Hydraulic conductance as well as nitrogen accumulation plays a role in the higher rate of leaf photosynthesis of the most productive variety of rice in Japan

An indica variety Takanari is known as one of the most productive rice varieties in Japan and consistently produces 20-30% heavier dry matter during ripening than Japanese commercial varieties in the field. The higher rate of photosynthesis of individual leaves during ripening has been recognized in Takanari. By using pot-grown plants under conditions of minimal mutual shading, it was confirmed that the higher rate of leaf photosynthesis is responsible for the higher dry matter production after heading in Takanari as compared with a japonica variety, Koshihikari. The rate of leaf photosynthesis and shoot dry weight became larger in Takanari after the panicle formation and heading stages, respectively, than in Koshihikari. Roots grew rapidly in the panicle formation stage until heading in Takanari compared with Koshihikari. The higher rate of leaf photosynthesis in Takanari resulted not only from the higher content of leaf nitrogen, which was caused by its elevated capacity for nitrogen accumulation, but also from higher stomatal conductance. When measured under light-saturated conditions, stomatal conductance was already decreased due to the reduction in leaf water potential in Koshihikari even under conditions of a relatively small difference in leaf-air vapour pressure difference. In contrast, the higher stomatal conductance was supported by the maintenance of higher leaf water potential through the higher hydraulic conductance in Takanari with the larger area of root surface. However, no increase in root hydraulic conductivity was expected in Takanari. The larger root surface area of Takanari might be a target trait in future rice breeding for increasing dry matter production.     

Cultivar differences in leaf photosynthesis of rice bred in Japan

The grain yield of rice (Oryza sativa L.), as well as of other cereal crops, is limited to a large extent, by the supply of photosynthates produced during grain filling period. In this study, flag leaf photosynthesis (LPS) after heading was compared among 32 cultivars bred during the past century in Japan, to determine if the improvement of LPS has occurred with the breeding advance of high yielding cultivars. Measurement of LPS was made for 5 consecutive years in the paddy field, on the flag leaf of the main stem, at heading (LPS-0), and 2 weeks (LPS-2) and 4 weeks (LPS-4) after heading. LPS decreased with advance of leaf senescence from LPS-0 to LPS-2, and then to LPS-4. However, if nitrogen was top-dressed at the heading time, high LPS-2 was maintained, particularly in the newer cultivars. A significant positive correlation between LPS and the released year of cultivar was found at LPS-2, especially in the nitrogen top-dressed plot, but not at LPS-0 or LPS-4. Cultivar difference in LPS of the senescing leaves were not stable through the different years, whereas LPS-0 was stable over years, suggesting that the LPS in the senescent leaf is susceptible to the environmental variation due to the effects on leaf senescence. Cultivar difference in LPS at any stage was closely associated with mesophyll conductance to CO₂, and stomatal conductance was also associated with cultivar difference in such a high LPS as LPS-0 and nitrogen top-dressed LPS-2. Significant correlation between LPS and specific leaf weight was not observed at any stage of the flag leaf.Abbreviations CV coefficient of variation - g_m mesophyll conductance - g_s stomatal conductance - LPS apparent photosynthetic rate per unit leaf area (leaf photosynthesis) - LPS-0 LPS at heading - LPS-2 LPS at active grain filling - LPS-4 LPS at maturity of grain - NT non-top dressed plot - PPFD photosynthetic photon flux density - r_m mesophyll resistance - r_s stomatal diffusion resistance against CO₂ - r_s(H₂O) stomatal diffusion resistance against H₂O - RuBisCO ribulose-1,5-bisphosphate carboxylase/oxygenase - SLW specific leaf weight - TD nitrogen top-dressed plot     

A Mathematical Model for Leaf Photosynthesis of Mulberry

A mathematical model of leaf photosynthesis has been established. In this model, the processes of photosynthesis are divided into two parts, ie., the carboxylation process driven by light which is dependent on temperature and CO2 concentration, and the diffusion of CO2 from atmosphere to the carboxylation site. Finatly, CO2 uptake by the leaf is understood as dependent on 1), the CO2 response curve of the leaf mesophyll and 2). the CO2 partial pressure in the intercellular space in leaf. The COs response curve of the leaf photosynthesis is described mathematically in terms of carboxylation efficiency (Ca) or its initial slope and the photosynthetic capacity (Pm) or the CO2-saturated uptake rate of CO2 uptake, and dark respiration (Rd). The dependency of photosynthesis on leaf temperature and incident light intensity is incorporated into variations of those parameters which establish an appropriate response to internal CO2 pressure for particular light and temperature conditions prevailing at any time. Secondly the interactiion of stomata with photosynthesis is represented as an empirical relation between stomatal conductance and a combined environmental physiological index, APn·Hx/CaThe parameters used in the modelwere estimated with Marquardt-Newton method for non-linear function. Field measurements of mulberry leaf photosynthesis provided a data set for model testing. The resuks show that the simulated values of the model agree well with observed data. The model was used to analyse the response surface of leaf conductance and photosynthesis to environmental factors—Applications and limitations of the model are discussed     

