Increase In Leaf Temperature Research Articles

Yield, Water Use Efficiency and Physiological Characteristic of “Tommy Atkins” Mango under Partial Rootzone Drying Irrigation System

This study was conducted to evaluate the yield, water use efficiency and physiologic characteristics of “Tommy Atkins” mango under partial rootzone drying. The experiment was carried out in an orchard of mango in the irrigated perimeter of Ceraíma, BA. Five treatments and six repetitions were used with one tree per experimental plot: 01—Full Irrigation, 100% of ETc, 02—100% of ETc with frequency of alternance (FA) of 15 days, 03—80% ETc with FA of 15 days, 04—60% of ETc with FA of 15 days, 05—40% ETc with FA of 15 days. The treatments were conductedfrom the beginning of flowering to the harvest of mango in an orchard irrigated by drip. There was no significant reduction in productivity of “Tommy Atkins” mango under PRD up to 40% of ETc and PRD with 40% ETc resulted in greater water use efficiency. There was no significant difference among the averages of photosynthetically active radiation, Qleaf; leaf temperature, Tl; internal CO2 concentration, Ci; transpiration, E; stomatal conductance, gs; photosynthesis, A; carboxylation efficiency, A/Ci; quantum efficiency of photosynthesis, A/Qleaf and instantaneous water use efficiency, A/E between full irrigation and PRD with different water depth. The increase in leaf temperature causes reduction in A/Qleaf and A/E, however, it increases the transpiration. Increased gs results in higher rates of E, A and A/Ci. The use of the PRD with 40% of ETc causes no interference in gas exchange, maintains the yield and increases water use efficiency in “Tommy Atkins” mango tree.

Effect of drought stress on epicuticular wax load in peanut genotypes

The changes in epicuticular wax load (EWL) and the leaf temperature in two peanut genotypes such as JL-24 (drought susceptible) and K-9 (drought tolerant) was studied under drought stress and its recovery. The drought stress was induced at different soil moisture level (100%, 60%, 40% and 20% FC) for 7 days and subsequent recovery for 7 days. In both JL-24 and K-9 genotypes, the EWL was found to be increase with the increase in the intensity of drought stress. However, the increase in EWL in K-9 genotype was found to be significantly higher than JL-24 genotype. Moreover, the leaf temperature was also found to be increased with the increase in the intensity of drought stress and the degree of increase in leaf temperature was more pronounced in JL-24 compared to K-9 genotype. Further, after the recovery of drought stress, the EWL and leaf temperature decreased consistently in both the genotypes. The results are discussed in terms of the differences in EWL and temperature of leaf in two genotypes studied under drought stress.

Root-mediated allelopathic interference of bhringraj (Eclipta alba L.) Hassk. on peanut (Arachis hypogaea) and mung bean (Vigna radiata)

The root mediated allelopathic interference of Eclipta alba infested soil on growth, physiological parameters and antioxidant enzyme activity was conducted on Arachis hypogaea L. and vigna radiata L. It was found that rhizosphere soil significantly reduced the germination percentage, seedling growth and dry biomass depending upon the species sensitivity. The germination inhibition was correlated with membrane deterioration as proved by a strong electrolyte leakage, increase in malondialdehyde (MDA) and H2O2 content. The physiological parameters like chlorophyll content, photosynthetic rate (Pn), intercellular CO2 concentration (Ci), stomatal conductance (Gs), and transpiration (E) also showed significant reduction in E. alba infested soil and non-significant increase in leaf temperature (Lt) of two test species. The test seedlings have circumvented the allelochemicals stress, by both significant decrease and non-significant increase in the antioxidant activities in E. alba infested soil in contrast to control soil. Rhizosphere soil contained significantly higher amount of water-soluble phenolics as the putative allelochemicals, which were vanillic acid, benzoic acid, ferulic acid, and p-coumaric acid. The study concluded that rhizosphere soil exerts an allelopathic influence on peanut and mung bean by releasing water soluble phenolic acids as putative allelochemicals in soil.

