Net CO2 Exchange Rate and Shoot Growth of Young Poplar (Populus) Clones

Eighteen poplar (Populus) clones, varying in growth capacitywere grown in plastic containers under outdoor conditions. Duringthe first year of growth their net CO₂ exchange rate (NCER)was studied by infra-red gas analysis as a function of photosyntheticphoton flux density (PPFD) under controlled environment conditions.Maximal NCER (under saturating PPFD) and the PPFD compensationpoint were significantly correlated with the first year's shootlength and hence with the above ground biomass production ofthe various clones. Key words: Poplar, Shoot growth, CO₂ exchange rate     

A Fast, Low Cost and Low Power Requiring Device for Improving Closed Loop CO2 Measuring Systems

An improved and fast version of a closed loop system for measuringnet CO₂ exchange rates (NCER) in the field using a portableinfrared gas analyser (IRGA) is described. An electronic timer-differentiatordevice measures and displays very accurately the time periodnecessary to bridge over a constant and preselected CO₂ concentrationdifference. The time required for each measurement from startof the measurement to display of final results is c. 9 s forNCER of 24 µmol m^–2 s^–1 The measurement interval is sufficiently short that no environmentalcontrol in the perspex mini-cuvette is needed. Some satisfactorydata of NCER measurements obtained under field and glasshouseconditions on poplar, sugar bcct and winter wheat are presented. Key words: Infrared gas analysis, mobile gas exchange unit, photosynthesis     

Whole Plant and Leaf Steady State Gas Exchange during Ethylene Exposure in Xanthium strumarium L

The effects of ethylene evolved from ethephon on leaf and whole plant photosynthesis in Xanthium strumarium L. were examined. Ethylene-induced epinasty reduced light interception by the leaves of ethephon treated plants by up to 60%. Gas exchange values of individual, attached leaves under identical assay conditions were not inhibited even after 36 hours of ethylene exposure, although treated leaves required a longer induction period to achieve steady state photosynthesis. The speed of translocation of recently fixed ¹¹C-assimilate movement was not seriously impaired following ethephon treatment; however, a greater proportion of the assimilate was partitioned downward toward the roots. Within 24 hours of ethephon treatment, the whole plant net carbon exchange rate expressed on a per plant basis or a leaf area basis had dropped by 35%. The apparent inhibition of net carbon exchange rate was reversed by physically repositioning the leaves with respect to the light source. Ethylene exposure also inhibited expansion of young leaves which was partially reversed when the leaves were repositioned. The data indicated that ethylene indirectly affected net C gain and plant growth through modification of light interception and altered sink demand without directly inhibiting leaf photosynthesis.     

Responses of Net Photosynthesis and Conductance to Independent Changes in the Humidity Environments of the Upper and Lower Surfaces of Leaves of Sunflower and Soybean

A dual-surface leaf chamber was used to investigate the responsesof net photosynthesis and leaf conductance to independent changesin the humidity environments of the upper and lower surfacesof leaves of sunflower and soybean. In sunflower decreasingthe humidity around the upper leaf surface while maintainingthat of the lower surface constant and high reduced both thephotosynthetic rate and the conductance of the lower surface.These reductions could not be attributed to changes in bulkleaf water potential since the transpiration rate of the wholeleaf remained constant. Similarly, the reductions were not relatedto localized water deficits in the lower epidermis or lowermesophyll since the transpiration rate of the lower surfacewas reduced. Possible mechanisms whereby the gas exchange characteristicsof the lower leaf surface of sunflower respond to the humidityenvironment of the upper surface are discussed. In contrastto sunflower, the photosynthetic rate of the lower surface ofsoybean was insensitive to the humidity environment of the uppersurface. In leaves of sunflower grown under a moderate temperature anda medium light level, simultaneous decreases of humidity atboth leaf surfaces reduced the photosynthetic rate of the wholeleaf without affecting the substomatal partial pressure of CO₂.In contrast, with leaves developed under a cool temperatureand a high light level, both the photosynthetic rate and thesubstomatal partial pressure of CO₂ were reduced. Evidently,the occurrence in sunflower of the response pattern suggestinga non-stomatal inhibition of photosynthesis by low humiditydepends upon the environment during growth. The possibilitythat this non-stomatal inhibition may be an artifact due toan error in the assumption of water vapour saturation withinthe leaf airspace is considered. Key words: Vapour pressure deficit, photosynthesis, conductance, non-stomatal inhibition, Helianthus annuus, Glycine max     

Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expandedleaves and whole plants of Amaranthus hypochondriacus L., Glycinemax (L.) Merr., and Lycopersicon esculentum Mill. grown in controlledenvironments at 35 and 70 Pa carbon dioxide pressure were measuredat 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant24-h carbon dioxide exchange were used to determine relativegrowth rates, net assimilation rates, leaf area ratios, andthe ratio of respiration to photosynthesis under the growthconditions. Biomass at a given time after planting was greaterat the higher carbon dioxide pressure in G. max and L. esculentum,but not the C₄ species, A. hypochondriacus. Relative growthrates for the same range of masses were not different betweencarbon dioxide treatments in the two C₃ species, because highernet assimilation rates at the higher carbon dioxide pressurewere offset by lower leaf area ratios. Whole plant carbon dioxideefflux rates per unit of mass were lower in plants grown andmeasured at the higher carbon dioxide pressure in both G. maxand L. esculentum, and were also smaller in relation to daytimenet carbon dioxide influx. Short-term responses of respirationrate to carbon dioxide pressure were found in all species, withcarbon dioxide efflux rates of leaves and whole plants lowerwhen measured at higher carbon dioxide pressure in almost allcases. Amaranthus hypochondriacus L., Glycine max L. Merr., Lycopersicon esculentum Mill., soybean, tomato, carbon dioxide, respiration, growth     

Effect of Nitrogen Supply on the Photosynthetic Performance of Leaves from Coffee Plants Exposed to Bright Light

Although Coffea arabica L. grows naturally in shaded habitats,it can be cultivated under high light intensity, but not withoutsevere photoinhibition mainly during the period of transferfrom the nursery into the field. The present work examines someof the changes in the photosynthetic performance induced byexposure to high light and the possibility of using enhancednitrogen levels to overcome photoinhibition. For that purpose,young plants of Coffea arabica L. (cv. Catuai) grown in a shadedgreenhouse were treated with 0, 1 and 2 mmol of nitrogen and4 weeks later exposed to full solar irradiation, outside. Visible damage due to exposure to full sunlight appeared within2 d in all plants, resulting in a reduced photosynthetic leafarea and drastic shedding of leaves in the unfertilized plants.These effects were considerably less in plants with the highestN dose. After 130 d of exposure, there was 100% mortality inplants receiving no extra nitrogen, compared with 30% in theplants treated with 2 mmol nitrogen. Photosynthesis rates, leafconductance and transpiration presented minimum values after4 d of light stress. Large changes in the photosynthetic capacity(measured at high CO₂ concentration and high light intensity),quantum efficiency and fluorescence yield (F_v/F_m) indicate thatnet photosynthesis rate in the air had been reduced by bothstomatal closure and by changes at the photochemical level.All indicators show that N-fertilized plants were less affectedby photoinhibition. Key words: Coffee plant, nitrogen, photoinhibition, photosynthesis     

Photosynthesis and Transpiration in Rice as Influenced by Soil Moisture and Air Humidity

The paper describes the effect of soil moisture content andair humidity on CO₂ exchange (P_N), CO₂ diffusion resistance(Cr) and transpiration (E) in four varieties of japonica rice(Oryza sativa L.). A decrease in soil moisture content reducedthe rate of photosynthesis to a varying degree in the varieties.Reduction in photosynthesis was attributed to increase in Cr.The effect of low soil moisture on photosynthesis and CO₂ diffusionwas further intensified by decrease in air humidity. By maintaininga high humidity in the air around the leaves however, the effectof soil moisture deficiency was reduced considerably, exceptin Rikuto Norin 21 which was very sensitive to soil-moisturedeficiency alone. Dryness of the air enhanced the transpirationrate, although the increase was relatively less in the plantsfacing a simultaneous water crisis at the root surface. In plantsgrowing under flooded conditions, a decrease in air humiditycaused a slight depression in P_N despite the simultaneous decreasein Cr. Oryza sativa L., rice, photosynthesis, transpiration, diffusion resistance, soil moisture, air humidity     

