Inhibitory effect of flowering and early fruit growth on leaf photosynthesis in mango

Carbohydrate and nitrogen contents, chlorophyll fluorescence and gas exchange were measured in leaves from both vegetative and reproductive terminal shoots of 12-year-old flowering mango trees. Reproductive shoot leaves were close to swelling floral buds, inflorescences or panicles bearing set fruits. Leaves close to inflorescences had lower rates of mitochondrial respiration (Rd) and net photosynthesis (Anet), and lower stomatal conductance (gs) and quantum efficiency of photosystem II under actinic light than vegetative shoot leaves. Leaf nitrogen concentration, which decreased from the beginning until the end of flowering, was lower in leaves close to inflorescences than in vegetative shoot leaves. However, these differences and changes were counterbalanced by an increase in leaf mass-to-area ratio so that leaf nitrogen per unit leaf area (Na) remained nearly constant during the whole flowering period, except in leaves close to panicles bearing set fruits. Net CO2 assimilation rate simulated by a biochemical model of leaf photosynthesis (Urban et al. 2003) was much higher than Anet measured at an ambient CO2 partial pressure (Ca) of either 36 or 70 Pa. The overestimation of Anet was more pronounced in leaves close to inflorescences, to panicles bearing set fruits and to reversing inflorescences (characterized by the appearance of leaves in terminal positions on inflorescences) than in vegetative shoot leaves. It is concluded that low Anet in leaves close to inflorescences was probably due neither to changes in Na nor to a decrease in Rubisco activity induced by low gs, but rather to a decrease in electron flow in photosystem II. This decrease was not directly associated with higher starch or soluble sugar contents.     

The effect of defruiting at different stages of fruit development on leaf photosynthesis of "Golden Delicious" apple

Net photosynthetic rates (A) of leaves on 11-year-old, field-grown apple trees (Malus domestica Borkh. cv. Golden Delicious) were measured after removal of fruits at four different stages of development. Defruiting decreased A by 21, 42, 27 and 7% when fruits were growing at 311, 293, 229 and 113 mg(DW) day(-1), respectively. Photosynthesis was inhibited more in the afternoon than in the morning, but it was not affected during the first 8 h after fruit removal. Inhibition of A was positively correlated with crop sink strength, but it was not correlated with fruit relative growth rate or crop load. Defruiting decreased A at saturating irradiances (PPFD > 1000 micro mol m(-2) s(-1)), but did not modify the apparent quantum yield of single leaves. These results suggest that the overall effect of defruiting on carbon fixation is negligible in dense canopies, but it may be significant in sparse canopies and in single shoots.     

The effect of different atmospheric ozone partial pressures on photosynthesis and growth of nine fruit and nut tree species

Nursery stock of peach (Prunus persica L. Batsch, cv. O'Henry), nectarine (P. persica L. Batsch, cv. Fantasia), plum (P. salicina Lindel., cv. Casselman), apricot (P. armeniaca L., cv. Tilton), almond (P. dulcis Mill., cv. Nonpareil), prune (P. domestica L., cv. Improved French), cherry (P. avium L., cv. Bing), oriental pear (Pyrus pyrifolia Rehd., cv. 20th Century), and apple (Malus pumula Mill., cv. Granny Smith) were planted in open-top chambers on April 1, 1988 at the University of California's Kearney Agricultural Center located in the San Joaquin Valley (30 degrees 40' N 119 degrees 40' W). Trees were exposed to three atmospheric ozone partial pressures (charcoal-filtered air (C), ambient air (A), or ambient air + ozone (T)) from August 1 to November 17, 1988. The mean 12-h (0800 to 2000 h) ozone partial pressures measured in open-top chambers during the experimental period were 0.030, 0.051, and 0.117 microPa Pa(-1) in the C, A and T treatments, respectively. Leaf net CO(2) assimilation rate decreased linearly with increasing 12-h mean ozone partial pressure for the almond, plum, apricot, prune, pear, and apple cultivars. Stomatal conductances of apricot, apple, almond, and plum decreased linearly with increasing ozone partial pressure. Cross-sectional area relative growth rates of almond, plum, apricot, and pear decreased linearly with increasing ozone partial pressure. Net CO(2) assimilation rate, stomatal conductance, and trunk growth of cherry, peach and nectarine were unaffected by the ozone treatments. Reduced leaf gas exchange probably contributed to ozone-induced growth reduction of the susceptible species and cultivars. Several of the commercial fruit tree species and cultivars studied were relatively tolerant to the ozone treatments.     

