Effect of fruiting on carbon budgets of apple tree canopies

Summary Carbon budgets were calculated from net photosynthesis and dark respiration measurements for canopies of field-grown, 3-year-old apple trees (Malus domestica Borkh.) with maximum leaf areas of 5.4 m² in a temperature-controlled Perspex tree chamber, measured in situ over 2 years (July 1988 to October 1990) by computerized infrared gas analysis using a dedicated interface and software. Net photosynthesis (Pn) and carbon assimilation per leaf area peaked at respectively 8.3 and 7.7 mol CO₂ m^–2 s^–1 in April. Net photosynthesis (Pn) and dark respiration (Rd) per tree peaked at 3.6 g CO₂ tree^–1 h^–1 (Pn) and 1.2 g CO₂ tree^–1 h^–1 (Rd), equivalent to 4.2 mol CO₂ (Pn) and 1.4 mol CO₂ (Rd) m^–2 s^–1 with maximum carbon gain per tree in August and maximum dark respiration per tree in October 1988 and 1989. In May 1990, a tree was deblossomed. Pn (per tree) of the fruiting apple tree canopy exceeded that of the non-fruiting tree by 2–2.5 fold from June to August 1990, attributed to reduced photorespiration (RI), and resulting in a 2-fold carbon gain of the fruiting over the non-fruiting tree. Dark respiration of the fruiting tree canopy progressively exceeded, with increasing sink strength of the fruit, by 51% (June–August), 1.4-fold (September) and 2-fold (October) that of the non-fruiting tree due to leaf (i. e. not fruit) respiration to provide energy (a) to produce and maintain the fruit on the tree and (b) thereafter to facilitate the later carbohydrate translocation into the woody perennial parts of the tree. The fruiting tree reached its optium carbon budget 2–4 weeks earlier (August) then the non-fruiting tree (September 1990). In the winter, the trunk respired 2–100 g CO₂ month^–1 tree^–1. These data represent the first long-term examination of the effect of fruiting without fruit removal which shows increased dark respiration and with the increase progressing as the fruit developed.     

Gas exchange parameters, water relations and carbohydrate partitioning in leaves of field-grown Prunus domestica following fruit removal

The effect of fruit removal on gas exchange, water relations, chlorophyll and non-structural carbohydrate content of leaves from mature, field-grown plum trees ( Prunus domestica L. cv. Stanley) was determined over 2 consecutive growing seasons. Removal of fruits during stage II of fruit development decreased CO₂ assimilation rate within 24 h from 12.6 to 8.5 μmol m^-2 s^-1 in 1986, and from 12.1 to 10.2 μmol m^-2 s^-1 in 1987. Depression of net photosynthesis persisted for at least 5 days and was greatest in the early afternoon. Recovery of the CO₂ assimilation rate to pretreatment levels coincided in defruited trees with vegetative growth that was more than 5-fold that of fruiting trees in the first 6 weeks after fruit removal in 1986. Estimated photorespiration was similar in both fruiting and defruited trees. The stomatal contribution to the decrease of CO₂ assimilation rate, calculated from assimilation/intercellular CO₂ curves, ranged from 31 to 46%. Defruiting did not affect leaf water potential, but decreased leaf osmotic potential. Leaf levels of chlorophyll, fructose, glucose, sorbitol and sucrose were not affected by defruiting, whereas starch content increased up to 51% in leaves of defruited trees within 24 h after fruit removal. However, because of the small starch pool present in plum leaves (<1.9% dry weight) it is unlikely that starch accumulation was responsible for the observed decline in CO₂ assimilation rate after fruit removal. The decrease of CO₂ assimilation rate is discussed in relation to the hypothesis of assimilate demand regulating photosynthesis through a feedback mechanism.     