不同有机肥量对旱地玉米光合特性和产量的影响

在渭北旱塬合阳试验基地进行了4年的旱地有机培肥试验, 研究不同有机肥施用量对旱地玉米光合特性和产量的影响.结果表明： 与单施化肥相比,施有机肥处理的玉米各生育时期的叶片光合速率和气孔导度显著增大,胞间CO2浓度显著减小;随着有机肥施用量的增加,玉米叶片各生育时期的叶片光合速率和气孔导度逐渐增大,胞间CO2浓度逐渐减小.玉米各生育时期的光合作用主要受非气孔因素限制,施用有机肥显著降低了非气孔因素对光合的限制.连续4年施用有机肥,改善了土壤养分状况,使养分不再是玉米光合速率和产量的主要限制因子.     

Identification and characterization of genomic regions on chromosomes 4 and 8 that control the rate of photosynthesis in rice leaves

DNA marker-assisted selection appears to be a promising strategy for improving rates of leaf photosynthesis in rice. The rate of leaf photosynthesis was significantly higher in a high-yielding indica variety, Habataki, than in the most popular Japanese variety, Koshihikari, at the full heading stage as a result of the higher level of leaf nitrogen at the same rate of application of nitrogen and the higher stomatal conductance even when the respective levels of leaf nitrogen were the same. The higher leaf nitrogen content of Habataki was caused by the greater accumulation of nitrogen by plants. The higher stomatal conductance of Habataki was caused by the higher hydraulic conductance. Using progeny populations and selected lines derived from a cross between Koshihikari and Habataki, it was possible to identify the genomic regions responsible for the rate of photosynthesis within a 2.1 Mb region between RM17459 and RM17552 and within a 1.2 Mb region between RM6999 and RM22529 on the long arm of chromosome 4 and on the short arm of chromosome 8, respectively. The designated region on chromosome 4 of Habataki was responsible for both the increase in the nitrogen content of leaves and hydraulic conductance in the plant by increasing the root surface area. The designated region on chromosome 8 of Habataki was responsible for the increase in hydraulic conductance by increasing the root hydraulic conductivity. The results suggest that it may be possible to improve photosynthesis in rice leaves by marker-assisted selection that focuses on these regions of chromosomes 4 and 8.     

A coupled model of photosynthesis,stomatal conductance and transpiration for a rose leaf (Rosa hybrida L.)

The following three models were combined to predict simultaneously photosynthesis, stomatal conductance, transpiration and leaf temperature of a rose leaf: the biochemical model of photosynthesis of Farquhar, von Caemmerer and Berry (1980, Planta 149: 78-90), the stomatal conductance model of Ball, Woodrow and Berry (In: Biggens J, ed. Progress in photosynthesis research. The Netherlands: Martinus Nijhoff Publishers), and an energy balance model. The photosynthetic parameters: maximum carboxylation rate, potential rate of electron transport and rate of triose phosphate utilization, and their temperature dependence were determined using gas exchange data of fully expanded, young, sunlit leaves. The stomatal conductance model was calibrated independently. Prediction of net photosynthesis by the coupled model agreed well with the validation data, but the model tended to underestimate rates of stomatal conductance and transpiration. The coupled model developed in this study can be used to assist growers making environmental control decisions in glasshouse production.     