Recovery of photosynthetic capacity in Scots pine: a model analysis of forest plots with contrasting soil temperature

Both aboveground and belowground climate affects net primary production (NNP) and forest growth. Little is known about how above and belowground factors interact. The BIOMASS-model was tested to simulate photosynthetic recovery over a wide range of soil temperatures created by snow cover manipulations on tree-scale plots in a 20-year-old Scots pine stand in northern Sweden. The differences in timing of soil warming between the plots covered a span of two months. Carbon assimilation in needles, sap flow, needle water potential and climatic parameters were measured in the field. The simulations revealed that an early start of soil warming gave a relatively early photosynthetic recovery and a 7.5% increase of NPP. Late soil warming delayed the photosynthetic recovery and reduced the NPP by 13.7%. This indicated that soil temperature needed to be accounted for, as well as air temperature, when analysing photosynthetic recovery and NPP in boreal environment. The effects of differences in soil temperature were reflected in the simulated photosynthetic recovery. The model did not fully capture the delay of photosynthetic recovery caused by a late soil warming. It was possible to integrate the complexity of the soil climate effects into a threshold date for soil thaw, using sapflow measurements together with information about air temperature and a day degree sum, as long as water availability was not limiting water uptake by roots. Although a more realistic mechanism than that currently in BIOMASS is desirable as climate change shifts the typical patterns of interplay between air and soil temperature dynamics.     

A virtual peach fruit model simulating changes in fruit quality during the final stage of fruit growth

A virtual fruit model simulating seasonal changes in several peach (Prunus persica (L.) Batsch) fruit quality traits during the final growth stage is presented. The quality traits considered are fruit size, the proportion of total fruit mass consisting of fruit flesh, dry matter content of the flesh and the concentrations of sucrose, glucose, fructose and sorbitol in the flesh, which are used to calculate a sweetness index. The virtual peach fruit model was developed by adapting and integrating three existing process-based models describing fruit dry mass growth, fruit fresh mass growth and sugar accumulation in the flesh into one complex system. Data sets of peach fruit growth and quality obtained from one field site over several years were used to estimate parameters and evaluate the virtual peach fruit model. Output from the model showed good agreement with the field data. Insight into the complex nature of the virtual peach fruit model, i.e., its ability to show emergent properties, was accomplished by conducting a series of theoretical experiments. The virtual peach fruit model was shown to be sensitive to management and environmental factors (leaf:fruit ratio, stem water potential and, to a lesser extent, weather). Its ability to generate simple laws relating to physiological variables and quality parameters was also demonstrated. Finally, the virtual peach fruit model was able to reveal complex behaviors resulting from changes in water potentials or leaf:fruit ratios over time.     

An integrated model for predicting maximum net photosynthetic rate of cocksfoot (Dactylis glomerata) leaves in silvopastoral systems

Net light-saturated photosynthetic rate (A_max) of field grown cocksfoot (Dactylis glomerata L.) leaves in a radiata pine (Pinus radiata D. Don) silvopastoral system (Canterbury, New Zealand) was measured at different times under severe shade (85–95 μmol m^–2 s^–1 photosynthetic photon flux density, PPFD) and in full sunlight (1900 μmol m^–2 s^–1 PPFD). The aim was to integrate individual functions for A_max against air temperature (2 to 37 oC), water status, expressed as pre-dawn leaf water potential (ψ_lp) (-0.01 to −1.6 MPa), herbage nitrogen (N) (1.5 to 5.9%), regrowth duration (20 to 60 days) and time under shade (1 to 180 min) into a multiplicative model. The highest A_max value obtained was 27.4 μmol CO₂ m^–2 s^–1 in non-limiting conditions with full sunlight. This value was defined as standardised dimensionless A_maxs = 1 for comparison of factor effects. The canopy temperature of the cocksfoot sward was up to 7.4 oC cooler than air temperature for plants under shade. Therefore, canopy temperature was used to predict A_max. The only interaction was between time under severe shade (5% of the open PPFD) and water stress (ψ_lp = −0.4 to −1.3 MPa) and this was included in the model. Validation of this model indicated 78% of the variation in A_max could be accounted for using these five factors by the addition of the interaction function. This model could be used to assist the prediction of pasture growth in silvopastoral systems through incorporation into a canopy photosynthesis model. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of flooding stress on the photosynthetic apparatus of leaves of two Physocarpus cultivars