Effects of kaolin application on light absorption and distribution, radiation use efficiency and photosynthesis of almond and walnut canopies

BACKGROUND AND AIMS: Kaolin applied as a suspension to plant canopies forms a film on leaves that increases reflection and reduces absorption of light. Photosynthesis of individual leaves is decreased while the photosynthesis of the whole canopy remains unaffected or even increases. This may result from a better distribution of light within the canopy following kaolin application, but this explanation has not been tested. The objective of this work was to study the effects of kaolin application on light distribution and absorption within tree canopies and, ultimately, on canopy photosynthesis and radiation use efficiency. METHODS: Photosynthetically active radiation (PAR) incident on individual leaves within the canopy of almond (Prunus dulcis) and walnut (Juglans regia) trees was measured before and after kaolin application in order to study PAR distribution within the canopy. The PAR incident on, and reflected and transmitted by, the canopy was measured on the same day for kaolin-sprayed and control trees in order to calculate canopy PAR absorption. These data were then used to model canopy photosynthesis and radiation use efficiency by a simple method proposed in previous work, based on the photosynthetic response to incident PAR of a top-canopy leaf. KEY RESULTS: Kaolin increased incident PAR on surfaces of inner-canopy leaves, although there was an estimated 20 % loss in PAR reaching the photosynthetic apparatus, due to increased reflection. Assuming a 20 % loss of PAR, modelled photosynthesis and photosynthetic radiation use efficiency (PRUE) of kaolin-coated leaves decreased by only 6.3 %. This was due to (1) more beneficial PAR distribution within the kaolin-sprayed canopy, and (2) with decreasing PAR, leaf photosynthesis decreases less than proportionally, due to the curvature of the photosynthesis response-curve to PAR. The relatively small loss in canopy PRUE (per unit of incident PAR), coupled with the increased incident PAR on the leaf surface on inner-canopy leaves, resulted in an estimated increase in modelled photosynthesis of the canopy (+9 % in both walnut and almond). The small loss in PRUE (per unit of incident PAR) resulted in an increase in radiation use efficiency per unit of absorbed PAR, which more than compensated for the minor (7 %) reduction in canopy PAR absorption. CONCLUSIONS: The results explain the apparently contradictory findings in the literature of positive or no effects of kaolin applications on canopy photosynthesis and yield, despite the decrease in photosynthesis by individual leaves when measured at the same PAR.     

Effects of fruit thinning agents on apple tree canopy photosynthesis and dark respiration

Effects on photosynthesis of the fruit thinning agents naphthaleneaceticacid (NAA) and three commercial plant growth regulator formulations,naphthaleneacetic acid ('Rhodofix') and naphthaleneacetamide('Amidthin') and 2-chloroethylphosphonic acid('Ethrel')were evaluated with respect to the stress they impose on the fruit tree, usingthe alternate-bearing sensitive apple cv. 'Elstar'. This work wasbased on the hypothesis that plant stress in the form of large reductions inleaf photosynthesis are a pre-requisite for successful fruit thinning. A newtechnology was employed for continuous recording of tree canopyphotosynthesis, dark respiration and carbon balance of apple trees. This wasbased on six canopy chambers, which enclosed apple trees under naturalconditions in the field, with on-line measurements and continuous analysis ofCO₂ exchange and automated data acquisition. All employed thinningagents reduced whole tree canopy photosynthesis consistently by3–34% on the five days following their application, withphotosynthesis still declining thereafter in the case of the NAA and'Amid-thin' application. The reduction after application of either'Rhodofix' or 'Ethrel', declined within five days, suchthat most of the original photosynthetic potential was restored, indicatingacceptable phytotoxicity of these three plant growth regulators at theconcentrations used. The effects on dark respiration differed markedly. NAA and'Ethrel' increased dark respirationover-proportionally by up to 106%, whereas 'Amid-thin' and'Rhodofix' decreased it by up to 46%inthe first night after application, thereby drastically affecting the carbonbalance of the tree in opposite ways. These results are integrated into ahypothesis linking basipetal auxin transport, phloem loading, translocation anddeficiency of photoassimilates.     