Temperature responses of mesophyll conductance differ greatly between species.

The temperature responses of mesophyll conductance (gm ) were investigated for nine species using carbon isotope techniques combining tunable diode laser spectroscopy and gas exchange measurements. Species included the evergreen trees Eucalyptus pauciflora and Quercus engelmannii; the tropical evergreen tree Lophostemon confertus; as well as the herbaceous species Nicotiana tabacum, Oryza sativa, Triticum aestivum, Gossypium hirsutum, Glycine max and Arabidopsis thaliana. Responses varied from a two- to threefold increase in mesophyll conductance between 15 and 40 °C observed for N. tabacum, G. hirsutum, G. max and E. pauciflora to almost no change in L. confertus and T. aestivum. To account for the different temperature responses between species, we suggest that there must be variation in both the activation energy for membrane permeability and the effective pathlength for liquid phase diffusion. Stomatal conductance was relatively independent of increases in leaf temperature and concomitant increases in leaf to air vapour pressure difference. Two exceptions were Eucalyptus and Gossypium, where stomatal conductance increased with temperature up to 35 °C despite increasing leaf to air vapour pressure. For a given species, temperature responses of stomatal and mesophyll conductance were independent of one another.

Thermal acclimation of leaf respiration of tropical trees and lianas: response to experimental canopy warming, and consequences for tropical forest carbon balance

Climate warming is expected to increase respiration rates of tropical forest trees and lianas, which may negatively affect the carbon balance of tropical forests. Thermal acclimation could mitigate the expected respiration increase, but the thermal acclimation potential of tropical forests remains largely unknown. In a tropical forest in Panama, we experimentally increased nighttime temperatures of upper canopy leaves of three tree and two liana species by on average 3 °C for 1 week, and quantified temperature responses of leaf dark respiration. Respiration at 25 °C (R25 ) decreased with increasing leaf temperature, but acclimation did not result in perfect homeostasis of respiration across temperatures. In contrast, Q10 of treatment and control leaves exhibited similarly high values (range 2.5-3.0) without evidence of acclimation. The decrease in R25 was not caused by respiratory substrate depletion, as warming did not reduce leaf carbohydrate concentration. To evaluate the wider implications of our experimental results, we simulated the carbon cycle of tropical latitudes (24°S-24°N) from 2000 to 2100 using a dynamic global vegetation model (LM3VN) modified to account for acclimation. Acclimation reduced the degree to which respiration increases with climate warming in the model relative to a no-acclimation scenario, leading to 21% greater increase in net primary productivity and 18% greater increase in biomass carbon storage over the 21st century. We conclude that leaf respiration of tropical forest plants can acclimate to nighttime warming, thereby reducing the magnitude of the positive feedback between climate change and the carbon cycle.

Increasing leaf temperature reduces the suppression of isoprene emission by elevated CO2 concentration

Including algorithms to account for the suppression of isoprene emission by elevated CO2 concentration affects estimates of global isoprene emission for future climate change scenarios. In this study, leaf-level measurements of isoprene emission were made to determine the short-term interactive effect of leaf temperature and CO2 concentration. For both greenhouse plants and plants grown under field conditions, the suppression of isoprene emission was reduced by increasing leaf temperature. For each of the four different tree species investigated, aspen (Populus tremuloides Michx.), cottonwood (Populus deltoides W. Bartram ex Marshall), red oak (Quercus rubra L.), and tundra dwarf willow (Salix pulchra Cham.), the suppression of isoprene by elevated CO2 was eliminated at increased temperature, and the maximum temperature where suppression was observed ranged from 25 to 35°C. Hypotheses proposed to explain the short-term suppression of isoprene emission by increased CO2 concentration were tested against this observation. Hypotheses related to cofactors in the methylerythritol phosphate (MEP) pathway were consistent with reduced suppression at elevated leaf temperature. Also, reduced solubility of CO2 with increased temperature can explain the reduced suppression for the phosphoenolpyruvate (PEP) carboxylase competition hypothesis. Some global models of isoprene emission include the short-term suppression effect, and should be modified to include the observed interaction. If these results are consistent at longer timescales, there are implications for predicting future global isoprene emission budgets and the reduced suppression at increased temperature could explain some of the variable responses observed in long-term CO2 exposure experiments.