Limitations of Gas Exchanges in Intact Leaves during Ontogeny of Field-grown Chickpeas

The ontogenic changes in several component processes of photosynthesiswere measured in chickpeas. Gas exchange characteristics ofintact leaves were studied to analyse the effects of ambientconditions under which chickpeas are usually grown. The CO₂assimilation rate per unit leaf area remained fairly high duringthe vegetative stage, reaching a peak at early pod-fill anddeclining subsequently throughout pod development. The intercellularCO₂ partial pressure (C₁) remained more or less constant (195µbar) during vegetative growth and the early stages ofseed-filling. With falling RWC and PAR interception, the stomatalconductance declined more rapidly than the CO₂ assimilationrate resulting in a value of C₁ less than that normally existingunder ambient conditions. From the A/C₁-analysis, CO₂ assimilationduring pod-filling appears to be limited by the RuBP-regenerationcapacity because the carboxylation efficiency and in vitro RuBPCaseactivity were initially unaffected. However, as leaves aged,the carboxylation efficiency and in vitro RuBPCase activitydecreased abruptly with increasing leaf temperatures above 30°C, and the C₁ was greater than normally existing values(195 µbar), suggesting an increased mesophyll limitationof photosynthesis. It is suggested that a decline in the CO₂assimilation rate of leaves during pod development and an acceleratedsenescence are induced by adverse ambient conditions, particularlyplant water stress and high leaf temperature. Key words: Cicer arietinum L., gas exchange, photosynthesis, ribulose-1,5-bisphosphate carboxylase     

A method for measuring whole plant photosynthesis in Arabidopsis thaliana

Measurement of photosynthesis of intact leaves of Arabidopsis thaliana has been prohibitive due to the small leaf size and prostrate growth habit. Because of the widespread use of Arabidopsis for plant science research it is important to have a procedure for accurate, nondestructive measurement of its photosynthesis. We developed and tested a method for analysis of photosynthesis in whole plants of Arabidopsis. Net carbon assimilation and stomatal conductance were measured with an open gas exchange system and photosynthetic oxygen evolution was determined from chlorophyll fluorescence parameters. Individual plants were grown in 50 cubic centimeter tubes that were attached with an air tight seal to an enclosed gas exchange chamber for measurement of carbon dioxide and water exchange by the whole plant. Chlorophyll fluorescence from intact leaves was simultaneously measured with a pulse modulated fluorometer. Photosynthetic CO₂ assimilation and stomatal conductance rates were calculated with established gas exchange procedures and O₂ evolution was determined from chlorophyll fluorescence measurement of Photosystem II yield. Carbon assimilation and oxygen evolution in response to light intensity and ambient CO₂ concentration was measured and is presented here to demonstrate the potential use of this method for investigation of photosynthesis of Arabidopsis plants in controlled environment conditions.     

Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Vegetative crops of chrysanthemum were grown for 5 or 6 weekperiods in daylit assimilation chambers. Crop responses to differentradiation levels and temperatures were analysed into effectson dry matter partitioning, specific leaf area, leaf photosynthesisand canopy light interception. The percentage of newly formed dry matter partitioned to theleaves was almost constant, although with increasing radiationor decreasing temperature, a greater percentage of dry matterwas partitioned to stem tissue at the expense of root tissue.There was a positive correlation between the percentage of drymatter in shoot material and the overall carbon: dry matterratio. Canopy photosynthesis was analysed assuming identical behaviourfor all leaves in the crop. Leaf photochemical efficiency wasonly slightly affected by crop environment. The rate of grossphotosynthesis per unit leaf area at light saturation, P_A (max),increased with increasing radiation integral, but the same parameterexpressed per unit leaf dry matter, P_w (max) was almost unaffectedby growth radiation. In contrast, P_A (max) was hardly affectedby temperature but P_w (max) increased with increasing growthtemperature. This was because specific leaf area decreased withdecreasing temperature and increased with decreasing radiation.There was a positive correlation between canopy respirationintegral and photosynthesis integral, and despite a four-foldchange in crop mass during the experiments, the maintenancecomponent of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variationwith radiation integral but was negatively correlated with temperature.This decrease in the efficiency of the canopy at interceptingradiation exactly cancelled the increase in specific carbonassimilation rate that occurred with increasing growth temperature,giving a growth rate depending solely on the incident lightlevel. Chrysanthemum, dry matter partitioning, photosynthesis, specific leaf area     

