Discipline of Horticultural Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, Pietermaritzburg, South Africa.
Discipline of Horticultural Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, Pietermaritzburg, South Africa; Discipline of Crop Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, Pietermaritzburg, South Africa.
J Plant Physiol. 2020 Mar-Apr;246-247:153130. doi: 10.1016/j.jplph.2020.153130. Epub 2020 Feb 7.
A reduction in photosynthesis results in a reduced CO 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 (WUE), instantaneous water use efficiency (WUE), intercellular CO 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 CO ms); gs (0.078 mol CO ms); ΦPS II (0.32); and qP (0.52) compared to those within the canopy position with lower A (19.27 mol CO ms); gs (0.0037 mol CO ms); 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 WUE, 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.
光合作用的减少会导致 CO 同化率降低，以及果实生长和发育所必需的碳水化合物的供应减少。本研究旨在确定‘Gem’鳄梨树冠内外叶片位置的光合作用效率和光保护机制及其与鳄梨果实成熟度的关系。该研究在南非夸祖鲁-纳塔尔省埃弗顿庄园的一个商业果园进行。在完全随机设计中，选择了 15 棵 8 年生的鳄梨树（cv.Gem），每个重复包括 5 棵树，共 3 个重复。从盛花期到果实生理成熟（约 25%干物质含量（DM）），每两周采集一次光合作用速率（A）、光合作用系统 II 的有效量子效率（ϕPSII）、气孔导度（gs）、蒸腾速率（T）、电子传递速率（ETR）、最小荧光（Fo'）、最大荧光（Fm'）、可变荧光（Fv'）、内在水分利用效率（WUE）、瞬时水分利用效率（WUE）、胞间 CO 浓度（Ci）和光化学猝灭（qP）的数据。结果表明，与冠层内的叶片相比，冠层外的叶片具有更高的 A（29.46mol CO ms）、gs（0.078mol CO ms）、ϕPS II（0.32）和 qP（0.52），而冠层内的叶片具有更低的 A（19.27mol CO ms）、gs（0.0037mol CO ms）、ϕPS II（0.044）和 qP（0.075）。相反，冠层内的叶绿素荧光和光保护参数高于冠层外的参数，这表明冠层内积累的能量更多地用于光保护而不是光化学。光合作用速率（A）、gs、Ci、T、WUEi 和 WUE 与中果皮干物质（DM）显著相关，而其他参数相关性较差。冠层外叶片的高光合效率导致平均 DM 为 28.9%，而冠层内果实的平均 DM 为 26.9%。本研究结果表明，冠层内‘Gem’鳄梨树叶片光合作用效率的降低并没有通过为光保护保留更多的能量来降低果实的 DM，而是使果实成熟推迟了大约两周。