Measuring leaf temperature and stomatal conductance to evaluate leaf water content in barley cultivars under terminal drought stress

Drought stress is the main abiotic stress that limits crop production especially cereals that cope with water limitation in reproductive stage in semi arid areas. In this study, stomatal conductance and leaf temperature were consider as the precise and non destructive methods to evaluate water status in 3 barley cultivars under stress (withholding irrigation from anthesis until the end of growth season), and non stress (normal) conditions. The experiment was conducted in factorial based on CRD with three replications in greenhouse in Iran. Results indicated drought stress conditions significantly reduced leaf water content, stomatal conductance, cell membrane stability, number of tiller per plant, grain yield and harvest index. On the other hand, drought stress increased leaf temperature and hollow percent of grains in all cultivars (P<0.01). A significant correlation was observed between grain yield and stomatal conductance (r=+0.94), water content (r=+0.95), leaf temperature (r=-0.66), cell membrane stability (r=+0.62), number of tiller per plant (r=+0.65), number of grain per spike (r=+0.51) and harvest index (r=+0.96) in 20 days after anthesis. According to significant correlation between stomatal conductance and leaf temperature with other traits, using the infrared thermal image and prometer as the reliable methods to study water status in drought stress condition instead of other destructive methods are

Linkages between diurnal patterns of root respiration and leaf photosynthesis in Quercus crispula and Fagus crenata seedlings

The physiological traits of tree roots have been considered associating with photosynthetic capacity; however, the linkages between diurnal patterns of root respiration and assimilation in individual leaves are poorly understood. Our objectives were to investigate the diurnal patterns of tree root respiration and the assimilation under natural luminous environments and to explore the potential environmental drivers of root respiration and the assimilation by relating trees' diurnal cycle to commonly measured variables. We simultaneously and continuously measured individual leaf assimilation and root respiration in 3-year-old seedlings of Quercus crispula and Fagus crenata, which are commonly the dominant tree species in deciduous broad-leaved forests in Japan, in full-sun and in the dark. Net assimilation rates followed a diurnal pattern in both species, with a marked decline in the morning that corresponded to a rapid increase in photosynthetic photon flux density, an increase in leaf temperature, and a vapor pressure deficit. Similarly, root respiration rates in both species decreased around noon in the sun treatment, although the soil temperature continued to increase. Seedlings in the sun treatment had significantly higher rates of root respiration than seedlings that were kept in the dark. Our results suggest that the midday depression of leaf assimilation could lead to downward transport of photosynthetic products, causing a midday depression in root respiration on a diurnal time scale. Furthermore, the effects of changes in the assimilated carbon supply on root respiration are likely to vary with light conditions experienced by leaves.

The contribution of SERF1 to root-to-shoot signaling during salinity stress in rice

Stress perception and communication play important roles in the adaptation of plants to changing environmental conditions. Plant roots are the first organs to detect changes in the soil water potential induced by salt stress. In the presence of salinity stress, root-to-shoot communication occurs to adjust the growth of the whole plant. So far, the phytohormone abscisic acid (ABA), hydraulic signals and reactive oxygen species (ROS) have been proposed to mediate this communication under salt stress. Recently, we identified the rice transcription factor SALT-RESPONSIVE ERF1 (SERF1), which regulates a ROS-dependent transcriptional cascade in roots required for salinity tolerance. Upon salt stress, SERF1 knockout mutant plants show an increased leaf temperature as compared with wild type. As this occurs within the first 20 min of salt stress, we here evaluated the involvement of SERF1 in the perception of salt stress in the shoot. By metabolic profiling and expression analysis we show that the action of SERF1 in signal communication to the shoot is independent from ABA, but does affect the accumulation of ROS-related metabolites and transcripts under short-term salt stress.