Seasonal and diurnal changes in photosynthesis and carbon partitioning in Vitis vinifera leaves in vines withand without fruit

In Vitis vinifera L. cv. Chardonnay maintained in a greenhouse,the maximum rate of photosynthesis, the measured rates of denovo sucrose and starch synthesis and the total leaf sucroseand starch contents were relatively constant throughout theperiod from April to July although the partitioning of newlyfixed carbon was modified in favour of sucrose synthesis half-waythrough the growing period. In these experimental conditions,no significant differences in these parameters were observedin plants from which the fruit had been removed in comparisonto the controls. In field-grown vines, photosynthesis rose toa maximum in the early morning consistent with the increasein ambient irradiance and then subsequently progressively decreased.This occurred every day. On clear days the mid-morning depressionin the rate of CO₂ assimilation was closely linked to decreasein stomatal conductance, but there was no correlation betweenthese parameters on days when the sun was overcast. There wasno correlation between leaf sucrose content and the depressionin photosynthesis. The calculated rate of non-cyclic electronflow did not decline in parallel with the mid-morning depression and the quantum efficiency of photosystem II was constantfor the whole of the period when the CO₂ assimilation was decreasing.The mid-morning depression of photosynthetic CO₂ assimilationwas related to both stomatal and non-stomatal effects. In neithersituation did it have any measurable feedback effect on theelectron transport rate or on the carbo hydrate contents ofthe leaves. Key words: Vitis vinifera L., source-sink interactions, sucrose, starch, photosynthesis     

Effect of Elevated CO2 on the Photosynthesis, Respiration and Growth of Perennial Ryegrass

Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO₂ concentration of either 340 or680µI 1^–1 CO₂. Following complete acclimation tothe environmental regimes, leaf and whole plant CO₂ effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO₂ increased rates of photosynthesis of young, fullyexpanded leaves by 35–46% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI^–1 CO₂ reduced rates of photosynthesis in bothCO₂ regimes, compared with plants acclimated to 340µll^–1. There was no significant effect of CO₂ regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO₂ exhibited generally lower ratesthan those developed in 340µI I^–1 CO₂. Initially the seedling plants in elevated CO₂ grew faster thantheir counterparts in 340µI I^–1 CO₂, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO₂ regime, specific leaf area was persistently13–40% lower in elevated CO₂ while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO₂reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO₂ on plant growthwas primarily due to the fact that CO₂ concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO₂, photosynthesis, respiration, growth, development     

农田冬小麦生长和产量对臭氧动态暴露的响应

 评估臭氧(O₃)污染对农田冬小麦生长和产量的影响是污染生态学和生理生态学研究的重要内容之一。该研究运用开顶式气室(OTC),对冬小麦‘ 嘉403’(Triticum aestivum cv. Jia 403)进行了O₃动态暴露的田间原位试验。实验设置过滤空气组(CF)、自然大气组(NF)和两个不同浓度的 O₃动态暴露组(DO100和DO150)。结果表明：1) O₃浓度增加,一方面可以改变灌浆期冬小麦叶片气体交换参数的日变化规律;另一方面引起表观 光量子产额、光饱和点和光补偿点等光响应参数的显著降低。这表明灌浆期叶片光合能力的下降是气孔因素和非气孔因素共同作用的结果。2) O₃暴露可以改变小麦形态特征,如植株变矮、叶片衰老加速、 叶面积变小,并最终导致产量大幅下降。     