We applied under pot-culture conditions and the double-casing pot method to study the characteristics of photosynthetic gas exchange and chlorophyll fluorescence in the leaves of Physocarpus amurensis Maxim(PA) and Physocarpus opulifolius under flooding stress.Our results indicate a significantly higher flooding tolerance of P.opulifolius compared to P.amurensis.Especially in P.amurensis, the limitation of non-stomatal factors played a major role in the advanced stages of flooding stress,observed as a rapid increase of the intercellular CO_2 concentration(C_i) and a decrease of the stomatal limitation value(L_s).The maximal PSII photochemical efficiencies(F_v/F_m) and actual photochemical efficiency(?_(PSII)) in the leaves of P.opulifolius were significantly higher, and the extent of decrease during the flooding process was smaller than in P.amurensis.In addition, the non-chemical quenching(NPQ) in the leaves of P.opulifolius significantly increased from the 10 th day under flooding stress,while the variation of NPQ in the leaves of P.amurensis was much smaller.This indicates that the leaves of P.opulifolius had not only higher PSII photochemical activity, but also improved tolerance to flooding stress, which may be caused by its ability to dissipate excess excitation energy by starting NPQ.At the 16 th day under flooding stress, the PIABSsignificantly decreased with greater extent of decrease than F_v/F_m in the leaves of both Physocarpus,but the decreasing extent of PIABSin P.opulifolius was significantly smaller than in P.amurensis.In the 16 th day under flooding stress, the fluorescence at J and I point(V_J and V_I) in P.amurensis were significantly higher, and the extent of increase in V_J was greater than V_I.However, the variations of V_Jand V_I in the leaves of P.opulifolius were smaller, suggesting that the damage sites of flooding stress to PSII in the leaves of P.amurensis were mainly located in the electron transport process from Q_A at the PSII receptor side to Q_B.Flooding stress reduced the proportion(φ Eo) of luminous energy absorbed by the PSII reaction center for the electron transport following Q_A~-, while the maximum quantum yield(φ Do) of non-photochemical quenching increased.However, the TR_o/RC and ETo/RC in the leaves of P.amurensis decreased accompanied by a dramatic increase of energy(DI_o/RC) from the dissipation in the reaction center.This further indicated that the function of the PSII reaction center in the leaves of P.amurensis was significantly lower than in P.opulifolius.     

Increased atmospheric CO2 concentration enhances the development of photosynthetic capacity beyond the temperature effect for silver birch in simulated future climate

We conducted an experiment to find out how future climate conditions will impact the spring development of photosynthetic capacity of silver birch leaves. We had two greenhouse conditions. In the simulated future climate condition, we had both elevated temperatures and CO₂ concentration, while for reference we had trees growing under current climate conditions. We used two methods to measure the development of photosynthetic capacity: first, the maximum quantum efficiency of photosystem II with a fluorescence meter; and second, the CO₂ assimilation rate with gas exchange measurements. The development of full photosynthetic capacity took around two weeks following the bud burst. The maximum quantum efficiency developed slightly faster than the CO₂ assimilation rate. Both measurement methods showed that an elevated CO₂ concentration enhanced the development of photosynthetic capacity beyond the impact of temperature only. The enhancement under the conditions of our simulated climate change translates to achieving photosynthetic capacity up to five days earlier, which impact should be taken into account in simulations of photosynthetic productivity.     

