The effects of artificial solar radiation on wind-stressed tufted titmice (Parus bicolor) and Carolina chickadees (Parus carolinensis) at low temperatures

• 1.1. Changes in metabolic rates and behavior were observed in tufted titmice (Parus bicolor) and Carolina chickadees (Parus carolinensis) exposed to varying conditions of artificial solar radiation, wind, and temperature in a wind tunnel experiment.
• 2.2. During the wind-on condition, both species showed a significant decrease in mean metabolic rates in the high radiation treatments when compared to the low radiation treatments (P < 0.05).
• 3.3. Titmouse orientation, posture and level of activity were significantly affected by radiation and wind conditions.
• 4.4. Metabolic rates observed in the wind tunnel treatments without wind and at low radiation did not significantly differ from similar standard metabolic (black box) treatments (P > 0.05).
• 5.5. Activity levels did not appear to directly affect metabolic rates observed in the wind tunnel treatments.

     

Effect of elevated temperatures on the radiation sensitivity of yeast cells of different species

Summary The influence of hyperthermia on the survival of irradiated yeast cells of different species has been studied. The experiments reported in the paper have shown: (1) simultaneous action of ionizing radiation and high temperatures appeared to increase the radiation response by a factor of approximately 2.7 for diploid and only by a factor of 1.5 for haploid cells of wild-type; (2) the combined action of high temperature and ionizing radiation had no synergistic effect for rad51 mutant diploid yeast cells; (3) heating before or after irradiation did not alter the radiation response of yeast cells; (4) enhancement of yeast cell sensitivity by simultaneous action of hyperthermia and²³⁹Pu--particles was negligible; (5) the magnitude and the rate of liquid holding recovery is lowered with increasing of irradiation temperature. On this basis, it was concluded that possible mechanism for thermal sensitization of yeast cells may involve the reduced capacity of cells to recover damages resulted from the combined action of both modalities.     

Fitness consequences of low temperature storage of Aphidius ervi

In biological control programs, storage at low temperatures is used to produce large number of individuals before inundative releases. However, an exposure to low temperatures may affect the survival of exposed individuals and some life history traits such as the daily fecundity or the longevity of the survivors. This impact on life history traits is important because they will determine the growth potential of the population. To estimate the costs of different treatments of low temperature exposure, we analyzed the main instantaneous demographic parameters of the parental generation of Aphidius ervi Haliday (Hymenoptera: Braconidae: Aphidiinae) when exposed to three storage temperatures (7, 4 and 0 °C), combined with two storage durations (one and two weeks) and two thermal regimes (constant and fluctuating), which represents a total of 12 treatments and a control. The average cohort generation time (Tc) decreased significantly after exposure to low temperature, particularly in fluctuating treatments. This means that development continues during storage. Cumulative fecundity and the net reproductive rate (R ₀ ) decreased significantly for most of the storage treatments. This decrease was most pronounced in the constant temperature treatments. Females under fluctuating thermal regime produced a higher cumulative fecundity than those exposed to constant temperatures. Surprisingly, an exposure to 0 °C over one week did not affect emergence rate and fecundity whereas all other treatments did. Storage at low temperatures may affect the efficiency of inundative releases, with the exception of storage for one week at 0 °C. Moreover, cumulative fecundity and net reproductive rate (R ₀ ) represent a more immediate prediction of the increase of the population after low temperature exposure than the intrinsic rate of increase (r _m ), and reflect the qualities required in an inundative release context.     

Changes in photosynthetic capacity,carboxylation efficiency,and CO2 compensation point associated with midday stomatal closure and midday depression of net CO2 exchange of leaves of Quercus suber

The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a standard time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO₂ pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO₂ uptake. Midday depression of CO₂ uptake is the result of i) a decrease in CO₂-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO₂ response curve (carboxylation efficiency), and iii) a substantial increase in the CO₂ compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO₂ pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO₂ may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.Abbreviations and symbols CE carboxylation efficiency - NP net photosynthesis rate - PAR photosynthetically active radiation - P_i leaf internal CO₂ partial pressure - W water vapor mole fraction difference between leaf and air - T CO₂ compensation pressure Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday     

Effects of CO<Subscript>2</Subscript> concentration on acclimatization and physiological responses of two cultivars of carob tree