Whole Plant Carbon Gain of an Endangered Herbaceous Species Aster kantoensis and the Influence of Shading by an Alien Grass Eragrostis curvula in its Gravelly Floodplain Habitat

Aster kantoensis, an endangered plant species, is endemic togravelly floodplains of a few large rivers in central Japan.In recent years, competitive exclusion by alien perennial grassesin its natural habitat has been suspected to be one of the majorfactors threatening this species. In the River Kinu, increasedshading by the perennial alien grass Eragrostis curvula reduceslight availability for A. kantoensis. To reveal the influenceof shading on the establishment and growth of A. kantoensisrosettes, the potential carbon gain of A. kantoensis in itsnatural habitat was estimated using microenvironmental dataand whole plant photosynthetic and respiratory responses tolight and temperature. Whole plant CO₂exchange responses weremeasured with a specifically designed ‘double chamber’,which enabled measurement of the CO₂gas exchange rates of thefoliage (F) and the culm (C; stem and roots) separately. Itwas demonstrated that in a plant with average C/F ratio, positivecarbon gain could be maintained only in the microsites wherethe relative PPFD (photosynthetically active photon flux density)was above 15 or 30% of unshaded conditions in early- or mid-summer,respectively. Increasing C/F ratio, caused by an increase inroot biomass as an adaptive response to drought, resulted ina large reduction in the carbon gain irrespective of microsite,weather and season. The high light requirement of A. kantoensisis interpreted as a cost of the morphological responses necessaryto avoid stresses characteristic of this gravelly floodplainhabitat. Copyright 2000 Annals of Botany Company Aster kantoensis Kitam., Eragrostis curvula Nees, biomass distribution, carbon gain, gravelly floodplain, respiration, shading, whole plant photosynthesis     

Simultaneous CO2- and 16O2/18O2-gas exchange and fluorescence measurements indicate differences in light energy dissipation between the wild type and the phytochrome-deficient aurea mutant of tomato during water stress

The CO₂-, H₂O- and ¹⁶O₂/¹⁸O₂ isotopic-gas exchange and the fluorescencequenching by attached leaves of the wild-type and of the phytochrome-deficienttomato aurea mutant was compared in relation to water stressand the photon fluence rate. The chlorophyll content of aurealeaves was reduced and the ultra-structure of the chloroplastswas altered. Nevertheless, the maximum rate of net CO₂ uptakein air by the yellow-green leaves of the aurea mutant was similarto that by the dark-green wild-type leaves. However, less O₂was produced by the leaves of the aurea mutant than by leavesof the wild-type. This result indicates a reduced rate of photosyntheticelectron flux in aurea mutant leaves. No difference in bothphotochemical and non-photochemical fluorescence quenching wasfound between wild-type and aurea mutant leaves. Water stresswas correlated with a reversible decrease in the rates of bothnet CO₂ uptake and transpiration by wild-type and aurea mutantleaves. The rate of gross ¹⁶O₂ evolution by both wild-type andaurea mutant leaves was fairly unaffected by water stress. Thisresult shows that in both wild-type and aurea leaves, the photochemicalprocesses are highly resistant to water stress. The rate ofgross ¹⁸O₂ uptake by wild-type leaves increased during waterstress when the photon fluence rate was high. Under the sameconditions, the rate of gross ¹⁸O₂ uptake by ^aurea mutant leavesremained unchanged. The physiological significane of this differencewith respect to the (presumed) importance of oxygen reductionin photoprotection is discussed. Key words: Water stress, gas exchange, fluorescence quenching, Lycopersicon esculentum, mutant (tomato, aurea), energy dissipation     

Characterisation of Non-Uniform Photosynthesis Induced by Abscisic Acid in Leaves Having Different Mesophyll Anatomies