Influence of Seasonal Variations in Soil Water Availability on Gas Exchange of Tropical Canopy Trees

Seasonal variations in environmental conditions influence the functioning of the whole ecosystem of tropical rain forests, but as yet little is known about how such variations directly influence the leaf gas exchange and transpiration of individual canopy tree species. We examined the influence of seasonal variations in relative extractable water in the upper soil layers on predawn leaf water potential, saturated net photosynthesis, leaf dark respiration, stomatal conductance, and tree transpiration of 13 tropical rain forest canopy trees (eight species) over 2 yr in French Guiana. The canopies were accessed by climbing ropes attached to the trees and to a tower. Our results indicate that a small proportion of the studied trees were unaffected by soil water depletion during seasonal dry periods, probably thanks to efficient deep root systems. The trees showing decreased tree water status (i.e., predawn leaf water potential) displayed a wide range of leaf gas exchange responses. Some trees strongly regulated photosynthesis and transpiration when relative extractable water decreased drastically. In contrast, other trees showed little variation, thus indicating good adaptation to soil drought conditions. These results have important applications to modeling approaches: indeed, precise evaluation and grouping of these response patterns are required before any tree‐based functional models can efficiently describe the response of tropical rain forest ecosystems to future changes in environmental conditions.     

Sap flow, gas exchange, and hydraulic conductance of young apricot trees growing under a shading net and different water supplies

The experiment was carried out in a research field near Murcia, Spain, over a 3-week period between September 26 and October 16, 2000. Sixteen trees were used in the experiment, eight of which were placed under a rectangular shading net, while the other eight were maintained in the open air. Trees were irrigated once per day and, after October 5th, water was witheld from eight trees (four shaded and four unprotected for 5 days). The leaf stomatal conductance and the photosynthesis rates were higher in the shaded trees than in the exposed plants, probably because the leaf water potential was lower in the unshaded plants. This higher leaf conductance partially compensated for the effect of low radiation on transpiration, and the reduction of daily sap flow registered in shaded trees was only around 10-20%. The net also affected trunk diameter changes, with the shaded trees showing lower values of maximum daily shrinkage. Soil water deficit and high radiation had a similar effect on plant water parameters, lowering leaf water potential, leaf stomatal conductance, and the photosynthesis rate. The effects of both conditions were accumulative and so the exposed water-stressed plants showed the lowest values of total hydraulic resistance and water use efficiency, while the shaded well-irrigated trees registered the highest values for both parameters. For this reason, we think that net shading could be extended to apricot culture in many areas in which irrigation water is scarce and insolation is high.     

Sustained enhancement of photosynthesis in mature deciduous forest trees after 8 years of free air CO2 enrichment

Carbon uptake by forests constitutes half of the planet’s terrestrial net primary production; therefore, photosynthetic responses of trees to rising atmospheric CO₂ are critical to understanding the future global carbon cycle. At the Swiss Canopy Crane, we investigated gas exchange characteristics and leaf traits in five deciduous tree species during their eighth growing season under free air carbon dioxide enrichment in a 35-m tall, ca. 100-year-old mixed forest. Net photosynthesis of upper-canopy foliage was 48% (July) and 42% (September) higher in CO₂-enriched trees and showed no sign of down-regulation. Elevated CO₂ had no effect on carboxylation efficiency (V _cmax) or maximal electron transport (J _max) driving ribulose-1,5-bisphosphate (RuBP) regeneration. CO₂ enrichment improved nitrogen use efficiency, but did not affect leaf nitrogen (N) concentration, leaf thickness or specific leaf area except for one species. Non-structural carbohydrates accumulated more strongly in leaves grown under elevated CO₂ (largely driven by Quercus). Because leaf area index did not change, the CO₂-driven stimulation of photosynthesis in these trees may persist in the upper canopy under future atmospheric CO₂ concentrations without reductions in photosynthetic capacity. However, given the lack of growth stimulation, the fate of the additionally assimilated carbon remains uncertain.     

