Increase In Stomatal Resistance Research Articles

Differences between sun and shade habitats on the invasive shrub Lantana camara and its biocontrol agent Teleonemia scrupulosa

The sap-sucking lace bug, Teleonemia scrupulosa (Hemiptera: Tingidae), was released as a biocontrol agent against the invasive shrub Lantana camara (Verbenaceae) in South Africa in 1961. Like many agents released against the weed in South Africa, success has been varied, largely attributed to the sheer number of L. camara varieties involved and the habitat types they invade. This study assessed the effects of L. camara variety (floral colour) and light microhabitat (sun/shade) on the preference, proliferation and feeding damage of T. scrupulosa. Using a cage choice test, varietal preference of T. scrupulosa between two of the most abundant (invasive) L. camara varieties (pink and orange) was assessed under both shaded and well-lit conditions. Secondly, the effect of T. scrupulosa chlorotic feeding damage on leaf physiology was evaluated. Results indicated that T. scrupulosa preferred the orange flower variety in high light environments but did not proliferate on either variety in the shade. At approximately 20% herbivory damage, photosynthesis declined by 90%, which was primarily attributed to the rapid increase in stomatal resistance. These results indicate that microhabitat, particularly sunlight intensity, is more important than L. camara variety to T. scrupulosa host preference. Mass release strategies should therefore consider microhabitat, prioritising releases on plants in open sunny locations to encourage agent persistence and proliferation.

Morpho-anatomical and physiological traits of two Bougainvillea genotypes trained to two shapes under deficit irrigation

The analysis of the growth behaviour, wood anatomical, and eco-physiological traits of two Bougainvillea genotypes, trained to two shapes and subjected to different irrigation regimes, fully supports the idea that structural properties interact with cultural practices (i.e., training) in determining the adaptive capability of plants, hence their productivity and survival. Bougainvillea species are cultivated for landscaping in the arid Mediterranean region. In Bougainvillea spp., secondary xylem and phloem are formed by successive cambia leading to a peculiar stem anatomy which could favour water storage and plant adaptation under drought conditions. To achieve sustainable production of Bougainvillea ornamental shrubs, it is crucial to understand how different genotypes respond to deficit irrigation and how cultural practices, such as canopy training, may interact with morpho-anatomical traits in modifying the plants’ ability to withstand water deficit. A greenhouse experiment was conducted to determine the effects of deficit irrigation on plant growth, ecophysiology, and branch anatomy in two Bougainvillea genotypes [B. × buttiana ‘Rosenka’, B. ‘Lindleyana’ (=B. ‘Aurantiaca’)] trained to globe and pyramid shapes. Irrigation treatments were based on daily evapotranspiration (ET): control (C, 100 % ET) or deficit irrigation (DI, 25 % ET). The two genotypes exhibited morphological adaptations to cope with water deficit, including reductions in dry weight, leaf number, and lamina size. In both genotypes, the DI-induced increase in stomatal resistance was accompanied by a decrease in stomata size. Water deficit triggered adjustments in wood anatomical functional traits, also depending on canopy shape and genotype, favouring either water conduction efficiency or safety against embolism. The occurrence of a safer hydraulic system in the pyramid-trained plants suggests a better control of water transport, thus supporting better growth performance under DI conditions compared to globe-trained plants. Such differences, induced by different canopy-shape trainings, should be considered in the management of DI.

Effect of temperature on oxidative stress induced by lead in the leaves of Plantago major L.

Abstract Fluctuation of the summer day-time temperatures in the mid-latitudes in a range from 16 to 30°C should not have irreversible negative effects on plants, but may influence metabolic processes including the oxidative stress. To test the effect of moderately high temperature on oxidative stress induced by lead in the leaves of Plantago major L.; the plants were incubated in a water solution of 0, 150, 450, and 900 μM Pb (NO3)2 at 20 and 28°C. Plant reactions were evaluated by the content of thiobarbituric acid reactive substances and ascorbate peroxidase and glutathione reductase activities in leaves after 2, 24, 48, and 72 h. The Pb concentration in the leaves rose with the increase in the Pb content and was higher at 20°C. The increase in stomatal resistance caused by Pb was higher at 28°C. The contents of TBARS increased after 2 h of plant exposure to Pb and the increase was the highest at 900 μM Pb, 28°C. The AsP activity increased up to 50% after 24 h of Pb-treatment at 28°C; the highest increase in glutathione reductase activity was observed after 72 h at 20°C. Thus, the moderately high temperature 28°C compared with optimal 20°C caused a decrease in Pb accumulation in Plantago leaves but amplified the negative effects of lead, especially in the beginning of stress development.