The effects of abscisic acid (ABA) on photosynthesis in leavesof Helianthus annuus L. were compared with those in leaves ofVicia faba L. After the ABA treatment, the response of photosyntheticCO₂ assimilation rate, A, to calculated intercellular partialpressure of CO₂, P_i, (A(p_i) relationship) was markedly depressedin H. annuus. A less marked depression was also observed inV.faba. However, when the abaxial epidermes were removed fromthese leaves, neither the maximum rate nor the CO₂ responseof photosynthetic oxygen evolution was affected by the applicationof ABA. Starch-iodine tests revealed that photosynthesis was not uniformover the leaves of H. annuus treated with ABA. The starch contentwas diffferent in each bundle sheath extension compartment (thesmallest subdivision of mesophyll by veins with bundle sheathextensions, having an area of ca. 0.25 mm² and ca. 50 stomata).In some compartments, no starch was detected. The distributionof open stomata, examined using the silicone rubber impressiontechniques, was similar to the pattern of starch accumulation.In V.faba leaves, which lack bundle sheath extensions, distributionof starch was more homogeneous. These results indicate that the apparent non-stomatal inhibitionof photosynthesis by ABA deduced from the depression of A(pⁱ)relationship is an artifact which can be attributed to the non-uniformdistribution of transpiration and photosynthesis over the leaf.Intercellular gaseous environment in the ABA-treated leavesis discussed in relation to mesophyll anatomy. ¹ Present address: Department of Botany, Duke University, Durham,NC 27706, U.S.A. (Received September 30, 1987; Accepted January 13, 1988)     

Impact of elevated atmospheric CO2 and O3 on gas exchange and chlorophyll content in spring wheat (Triticum aestivum L.)

Stands of spring wheat grown in open-top chambers (OTCs) wereused to assess the individual and interactive effects of season-longexposure to elevated atmospheric carbon dioxide (CO₂ and ozone(O₃) on the photosynthetic and gas exchange properties of leavesof differing age and position within the canopy. The observedeffects were related to estimated ozone fluxes to individualleaves. Foliar chlorophyll content was unaffected by elevatedCO₂ but photosynthesis under saturating irradiances was increasedby up to 100% at 680 µmol mol^–1 CO₂ relative tothe ambient CO₂ control; instantaneous water use efficiencywas improved by a combination of increased photosynthesis andreduced transpiration. Exposure to a seasonal mean O₃ concentration(7 h d^–1) of 84 nmol mol^–1 under ambient CO₂ acceleratedleaf senescence following full expansion, at which time chlorophyllcontent was unaffected. Stomatal regulation of pollutant uptakewas limited since estimated O₃ fluxes to individual leaves werenot reduced by elevated atmospheric CO₂, A common feature ofO₃-treated leaves under ambient CO₂ was an initial stimulationof photosynthesis and stomatal conductance for up to 4 d and10 d, respectively, after full leaf expansion, but thereafterboth variables declined rapidly. The O₃-induced decline in chlorophyllcontent was less rapid under elevated CO₂ and photosynthesiswas increased relative to the ambient CO₂ treatment. A/C_i analysessuggested that an increase in the amount of in vivo active RuBisCOmay be involved in mitigating O₃-induced damage to leaves. Theresults obtained suggest that elevated atmospheric CO₂ has animportant role in restricting the damaging effects of O₃ onphotosynthetic activity during the vegetative growth of springwheat, and that additional direct effects on reproductive developmentwere responsible for the substantial reductions in grain yieldobtained at final harvest, against which elevated CO₂ providedlittle or no protection. Key words: Elevated CO₂ and O₃, gas exchange, O₃ flux, stomata, chlorophyll, Triticum aestivum     

温度对黄瓜幼苗光合生理弱光耐受性的影响

以不耐弱光的津研2号和较耐弱光的戴多星黄瓜(Cucumis sativus L.)为试材,在人工气候室内研究适温25 ℃/18 ℃（昼/夜）、亚适温15 ℃/9 ℃和低温9 ℃/7 ℃对弱光(75～85 μmol·m^-2·s^-1)耐受性的影响.结果表明：弱光下黄瓜叶片的SPAD、净光合速率（P_n）、气孔导度（G_s）、蒸腾速率（T_r）、水分利用效率（WUE）、实际光化学效率（Φ_PSⅡ）、光化学猝灭（q_P）等指标下降,下降程度随温度的降低而加剧,而超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性上升.逆境解除后的恢复过程中,光合和荧光参数逐渐恢复,荧光参数恢复速度快于气体交换参数.弱光下温度越低对黄瓜幼苗叶片光合机构造成的伤害越重,低温降低了叶片对弱光的耐受性.在低温、弱光处理过程中,津研2号P_n、Φ_PSⅡ、q_P等下降程度较戴多星明显,而在随后的恢复过程中其回升速度较戴多星迟缓,表明弱光下戴多星对低温的耐受性强于津研2号.     