Phenology of Tree Species in Bolivian Dry Forests

Phenological characteristics of 453 individuals representing 39 tree species were investigated in two dry forests of the Lomerío region, Department of Santa Cruz, Bolivia. The leaf, flower, and fruit production of canopy and sub–canopy forest tree species were recorded monthly over a two–year period. Most canopy species lost their leaves during the dry season, whereas nearly all sub–canopy species retained their leaves. Peak leaf fall for canopy trees coincided with the peak of the dry season in July and August. Flushing of new leaves was complete by November in the early rainy season. Flowering and fruiting were bimodal, with a major peak occurring at the end of the dry season (August–October) and a minor peak during the rainy season (January). Fruit development was sufficiently long in this forest that fruiting peaks actually tended to precede flowering peaks by one month. A scarcity of fruit was observed in May, corresponding to the end of the rainy season. With the exception of figs (Ficus), most species had fairly synchronous fruit production. Most canopy trees had small, wind dispersed seeds or fruits that matured during the latter part of the dry season, whereas many sub–canopy tree species produced larger animal– or gravity–dispersed fruits that matured during the peak of the rainy season. Most species produced fruit annually. Lomerio received less rainfall than other tropical dry forests in which phenological studies have been conducted, but rainfall can be plentiful during the dry season in association with the passage of Antarctic cold fronts. Still, phenological patterns in Bolivian dry forests appear to be similar to those of other Neotropical dry forests.     

The effect of water stress on photosynthesis and related parameters in Pinus halepensis

Net photosynthesis, transpiration, dark respiration rates and stomatal and mesophyll resistances were studied in young potted seedlings of Pinus halepensis Mill. under gradually decreasing soil and leaf water potentials. Stomatal resistance under non-limiting xylem water potentials was 6–7 times higher than mesophyll resistance. Stomata started to close at threshold xylem water potentials of −0.8 MPa, whereas mesophyll resistance started to increase at about −1.4 MPa. Decreasing xylem water potentials increased the CO₂ compensation point and decreased the water use efficiency (expressed by the photosynthesis to transpiration ratio) and dark respiration rate. It is concluded that at least part of the drought resistance characteristics of P. halepensis are associated with a sensitive stomatal mechanism which enables an efficient control of water loss.     

北京山区油松和元宝槭冠层气孔导度特征及其环境响应

叶片气孔是植物进行水汽交换的通道, 影响着植物的蒸腾和光合作用。然而叶片气孔行为受环境条件和树种类型的影响, 不同树种冠层气孔导度对环境因子响应的差异性, 以及在生长季不同时期叶片气孔对冠层蒸腾的调节作用是否会发生改变, 仍不清楚。该研究目的是通过探究各环境因子对不同树种冠层气孔导度的相对贡献率以及叶片气孔对冠层蒸腾的调节作用, 为深入了解植物水分利用状况和山区森林经营提供参考依据。于2018年生长季以北京八达岭国家森林公园内的58年生油松(Pinus tabuliformis)和39年生元宝槭(Acer truncatum)为研究对象, 利用热扩散技术对其树干液流进行连续监测, 并同步监测环境因子。利用彭曼公式计算冠层气孔导度(G_s)。主要结果: (1)油松和元宝槭日间G_s在日、月时间尺度上存在明显差异。5-7月油松和元宝槭日动态G_s均随饱和水汽压差(VPD)和太阳辐射(GR)的增加呈上升趋势, 上升持续时间比8月和9月长; 在月尺度上, 随着VPD、GR的降低和土壤湿度(VWC)的升高, G_s从5月到9月整体上升。(2)利用增强回归树法分析得到VWC和VPD对G_s的贡献率最大, 其次是GR、气温和风速。VWC和VPD对油松G_s的贡献率分别为66.4%和17.4%, 对元宝槭G_s的贡献率分别为54.8%和21.0%。(3)油松和元宝槭的dG_s/dlnVPD值与参考冠层气孔导度之间的斜率均显著高于0.6, 气孔调节作用相对较强。综上所述, 气孔对环境因子的响应在树种以及生长季不同时期之间存在差异, 为防止水分过度散失, 两树种在不同土壤水分条件下均通过严格的气孔调节控制蒸腾量。     