Does Prescribed Burning Affect Leaf Secondary Metabolites in Pine Stands?

Prescribed burning (PB) is gaining popularity as a low-cost forest protection measure that efficiently reduces fuel build-up, but its effects on tree health and growth are poorly understood. Here, we evaluated the impact of PB on plant defenses in Mediterranean pine forests (Pinus halepensis and P. nigra ssp. laricio). These chemical defenses were estimated based on needle secondary metabolites (terpenes and phenolics including flavonoids) and discussed in terms of chlorophyll fluorescence and soil nutrients. Three treatments were applied: absence of burning (control plots); single burns (plots burned once); and repeated burns (plots burned twice). For single burns, we also explored changes over time. In P. laricio, PB tended to trigger only minor modifications consisting exclusively of short-lived increases (observed within 3 months after PB) in flavonoid index, possibly due to the leaf temperature increase during PB. In P. halepensis, PB had detrimental effects on physiological performance, consisting of (i) significant decreases in actual PSII efficiency (ΦPSII) in light-adapted conditions after repeated PB, and (ii) short-lived decreases in variable-to-maximum fluorescence ratio (Fv/Fm) after single PB, indicating that PB actually stressed P. halepensis trees. Repeated PB also promoted terpene-like metabolite production, which increased 2 to 3-fold compared to control trees. Correlations between terpene metabolites and soil chemistry were found. These results suggest that PB impacts needle secondary metabolism both directly (via a temperature impact) and indirectly (via soil nutrients), and that these impacts vary according to species/site location, frequency and time elapsed since last fire. Our findings are discussed with regard to the use of PB as a forest management technique and its consequences on plant investment in chemical defenses.

Effect of Water Stress on Leaf Temperature, Transpiration Rate, Stomatal Diffusive Resistance and Yield of Banana

The present investigation was undertaken under field condition to study the effect of water deficit on leaf temperature, transpiration rate, stomatal diffusive resistance and yield of banana cultivars and hybrids. Stress was imposed at different critical stages viz., 3 rd , 5 th , 7 th and 9 th month after planting. The stress was given by scheduling irrigation at the 50% available soil moisture (ASM) characteristic during critical stages. The soil moisture content was analyzed by using pressure plate membrane apparatus. In control plots, the irrigation was given at the ASM of 80% with the soil water potential of around - 6 bars and in the case of stressed plots; the irrigation was given when an ASM reached 50% with the soil water potential of - 14 bars. In stressed plots, 50% ASM was reached around 30 days. In this present study conducted with twelve cultivars and hybrids with three replications. The data were analyzed by using split plot design. The research revealed that, leaf temperature was usually negatively correlation with transpiration rate. Transpiration rate revealed a decreasing trend throughout the growth period of the crop with increasing in leaf temperature and stomatal diffusive resistance. The cultivars and hybrids of Karpuravalli, Karpuravalli×Pisang Jajee, Saba, and Sannachenkathali was identified as tolerant to water stress with highly accelerated in transpiration rate by water stress treatment with slight increase in leaf temperature over control.

Growth under elevated CO2 concentration affects the temperature response of photosynthetic rate

In this study, we tested the hypothesis that an elevated CO2 concentration leads to a shift of the temperature optimum of the photosynthetic rate in trees. Since the elevated CO2 treatment usually leads to a significant decrease in stomatal conductance and consequently to decrease in transpiration followed by an increase in leaf temperature, we hypothesized that elevated CO2 results in the acclimation of photosynthetic apparatus to the higher temperature.We studied the two most common species in the Czech Republic – European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karsten). The eight-year-old trees were grown in glass domes at the experimental research site Bílý Kříž in the Beskydy Mts. and they were exposed to ambient (AC; 385 µmol CO2 mol-1) and elevated CO2 concentrations (EC; 700 µmol CO2 mol-1). Based on the gas-exchange and fluorescence techniques we determined the basic photosynthetic characteristics in the range of leaf temperatures from 10 to 45 °C. The changes in temperature acclimation of tree species studied were evaluated on the basis of the shift of temperature optima. EC treatment led indeed to an increase of leaf temperature up to 3.5 °C in both species studied. The temperature optimum of the light-saturated rate of CO2 assimilation, measured at the growth CO2 concentration (i.e. 385 for AC and 700 µmol CO2 mol-1 for EC trees), was higher by 3 °C in both tree species of the EC variant. Although the shift in photosynthetic temperature optimum disappeared when the AC plants were exposed to an elevated CO2 concentration, an acclimation of Rubisco carboxylation and electron transport to higher temperature was observed.