Impactos das mudanças climáticas na demanda hídrica e duração do ciclo do sorgo forrageiro e feijão-caupi no estado de Pernambuco

O aumento na ocorrência de eventos climáticos extremos nas últimas décadas é uma forte evidência das mudanças climáticas. Em regiões Semiáridas, onde a pressão de desertificação tem se intensificado, são esperadas diminuição da disponibilidade de água e maior ocorrência de períodos seca, e, consequentemente, efeitos na resposta fisiológica das plantas. Assim, objetivou-se analisar os impactos dos cenários de mudanças climáticas sobre a duração do ciclo fenológico e a demanda de água do sorgo forrageiro e do feijão-caupi cultivados no Estado de Pernambuco. Foram utilizados os valores mensais da normal climatológica brilho solar, temperatura do ar, umidade relativa do ar e velocidade do vento de dez municípios. Considerou-se um aumento de 1,8°C (Cenário B2) e 4,0°C (Cenário A1F1) na temperatura do ar e um decréscimo de 5,0% dos valores absolutos de umidade relativa do ar, além do aumento de 22% na resistência estomática e de 4% no índice de área foliar. Com base nessas informações foram gerados três cenários: situação atual e projeções futuras para B2 e A1F1. Os resultados revelaram uma redução média de 11% (B2) e 20% (A1F1), e de 10% (B2) e 17% (A1F1) na duração do ciclo, e de 4% (B2) e 8% (A1F1), e 2% (B2) e 5% (A1F1) na demanda de água acumulada para o sorgo forrageiro e feijão-caupi, respectivamente. Conclui-se que a magnitude das reduções da duração do ciclo e a demanda de água simulada para as culturas do sorgo forrageiro e do feijão-caupi variaram espaço-temporalmente no Estado de Pernambuco com os cenários de mudanças climáticas.ABSTRACT The increase in the occurrence of extreme weather events in recent decades is a strong evidence of climate change. In semiarid regions, where the pressure of desertification has intensified, are expected to decrease in the availability of water and higher occurrence of drought periods, and, consequently, effects on physiological response of plants. Thus, the objective of analyzing the impacts of climate change scenarios on the duration of phenological cycle and water demand of forage sorghum and cowpea, grown in the State of Pernambuco. Monthly values were used normal climatological solar brightness, air temperature, relative humidity and wind speed of ten municipalities. It was considered an increase of 1.8° C (B2 Scenario) and 4.0° C (A1F1 Scenario) on air temperature and a decrease of 5.0% of the absolute values of relative humidity, in addition to the 22% increase in stomatal resistance and 4% in leaf area index. Based on this information were generated three scenarios: current situation and future projections for B2, A1F1. The results revealed an average reduction of 11% (B2) and 20% (A1F1), and 10% (B2) and 17% (A1F1) for the duration of the cycle, and 4% (B2) and 8% (A1F1), and 2% (B2) and 5% (A1F1) in accumulated water demand for forage sorghum and cowpea, respectively. It is concluded that the magnitude of the reductions in the duration of the cycle and the simulated water demand for crops of forage sorghum and cowpea ranged space-temporarily in the State of Pernambuco with climate change scenarios.

Cumulative ozone effect on canopy stomatal resistance and the impact on boundary layer dynamics and CO2 assimilation at the diurnal scale: A case study for grassland in the Netherlands