间伐改形对陇东旱塬密闭苹果园树体冠层结构和发育后期叶片质量的影响

为研究间伐改形对红富士成龄乔化密植果园树体冠层特征、生育后期叶片生理特性、养分积累分配规律、光合生产力和土壤水分时空分布动态的影响,以18年生‘红富士’苹果密闭园为试材,对苹果树单株结构参数、枝量、枝类组成、覆盖率、叶片光合速率等参数进行测定.结果表明: 密闭果园叶片光合作用受非气孔因素限制,导致PSII最大光化学效率、PSII光合潜能、光合性能指数下降了1.2%、11.5%、13.9%.间伐改形后,叶面积指数、树冠覆盖率有所降低,使得冠层直射光透过系数增加了79.0%,树形结构有所改善.苹果园总枝数降低到约1100400条·hm^-2,单株枝量增加了5.0%,短枝比例提高至73.0%.由于冠层光照条件的改善,叶面积、比叶质量、百叶重、叶绿素含量有不同程度的提高.叶片光合速率的提高促进了光合产物的积累,淀粉、蛋白质含量为密闭果园的143.5%、107.8%.叶片的发育质量与其所处的光照辐射环境有着密切联系,密闭果园经间伐、改形后,果园群体结构和冠层光照得以改善,促进了叶片生长发育,提高了叶片光合效能,降低了果园土壤水分的无效消耗,是陇东旱塬苹果产区密闭果园适宜的调整、优化方案.     

Seasonal Changes in the Photosynthetic Rate in Apple Trees : A Comparison between Fruiting and Nonfruiting Trees

Seasonal changes in photosynthesis of apple trees (Malus domestica Borkh.) were monitored to examine the effect of source-sink interactions on photosynthesis and photorespiration. Elevated photosynthetic rates were observed during two periods of the growing season and correlated with the fruiting process. The first period of increased photosynthetic rates was during the bloom period, when spur leaves on flowering shoots exhibited up to 25% higher photosynthetic rates than vegetative spur leaves on a leaf area basis. CO₂ assimilation rates were also higher in fruiting trees than nonfruiting trees during the period of rapid fruit growth from July to September. Photorespiration, dark respiration, leaf resistance, and transpiration exhibited no seasonal changes which correlated to the presence or absence of fruit. These data represent the first comprehensive examination of the effects of flowering/fruit formation on photosynthesis and photorespiration in perennial plants.     

Whole-tree water use efficiency is decreased by ambient ozone and not affected by O3-induced stomatal sluggishness

Steady-state and dynamic gas exchange responses to ozone visible injury were investigated in an ozone-sensitive poplar clone under field conditions. The results were translated into whole tree water loss and carbon assimilation by comparing trees exposed to ambient ozone and trees treated with the ozone-protectant ethylenediurea (EDU). Steady-state stomatal conductance and photosynthesis linearly decreased with increasing ozone visible injury. Dynamic responses simulated by severing of a leaf revealed that stomatal sluggishness increased until a threshold of 5% injury and was then fairly constant. Sluggishness resulted from longer time to respond to the closing signal and slower rate of closing. Changes in photosynthesis were driven by the dynamics of stomata. Whole-tree carbon assimilation and water loss were lower in trees exposed to ambient O(3) than in trees protected by EDU, both under steady-state and dynamic conditions. Although stomatal sluggishness is expected to increase water loss, lower stomatal conductance and premature leaf shedding of injured leaves aggravated O(3) effects on whole tree carbon gain, while compensating for water loss. On average, WUE of trees exposed to ambient ozone was 2-4% lower than that of EDU-protected control trees in September and 6-8% lower in October.     

The hydraulic limitation hypothesis revisited

We proposed the hydraulic limitation hypothesis (HLH) as a mechanism to explain universal patterns in tree height, and tree and stand biomass growth: height growth slows down as trees grow taller, maximum height is lower for trees of the same species on resource-poor sites and annual wood production declines after canopy closure for even-aged forests. Our review of 51 studies that measured one or more of the components necessary for testing the hypothesis showed that taller trees differ physiologically from shorter, younger trees. Stomatal conductance to water vapour (g(s)), photosynthesis (A) and leaf-specific hydraulic conductance (K L) are often, but not always, lower in taller trees. Additionally, leaf mass per area is often greater in taller trees, and leaf area:sapwood area ratio changes with tree height. We conclude that hydraulic limitation of gas exchange with increasing tree size is common, but not universal. Where hydraulic limitations to A do occur, no evidence supports the original expectation that hydraulic limitation of carbon assimilation is sufficient to explain observed declines in wood production. Any limit to height or height growth does not appear to be related to the so-called age-related decline in wood production of forests after canopy closure. Future work on this problem should explicitly link leaf or canopy gas exchange with tree and stand growth, and consider a more fundamental assumption: whether tree biomass growth is limited by carbon availability.     

