Abbreviations: N A , N per unit leaf area; N w , leaf N concentration; SLW, specific leaf weight. 1 On sabbatic leave from the Institute of Horticulture, ARO, The Volcani Center, Bet-Dagan, 50250 Israel. 2 To whom all correspondence should be
I. Klein, S.A. Weinbaum, T.M. DeJong, and T.T. Muraoka
Richard P. Marini and Donald L. Sowers
`Redhaven' peach [Prunus persica (L.) Batsch] trees were shaded to five light levels [100%, 45%, 23%, 17%, and 9% photosynthetic photon flux (PPF)] for four different periods. Net photosynthesis (Pn), measured under the various shade levels, increased nonlinearly with increasing percent PPF. After 18 days of shading, specific leaf weight (SLW) was positively and linearly related to percent PPF. After shade removal, Pn and SLW returned to control levels in 26 and 4 days, respectively. Flower density was positively related to percent PPF when trees were shaded from 16 June to 4 July or 4-31 July, but not from 31 July to 30 Sept. of the previous year.
M.E. Garcia, C.R. Rom, and J.B. Murphy
The effects of shading and leaf age on the production of foliar phenolics of two apple (Malus domestica Borkh.) cultivars, `Liberty' and `Red Rome Beauty', were studied. Potted trees were grown outdoors and their leaves tagged weekly when they reached 20 mm in length. This process continued for the duration of the experiment. At 3 weeks from budbreak, the trees were placed in three shade treatments: 0% shade (control), 60% shade, and 90% shade. After 5 weeks, the leaves were collected for phenolic assay. Specific leaf weight (SLW) was determined from the leaf below the tagged leaf. Shade significantly affected the total phenolic content. Leaves in 0% shade had the highest levels of total phenolics. The phenolic content decreased with increasing shade, with trees in 90% shade having a 72% reduction in total phenolics. There was a significant shade by leaf age interaction. There was a decrease in total phenolic content with increasing leaf age except for those leaves whose development occurred before the experiment was started. The 1-week-old leaf had the highest phenolic content, while 4-week-old leaf had the lowest amount. The 5- and 6-week-old leaves that had been tagged prior to the onset of the shade treatments has similar phenolic content in all treatment. SLW significantly decreased with increasing shade and increased with leaf age. Results of this study indicate that light and leaf developmental stage are important factors in the total foliar phenolic content, but, once phenolics are synthesized, shading does not affect their content.
Ido Schechter, J.T.A. Proctor, and D.C. Elfving
Mature apple trees (Malus domestica Borkh.) were studied in the 1989 and 1990 seasons to explore the effect of differential crop load on fruit dry weight (DW), DW content, specific leaf weight, and leaf carbon exchange, using girdled and non-girdled limbs. Fruit DW and DW content decreased with heavier fruit loads, however, fruit on girdled limbs had higher fruit DW and DW content. Specific leaf weight did not differ in leaves on non-girdled limbs along the crop load gradient, but increased dramatically in leaves on girdled limbs with crop load lighter than one fruit per cm2 cross-sectional area. These leaves also had a low photosynthetic rate, high stomatal resistance, and high internal CO2 concentration. The results suggest a physiological limit for photoassimilate usage by the tree. Exceeding this limit by reducing sink strength resulted in excessive carbohydrate accumulation in leaves, causing physical damage to the photosystem.
Juanita Popenoe and Tara Auxt Baugher
Photosynthesis, light (PAR) and transpiration were measured with an ADC portable infrared gas analyzer on apples and grapes. Measurements were taken on north and south sides of the rows, in the morning and afternoon, on sun and shade leaves, and with the leaf chamber in a horizontal position and in a natural leaf orientation position. Measurements were made on three cloudless days in August 1990 and 1991. Subsequently, fruit adjacent to sampled leaves were harvested and soluble solids determined. Sampled leaves were then harvested and leaf areas and dry weights measured. Correlation coefficients of variables were then subjected to analysis of variance to determine which techniques gave the best correlations. Grapes and apples responded differently. For grapes, soluble solids were most closely correlated to light and photosynthesis measurements when measured on south side shade leaves, while with apples, blush side soluble solids were best correlated with measurements on south side sun leaves in the afternoon. Specific leaf weight was best correlated to photosynthesis and light with grapes when measured on north side sun leaves and with apples when measured on the south side in the morning.
