S. A. Weinbaum

Leaf potassium concentration, CO2 exchange and light interception in almond trees (Prunus dulcis (Mill) D.A. Webb)

Abstract The goal of this study was to determine the effect of tree potassium status on CO2 exchange and light interception of field-grown almond trees (Prunus dulcis (Mill) D.A. Webb). Treatments consisted of four levels of potassium fertilization applied for three consecutive seasons. Potassium deficiency negatively affected tree light interception. Defoliation after mechanical harvesting indicated that potassium deficiency accelerated premature leaf senescence and premature leaf abscission. CO2 exchange rates were curvilinearly related to leaf potassium concentration during mid-summer after most vegetative shoot growth was completed. Leaf potassium concentrations less than 0.5–0.6% appeared to limit leaf CO2 exchange rate. Large variations in leaf potassium concentration were found in the non-fertilized trees. Indeed, most of the response curve of leaf CO2 exchange rate to leaf potassium concentration could be described by analyzing the leaves of non-fertilized trees. Stomatal conductance was not affected significantly by leaf potassium concentration and leaves with low potassium concentration had the highest calculated internal CO2 concentrations. Thus it appears that potassium deficiency in almond affected the leaf photosynthetic capacity via biochemical limitations and not through an effect on stomatal conductance.

Use of labeled nitrogen to monitor transition in nitrogen dependence from storage to current-year uptake in mature walnut trees

SummaryNitrogen (N) derived from both the soil during current-year uptake, and the withintree pool of storage N was distinguished in two groups of “Serr” walnut trees using labeled fertilizer (15N-depleted ammonium sulfate) applied in different years. Mass spectrometric analysis of N in xylem sap collected periodically in spring allowed quantification of the relative contributions of N from storage and current season uptake and the transition in N usage from previously assimilated (storage) N to the onset of current season uptake of soil N. N derived from storage accounted for > 50% of the xylem sap N during the staminate and pistillate bloom periods and throughout the period of spur leaf expansion.

Use of isotopic nitrogen to demonstrate dependence of mature almond trees on annual uptake of soil nitrogen

Abstract The present study was to assess the relationship between timing of fertilizer N applications and the contribution of that N to developing fruit and leaves. Nitrogen was applied as N‐depleted (NH4)2SO4 to mature almond [Prunus dulcis (Mill.) D.A. Webb, cv. Nonpareil] trees in a comercial orchard. The kinetics of isotopic N accumulation by developing fruit and leaves permitted some discrimination between the 2 principal N pools: the N previously assimilated and stored within the trees, and the N newly absorbed from the soil. Less than 15% of fruit N was contributed by the N applied the previous year in March or June. Thus, despite the occurrence of an endogenous pool of previously assimilated N, the almond appeared to be highly dependent on the annual availability of N from the soil. This concept was supported by the occurrence of incipient N deficiency within 14 months of fertilizer N application, as evidenced by reduced fruit dry weight and total N/fruit. The occurrence of these deficiencies coin...

Relationship between K15NO3 application period and 15N enrichment of apricot blossoms and developing fruit.

Abstract The relationship was assessed between the period of K15 NO3 application and the level of 15N in the blossoms of ‘Royal’ apricot (Prunus armen iaca L.). Late summer applications of K15NO, resulted in a 34 fold greater 15N enrichment of apricot blossoms the following year than K15NO3 applied during the dormant period. In contrast, 15N enrichment was 60% higher in vegetative shoots 30 days after anthesis when K15NO3 was applied during the dormant period as occurred following summer applications. Thus, fertilizer nitrogen applied in summer may support the early development of fruit to a greater extent than nitrogen applied during the dormant period. When K15NO3 was applied in Jan, 15N accumulation in reproductive organs occurred after anthesis and corresponded with the period of shoot elongation and leaf expansion. It appears that fertilizer N must be absorbed prior to leaf fall to reach reproductive organs during anthesis.

Is nitrogen stress more apparent in shaded, fruiting almond spurs than in exposed, non-fruiting spurs?

Summary Leaf abscission rates and nitrogen concentrations in persistent leaves were tracked on non-fruiting and fruiting almond [Prunus dulcis (Mill.) D.A.Webb] spurs located in either well-exposed or shaded canopy positions. Fruiting spurs, especially in shaded positions, had higher mid-season leaf abscission rates than did non-fruiting spurs, and the difference in abscission rates between shaded, fruiting spurs and other spur sub-populations increased with tree nitrogen deficiency. Nitrogen concentrations and contents of persistent leaves were lower on fruiting spurs than on non-fruiting spurs. Nitrogen contents of persistent leaves did not decline substantially over the period of kernel development (a period of high nitrogen demand by the fruit) regardless of spur shading and fruiting status, or tree nitrogen status. This indicates that little net nitrogen remobilisation from persistent leaves occurred during this period, even on fruiting spurs on nitrogen-deficient trees. Nitrogen deficiency accentuated nitrogen stress in shaded and fruiting spurs, as indicated by early leaf abscission. However, such differential stress was not reflected by the nitrogen concentration or content of persistent leaves during kernel development. Thus, sampling of persistent leaves from the shaded, fruiting spur sub-population for nitrogen analyses did not provide a practical, more sensitive diagnostic indicator of tree nitrogen status than did conventional leaf sampling from non-fruiting spurs.