AbstractBiological, chemical, and dynamical processes occurring at the surface strongly interact at diurnal scales. Therefore, this study examines the seasonal ozone impact on stomatal resistance, surface energy balance, boundary layer dynamics, and CO2 assimilation at this (sub)diurnal scale under changing conditions. We combine a seasonal canopy resistance module with a surface‐boundary layer model that solves the diurnal evolution of dynamical and chemical variables in a well‐mixed, convective boundary layer. The model is constrained with observations from Cabauw (Netherlands) for the dry year 2003, representing a well‐mixed boundary layer at midlatitudes over water‐stressed grassland. To quantify the ozone impact, the Cumulative Uptake of Ozone is calculated over a growing season, which gives an estimate of the reduction in stomatal aperture and photosynthesis. From a sensitivity analysis with mixed‐layer temperature and soil moisture content we conclude that drought is the dominant factor that determines the surface energy partitioning and limits CO2 assimilation. Although drought causes stomatal closure, the results indicate that ozone damage, nevertheless, occurs. A second sensitivity analysis with CO2 and ozone shows that ozone damage causes an increase in stomatal resistance of up to 40% under high ozone levels and that CO2‐induced stomatal closure limits ozone damage. The impact on boundary layer development through the effect of CO2 and ozone on the stomatal resistance is much smaller. At the diurnal scale soil moisture influences the surface energy partitioning, which affects the entrainment of ozone‐rich air. Due to ozone damage, the CO2 assimilation flux is reduced by about 15%.

Impacts of climate change on water demand and duration forage sorghum and cowpea cycle in the state of Pernambuco

The increase in the occurrence of extreme weather events in recent decades is a strong evidence of climate change. In semiarid regions, where the pressure of desertification has intensified, are expected to decrease in the availability of water and higher occurrence of drought periods, and, consequently, effects on physiological response of plants. Thus, the objective of analyzing the impacts of climate change scenarios on the duration of phenological cycle and water demand of forage sorghum and cowpea, grown in the State of Pernambuco. Monthly values were used normal climatological solar brightness, air temperature, relative humidity and wind speed of ten municipalities. It was considered an increase of 1.8° C (B2 Scenario) and 4.0° C (A1F1 Scenario) on air temperature and a decrease of 5.0% of the absolute values of relative humidity, in addition to the 22% increase in stomatal resistance and 4% in leaf area index. Based on this information were generated three scenarios: current situation and future projections for B2, A1F1. The results revealed an average reduction of 11% (B2) and 20% (A1F1), and 10% (B2) and 17% (A1F1) for the duration of the cycle, and 4% (B2) and 8% (A1F1), and 2% (B2) and 5% (A1F1) in accumulated water demand for forage sorghum and cowpea, respectively. It is concluded that the magnitude of the reductions in the duration of the cycle and the simulated water demand for crops of forage sorghum and cowpea ranged space-temporarily in the State of Pernambuco with climate change scenarios.

Disentangling the response of forest and grassland energy exchange to heatwaves under idealized land–atmosphere coupling

Abstract. This study investigates the difference in land–atmosphere interactions between grassland and forest during typical heatwave conditions in order to understand the controversial results of Teuling et al. (2010) (hereafter T10), who found the systematic occurrence of higher sensible heat fluxes over forest than over grassland during heatwaves. With a simple but accurate coupled land–atmosphere model, we show that existing parametrizations are able to reproduce the findings of T10 for normal summer and heatwave conditions. Furthermore, we demonstrate the sensitivity of the coupled system to changes in incoming radiation and early-morning temperature typical for European heatwaves. Our results suggest that the fast atmospheric control of stomatal resistance can explain the observed differences between grassland and forest. The atmospheric boundary layer has a buffering function therein: increases in stomatal resistance are largely compensated for by increases in the potential evaporation due to atmospheric warming and drying. In order to disentangle the contributions of differences in several static and dynamic properties between forest and grassland, we have performed a virtual experiment with artificial land-use types that are equal to grassland, but with one of its properties replaced by that of forest. From these, we confirm the important role of the fast physiological processes that lead to the closure of stomata. Nonetheless, for a full explanation of T10's results, the other properties (albedo, roughness and the ratio of minimum stomatal resistance to leaf-area index) play an important but indirect role; their influences mainly consist of strengthening the feedback that leads to the closure of the stomata by providing more energy that can be converted into sensible heat. The model experiment also confirms that, in line with the larger sensible heat flux, higher atmospheric temperatures occur over forest. As our parametrization for stomatal resistance is empirical rather than mechanical, our study stresses the demand for a better mechanistic understanding of physiological processes in plants.