Size-dependency in hydraulic and photosynthetic properties of three <Emphasis Type="Italic">Acer</Emphasis> species having different maximum sizes

Recent studies suggest that physiological traits can be affected by tree size due to stronger hydraulic limitation in taller trees. As trees vary greatly in size, both within and among species, the adaptive responses to hydraulic limitation may be different among species with different maximum sizes. To investigate this, we explored size-dependency in photosynthetic and hydraulic parameters of three Acer species (Acer mono Maxim., Acer amoenum Carr and Acer japonicum Thunb.) using trees of various sizes under well-lit conditions. Leaf stomatal conductance of the Acer species decreased with tree size, implying that water supply to leaves decreases as trees grow. In contrast, content of nitrogen increased with tree size, which may compensate for the decrease in stomatal conductance to maintain the photosynthetic rate. Although the increase in nitrogen and leaf mass per area were larger in species with larger statures, the size-dependency in stomatal conductance was not different among species, and photosynthetic rate and hydraulic conductance were maintained in the three Acer species. Therefore, we suggest that hydraulic limitation on gas exchange does not necessarily depend on the maximum height of the species and that maintenance of photosynthesis and hydraulic properties is a fundamental physiological process during tree growth.     

Photosynthetic performance along a light gradient as related to leaf characteristics of a naturally occurring <Emphasis Type="Italic">Cypripedium flavum</Emphasis>

Photosynthesis, leaf structure, nitrogen content and nitrogen allocation in photosynthetic functions of Cypripedium flavum were studied in a naturally varying light regime. Light-saturated leaf net photosynthetic rate (A (max)) was strongly correlated with leaf dry mass per area (LMA), mesophyll conductance (g (m)) and area-based leaf nitrogen content (N(area)), with all variables increasing with increasing irradiance. Such coordinate variation of all these parameters illustrates the plastic response of leaf structure to high light (HL). Leaf N(area) was greater under HL than in low light (LL). The fractions of leaf nitrogen partitioning in carboxylation (P (R)) and bioenergetics (P (B)) were positively related to LMA. In contrast, P (R) and P (B) decreased with increasing mass-based leaf nitrogen content (N(mass)). However, no correlation was found between leaf nitrogen investment in light harvesting (P (L)) and either LMA or N(mass). Like maximum rate of carboxylation (V (cmax)) and electron transport (J (max)), the J (max)/V (cmax) ratio, which was strongly correlated to LMA, also increased significantly with irradiance. Under HL, leaf maximum photosynthetic nitrogen efficiency (ANUE) and intrinsic water use efficiency (WUE) were greater than in LL conditions, despite a small difference in WUE. This suggests that a functional balance in the photosynthetic machinery favors leaf photosynthetic plasticity of C. flavum in response to different light conditions. Given an ample soil nitrogen supply, C. flavum may offset its susceptibility to HL by efficient nitrogen use and higher stomatal and mesophyll conductance against photoinhibition so as to keep leaf photosynthesis positive.     

麦田冠层气孔导度的分层研究

小麦灌浆期和乳熟期冠层各层叶片上、下表面的气孔导度之间呈正相关关系;冠层不同层的叶片气孔导度从早到傍晚有平行变化的趋势,数值上存在较大的差异,一般从冠层上到下递减。经分析,这主要与冠层叶片接受的光强自上而下递减有关,且这时所对应的叶片水势自冠层上到下递增的幅度大。测算结果表明,冠层气孔导度白天亦呈明显的日变化,灌浆期的值大于乳熟期的值。     

A coupled model of stomatal conductance, photosynthesis and transpiration

A model that couples stomatal conductance, photosynthesis, leaf energy balance and transport of water through the soil–plant–atmosphere continuum is presented. Stomatal conductance in the model depends on light, temperature and intercellular CO₂ concentration via photosynthesis and on leaf water potential, which in turn is a function of soil water potential, the rate of water flow through the soil and plant, and on xylem hydraulic resistance. Water transport from soil to roots is simulated through solution of Richards’ equation. The model captures the observed hysteresis in diurnal variations in stomatal conductance, assimilation rate and transpiration for plant canopies. Hysteresis arises because atmospheric demand for water from the leaves typically peaks in mid‐afternoon and because of uneven distribution of soil matric potentials with distance from the roots. Potentials at the root surfaces are lower than in the bulk soil, and once soil water supply starts to limit transpiration, root potentials are substantially less negative in the morning than in the afternoon. This leads to higher stomatal conductances, CO₂ assimilation and transpiration in the morning compared to later in the day. Stomatal conductance is sensitive to soil and plant hydraulic properties and to root length density only after approximately 10 d of soil drying, when supply of water by the soil to the roots becomes limiting. High atmospheric demand causes transpiration rates, LE, to decline at a slightly higher soil water content, θ_s, than at low atmospheric demand, but all curves of LE versus θ_s fall on the same line when soil water supply limits transpiration. Stomatal conductance cannot be modelled in isolation, but must be fully coupled with models of photosynthesis/respiration and the transport of water from soil, through roots, stems and leaves to the atmosphere.     