This study reports survival and physiological responses of micropropagated Ceratonia siliqua L. cvs. Galhosa and Mulata plants during ex vitro acclimatization under ambient (AC; 330 mol mol^–1) or elevated (EC; 810 mol mol^–1) CO₂ concentration and a photosynthetic photon flux density of 125 mol m^–2 s^–1. CO₂ enrichment during acclimatization did not improve survival rate that was around 80 % for both treatments. Eight weeks after ex vitro transplantation, photosynthetic capacity and apparent quantum yield in acclimatized leaves were higher in comparison with those in in vitro-grown leaves, without any significant difference between CO₂ treatments. Chlorophyll content increased after acclimatization. However, EC led to a decrease in the total amount of chlorophyll in new leaves of both cultivars, compared to those grown at AC. Soluble sugars and starch contents were not markedly affected by growth EC, although starch had significantly increased after transfer to ex vitro conditions. EC induced an increase in the stem elongation and in the effective life of leaves, and a decrease in the number of new leaves.     

Oxidations in kidney mitochondria of heat-exposed rats: Regulation by cytochromec

Exposure of rats to higher environmental temperature (36–37°C) decreased the capacity of their kidney mitochondria to oxidize succinate. The decrease was corrected on the addition of exogenous cytochromec. Kidney mitochondria of heat-exposed animals showed decreased rates of H₂O₂ generation when -glycerophosphate, but not succinate, was used as electron donor. These mitochondria also showed decreased activity of -glycerophosphate dehydrogenase but not of succinate dehydrogenase. The content of cytochromec in kidney mitochondria of heat-exposed animals was low even though the concentration of the pigment in the whole tissue did not decrease. Starvation as well as administration of an antithyroid agent like propylthiouracil simulated some of the effects of heat exposure on kidney mitochondria, but the cytochromec-dependent reversal of inhibition of oxidation was obtained only in heat exposure.     

Influence of Temperature on the Effects of Artificially Enhanced UV-B Radiation on Aquatic Bryophytes Under Laboratory Conditions

We examined, under laboratory conditions, the influence of temperature (2 °C vs. 10 °C) on the physiological responses of two aquatic bryophytes from a mountain stream to artificially enhanced UV-B radiation for 82 d. These organisms may be exposed naturally to relatively low temperatures and high levels of UV-B radiation, and this combination is believed to increase the adverse effects of UV-B radiation. In the moss Fontinalis antipyretica, UV-B-treated samples showed severe physiological damages, including significant decreases in chlorophyll (Chl) and carotenoid (Car) contents, Chl a/b and Chl/phaeopigment ratios, Chl a fluorescence parameters F_v/F_m and _PS2, electron transport rate (ETR_max), and growth. In the liverwort Jungermannia cordifolia, UV-B radiation hardly caused any physiological change except for growth reduction. Thus, this liverwort seemed to be more tolerant to UV-B radiation than the moss under the specific experimental conditions used, maybe partly due to the accumulation of UV-B absorbing compounds. The influence of temperature on the effects of UV-B radiation depended on the species: the higher the UV-B tolerance, the lower the influence of temperature. Also, different physiological variables showed varied responses to this influence. Particularly, the lower temperature used in our study enhanced the adverse effects of UV-B radiation on important physiological variables such as F_v/F_m, growth, and Chl/phaeopigment ratios in the UV-B-sensitive F. antipyretica, but not in the more UV-B-tolerant J. cordifolia. Thus, the adverse effects of cold and UV-B radiation were apparently additive in the moss, but this additiveness was lacking in the liverwort. The Principal Components Analyses (PCA) conducted for both species with the physiological data obtained after 36 and 82 d of culture confirmed the above results. Under natural conditions, the relatively high water temperatures in summer might facilitate the acclimation of aquatic bryophytes from mountain streams to high levels of UV-B radiation. This may be relevant to predict the consequences of concomitant global warming and increasing UV-B radiation.     