The Influence of Deficit Irrigation on Growth, Ornamental Quality, and Water Use Efficiency of Three Potted Bougainvillea Genotypes Grown in Two Shapes

Bougainvillea is widely used as flowering shrub in gardening and landscaping in the Mediterranean region characterized by limited water supply. The evaluation of deficit irrigation as a possible technique to improve water productivity and selection of genotypes that can better withstand soil water deficits are essential for sustainable production. A greenhouse experiment was conducted to determine the effects of deficit irrigation on three potted Bougainvillea genotypes [B. glabra var. Sanderiana, B. ×buttiana ‘Rosenka’, B. ‘Lindleyana’ (=B. ‘Aurantiaca’)] grown in two shapes, globe and pyramid, on agronomical and physiological parameters. Irrigation treatments were based on the daily water use (100%, 50%, or 25%). The shoot, total dry biomass, leaf number, leaf area, and macronutrient [nitrogen (N), phosphorus (P), and potassium (K)] concentration decreased in response to an increase in water stress with the lowest values recorded in the severe deficit irrigation (SDI) treatment. At 160 days after transplanting (DAT), the percentage of total dry biomass reduction caused by irrigation level was lower in B. ×buttiana ‘Rosenka’ compared with B. glabra var. Sanderiana and B. ‘Lindleyana’ (=B. ‘Aurantiaca’). At 160 DAT, the flower index increased in response to an increase in water stress with the highest values recorded under both moderate deficit irrigation (MDI) and SDI for B. ×buttiana ‘Rosenka’. The biomass water use efficiency (WUE) increased under water stress conditions with the highest values recorded in B. glabra var. Sanderiana and B. ×buttiana ‘Rosenka’ grown under MDI (average 1.43 and 1.25 g·L−1, respectively) and especially with SDI (average 1.68 and 1.36 g·L−1, respectively). A number of tolerance mechanisms such as increase in stomatal resistance, decrease in leaf water potential, and decrease in leaf osmotic potential have been observed, especially under SDI. The MDI treatment can be used successfully in Bougainvillea to reduce water consumption while improving the overall quality and WUE, whereas the genotypes B. glabra var. Sanderiana and B. ×buttiana ‘Rosenka’ could be considered suitable for pot plant production.

Anatomic and physiological modifications in seedlings of Coffea arabica cultivar Siriema under drought conditions

Due to the weather changes prognostic for the coming years, the understanding of water deficit and physiological responses of plants to drought becomes an important requirement in order to develop technologies such as mechanisms to assist plants to cope with longer drought periods, which will be essential to maintenance of Brazilian and worldwide production. This study aimed to evaluate ecophysiological and anatomical aspects as well as the nitrate reductase activity in Siriema coffee seedlings subjected to four treatments: Daily irrigated, non-irrigated, re-irrigated 24 hours and re-irrigated 48 hours after different stress periods. Non-irrigation promoted a reduction in leaf water potential being accented from the ninth day of evaluation onwards. Re-irrigation promoted a partial recovery of the plant water potential. Non-irrigated plants showed an increase in stomatal resistance and reduction of transpiration and nitrate reductase activity. In the roots, there was a decrease in nitrate reductase activity under water stress. Leaf anatomical modifications were significant only for the adaxial surface epidermis and palisade parenchyma thickness, this latter characteristic being higher in control plants. Stomatal density and polar and equatorial diameter ratios showed the highest values in plants under water stress. In the roots, differences only in the cortex thickness being bigger in the non-irrigated treatment could be observed. Therefore, Siriema coffee plants under water stress show physiological, biochemical and anatomical modifications that contribute to the tolerance of this genotype to these conditions.

The response of pigeonpea cultivars to short durations of waterlogging

The effects of short durations of waterlogging was investigated in three cultivars of pigeonpea ( Cajanus cajan (L.) Millps); Tobago pea, Chag pearl and ICPL-19 grown in pots under greenhouse conditions at four waterlogging treatments (Control, WL1, WL2, WL3, and WL4). Waterlogging treatments resulted in an increase in stomatal resistance, and reduced rates of transpiration and net photosynthesis in all the cultivars, but cultivar differences were not evident. With increasing number of cycles of waterlogging, there were increases in the stomatal resistance and reduction in rates of transpiration and net photosynthesis. Waterlogging also resulted in wilting, chlorosis, senescence and abscission of lower leaves after as little as two days of waterlogging. Leaf area development, dry weight accumulation per plant and partitioning were substantially reduced by waterlogging treatments, but the reduction in leaf area and dry weights were consistently greatest in ICPL-19 than Tobago pea and Chag pearl. The adverse effect of waterlogging observed in this study was associated to the greater degree of root damage in all cultivars which in turn resulted in an increase in the resistance to water flow.