Effects of water stress on the chlorophyll content,nitrogen level and photosynthesis of leaves of two maize genotypes

The dynamics of leaf chlorophyll level, nitrogen content, photosynthesis and stomatal conductance were followed in detail in two cultivars of maize (Zea mays) during a short period of water stress, applied at tasseling, and during the subsequent recovery phase. Plants used in the experiment were grown in sand-nutrient solution culture under field weather conditions. Water stress reduced chlorophyll levels, stomatal conductance and photosynthesis, but the nitrogen content of the leaves was not affected. It is concluded that the stress-induced loss of chlorophyll is not mediated by a lack of nitrogen. Considerable differences were observed between genotypes in the rate of post-stress recovery of chlorophyll level. Recovery, upon rewatering, of stomatal conductance and photosynthesis preceded that of chlorophyll level. Losses of up to 40% of leaf chlorophyll content were insufficient to affect rates of photosynthesis measured at mid-day.     

全膜覆土下施有机肥对春小麦旗叶碳氮比、光合特性和产量的影响

于2016和2017年,以春小麦品种‘陇春27'为试验材料,在甘肃省中部半干旱雨养农业区设置定位试验,分析全膜覆土平作穴播(PMS)、全膜覆土平作穴播+有机肥(PMO)、裸地平作穴播(CK)3个处理春小麦抽穗至灌浆阶段土壤水分与群体冠层温度、净光合速率(P_n)、气孔导度(g_s)、蒸腾速率(T_r)、旗叶C/N、旗叶全氮之间的相互关系,探讨不同处理对产量及其构成要素的影响。结果表明: 施用有机肥可提高小麦生育中后期土壤含水量,PMO抽穗至灌浆阶段0～300 cm土层土壤贮水量较PMS和CK分别提高4.6%和8.5%,群体冠层温度分别降低0.1～1.3 ℃和1.4～4.9 ℃,P_n分别提高9.3%和29.7%,g_s分别提高30.9%和103.8%,T_r分别提高5.1%和55.0%,全氮含量分别提高6.6%和18.9%,C/N分别降低6.4%和22.8%。收获后,PMO较PMS和CK显著促进穗粒数和千粒重增加,籽粒产量分别提高9.1%和53.7%。抽穗至灌浆阶段旗叶P_n和g_s与C/N呈负相关性;C/N与籽粒产量呈显著负相关。因此,半干旱区全膜覆土穴播条件下施有机肥可提高春小麦抽穗至灌浆阶段土壤含水量,促进旗叶光合作用,有利于降低生理干旱胁迫强度和旗叶氮吸收同化限制,促进穗粒数和粒重增加,使产量提升。     

Diurnal Oscillation in the Intercellular CO2 Concentration of Spring Wheat Under the Semiarid Conditions

Yields of wheat in semiarid and arid zones are limited by drought, and water condition is very important at each stage of development. Studies carried out at Loess Plateau in the northwestern part of China indicated that yield of spring wheat (Triticum aestivum L.) cv. Dingxi 81-392 was reduced by 41% when subjected to water stress. The effects of two water regimens on net photosynthetic rate (P _N), stomatal conductance (g _s), and intercellular CO₂ concentration (C _i) were investigated at the jointing, booting, anthesis, and grain filling stages. Low soil moisture in comparison to adequate one had invariably reduced P _N during the diurnal variations at the four growth stages. P _N and g _s in both soil moisture regimes was maximally reduced at midday. C _i and the stomatal limitation fluctuated remarkably during photosynthesis midday depression processes, especially at the grain filling stage. Hence atmospheric drought at midday was one of the direct causes inducing stomata closure and the g _s depression, but it was beneficial for maintaining stable intrinsic water use efficiency. Fluctuation in C _i implicated that non-stomatal limitation also plays an important role during the period of photosynthesis midday depression. Consequently stomatal and/or non-stomatal limitation are the possible cause of the midday photosynthesis decline.     