Estimating plant crown transpiration and water use efficiency by vegetative reflectance indices associated with chlorophyll fluorescence

This research developed estimates of plant crown transpiration and water-use-efficiency using reflectance and derivative indices extracted from remotely sensed chlorophyll fluorescence measurements under natural conditions. Diurnal changes of leaf-level gas exchange (carbon assimilation rate (A), stomatal conductance (gs), transpiration rate (E)), chlorophyll fluorescence and canopy-scale remote sensing were measured on top crown of valley oak (Quercus lobata) in the foothills of central California, USA. The results indicated Q. lobata experienced saturating irradiance (PAR), which induced photoinhibition indicated by a decrease in the quantum efficiency of photosystem II (r2 = 0.648 with Fv ′/Fm′ and r2 = 0.73 with FPSII) and open reaction centers (qP; r2 = 0.699). The excess absorbed quantum energy was dissipated as heat through the Xanthophyll cycle and other processes (photorespiration and the water-water cycle) rather than energy emission as steady state chlorophyll fluorescence (Fs). An increase in leaf temperature caused by the activity of Xanthophyll cycle was correlated to a decrease in Fs (r2 = 0.381) and an increase in evaporative cooling through E (r2 = 0.800) and water use efficiency (WUE; r2 = 0.872).

Effects of Long-term Exposure to Black Carbon Particles on Growth and Gas Exchange Rates of Fagus crenata, Castanopsis sieboldii, Larix kaempferi and Cryptomeria japonica Seedlings

To clarify the effects of black carbon (BC) particles on growth and gas exchange rates of Asian forest tree species, the seedlings of Fagus crenata, Castanopsis sieboldii, Larix kaempferi and Cryptomeria japonica were exposed to BC particles with sub-micron size for two growing seasons from 1 June 2009 to 11 November 2010. The BC particles deposited after the exposure to BC were observed on the foliar surface of the 4 tree species. At the end of the experiment, the amount of BC accumulated on the foliar surface after the exposure to BC aerosols were 0.13, 0.69, 0.32 and 0.58 mg C <TEX>$m^{-2}$</TEX> total leaf area in F. crenata, C. sieboldii, L. kaempferi and C. japonica seedlings, respectively. In August 2010, the exposure to BC particles did not significantly affect net photosynthetic rate under any light intensity, stomatal diffusive conductance to water vapour (<TEX>$g_s$</TEX>), stomatal limitation of photosynthesis, response of <TEX>$g_s$</TEX> to increase in vapour pressure deficit and leaf temperature under light saturated condition in the leaves or needles of the seedlings. These results suggest that the BC particles deposited on the foliar surface did not reduce net photosynthesis by shading, did not increase leaf temperature by absorption of irradiation light, and did not induce plugging of stomata in the leaves or needles of the seedlings. There were no significant effects of BC particles on the increments of plant height and stem base diameter during the experimental period and the whole-plant dry mass at the end of the experiment. These results indicate that the exposure to BC particles with sub-micron size for two growing seasons did not significantly affect the growth and leaf or needle gas exchange rates of F. crenata, C. sieboldii, L. kaempferi and C. japonica seedlings.