EFFECTS OF ANTI-TRANSPIRANTS ON TRANSPIRATION AND ENERGY USE IN GREENHOUSE CULTIVATION

Greenhouse production in North-West Europe consumes a lot of energy. The energy is needed for heating the greenhouse and controlling air humidity. Transpiration of a crop increases the energy use. The aim of this study was to explore the possibilities for the application of anti-transpirants to save energy by reducing crop transpiration without reducing crop yield. Literature and model calculations were used to explore the effects of increased leaf resistances on transpiration, energy use and production in tomato, cucumber and sweet pepper. In literature a large number of compounds are described that act as anti-transpirant. A two to five fold increase in stomatal resistance can be expected from treatment with anti-transpirants. Model calculations for tomato showed that increasing the stomatal resistance (from 2 to 5 times) throughout the whole year leads to substantial yield reduction: crop growth was reduced by 6-19%, while transpiration by 15-42% and consequently energy use by 9-16%. However, in the winter period (beginning of October/end of March) the growth reduction was only 0.3-1.3%, as in this period light levels are low and CO2 concentrations in the greenhouse are relatively high. Raising the (maximum) set-point for CO2 concentration from 1000 ppm to 3000 ppm, increased the actual concentration during day-time from 892 to 1567 ppm (flue gases were the only source of CO2). When the application of anti-transpirants was combined with raising the set-point for CO2 concentration, the model showed no growth reduction due to the application of anti-transpirants, while the annual energy use was reduced by 5.5-10.4% in tomato. Similar results were obtained for sweet pepper (5-9% energy saving) and cucumber (2-5% energy saving). These model calculations show that increasing stomatal resistance by anti-transpirants during the winter period may potentially save a substantial amount of energy (2-10%), without affecting yield of vegetables such as tomato, cucumber and sweet pepper. It is concluded that increasing the stomatal resistance by anti-transpirants in wintertime may lead to substantial energy saving due to the reduced transpiration and need for humidity management, without yield reduction. Such model calculations are useful to analyse beforehand the chances of a good combination of energy saving and yield loss of a possible application. Experiments will be needed to verify the results

Water Potential Characteristics of Transgenic Petunias Over-expressing Two Arabidopsis C-repeat Binding Factor cDNAs

Petunia × hybrida `Electric Purple' plants, genetically transformed (Selecta Klemm Co.) via Agrobacterium tumefaciens to constitutively express the Cauliflower Mosaic Virus 35S promoter (CaMV35S) fused to two separate Arabidopsis c-repeat binding factor cDNAs (CBF3 & CBF4), were utilized to evaluate water relations. Non-stressed plants followed a classical stomatal conductance pattern, with maximum conductance between 1000 hr and 1400 hr. CBF3 and CBF4 plants showed an increase in transpiration rates and a decrease in stomatal resistance at 1230 hr, compared to `Electric Purple'. Transpiration rates (per unit leaf area) were similar in CBF3 and `Electric Purple' plants, but CBF4 plants were 12% less than `Electric Purple'. Xylem water potentials at visible wilt were between –1.4 and –1.5 MPa and there were no significant differences between line or irrigation treatment. A fourth experiment observed differential plant responses to stress cycles. Under non-stress irrigation conditions, CBF4 plants showed an increase in stomatal resistance and a decrease in transpiration rate compared to `Electric Purple' plants. There were no differences in the xylem water potential at visible wilt for the first and third stress cycles, but, for the second cycle, xylem water potentials at wilt were –1.9, –1.7 and –1.4 Mpa for CBF4, `Electric Purple' and CBF3 plants, respectively. CBF3 and CBF4 plants showed small differences in performance as compared to `Electric Purple' and under mild stress conditions as imposed in these experiments apparent heterologous overexpression of the Arabidopsis CBF3 & 4 transgenes may not be sufficient for conferring drought tolerance in petunia.