Seasonal and diurnal changes in photosynthetic limitation of young sweet orange trees

This study tests the hypothesis that potted sweet orange plants show a significant variation in photosynthesis over seasonal and diurnal cycles, even in well-hydrated conditions. This hypothesis was tested by measuring diurnal variations in leaf gas exchange, chlorophyll fluorescence, leaf water potential, and the responses of CO₂ assimilation to increasing air CO₂ concentrations in 1-year-old ‘Valência’ sweet orange scions grafted onto ‘Cleopatra’ mandarin rootstocks during the winter and summer seasons in a subtropical climate. In addition, diurnal leaf gas exchange was evaluated under controlled conditions, with constant environmental conditions during both winter and summer. In relation to our hypothesis, a greater rate of photosynthesis is found during the summer compared to the winter. Reduced photosynthesis during winter was induced by cool night conditions, as the diurnal fluctuation of environmental conditions was not limiting. Low air and soil temperatures caused decreases in the stomatal conductance and in the rates of the biochemical reactions underlying photosynthesis (ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration) during the winter compared to the values obtained for those markers in the summer. Citrus photosynthesis during the summer was not impaired by biochemical or photochemical reactions, as CO₂ assimilation was only limited by stomatal conductance due to high leaf-to-air vapor pressure difference (VPD) during the afternoon. During the winter, the reduction in photosynthesis during the afternoon was caused by decreases in RuBP regeneration and stomatal conductance, which are both precipitated by low night temperature.     

豆科复叶和单叶树种的光合-水分关系分析

以豆科（Fabaceae）11个复叶树种和6个单叶树种为材料,测定他们的气孔导度、叶片水力导度、水势、相对含水量等指标,分析叶型对枝叶光合水分关系的影响。结果显示,复叶树种正午叶轴水势（-0.91 MPa）与单叶树种正午枝条水势（-0.88 MPa）间无显著差异,但正午枝条水势（-0.60 MPa）显著高于单叶树种。复叶树种正午气孔导度降低的百分比（55.3%）显著高于单叶树种（34.1%）。叶片、叶轴和枝条正午水势两两之间均显著正相关,但与正午气孔导度之间均不存在相关性。本研究中,17个树种的正午叶片水力导度与气孔导度间显著正相关（r=0.79,P<0.001）,但他们与气孔导度降低百分比间呈负相关（r=-0.81,P<0.001）,说明叶片导水率对日间气孔导度的维持具有重要作用。研究结果表明单叶和复叶树种在光合水分关系上存在明显差异,说明他们对环境条件具有不同的适应策略。     

Photosynthesis in Encelia farinosa Gray in Response to Decreasing Leaf Water Potential

Photosynthetic responses of intact leaves of the desert shrub Encelia farinosa were measured during a long term drought cycle in order to understand the responses of stomatal and nonstomatal components to water stress. Photosynthetic rate at high irradiance and leaf conductance to water vapor both decreased linearly with declining leaf water potential. The intercellular CO₂ concentration (c_i) remained fairly constant as a function of leaf water potential in plants subjected to a slow drought cycle of 25 days, but decreased in plants exposed to a 12-day drought cycle. With increasing water stress, the slope of the dependence of photosynthesis on c_i (carboxylation efficiency) decreased, the maximum photosynthetic rates at high c_i became saturated at lower values, and water use efficiency increased. Both the carboxylation efficiency and photosynthetic rates were positively correlated with leaf nitrogen content. Associated with lower leaf conductances, the calculated stomatal limitation to photosynthesis increased with water stress. However, because of simultaneous changes in the dependence of photosynthesis on c_i with water stress, increased leaf conductance alone in water-stressed leaves would not result in an increase in photosynthetic rates to prestressed levels. Both active osmotic adjustment and changes in specific leaf mass occurred during the drought cycle. In response to increased water stress, leaf specific mass increased. However, the increases in specific leaf mass were associated with the production of a reflective pubescence and there were no changes in specific mass of the photosynthetic tissues. The significance of these responses for carbon gain and water loss under arid conditions are discussed.     

The importance of mesophyll conductance in regulating forest ecosystem productivity during drought periods

Water availability is the most limiting factor to global plant productivity, yet photosynthetic responses to seasonal drought cycles are poorly understood, with conflicting reports on which limiting process is the most important during drought. We address the problem using a model‐data synthesis approach to look at canopy level fluxes, integrating twenty years of half hour data gathered by the FLUXNET network across six Mediterranean sites. The measured canopy level, water and carbon fluxes were used, together with an inverse canopy ecophysiological model, to estimate the bulk canopy conductance, bulk mesophyll conductance, and the canopy scale carbon pools in both the intercellular spaces and at the site of carboxylation in the chloroplasts. Thus the roles of stomatal and mesophyll conductance in the regulation of internal carbon pools and photosynthesis could be separated. A quantitative limitation analysis allowed for the relative seasonal responses of stomatal, mesophyll, and biochemical limitations to be gauged. The concentration of carbon in the chloroplast was shown to be a potentially more reliable estimator of assimilation rates than the intercellular carbon concentration. Both stomatal conductance limitations and mesophyll conductance limitations were observed to regulate the response of photosynthesis to water stress in each of the six species studied. The results suggest that mesophyll conductance could bridge the gap between conflicting reports on plant responses to soil water stress, and that the inclusion of mesophyll conductance in biosphere–atmosphere transfer models may improve their performance, in particular their ability to accurately capture the response of terrestrial vegetation productivity to drought.     