Studies of 13C in the foliage reveal interactions between nutrients and water in forest fertilization experiments

The severity of a root rot disease of cereals, caused by Rhizoctonia solani Kühn AG8, was inversely correlated to the Zn status of plants in field studies in 1989 and 1990. In 1989, a preliminary survey was conducted in a farmer's field in South Australia where Zn deficiency and disease were both widespread. Zn concentration in Spear wheat plants at the 3-leaf to early tillering stage was negatively correlated with severity of the disease. For the elevent elements analysed, a correlation matrix showed that Zn had the highest, and only significant (R²=0.52^**) association with disease. The effect of Zn applications and their residual value on disease severity was further studied in a long-term field experiment in 1989 and 1990 to which Zn had been applied in 1986. There was a decrease in the area of Rhizoctonia bare patch as Zn rate was increased, a result consistent with the field survey results; the recommended rate of 2.5 kg Zn ha^–1 reduced the area affected by bare patch from 42% to 21% of the total crop area compared with no Zn application, overcame Zn deficiency and increased grain yield from 1.1 to 2.8 t ha^–1. In 1990, fresh Zn application treatments were applied to trial plots designed for this purpose, in order to compare the response with the older Zn treatments applied in 1986. The areas of bare patch in the older Zn treatments were approximately 5% greater than those in the fresh Zn treatments. The results are consistent with the hypothesis that Zn deficient plants are more susceptible to root rot caused by R. solani. Testing this hypothesis is the subject of a companion paper.     

樟子松幼苗生长及光合特性对强风沙流吹袭的响应

为了解樟子松幼苗对不同时间强风沙流吹袭的生理生态响应,2013年春季在内蒙古科尔沁沙地研究了8级大风风沙流(风速18m·s-1,风沙流强度173g·cm-1·min-1)吹袭10、20和30min下樟子松幼苗生长与光合特性的变化。结果显示:(1)随着风吹时间的增加,樟子松的株高生长量减少、茎粗生长加快,落叶数量增加,其中30min处理与CK相比的株高生长量下降52.63%,茎粗生长量增加233.30%,落叶指数增加466.70%。(2)风沙流吹袭没有改变樟子松幼苗的净光合速率、蒸腾速率、气孔导度和胞间CO2浓度的日变化规律,但日光合峰值下降,日最大蒸腾速率增加;与CK相比,30min处理的日最大光合速率下降22.69%,日最大蒸腾速率增加11.89%。(3)随风吹时间增加,其叶片温度、叶片相对含水量、日均光合速率、水分利用效率下降,30min处理较CK依次下降0.60%、4.37%、28.57%和31.58%,且日均蒸腾速率、气孔导度和胞间CO2浓度增加,30min处理较CK依次增加6.25%、6.67%和12.60%。研究表明,在持续风沙流胁迫下,樟子松幼苗光合作用受到抑制,蒸腾耗水增加,水分利用效率降低;樟子松幼苗生长速率降低主要源于光合面积减少和光合作用受到抑制,而其光合速率下降主要因幼苗叶片叶温和叶片含水量下降所致,蒸腾速率的增加主要源于气孔导度的增加;为了适应风沙流持续吹袭的胁迫,樟子松幼苗采取了降低株高生长速率,加快茎粗生长速率的适应策略。     

Optimization of <Emphasis Type="Italic">Streptomyces peucetius</Emphasis> var. <Emphasis Type="Italic">caesius</Emphasis> N47 cultivation and ε-rhodomycinone production using experimental designs and response surface methods

Streptomyces peucetius var. caesius is an aerobic bacterium that produces doxorubicin as a secondary metabolite. A mixture design was applied for the screening of suitable complex medium components in the cultivation of S. peucetius var. caesius N47, which is an -rhodomycinone-accumulating mutant strain. -Rhodomycinone is a non-glycosylated precursor of doxorubicin. Best growth results were obtained with soy peptone and beef extract. A central composite face-centered (CCF) experimental design was constructed for the investigation of pH, temperature and dissolved oxygen (DO) effects on the cultivation growth phase. Another CCF was applied to the production phase to investigate the effects of aeration, pH, temperature and stirring rate on -rhodomycinone production. An increase in cultivation temperature increased both cell growth and glucose consumption rate. Best -rhodomycinone productivities were obtained in temperatures around 30°C. DO control increased all growth phase responses, but aeration in the production phase coupled with pH decrease resulted in rapid -rhodomycinone decay in the medium. In non-aerated production phases a pH change resulted in better productivity than in experiments without pH change. A pH increase with a temperature decrease seemed most beneficial for productivity. This implies that dynamic control strategies in batch production of -rhodomycinone could increase the overall process productivity.     