Photosynthesis of Eucalyptus globulus with Mycosphaerella leaf disease

Mycosphaerella leaf disease (MLD) is a major cause of foliage damage in Eucalyptus globulus plantations. Our study is the first to describe the physiological effects of MLD on E. globulus leaves. It involved measurements on both field and potted plants. Changes in photosynthetic parameters in response to MLD were quantified in a study using gas exchange techniques. There was a negative linear relationship between light-saturated photosynthesis (A(max)) and leaf-level damage from MLD. Reductions in A(max) were proportionally greater than might be expected from the reduction in green leaf area as a result of the disease, indicating that asymptomatic tissue also was affected by MLD. The reductions in A(max) were not related to increases in stomatal resistance, but were a result of reduced activity of ribulose bisphosphate carboxylase (Rubisco) and changes in the capacity for ribulose bisphosphate (RuBP) regeneration. Changes in mesophyll resistance to CO2 were also implicated. The effect of MLD was similar at different sites and irrespective of tree-level infection, suggesting a general leaf-level response of E. globulus to MLD.

Effects of partial rootzone drying (PRD) on adult olive tree (Olea europaea) in field conditions under arid climate

The limited water availability in the Mediterranean ecosystems and the current and predicted decrease of water resources are leading to the urgent need to reduce water use for irrigation in the arid and semi-arid regions. This study was conducted to evaluate the effects of partial rootzone drying (PRD) irrigation technique on plant growth, yield and water use efficiency of olive tree (Olea europaea) grown under arid conditions in southern Morocco. The PRD consists in exposing one-half of the plant root system to drying soil, whereas the other half is kept in wet soil. Field experiments were conducted on adult olive trees and subjected to four irrigation treatments using a localized irrigation system: Control (irrigated with 100% of ETc on both sides of the root system), PRD1 (irrigation with 50% of the control, on one side of the root system and switched every 2 weeks), PRD2 (same switched every two irrigations: 4 weeks) and PRD3 (with same amount of water than the control applied on one side of the root system, switched every 2 weeks). The PRD treatments affected significantly olive water relations, starting with an increase in stomatal resistance, and subsequently leaf water potential (ψ), with a small non-significant effect on leaf relative water content. The hypothesis of a PRD-induced chemical signal was supported by the observation that stomatal closure was similar in all PRD treatments, including PRD 3, which had exactly the same level and evolution of leaf ψ than the control. The PRD1 and PRD2 treatments induced a slight reduction of the average shoot length, which was comparable to fruit yield reduction. Yield reduction under PRD1 and PRD2 was mainly due to a decrease in fruit numbers, whereas the average olive fruit diameter was slightly higher under PRD1 and PRD2 treatments than the control. Olive yield was significantly higher for the control and PRD3 treatments, compared to PRD1 and PRD2 treatments. The oil percentage in olive fruit and oil acidity did not show any significant differences between PRD treatments and the control. The slight PRD-induced yield reduction (15–20%) compared to the control was achieved with 50% reduction in the total amount of water applied, which resulted in a water use efficiency increase by 60–70% under PRD1 and PRD2 treatments, compared to the control and PRD3.

Stomatic behaviour and leaf water potential in young plants ofAnnona squamosasubmitted to saline stress

Introduction . In saline soils, the water absorption process of the plants is negatively affected, due to the permeability of the roots, leading to hydric stress. Plants under saline stress close their stomas earlier than plants not in these conditions; this causes an increase in stomatal resistance due to the decrease in water potential. The aim of the present research was to detect alterations in the stomatic behaviour and leaf water potential in young plants of Annona squamosa submitted to saline stress. Materials and methods . Sixty-day-old seedlings of A. squamosa were acclimated for 15 days in a greenhouse, before being submitted to different saline treatments. Five treatments (T0 = 0 mM; T1 = 25 mM; T2 = 50 mM; T3 = 75 mM and T4 = 100 mM of NaCl in a nutritive solution) were applied with six replications. The evaluations of the stomatic response occurred on the 20th, 30th, 40th, 60th, 80th and 90th days after the beginning of the saline treatments. The transpiration measures, diffusive resistance and leaf temperature were registered in the first mature leaf. The photosynthetically active radiation, relative humidity and air temperature within the greenhouse were simultaneously assessed 60 and 90 days after the beginning of treatments; then the leaf water potential (Rleaf ) was also measured. Results . During the time of the experiment the leaf temperature and its difference from the air temperature was not affected by NaCl levels, but only 90 days after the beginning of the treatments the values observed in the control plants were lower than those observed in the 25 mM treatment. The diffusive resistance after 40 days was increased in all NaCl treatments. The transpiration, independent of treatment, was reduced by 44.1% (at 60 days) and 13.4% (at 90 days) with the 100-mM treatment compared with the control treatment. The increment in NaCl induced a decrease in Rleaf in all treatments, but an equal reduction was observed for each treatment after 60 and 90 days. Conclusion . The NaCl levels affected the transpiration and leaf water potential; however, the leaf water potential showed an equal reduction in all treatments on the 60th and 90th days.