Stomatal responses to long-term high vapor pressure deficits mediated most limitation of photosynthesis in tomatoes

Plants grown at high vapor pressure deficit (VPD) usually present decreased photosynthesis, but stomatal and mesophyll limitation to photosynthesis remain poorly quantified. To better understand the regulation of high VPD on photosynthesis and plant growth in tomatoes, we investigated the limitation of stomatal conductance and mesophyll conductance to photosynthesis and relative importance of stomatal morphology and function in stomatal conductance. Both the net photosynthesis rate and total biomass were significantly limited by high VPD. Meanwhile, stomatal conductance and mesophyll conductance were decreased under high VPD. The stomatal conductance limitation was responsible for 60% of the total photosynthetic limitation. Moreover, a reduction in stomatal density and stomatal size occurred under high VPD, which was significantly correlated with the down-regulation of stomatal conductance. The stomatal morphology contributed to more than half the change in stomatal conductance. Nevertheless, stomatal movement was also an important factor in regulating stomatal conductance. The decrease of hydraulic conductance and transpiration rate with no significant difference in relative water content, leaf water potential, and/or osmotic potential suggested passive hydraulic regulation in the feedforward responses of stomata to high VPD.     

采煤塌陷影响下土壤含水量变化对柠条气孔导度、蒸腾与光合作用速率的影响

采煤塌陷引起的土壤环境因子的变化对矿区植物生长的影响越来越受到人们的关注,气孔导度、蒸腾与光合作用作为环境变化响应的敏感因子,研究植物气孔导度、蒸腾与光合作用的变化是揭示荒漠矿区自然环境变化及其规律的重要手段之一。研究采煤塌陷条件下植物光合生理的变化是探究煤炭开采对植物叶片水分蒸腾散失和CO_2同化速率影响的关键环节,是探讨采煤塌陷影响下植物能量与水分交换动态的基础,而采煤矿区植物叶片气孔导度、蒸腾与光合作用速率对采煤塌陷影响下土壤含水量变化的响应如何尚不清楚。选取神东煤田大柳塔矿区52302工作面为实验场地,以生态修复物种柠条为研究对象,对采煤塌陷区和对照区柠条叶片气孔导度、蒸腾和光合作用速率以及土壤体积含水量进行监测,分析了采煤塌陷条件下土壤含水量的变化以及其对柠条叶片气孔导度、蒸腾与光合作用速率的影响。结果显示:(1)煤炭井工开采在地表形成大量裂缝,破坏了土体结构,潜水位埋深降低,土壤含水量均低于沉陷初期,相对于对照区,硬梁和风沙塌陷区土壤含水量分别降低了18.61%、21.12%;(2)柠条叶片气孔导度、蒸腾和光合作用速率均与土壤含水量呈正相关关系;煤炭开采沉陷增加了地表水分散失,加剧了土壤水分胁迫程度,为了减少蒸腾导致的水分散失,柠条叶片气孔阻力增加,从而气孔导度降低,阻碍了光合作用CO_2的供应,从而导致柠条叶片光合作用速率的降低,蒸腾速率也显著降低。     

Fruit effects on photosynthesis in Prunus persica

Seasonal measurements of net CO₂ assimilation, leaf conductance and mesophyll conductance were made in the field on mature, fruiting and defruited Prunus persica L. Batsch trees. During early stages of fruit growth there were no significant differences in leaf gas exchange characteristics between fruiting and defruited trees. During the early part of the last stage of fruit growth, CO₂ assimilation rates were 11–15% higher in fruiting trees than defruited trees. These increased assimilation rates corresponded with approximately 30% increases in leaf conductance and only minor changes in mesophyll conductances or leaf CO₂ assimilation capacity as indicated by leaf nitrogen content. It is concluded that under the field conditions of this study the fruit effect on photosynthesis is primarily related to stomatal behavior.