美国梾木引种栽培果实落果生理生化分析研究

为了探明美国梾木引种栽培果实落果致败诱因,以不同发育阶段美国梾木果实为对象,采用实验室常规化学成分分析法、紫外分光光度法及色谱分析法等技术手段对果实发育过程各生理生化指标进行测定。结果表明:在逆境或衰老条件下,果实内可溶性糖含量是持续增长的,递增量0.67 mg/g,蛋白质含量在果实发育初期递增明显,平均递增量为0.6 mg/g,6月初开始下降呈抛物线变化后趋于稳定保持在1.14 mg/g,还原糖由于可能出现的呼吸骤变,含量持续增加,递增量为8.63 mg/g,淀粉含量在发育初期达到2.28 mg/g后急剧下降,从在6月初至落果前保持稳定,最终含量保持在1.96 mg/g;果实中过氧化氢活性在发育初期最强,达到0.018△OD/min·mg,6月底至7月初活性降至最低点,6月至7月突然出现的高温高湿气候导致果实发育受到影响,表现为对逆境的不适应过氧化氢酶活性;果实内源激素中细胞分裂素(ZT)和生长素(IAA)一直持续下降,降幅分别为109.68μg/g和38.97μg/g,赤霉素(GA)呈现抛物线变化,平均递减幅度5.89μg/g,落果前呈小幅度的增长,平均递增量3.79μg/g,脱落酸(ABA)含量急剧降低持续到6月中上旬,平均递减量3.06μg/g,在落果之前脱落酸(ABA)含量基本趋于稳定,ABA/ZT变化稳定,ABA/GA变化呈整体下降趋势,ABA/IAA变化呈缓慢增长趋势,脱落酸(ABA)占据主导地位导致落果;通过相关性分析,可溶性糖变化与还原糖变化呈极显著相关,与生长素(IAA)变化呈负极显著相关,可溶性糖含量增加,果实生长变慢,能耗过快,成为果实落果的诱因。     

持续干旱对油茶叶片及根系生理生化指标的影响

以"湘林52"2年生油茶嫁接苗为材料,采用盆栽的试验方法,利用自然干燥法获得控水梯度,测定持续干旱条件下油茶苗叶片光合色素,叶片及根系(D≤2 mm)丙二醛、脯氨酸、可溶性糖、可溶性蛋白、超氧化物歧化酶、过氧化物酶和过氧化氢酶生理生化指标,研究其对干旱胁迫的生理响应。结果表明:随着干旱程度的增加,叶片光合色素含量持续降低(P0.05);叶片及根系丙二醛、脯氨酸和可溶性糖含量均持续增加(P0.05),叶片可溶性蛋白含量持续降低(P0.05),根系可溶性蛋白含量先增加后下降(P0.05);叶片及根系超氧化物歧化酶活性持续增加(P0.05),过氧化物酶和过氧化氢酶活性均呈先升高后降低的变化趋势(P0.05)。当土壤相对含水量高于30.6%时,复水后油茶苗能恢复正常生长;当土壤相对含水量低于21.1%时,复水后油茶苗不能恢复正常生长。     

A simple size effect model for tension perpendicular to the grain

The strength in tension perpendicular to the grain is known to decrease with an increase in the stressed volume. Usually this size effect is explained on a stochastic basis, that is, an explanation relying on the increased probability of encountering a strength reducing flaw when the volume of the material under stress is increased. This paper presents an experimental investigation on specimens with a well-defined structural orientation of the material. The experiments exhibit a large size effect and the nature of the failures encountered suggests that the size effect can be explained on a deterministic basis. Arguments for such a simple deterministic explanation of size effect is found in finite element modelling, using the orthotropic stiffness characteristics in the transverse plane of wood.     

干旱胁迫对植物光合生理影响研究进展

水分作为植物生存、生长和发育的主要限制因子,会通过植物生理过程和状态的变化来影响植物生长和产量。为阐明植物在干旱环境下适应性变化,该文主要综述了植物在干旱胁迫下生长、叶绿素含量、光合参数、保护酶活性的变化情况,并提出了几点研究展望,如在今后的试验中可采用顶棚法模拟干旱,使试验环境更真实,结果更可靠;探究在严重干旱或持久干旱下,植物光合作用代谢机制的变化情况;以及探究长期干旱胁迫下常绿植物在不同季节下光合能力的变化。     

Effect of applying a calcined kaolin-based particle film on the photosynthetic capacity and growth of young eucalyptus plants

In scenarios of climatic change when increased global temperatures can be expected,it is essential to search for technologies that favor sapling survival and gr...     