Physiological Responses of Jatropha to Drought Stress in Coastal Sandy Land Conditions

Normal 0 false false false IN X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Jatropha curcas L ., an important tropical biofuel crop, is reputed for its drought resistance, however, its ability to perform in dry conditions has still hardly been investigated. Changes in leaf water status, chlorophyll content, leaf surface temperature, stomatal conductance, proline and abcisic acid (ABA) content, transpiration and photosynthetic rate were studied in four Jatropha genotypes (IP-1A, IP-2M, Local superior and Yellow leaf) and subjected to drought stress in coastal sandy land conditions in Central Java, Indonesia. Drought stress significantly decreased the leaf water status, leaf chlorophyll content, stomatal conductance, transpiration and photosynthetic rate, and increased leaf temperature, proline and ABA content. Resistant genotypes (IP-1A and IP-2M) had significantly higher leaf water status, chlorophyll content and photosynthetic rate than susceptible genotypes (Local superior and Yellow leaf). There were no differences between the Jatropha genotypes on leaf temperature, stomatal conductance and transpiration rate. Normal 0 false false false IN X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Keywords: ABA, biofuel , photosynthetic rate, proline, stomata, water status

Thermographic visualization of leaf response in cucumber plants infected with the soil-borne pathogen Fusarium oxysporum f. sp. cucumerinum

Infection with the soil-borne pathogen Fusarium oxysporum f. sp. cucumerinum (FOC), which causes Fusarium wilt of cucumber plants, might result in changes in plant transpiration and water status within leaves. To monitor leaf response in cucumber infected with FOC, digital infrared thermography (DIT) was employed to detect changes in leaf temperature. During the early stages of FOC infection, stomata closure was induced by ABA in leaves, resulting in a decreased transpiration rate and increased leaf temperature. Subsequently, cell death occurred, accompanied by water loss, resulting in a little decrease in leaf temperature. A negative correlation between transpiration rate and leaf temperature was existed. But leaf temperature exhibited a special pattern with different disease severity on light-dark cycle. Lightly wilted leaves had a higher temperature in light and a lower temperature in dark than did in healthy leaves. We identified that the water loss from wilted leaves was regulated not by stomata but rather by cells damage caused by pathogen infection. Finally, water balance in infected plants became disordered and dead tissue was dehydrated, so leaf temperature increased again. These data suggest that membrane injury caused by FOC infection induces uncontrolled water loss from damaged cells and an imbalance in leaf water status, and ultimately accelerate plant wilting. Combining detection of the temperature response of leaves to light-dark conditions, DIT not only permits noninvasive detection and indirect visualization of the development of the soil-borne disease Fusarium wilt, but also demonstrates certain internal metabolic processes correlative with water status.

Temperature response of carbon isotope discrimination and mesophyll conductance in tobacco

The partial pressure of CO2 at the sites of carboxylation within chloroplasts depends on the conductance to CO2 diffusion from intercellular airspace to the sites of carboxylation, termed mesophyll conductance (gm ). We investigated the temperature response of gm in tobacco (Nicotiana tabacum) by combining gas exchange in high light, ambient CO2 in either 2 or 21% O2 with carbon isotope measurements using tuneable diode laser spectroscopy. The gm increased linearly with temperature in 2 or 21% O2 . In 21% O2 , isotope discrimination associated with gm decreased from 5.0 ± 0.2 to 1.8 ± 0.2‰ as temperature increased from 15 to 40 °C, but the photorespiratory contribution to the isotopic signal is significant. While the fractionation factor for photorespiration (f = 16.2 ± 0.7‰) was independent of temperature between 20 and 35 °C, discrimination associated with photorespiration increased from 1.1 ± 0.01 to 2.7 ± 0.02‰ from 15 to 40 °C. Other mitochondrial respiration contributed around 0.2 ± 0.03‰. The drawdown in CO2 partial pressure from ambient air to intercellular airspaces was nearly independent of leaf temperature. By contrast, the increase in gm with increasing leaf temperature resulted in the drawdown in CO2 partial pressure between intercellular airspaces and the sites of carboxylation decreasing substantially at high temperature.