Effects of low temperatures on the loss of innate dormancy and the development of induced dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

Abstract It is possible to remove the innate dormancy of seeds of Rumex crispus L and Rumex obtusifolius L. by an initial period of low-temperature stratification, providing the seeds are then transferred to a higher temperature. The lower the initial temperature within the range 1.5°-15°C, the greater the germination; there is no stratification effect at 20°C. Although 10°C and 15°C were shown to be suitable for both stratification and for the process of germination itself, neither temperature results in any germination if given constantly: a change from a lower to a higher temperature is essential. The optimum period for stratification depends on two separate processes which occur during the treatment–a rapid loss of innate or primary dormancy and a slower development of induced or secondary dormancy. Within the range 1.5°-15°C the rate of loss of innate dormancy appears to be independent of light and is probably independent of temperature. In contrast, the rate of induction of secondary dormancy increases with increase in temperature, and is more rapid in the dark than the light. The rate of induction of secondary dormancy during stratification is greater in R. crispus than in R. obtusifolius. As a consequence, maximum germination was obtained in both species after stratification at 1.5°C in the light, the optimum period of treatment being about 4 weeks in R. Obtusifolius and 6 weeks in R. crispus, while the maximum germination obtained and the optimal period of stratification decrease in both species with increase in stratification temperature.     

Can increased glacial melting resulting from global change provide attached algae with transient protection against high irradiance?

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Tolerance of Borya nitida,a poikilohydrous angiosperm,to heat,cold and high-light stress in the hydrated state

Borya nitida Labill., a plant able to colonize rock outcrops and shallow sands in areas of high incident solar radiation in Western Australia, was examined for its tolerance to extremes of temperature, and to intense visible radiation. Stress injury to the leaves from heat, chilling or photoinhibitory light was followed by the decrease in in-vivo variable chlorophyll fluorescence. Heat injury was also ascertained by an increase in the constant fluorescence. Borya nitida leaves were extremely heat tolerant when heated at 1° C min^-1. In-vivo variable chlorophyll fluorescence was detectable up to 55° C, several degrees higher than either maize or barley which are, respectively, adapted to warm and cool climates. An increase in constant fluorescence occurred above 50° C in B. nitida. This compares with values in the literature of 48–49° C for three desert plants from Death Valley, California, and 44–48° C for ten species of tropical plants. Unlike the Death-Valley plants, the high degree of heat tolerance found in B. nitida did not require prior acclimation by growth at high temperatures. Borya nitida was also tolerant of a chilling temperature of 0° C. Plants grown at a low photon fluence rate (120 mol m^-2s^-1) were irreversibly photoinhibited by light at 650 mol m^-2s^-1. Plants grown in sunlight resisted photoinhibition; however, the capacity to withstand photoinhibition was no greater than that of plants from less extreme environments.     

The Effects of Increasing UV-B Radiation on Pigmentation, Growth and Survival of Coregonid Embryos and Larvae

In the northern regions UV-B radiation levels have increased due to ozone depletion. A two-week laboratory experiment was conducted to measure the effects of UV-B radiation on the pigmentation, growth, oxygen consumption rate and survival of whitefish, Coregonus lavaretus, and vendace, Coregonus albula, larvae. In May newly hatched embryos were exposed in laboratory aquaria to three CIE weighted UV-B radiation levels: subambient (daily dose 1.37kJm^–2), 9% (1.81kJm^–2) and 34% higher (2.24kJm^–2) than ambient. Control embryos and larvae were not exposed to UV-B. Larvae of whitefish and vendace that were irradiated with highest UV-B level had 32% and 31% more melanin than control larvae, respectively, which we interpret as an apparent induced response. In controls, the species difference revealed 53% more melanin in vendace larvae than in whitefish larvae. UV-B radiation had no effect on the mortality of either species, the survival being high in all treatments (>90%). Additionally, neither growth rate nor the metabolic rate of larvae of either species was affected by UV-B radiation. Thus, in relation to future scenarios UV-B radiation may not be a threat to whitefish or vendace larvae in current or expected radiation levels.     