Light interception in apple trees influenced by canopy architecture manipulation

Improvement of light penetration within tree canopies has been a constant objective of fruit tree architecture manipulation through the setting up of training systems. Recently, centrifugal training, i.e. the removal of fruiting shoots in the tree centre and on the underside of branches, has been proposed to improve fruit size and colour as well as return-bloom as compared to conventional solaxe-trained trees with equivalent crop loads. The present study was conducted to quantify the benefits of centrifugal training on light interception by the fruiting shoots via computer-assisted three-dimensional representations of foliage geometry. Data were collected on six 5-year-old apple trees cv.Galaxy, trained either with solaxe or centrifugal training systems, using an electromagnetic 3D digitiser. The 3D distribution of the foliage in the tree canopy was recreated by combining both the spatial locations of shoots (as measured from 3D digitising) and foliage reconstruction. Light interception efficiency properties of the trees were characterised by silhouette to total area ratio (STAR) values computed from images of the 3D mock-ups. Compared to the solaxe system, centrifugal training significantly improved the STAR of the whole tree by 20%. It also increased both leaf area and STAR of the fruiting shoots by approximately 15%, regardless of their position in the canopy. In this paper, we discuss the role of this enhanced light interception by the canopy in increasing the autonomy of the fruiting shoot, i.e. improved fruit size and colour, and return-bloom.     

Leaf area index, canopy structure and photosynthesis of red clover (Trifolium pratense L.)

Abstract. The influence of leaf age, total leaf area and its dispersion in space on canopy photosynthesis were studied using microswards of red clover ( Trifolium pratense L.) which were established in the greenhouse. Two varieties, Renova (flowering) and Molstad (non-flowering), were sown in separate plastic boxes at densities of 225, 400 and 625 plants per m².
Vertical distribution of photosynthetically active radiation (PAR), leaf area, leaf age and ¹⁴CO₂-fixation were determined periodically. Net photosynthesis and dark respiration of canopies were measured. Maximum photosynthetic capacity of individual leaves was measured on plants taken from the intact canopy or from plants where shading of the growing leaves had been prevented.
Net photosynthetic rate of canopies increased linearly with leaf area index (LAI) up to an LAI of 3.5 and then declined at higher LAI, independent of variety and sowing density. Below the optimum LAI, net photosynthesis depended mainly on interception of PAR. Decrease in canopy photosynthesis above the optimum LAI was due to a higher proportion of old leaves with decreased photosynthetic capacity, and not to an increase in respiring plant parts. It is concluded that LAI and position of leaf age categories in the canopy are more important than vertical distribution of leaf area in determining canopy photosynthesis of red clover.     

Causes of reduced leaf‐level photosynthesis during strong El Niño drought in a Central Amazon forest

Sustained drought and concomitant high temperature may reduce photosynthesis and cause tree mortality. Possible causes of reduced photosynthesis include stomatal closure and biochemical inhibition, but their relative roles are unknown in Amazon trees during strong drought events. We assessed the effects of the recent (2015) strong El Niño drought on leaf‐level photosynthesis of Central Amazon trees via these two mechanisms. Through four seasons of 2015, we measured leaf gas exchange, chlorophyll a fluorescence parameters, chlorophyll concentration, and nutrient content in leaves of 57 upper canopy and understory trees of a lowland terra firme forest on well‐drained infertile oxisol. Photosynthesis decreased 28% in the upper canopy and 17% in understory trees during the extreme dry season of 2015, relative to other 2015 seasons and was also lower than the climatically normal dry season of the following non‐El Niño year. Photosynthesis reduction under extreme drought and high temperature in the 2015 dry season was related only to stomatal closure in both upper canopy and understory trees, and not to chlorophyll a fluorescence parameters, chlorophyll, or leaf nutrient concentration. The distinction is important because stomatal closure is a transient regulatory response that can reverse when water becomes available, whereas the other responses reflect more permanent changes or damage to the photosynthetic apparatus. Photosynthesis decrease due to stomatal closure during the 2015 extreme dry season was followed 2 months later by an increase in photosynthesis as rains returned, indicating a margin of resilience to one‐off extreme climatic events in Amazonian forests.     