Black leaf-clips of a commercial fluorometer increased leaf temperature during dark adaptation under high solar radiation

The use of black leaf-clips for dark adaptation under high solar radiation conditions is reported to underestimate the maximum quantum yield of PSII photochemistry (Fv/Fm) measured by the continuous-excitation fluorometer Pocket PEA. The decrease in Fv/Fm was due to a rise in minimum fluorescence emission (Fo), probably resulting from increased leaf temperature (Tl). In field-grown tomato and pepper, fluorescence parameters and Tl in the region covered by the black leaf clip were measured in clipped leaves exposed to solar radiation during dark adaptation (clipped-only leaves) and in clipped leaves protected from solar radiation by aluminium foil (shrouded clipped leaves). Results confirmed significant Fv/Fm underestimates in clipped-only leaves primarily due to increased Fo. In one tomato experiment, Tl increased from 30 to 44.5°C in clipped-only leaves, with a negligible rise in shrouded clipped leaves. In two respective pepper experiments, Tl in clipped-only leaves increased from 27 to 36.2°C and 33 to 40.9°C. Based on the results of this study, a clip-effect parameter (PCE) on fluorescence emission is proposed as the difference for Fv/Fm (or −Fo/Fm) between shrouded clipped leaves and clipped-only leaves, which resulted to be 0.706 for tomato, and 0.241 and 0.358 for the two pepper experiments.

Physiological traits related to terminal drought resistance in common bean (Phaseolus vulgaris L.)

A major problem in common bean (Phaseolus vulgaris L.) agriculture is the low yield due to terminal drought. Because common beans are grown over a broad variety of environments, the study of drought-resistant genotypes might be useful to identify distinctive or common mechanisms needed for survival and seed production under drought. In this study the relationship between terminal drought resistance and some physiological parameters was analysed using cultivars contrasting in their drought response from two different gene pools. Trials were performed in three environments. As expected, drought treatments induced a decrease in leaf relative humidity and an increase in leaf temperature; however, when these parameters were compared between susceptible and resistant cultivars under optimal irrigation and drought, no significant differences were detected. Similar results were obtained for chlorophyll content. In contrast, analysis of relative water content (RWC) and stomatal conductance values showed reproducible significant differences between susceptible and resistant cultivars grown under optimal irrigation and drought across the different environments. The data indicate that drought-resistant cultivars maximise carbon uptake and limit water loss upon drought by increasing stomatal closure during the day and attaining a higher RWC during the night as compared with susceptible cultivars, suggesting a water balance fine control to achieve enough yield under drought.

The temperature response of CO2 assimilation, photochemical activities and Rubisco activation in Camelina sativa, a potential bioenergy crop with limited capacity for acclimation to heat stress

The temperature optimum of photosynthesis coincides with the average daytime temperature in a species' native environment. Moderate heat stress occurs when temperatures exceed the optimum, inhibiting photosynthesis and decreasing productivity. In the present study, the temperature response of photosynthesis and the potential for heat acclimation was evaluated for Camelina sativa, a bioenergy crop. The temperature optimum of net CO(2) assimilation rate (A) under atmospheric conditions was 30-32°C and was only slightly higher under non-photorespiratory conditions. The activation state of Rubisco was closely correlated with A at supra-optimal temperatures, exhibiting a parallel decrease with increasing leaf temperature. At both control and elevated temperatures, the modeled response of A to intercellular CO(2) concentration was consistent with Rubisco limiting A at ambient CO(2). Rubisco activation and photochemical activities were affected by moderate heat stress at lower temperatures in camelina than in the warm-adapted species cotton and tobacco. Growth under conditions that imposed a daily interval of moderate heat stress caused a 63% reduction in camelina seed yield. Levels of cpn60 protein were elevated under the higher growth temperature, but acclimation of photosynthesis was minimal. Inactivation of Rubisco in camelina at temperatures above 35°C was consistent with the temperature response of Rubisco activase activity and indicated that Rubisco activase was a prime target of inhibition by moderate heat stress in camelina. That photosynthesis exhibited no acclimation to moderate heat stress will likely impact the development of camelina and other cool season Brassicaceae as sources of bioenergy in a warmer world.