SALINITY EFFECTS ON FRUIT YIELD IN VEGETABLE CROPS: A SIMULATION STUDY

Salinity can reduce crop growth and yield through its impact on plant water relations by: (1) increased fruit dry matter content, (2) reduced leaf expansion and (3) stomatal closure. In this simulation study the tomato model TOMSIM was used to predict salinity impact on fruit fresh yield, based on single or combined effects through plant water relations. The following influences were tested: Increase in fruit dry matter content (5% at EC=2 dS m-1) by 0.2% per dS m-1; decrease in specific leaf area (SLA) by 8% per dS m-1 starting from a threshold of 3 or 6 dS m-1; increase in stomatal resistance (rs) by a factor 2 or 4 over the range 1 to 10 dS m-1. Simulations showed threshold salinity levels of 2.9-4.4 dS m-1, except when only rs or only SLA was affected (higher threshold). Impact of rs was small as total resistance for CO2 import is determined by a series of resistances in which rs is rather small, under non-stressed conditions. Yield decline in % per dS m-1 varied between 1.9 and 17.8. When only an effect of salinity on rs was simulated this decline was lowest, whereas a salinity effect on SLA from EC=3 dS m-1 onwards, gave the strongest decline per unit rise in EC. Simulations showed that delayed leaf picking or increased plant density mitigate the negative effect of salinity via leaf expansion, as average leaf area index increases. For example, at EC=7 dS m-1 one week delay in leaf picking resulted in 10% yield increase (24.2 instead of 22.0 kg m-2), whereas at EC=9 dS m-1 this was 25% (14.7 instead of 11.8 kg m-2). Applicability of these results, if confirmed by targeted experiments, would not be limited to tomato as the processes described in the model are general.

On ozone dry deposition—with emphasis on non-stomatal uptake and wet canopies

Measurements of O 3 fluxes and concentrations over five different sites were used to study O 3 dry deposition. It was found that high humidity, dew and rain increase O 3 uptake by canopy cuticles. However, the increase by cuticle uptake maybe offset by a decrease in stomatal uptake due to weak solar radiation or stomatal blocking under wet conditions. Thus, during nighttime the overall canopy resistances ( R c) for O 3 uptake under wet conditions was usually smaller than under dry conditions, while in the daytime, R c for wet canopies could be either larger or smaller compared to dry canopies. This will depend on the relative contributions of the decrease in cuticle resistance and the increase in stomatal resistance. The non-stomatal uptake of O 3 was found to be affected by friction velocity, relative humidity, canopy wetness, leaf area index, etc. Parameterizations for non-stomatal resistance for dry and wet canopies were developed based on the five site O 3 flux data. These equations were found to provide reasonable predictions of non-stomatal canopy resistance based upon comparisons with the nighttime and daytime measurements.

Physiological changes and growth of micropropagated chile ancho pepper plantlets during acclimatization and post-acclimatization

Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during acclimatization. Plantlets were transferred to ex vitro conditions to study selected physiological changes and growth performance during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM). Chile pepper plantlets became acclimatized within 6 days after transplantation. During this period, physiological adjustments occurred, which were critical for plantlet survival. After initial ex vitro transplanting, plantlets experienced water deficit [leaf wilting and reduced relative water content (RWC)], which corresponded with reduced stomatal conductance (gs) and transpiration (E), and an increase in stomatal resistance (rs). Thus, leaf stomata that developed in vitro were functional ex vitro. Because of this stomatal control, plantlets minimized transplant shock, recovered and survived. Prior to transplanting, plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, gs, E, and A were significantly lower two days after transplanting. However, within 6 days after transplanting, plantlets recovered and became photoautotrophic – attaining high A, gs, and E. Water use efficiency was initially low during the first days after transplanting, but increased dramatically at the end of the acclimatization period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with increased plantlet growth.

