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A monitoring and control system for sequentially measuring whole-tree-canopy gas exchange of four apple (Malus domestica Borkh.) trees in the field is described. A portable, highly transparent, open-top whole-canopy cuvette was developed for complete enclosure of the above-ground portion of the tree. The flux of whole-canopy CO2 and H2 0 vapor was estimated from differential CO2 concentration and H2O-vapor partial pressure between ambient/reference air entering the cuvette and analysis air leaving the cuvette, as measured by infrared gas analysis. The bulk air-flow rate through the chamber was measured with a Pitot static tube inserted into the air-supply duct and connected to a differential pressure transducer. Performance of the whole-canopy cuvette system was tested for its suitability for gas-exchange measurements under field conditions. The air flow through the whole-canopy cuvette was 22000 L·min-1 (≈5.5 air exchanges/min) during the day, providing adequate air mixing within the cuvette, and 4000 L·min-1 (≈1 air exchange/min) during the night. Daily average leaf temperatures within the cuvette were 2-3 °C higher than to those on trees outside the cuvette. Photosynthetic photon flux transmitted through the chamber walls was at least 92 % of the incident ambient radiation. Moreover, the whole-canopy cuvette was evaluated without tree enclosure to determine the degree of “noise” in differential CO2 concentration and H2O-vapor partial pressure and was found to be acceptable with ΔCO2 ± 0.3 (μmol·mol-1 and ΔH2O ± 5 Pa. Whole-canopy carbon gas exchange and transpiration of four cropping `Braeburn'/M.26 apple trees followed closely incident radiation over the course of a day.
Abstract
Leaf areas on individual spurs were modified in the pink stage of flower development on ‘Golden Delicious’ apple (Malus domestica Borkh.), and the effects on fruiting, mineral content, and net photosynthesis (Pn), of leaves on those spurs determined. Removal of a 3mm-ring of bark from the spur increased initial fruit set, determined 1 week after petal fall, compared to normal spurs. The combination of ringing and removal of all leaves resulted in a complete loss of fruit. Final fruit set was reduced by any treatment involving ringing, reduction in spur leaf area, or injury to the stigmas. The greatest number and total weight of fruit at harvest were given by undefoliated, unringed spurs where the bourse shoot was allowed to develop. Ringing reduced Pn at petal fall but had no effect later in the season. Presence of the bourse shoot reduced Pn of spur leaves in early June. Spur leaves on fruiting trees had an important localized influence on fruit set, ultimate fruit size, and fruit Ca level of fruit produced on that spur.
The effect of liquid lime sulfur (LS) and fish oil (FO) application during bloom on leaf photosynthesis (Pn) and pollen tube growth in apple (Malus ×domestica) flowers were investigated in order to determine their mode of action as a bloom thinning agent. LS increased the percentage of flowers with fewer than 10 pollen tubes per flower to more than 64% compared to 5% or less in the control. Pollen tubes were completely absent from 27% to 48% of flowers following LS treatment compared with fewer than 4% of flowers having no pollen tubes on control trees. These data indicate that 30% to 50% of flowers that open on the day of LS application are unlikely to set a fruit due to the complete inhibition of embryo fertilization. Increasing the rate of LS from 0.5% to 4% increased the proportion of flowers with limited pollen tube number in a concentration dependent manner. LS suppressed the rate of light saturated Pn; successive LS sprays during the bloom period had an additive effect on suppression of Pn and fruit set. In one study the reduction in Pn was greatest 12 days after application of LS but Pn recovered by about 19 days after initial treatment. In a second study Pn of primary spur leaves had still not recovered when measured 57 days after the first of three applications. FO had no effect on the number of pollen tubes per flower, but reduced Pn and fruit set by about 10% and 20% respectively. An increase in the proportion of flowers with no pollen tubes, and therefore no embryo development, can account, at least in part, for the thinning response following application of LS to apples during bloom. It is likely that suppression of Pn contributes to the thinning response, although the importance of this mechanism will depend on perturbation of the total carbohydrate supply to developing fruit.
Effect of crop load on tree growth, leaf characteristics, photosynthesis, and fruit quality of 5-year-old `Braeburn' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees on Malling 26 (M.26) rootstock was examined during the 1994-95 growing season. Crop loads ranged from 0 to 57 kg/tree [0 to 1.6 kg fruit/cm2 trunk cross sectional area (TCA) or 0 to 8.7 fruit/cm2 TCA]. Fruit maturity as indicated by background color, starch/iodine score, and soluble solids was advanced significantly on low-cropping trees compared to high-cropping trees. Whole-canopy leaf area and percentage tree light interception increased linearly with a significant trend as crop load decreased. From midseason until fruit harvest, leaf photosynthesis decreased significantly on lighter cropping trees and similarly, a positive linear trend was found between whole-canopy gas exchange per unit area of leaf and crop load. Leaf starch concentration in midseason increased linearly as crop load decreased, providing some explanation for the increased down-regulation of photosynthesis on trees with lower crop loads. After fruit harvest, the previous crop loads had no effect on leaf photosynthesis and preharvest differences in whole-canopy gas exchange per unit area of leaf were less pronounced. At each measurement date, daily whole-canopy net carbon exchange and transpiration closely followed the diurnal pattern of incident photosynthetic photon flux. The photochemical yield and electron transport capacity depended on crop load. This was due mostly to reaction center closure before harvest and an increased nonphotochemical quenching after harvest.