学以外的光保护。光合速率 (A)、gs、Ci、T、WUEi 和 WUEins 与中果皮干物质 (DM) 显着相关，而所有其他参数相关性较差。树冠外叶子的高光合效率导致平均 DM 为 28.9 %，而树冠内的果实为 26.9 %。目前的研究结果表明，树冠位置内“宝石”鳄梨的光合效率降低不会通过为光保护保留更多能量而影响果实 DM；然而，它推迟了大约两周的到期时间。树冠外叶子的高光合效率导致平均 DM 为 28.9 %，而树冠内的果实为 26.9 %。目前的研究结果表明，树冠位置内“宝石”鳄梨的光合效率降低不会通过为光保护保留更多能量而影响果实 DM；然而，它推迟了大约两周的到期时间。树冠外叶子的高光合效率导致平均 DM 为 28.9 %，而树冠内的果实为 26.9 %。目前的研究结果表明，树冠位置内“宝石”鳄梨的光合效率降低不会通过为光保护保留更多能量而影响果实 DM；然而，它推迟了大约两周的到期时间。