Effect of Enhanced UV-B Radiation on Polyamine Content and Membrane Permeability in Cucumber Leaves

Cucumber plants (Cucumis sativus L., cv. Jingchun 3) were grown in a greenhouse under PAR illumination of 400–600 mol/(m² s) at 30/15°C (day/night) temperature. Two enhanced biologically effective UV-B radiation levels per day were applied: 8.82 kJ/m² (T₁) and 12.6 kJ/m² (T₂). Cucumber seedlings were irradiated 7 h per day for 25 days under T₁ and T₂. A comparative study of growth, membrane permeability, and polyamine content in cucumber leaves under T₁ and T₂ treatments was conducted. UV-B radiation resulted in the dose-dependent decrease in leaf area, dry weight of foliage, and plant height. The T₁ and T₂ treatments caused an increase in the contents of putrescine, spermine, and spermidine. However, the total polyamine content declined slightly when electrolyte leakage increased dramatically on the 18th day of treatment, especially after T₂ treatment. It can be concluded that polyamine accumulation in the cucumber leaves is an adaptive mechanism to the stress caused by UV-B radiation.     

降雨量改变对黄河三角洲滨海湿地土壤呼吸的影响

全球变化背景下,降雨模式变化造成土壤水分波动是引起土壤呼吸动态变化的重要驱动力。但滨海湿地如何响应降雨模式变化,进而引起生态系统蓝碳功能改变的机制尚不清楚。依托黄河三角洲滨海湿地增减雨野外控制试验平台,采用土壤碳通量观测系统(LI—8100)对湿地土壤呼吸速率进行监测,探究了2017年黄河三角洲滨海湿地土壤呼吸及环境、生物因子对减雨60%、减雨40%、对照60%、对照40%、增雨40%、增雨60%等变化的响应及机制。结果表明:1)随着降雨量增加,湿地土壤温度逐渐降低;同时增雨和减雨处理均显著提高了湿地土壤湿度(P0.05)。(2)降雨量变化显著影响湿地植被物种组成、地上和地下生物量分配以及植被根冠比(P0.05)。增雨40%和增雨60%均显著提高了湿地植物种类和植被根冠比,但同时显著降低了湿地植被地上生物量。此外,增雨40%和减雨60%处理均显著提高了湿地植被地下生物量。(3)降雨量变化对2017年湿地季节土壤呼吸无显著影响,但在湿地非淹水期,增雨60%和增雨40%均显著提高了湿地土壤呼吸速率(P0.05)。(4)2017年湿地不同降雨处理的土壤呼吸与土壤湿度均呈二次曲线关系(P0.05),相关系数随降雨量增加而降低;同时在非淹水期不同降雨处理的土壤呼吸与土壤温度均指数相关(P0.05),土壤呼吸温度敏感性(Q_(10))随降雨量增加而增大。在淹水期不同降雨处理土壤呼吸与土壤温度无显著相关关系。(5)淹水期土壤呼吸速率与地表水位呈指数负相关(P0.001)。     

Developmental homeostasis in X-rayed populations ofDrosophila pseudoobscura

An experiment was designed to study the effects of various dosages of X-ray irradiation on different gene-arrangements (AR and CH) of the third chromosome ofD. pseudoobscura, with respect to quantitative characters.Egg production showed an insignificant decline at 1500r and an increasingly strong reduction by 3000 and 4500r. Other characters studied (emergence, longevity, body size and weight) generally showed the same trend.Irradiation of both gene-arrangements usually gave more reduction in fitness characters than did irradiation of one gene arrangement alone. Irradiation caused an increase in phenotypic variability as expressed by coefficients of variation.Heterosis in F₁ was observed for most of the characters studied, and a breakdown of heterosis in F₂. Heterosis was enhanced by irradiation at higher dosages.Relative indices of general performance indicate that the adaptive values decreased with the increase in radiation dosages. In all cases the heterozygous genotypes are the fittest while the CH/CH homozygote was the least fit.The present work was carried out during the author's tenure of a Fellowship (PHS Grant No. CRT-5013) given by the Roscoe B. Jackson Memorial Laboratory, Bar Harbor, Maine, U.S.A.     