黑莓幼树光合特性的研究

为探索美国黑莓优质、丰产栽培技术,对黑莓的光合特性进行了研究。结果表明,在河北省文安县栽培的黑莓叶片光合速率日变化呈双峰曲线,最高峰在9时,次高峰在13时,存在“午休”现象。光合速率的季节变化亦呈双峰曲线,最高峰在6月份,次高峰在8月份。光合速率的光补偿点和饱和点分别为60μmol.m-2.s-1和1 380μmol.m-2.s-1。     

揉搓型油茶果分类脱壳分选机的脱壳和清选效果研究

揉搓型油茶果分类脱壳分选机采用揉搓和挤压原理,通过利用分类滚动筛筛选大小不同的油茶果进入油茶果脱壳装置,在运输带与柔性揉搓板相互配合运动的揉搓作用下而脱壳。结果表明:在含水率低于55%,曲轴转速在240~260 r/min,履带速度在0.4~0.6 m/s,振动电动机频率50 Hz,分选带水平面倾角50°~55°工艺条件下,该机处理量≥900 kg/h,脱净率≥97%,清选率≥97%,碎籽率≤5%,损耗率≤1%。此设备在实际生产中具有普适性,适合大规模推广应用。     

A dynamic model for water flow in a single tree: evidence that models must account for hydraulic architecture

A model is presented for the dynamics of water flow in a single eastern white cedar tree (Thuja occidentalis L.). The model takes into account the spatial and temporal dependence of the evaporative flux from leaves in the crown. It also accounts for the quantitative hydraulic architecture of the tree, i.e., the model characterizes the tree as a branched catena of > 4000 stem segments in which account is taken of the segment length, diameter, hydraulic resistance, and the total area of leaves attached to the segment. Input values needed to run the model are measurements of evaporative flux, hydraulic conductance of stems versus stem diameter, and leaf and stem water storage capacitances. Output parameters are the spatial and temporal characterization of stem and leaf water potentials, stem and leaf water deficits, sap flow rate, and relative sap velocity. The input and output values of the branched catena model are compared and contrasted to that of an unbranched catena model. It is shown that the branched catena model fits independently measured field parameters better than an unbranched catena model. Close correspondence is found between model predictions and field measurements of shoot water potential, pressure gradients in stems, hysteresis in sap velocity between the lower and upper parts of the tree, and diurnal changes in stem and leaf water deficits. This model is discussed in terms of both the hydraulic architecture of trees and the potential application of the model to questions of tree morphology, ecology, physiology and evolution.     

杜仲原料叶采收期检测研究

通过重复采样检测及数值分析 ,初步揭示了杜仲原料叶内含胶药成分动态变化规律 ,证明采收时间不同胶药品质差异较大 ,最佳采收季节为药用叶 8月份 ,胶用叶 10月至 11月中旬     

水分胁迫对栓皮栎幼苗生理特性及生长的影响

通过盆栽实验，研究了在不同的水分条件下栓皮栎幼苗生理特性的变化和苗木生长量的变化。研究表明，在水分胁迫初期，随土壤含水量的降低，栓皮栎叶片的净光合速率、蒸腾速率下降，而水分利用效率提高。在水分胁迫末期，由于长期的干旱胁迫，水分条件最差的一组苗木已干枯死亡，土壤含水量从38．123％下降到20．323％时，净光合速率和蒸腾速率均下降，水分利用效率也下降。随着土壤含水量的降低，苗高、地径和生物量均有下降的趋势，其中生物量下降的幅度最大。     

银杏幼苗光合特性的研究

对３年生根杏“大佛手”品种的光合作用特性进行了研究。结果表明：光合作用的光补偿点和光饱和点分别为７０～８０μｍｏｌ／ｓ．ｍ＾２和１０００～１１００μｍｏｌ／ｓ．ｍ＾２不同天气条件下净光合速率的日变化规律存在明显的差异,在晴朗天气条件下,光合速率的日变化表现为双峰曲线,存在明显的“午休”现象,多云天气的光合速率日变化也表现双峰曲线,但“午休”现象不明显,阴天的光合速率为典型的单峰曲线,叶片的光合整编