Assessment of rest completion and its relationship to appearance of tetrads in anthers of 'Nonpareil' almond

The temporal association was assessed between pollen meiosis (as indicated by the appearance of tetrads) and rest completion in almond cultivar ‘Nonpareil’ (Prunus dulcis (Mill.) D.A. Webb). Rest completion, whether determined by macroscopic bud development or increased potentiality for growth of flower primordia, preceded the appearance of tetrads by 7–14 days under field conditions. In contrast, when detached dormant shoots (collected as early as 16 December) were maintained at 20°C for 7 days, tetrads were evident within 7 days, and the transition of pollen mother cells to tetrads occurred 7–14 days prior to rest completion. We conclude that tetrad formation and rest completion are not necessarily coupled. Tetrad formation may occur before rest completion if mild temperatures occur during winter. The occurrence of mild temperatures over several days during rest would presumably favor the earlier appearance of tetrads, relative to rest completion, than would occur in regions with colder winter temperatures. Relative growth rate of flower primordia may allow earlier and more accurate determination of rest completion than macroscopic bud development assessed conventionally as per cent bud break.

Spur light exposure as a primary external cause for derivation of dris norms in walnut trees

Abstract Spur leaf macroelement profile of walnut (Juglans regia, cvs. ‘Hartley’ and ‘Serr) was characterized by a modified diagnostic and recommendation integrated system (DRIS), using canopy photosynthetic photon flux (PPF) density exposure as a primary external determinant (5) of leaf mineral content. Spur N, P, Ca and Mg content was linearly correlated with PPF and SLW when expressed on the basis of leaf area (A) while that of K was linearly correlated with SLW on % DW basis (W). Mineral ratios, relevant for the DRIS analysis, were calculated using all four possible combinations of Area and Weight expressions (A/A, A/W, W/A, W/W) and correlated with spur leaf SLW. The particular expressions chosen for the DRIS analysis were based on their highest correlation to spur SLW and included N/K and P/K, based on A/W expression of the respective nutrients, and the reciprocal (W/A) expression for all other ratios. The dimensionless mineral ratios based on Weight per Weight (W/W) or Area per Area (A/A), which e...

Intraclonal variation in pollen germinability in kiwifruit, pistachio and walnut as influenced by tree age

Abstract Germinability in vitro of pollen collected from young (first year of flowering) and older (7 years), ontogenetically mature cultivars of walnut (Juglans regia), pistachio (Pistacia vera) and kiwifruit (Actinidia deliciosa) was evaluated at sub-optimal, optimal and supra-optimal temperatures. Throughout the temperature range that permitted pollen germination, pollen from young walnut and kiwifruit trees/vines had germination percentages consistently lower than those from the older trees/vines growing in the same location. At 20–26°C, germination of pistachio pollen collected from young trees was lower than that collected from older trees, but no differences were evident at higher temperatures. There was no evidence of a shift in the optimum temperature for pollen germination as a function of tree/vine age. The physiological basis for the influence of tree age on intraclonal variation in pollen germinability awaits further experimentation.

Field estimation of leaf nitrogen by light transmittance

Abstract A highly significant negative correlation was found between percentage transmittance of photosynthetically active radiation (%TPAR) through a varied sample of walnut leaves and their extractable chlorophyll content (expressed on a leaf‐area basis). The %TPAR was negatively correlated with leaf nitrogen (N) expressed on a leaf‐area basis. When leaves were sampled from throughout the canopy of a walnut tree, no correlation was obtained between either chlorophyll content or %TPAR and leaf N based on leaf dry wt.; this was due to variation between exposed and shaded leaves in leaf thickness and specific leaf weight (SLW). Regression analysis indicated better correlation between transmittance of photosynthetically active radiation (%TPAR) and leaf N when data were fitted to quadratic or exponential functions rather than to a linear formula. Thus, estimation of leaf N level by %TPAR is more sensitive at lower levels of leaf N. When exposed leaves from trees differing in N status were analyzed, %TPAR wa...

Foliar accumulation of NO3 ‐ in prune is not a sensitive indicator of impaired nitrogen assimilation under low irradiance 1

Abstract Light intensity and NO3 ‐ concentration in aerated nutrient solutions were varied to evaluate the sensitivity of NO3 ‐ assimilation in 1‐year‐old French prune (Prunus domestica L.) cv. Agen budded on Marianna 2624 rootstocks to low irradiance. The uptake and reduction of NO3 ‐ decreased in prune trees within 10 days at 3.2 klx. Foliar [NO3 ‐] increased in darkness but not at 3.2 klx. Thus, foliar [NO3 ‐ ] does not appear to be a potentially useful diagnostic parameter of carbon deprivation under field conditions at incipient stages of light‐limited nitrogen utilization. Free NH4 + and alpha‐amino N also increased in senescing prune leaves during a 25 day dark period.