Humidity Pretreatment Affects the Responses of Stomata and CO2 Assimilation to Vapor Pressure Difference in C3 and C4 Plants

Experiments were carried out to investigate the long-term influenceof humidity on the short-term responses of stomata and CO₂ assimilationto vapor pressure difference in Oryza sativa (rice, C₃ species)and Panicum maximum (green panic, C₄ species). Plants were grownfor four weeks in growth chambers set at 35% and 85% relativehumidity at 25C air temperature, 38+2 Pa CO₂ partial pressureand 1,700µmol m^-2s^-1 photon flux density. Soil was saturatedwith water in both humidity treatments. Low humidity pretreatmentscaused low leaf conductance and low rates of transpiration andCO₂ assimilation in O. sativa, but small changes in stomatalresponses to humidity and in CO₂ assimilation were found inP. maximum. From the short-term gas exchange experiments, itwas noted that the responsiveness of leaf conductance to vaporpressure difference were affected by humidity pretreatmentsin O. sativa, whereas unaffected in P. maximum. In O. sativameasurements of CO₂ assimilation as a function of internal CO₂partial pressure (A-Ci curve) indicated that low humidity pretreatmentsreduced the CO₂ assimilation at high internal CO₂ partial pressure,but the initial slope of the A-Ci curve was unaffected. Furthermore,plant characteristics such as total dry weight and leaf areaof plants subjected to low umidity were lower than plants subjectedto high humidity. The reductions in O. sativa, however, werelarger than in P. maximum. Stomatal frequency from low humiditygrown plant was higher than that from high humidity grown plantsin both species although there is no significant difference.The data indicated that if the short term inhibition of netCO₂ assimilation at a high vapor pressure difference was imposedduring vegetative growth, the photosynthetic biochemistry andthe resultant plant growth were largely depressed in O. sativa,a C₃ species. (Received May 26, 1992; Accepted November 2, 1992)     

Trade Winds Reduce Growth and Influence Gas Exchange Patterns in Papaya Seedlings

Four experiments were conducted to determine the effect of tradewinds in Guam, USA, on growth and gas exchange of three papaya(Carica papaya L.) cultivars. ‘Known You 1’, ‘Sunrise’,and ‘Tainung 2’ papaya seedlings at two differentstages of development were exposed to 0, 36 or 100% ambientwind. Wind exposure reduced stem height and leaf or stem dryweight in most cases, but had little influence on root growth.Net CO₂assimilation (A_CO2) at midday was lower for seedlingsexposed to wind than for those protected from wind. Dark respirationof exposed seedlings increased as much as 120% above that ofthe protected seedlings during the night. Wind exposure decreasedwhole plant evapotranspiration by up to 36% during the photoperiod,but increased evapotranspiration by 58–87% during thenocturnal period. Responses to wind exposure were similar amongcultivars, except that growth of ‘Tainung 2’ seedlingswas less affected by wind than that of the other cultivars.Seedlings that were exposed to the various wind treatments fromgermination onwards were less influenced by wind exposure thanwere seedlings that were grown in a protected nursery beforebeing exposed to the various wind treatments. These data indicatethat: (1) ambient trade winds in Guam are strong enough to decreasethe growth of papaya seedlings; (2) plant age influences theresponse; (3) stem and leaf growth are more influenced thanroot growth; and (4) decreasedA_CO2 and increased dark respirationmay be partly responsible for growth reduction. Copyright 2001Annals of Botany Company Carica papaya, gas exchange, wind