Physiological responses of dogwood (Cornus florida) to infestation by the dogwood borer (Thamnosphecia scitula)

Studies of a healthy dogwood tree ( Cornus florida ) and one suffering from a chronic infestation of Thamnosphecia scitula revealed some physiological responses of dogwood to insect damage. In high light the stomatal resistances, measured with a diffusion porometer, of leaves from the infested tree were more than double those of leaves from the healthy tree, indicating that the stomata were not open as wide in the infested tree. The greater stomatal resistance and the curling of leaves from the infested tree implied a deficiency of water, but measurements with a pressure chamber revealed only slight differences in dehydration between the two trees. Furthermore, the leaf curling was not relieved by allowing infested leaves to absorb water and attain full turgor. Leaves from the infested tree contained 35 % more reducing sugars and 63 % more sucrose, but only about half the nitrogen and ash of the healthy counterparts. Photosynthesis was significantly depressed, but dark respiration was not modified in leaves of infested compared with healthy trees. Leaves from the infested tree were 85 % as large and exhibited a 35 % greater specific leaf weight than those from the healthy tree. The conductance of water by stems from the infested tree was only 61–78 % of that by the healthy tree. It is suggested that the inferred disruption of the vascular system by insect activity alters the distribution of minerals and metabolites, hastens senescence and stomatal closure, and modifies growth by diminishing stem conductance, slowing photosynthesis, reducing leaf area, and changing leaf morphology.     

Integrated Use of Organic and Bio-fertilizers to Improve Yield and Fruit Quality of Olives Grown in Low Fertility Sandy Soil in an Arid Environment

Olive productivity should be improved through stimulating nutrition, particularly under poor fertility soils. Consequently, the objective of this study was to assess the efficacy of applying organic and bio-fertilizers on the physiological growth, yield and fruit quality of olive trees under newly reclaimed poor-fertility sandy soil in an arid environment. During a field experiment carried out at El-Qantara, North Sinai, Egypt over two consecutive seasons (2019–2020 and 2020–2021), olive Kalamata trees were evaluated under three organic fertilizer treatments alone or in combination with three bio-fertilizers treatments. Organic fertilizer was applied as goat manure (16.8 kg/tree/year), or olive pomace (8.5 kg/tree/year) in mid-December of each season vs. untreated trees. The bio-fertilizers were applied as N-fixing bacteria (150 g/tree) was inculated in early March of each season, or amino acid mixture (1.5%) was applied three times, at 70% of full bloom, 21 days after full bloom, and a month later in comparison to a non-fertilized trees (control). The cultivar used was Kalamata, a dual-purpose cultivar for oil and table olives whose value increases when processed as table olives. The results indicated that the goat manure followed by olive pomace significantly enhanced photosynthetic pigments (chlorophyll a, b, and carotenoids), leaf mineral contents (N, P, K, Ca, Mg and Fe), tree canopy volume, number of flowers per inflorescence, number of inflorescences per shoot, initial fruit set, fruit retention. For fruit quality, fruit length and width, fruit weight, and total fruit yield was increased compared to the non-fertilized control. Likewise, The bio-fertilizer N-fixing bacteria followed by the amino acid mixture significantly improved all of the aforementioned parameters. Accordingly, it is recommended, both environmentally and economically to utilize organic and bio-fertizers, particularly goat manure combined with N-fixing bacteria, in low-fertility soil to sustain olive production as well as reducing mineral fertilization.