I. Klein, T.M. DeJong, S.A. Weinbaum, and T.T. Muraoka
Exposure to photosynthetically active radiation and the consequent effect on leaf mass per unit leaf area (SLW) and nitrogen (percent dry weight and μg·mm-2) allocation within tree canopies was investigated in walnut (Juglans regia `Serr' and `Hartley') trees. Percent contribution of discrete light flux densities below light saturation (100-700 μmol·s-1·m-2) to the total light exposure of individual spurs, exposed up to 9 hour·day-1 to saturating light (>700 μmol·s-1·m-2), was minimal (<1 hour), indicating that individual spurs were either exposed or shaded most of the day. SLW and N content per unit leaf area of individual spurs were highly correlated (second-order polynomial curve fit) with light exposure within the tree canopy, indicating uneven allocation of available N for optimal utilization. Nitrogen expressed as percent dry weight was not correlated with light exposure and SLW. Leaf N content per leaf area was highly correlated (linear fit) with SLW.
Timothy E. Elkner, J. A. Barden, M. M. Kushad, and D. D. Wolf
Fruiting spurs (`Red Prince Delicious') (RD) and shoots (`Sundale Spur Golden Delicious') (CD) with three leaf:fruit ratios and comparable nonfruiting spurs and shoots were girdled on 7 September 1988. An interaction between fruiting status and time existed for most parameters measured on both cultivars while there was no effect of leaf:fruit ratio. At 1 day after treatment (DAT) few differences existed due to fruiting status on either cultivar. At 8 DAT with RD and at 4 and 8 DAT with GD, Pn, transpiration (Tr), leaf water potential (ψ L), and nonreducing sugars were greater on fruiting than nonfruiting spurs and shoots while leaf resistance (RL), SLW, and starch were lower on fruiting spurs. In nonfruiting spurs and shoots Pn, Tr, and ψL tended to decrease while RL and SLW increased with time whereas m fruiting spurs and shoots most parameters remained constant. Total nonstructural carbohydrates, reducing sugars, and starch were greater in nonfruiting than fruiting spurs and shoots.
P.C. Andersen, J.G. Norcini, and G.W. Knox
, specific leaf weight; tchl, total chlorophyll; VPD, vapor pressure deficit; WUE, water use efficiency. Florida Agricultural Experiment Station Journal Series no. R-O1O54. The cost of publishing this paper was defrayed in part by the payment of page charges
Kuo-Tan Li and Alan N. Lakso
Summer pruning increases canopy light penetration and re-exposes spur leaves of the interior canopy of apple trees (Malus ×domestica Borkh.). However, we hypothesized that leaf photosynthetic ability is determined by the pre-pruning light environment, and the re-exposure intensity after summer pruning is incapable of restoring the photosynthesis efficiency of shaded leaves. To test this hypothesis, a commercial-type thinning-cuts pruning was applied to mature central leader `Empire'/M.26 apple trees. Changes in light availability, leaf net photosynthesis (Pn), photosystem II efficiency, and specific leaf weight (SLW) were recorded periodically before and after pruning. Leaf photosynthesis declined slightly through the growing season and was well correlated with pre-pruning light availability until late September. Although Pn decreased more substantially late in the season on exterior leaves than on interior leaves, Pn of leaves in the inner and middle canopies was lower than exterior leaves until late October. Maximum efficiency of photosystem II of dark-adapted leaves, measured by chlorophyll fluorescence (Fv/Fm), was not related to prior exposure or re-exposure. Specific leaf weight was well correlated with pre-pruning light availability and with leaf Pn in August but not in October. Results suggested that commercial summer pruning significantly increases light environments in the inner and middle canopies. However, light availability at interior and middle canopy sites was still much lower than exterior canopy and, consequently, leaf photosynthetic ability did not increase after summer pruning.
J.G. Norcini, P.C. Andersen, and G.W. Knox
expanded; RLWC, relative leaf water content; SLW, specific leaf weight; VPD, vapor pressure deficit; WUE, water use efficiency. This is Florida Agricultural Station Series no. R-01055. The cost of puhlishing this paper was defrayed in part by the payment of