Importance of vegetation feedbacks in doubled‐CO2 climate experiments

The rising atmospheric concentration of carbon dioxide resulting from the burning of fossil fuels and deforestation is likely to provoke significant climate perturbations, while having far‐reaching consequences for the terrestrial biosphere. Some plants could maintain the same intake of CO2 for photosynthesis by reducing their stomatal openings, thus limiting the transpiration and providing a positive feedback to the projected surface warming. Other plants could benefit from the higher CO2 level and the warmer climate to increase their productivity, which would on the contrary promote the transpiration. The relevance of these feedbacks has been investigated with the Météo‐France atmospheric general circulation model. The model has been run at the T31 spectral truncation with 19 vertical levels and is forced with sea surface temperature and sea ice anomalies provided by a transient simulation performed with the Hadley Centre coupled ocean‐atmosphere model. Besides a reference doubled‐CO2 experiment with no modification of the vegetation properties, two other experiments have been performed to explore the impact of changes in the physiology (stomatal resistance) and structure (leaf area index) of plants. Globally and annually averaged, the radiative impact of the CO2 doubling leads to a 2°C surface warming and a 6% precipitation increase, in keeping with previous similar experiments. The vegetation feedbacks do not greatly modify the model response on the global scale. The increase in stomatal resistance does not systematically lead to higher near‐surface temperatures due to changes in the soil wetness annual cycle and the atmospheric circulation. However, both physiological and structural vegetation feedbacks are evident on the regional scale. They are liable to modify the CO2 impact on the hydrological cycle, as illustrated for the case of the European summertime climate and the Asian summer monsoon. The strong sensitivity of the climate in these areas emphasizes the large uncertainties of climate change predictions for some of the most populated regions of the world and argues for the need to include more interactive land surface processes in current generation climate models.

Effects of soil drought during the vegetative phase of seedling growth on the uptake of 14co2 and the accumulation and translocation of 14C in cultivars of field bean (vicia faba L. Var. Minor) and field pea (pisum sativum L.) Of different drought tolerance

During the vegetative phase of growth of two field bean and two field pea cultivars of different drought tolerance, the effect of short and prolonged soil drought on gas exchange (CO2 i H2O), leaf water potential (ψ), stomatal diffusive resistance (rS), uptake of CO2, and the distribution and accumulation of 14C was studied. Differences in the response to drought conditions between resistant and susceptible cultivars were marked. After 5 days of soil drought, the decrease in net photosynthesis and transpiration rate and the increase of stomatal resistance were greater in the drought‐resistant cultivars than in the drought‐susceptible ones. In contrast, after 10 days of drought the decrease of leaf PN (CO2 assimilation rate), E (rate of transpiration) and ψ (water potential) was greater in the susceptible cultivars than in the resistant ones. Significant differences between the resistant and the susceptible cultivars were also observed in the assimilation and translocation of 14C by the green parts of the plant. The amount of carbon accumulation in roots in drought‐susceptible cultivars increased less than in the drought‐resistant cultivars. For treatments in which optimal soil watering was resumed after 5 or 10 days of drought there was no evidence of effects of drought on the majority of measurements, but the drought‐resistant cultivars showed a general tendency for a more rapid recovery. Our results confirm the existence of genetic variability in drought tolerance among the cultivars of field bean and field pea. The recorded differences in the response to drought of experimental cultivars may indicate that, under water deficit in the soil and in plant tissues, they may use different strategies to avoid the damaging effects of temporary limitation of water supply; for example, the drought‐resistant cultivars may more effectively conserve tissue hydration through effective stomatal closure. Also, the observed changes in carbon assimilation and accumulation might be the reason for their different responses to drought. The change in radioactivity losses in the control and stressed plants may result from the differences in demand for energy to maintain cell structure and function. Similarly, the less intense carbon accumulation in the roots of the sensitive cultivars could be caused by more harmful effects of drought on root growth.