Effect of solar ultraviolet radiation on survival of krill larvae and copepods in Antarctic Ocean

The effect of solar ultraviolet radiation on the survival rate of Antarctic zooplankton was examined in February–March in 2002. We investigated survival rate of calyptopis larvae of Euphausia superba and late copepodite stages (IV and V) of large dominant calanoid species, Calanoides acutus and Calanus propinquus reared in quartz jars with three different radiation regimes (total radiation, exclusion of UVB, exclusion of UVA and UVB) and a dark control. The survival rates of the krill larvae decreased after 3 days from start of the experiment, being below 50% at 4 days in the treatments with total radiation and exclusion of UVB, although most individuals could survive until the end of the experiments in the treatments with exclusion of both UVA and UVB and dark control. The calanoid juveniles showed almost same pattern of survival curves as the krill larvae did, but survived slightly longer. Although >10% of surface UVA radiation at 340 and 380 nm penetrated down to 30 m, both C. acutus and C. propinquus were mostly distributed above 20 m. Surface swarm of the krill larvae can be often recognized in the previous studies. These results suggest that not only solar UVB but also UVA radiation potentially lower the survival rate of Antarctic zooplankton at depth less than 20 m.     

Inter-specific competitors reduce inter-gender competition in Negev Desert gerbils

We examined gender-dependent competitive interactions between two nocturnal desert gerbil species, Gerbillus andersoni allenbyi and G. pyramidum, by a field manipulation experiment. The study was done in two 1-ha enclosed plots and included allopatric (only G. a. allenbyi) and sympatric (both species together) treatments. Seed trays and thermal imaging cameras were used to observe the gerbils foraging activities and aggressive interactions. We found that the negative effect of the competitively dominant species, G. pyramidum, on time spent in seed trays, and ability to control these artificial food patches, was stronger on male than on female G. a. allenbyi. Consequently, the aggression of male G. a. allenbyi towards female G. a. allenbyi was markedly reduced, indicating that the dominant species mediated competition between the genders of the subordinate species. Furthermore, this interference-mediated indirect effect was associated with a decrease in the body mass of male G. a. allenbyi and an increase in the survival of female G. a. allenbyi. We suggest that both the reduction in intra-specific aggression and the positive effect on female survival can potentially stabilize competitive interactions and promote coexistence in this small mammal community.     

Seasonal evolution of diffusional limitations and photosynthetic capacity in olive under drought

This study tests the hypothesis that diffusional limitation of photosynthesis, rather than light, determines the distribution of photosynthetic capacity in olive leaves under drought conditions. The crowns of four olive trees growing in an orchard were divided into two sectors: one sector absorbed most of the radiation early in the morning (MS) while the other absorbed most in the afternoon (AS). When the peak of radiation absorption was higher in MS, air vapour pressure deficit (VPD) was not high enough to provoke stomatal closure. In contrast, peak radiation absorption in AS coincided with the daily peak in VPD. In addition, two soil water treatments were evaluated: irrigated trees (I) and non-irrigated trees (nI). The seasonal evolution of leaf water potential, leaf gas exchange and photosynthetic capacity were measured throughout the tree crowns in spring and summer. Results showed that stomatal conductance was reduced in nI trees in summer as a consequence of soil water stress, which limited their net assimilation rate. Olive leaves displayed isohydric behaviour and no important differences in the diurnal course of leaf water potentials among treatments and sectors were found. Seasonal diffusional limitation of photosynthesis was mainly increased in nI trees, especially as a result of stomatal limitation, although mesophyll conductance (g(m)) was found to decrease in summer in both treatments and sectors. A positive relationship between leaf nitrogen content with both leaf photosynthetic capacity and the daily integrated quantum flux density was found in spring, but not in summer. The relationship between photosynthetic capacity and g(m) was curvilinear. Leaf temperature also affected to g(m) with an optimum temperature at 29 degrees C. AS showed larger biochemical limitation than MS in August in both treatments. All these suggest that both diffusional limitation and the effect of leaf temperature could be involved in the seasonal reduction of photosynthetic capacity of olive leaves. This work highlights the need for models of plant growth and ecosystem function to incorporate new parameters affecting the distribution of photosynthetic capacity in canopies.