Constant Vapor Pressure Deficit Research Articles

Effects of simulated climate change conditions of increased temperature and [CO2] on the early growth and physiology of the tropical tree crop, Theobroma cacao L.

Despite multiple studies of the impact of climate change on temperate tree species, experiments on tropical and economically important tree crops, such as cacao (Theobroma cacao L.), are still limited. Here, we investigated the combined effects of increased temperature and atmospheric carbon dioxide concentration ([CO2]) on the growth, photosynthesis and development of juvenile plants of two contrasting cacao genotypes: SCA 6 and PA 107. The factorial growth chamber experiment combined two [CO2] treatments (410 and 700p.p.m.) and three day/night temperature regimes (control: 31/22°C, control+2.5°C: 33.5/24.5°C and control+5.0°C: 36/27°C) at a constant vapour pressure deficit (VPD) of 0.9kPa. At elevated [CO2], the final dry weight and the total and individual leaf areas increased in both genotypes, while the duration for individual leaf expansion declined in PA 107. For both genotypes, elevated [CO2] also improved light-saturated net photosynthesis (Pn) and intrinsic water-use efficiency (iWUE), whereas leaf transpiration (E) and stomatal conductance (gs) decreased. Under a constant low VPD, increasing temperatures above 31/22 °C enhanced the rates of Pn, E and gs in both genotypes, suggesting that photosynthesis responds positively to higher temperatures than previously reported for cacao. However, dry weight and the total and individual leaf areas declined with increases in temperature, which was more evident in SCA 6 than PA 107, suggesting the latter genotype was more tolerant to elevated temperature. Our results suggest that the combined effect of elevated [CO2] and temperature is likely to improve the early growth of high temperature-tolerant genotypes, while elevated [CO2] appeared to ameliorate the negative effects of increased temperatures on growth parameters of more sensitive material. The evident genotypic variation observed in this study demonstrates the scope to select and breed cacao varieties capable of adapting to future climate change scenarios.

Characterization of land surface energy fluxes in a tropical lowland rice paddy

A field experiment was conducted in 2015 to study the land surface energy fluxes from tropical lowland rice paddy in eastern India with an objective to determine the mass, momentum, and energy exchange rates between rice paddies and the atmosphere. All the land surface energy fluxes were measured by eddy covariance (EC) system (make Campbell Scientific) in dry season (DS, 1–125 Julian days), dry fallow (DF, 126–181 Julian days), wet season (WS, 182–324 Julian days), and wet fallow (WF, 325–365 Julian days). The rice was cultivated in dry season (January–May) and wet season (July–November) in low wet lands and the ground is kept fallow during the remainder of the year. Results showed that albedo varied from 0.09 to 0.24 and showed positive value from morning 6:00 h until evening 18:00 h. Mean soil temperature (Tg) was highest in DF, while the skin temperature (Ts) was highest in WS. Average Bowen ratio (B) ranged from 0.21 to 0.64 and large variation in B was observed during the fallow periods as compared to the cropping seasons. The magnitude of aerodynamic, canopy, and climatological resistances increased with the progress of cropping season and their magnitudes decreased during the end of both cropping seasons and found minimum during the fallow periods. At a constant vapor pressure deficit (VPD) at 0.16, 0.18, 0.15, and 0.43 kPa, latent heat flux (LE) initially increased, but later it tended to level off with an increase in VPD. The actual evapotranspiration (ETa) during both the cropping seasons was higher than the fallow period. This study can be used as a source of default values for many land surface energy fluxes which are required in various meteorological or air-quality models for rice paddies. A larger imbalance of energy was observed during the wet season as the energy is stored and perhaps advected in the fresh water.

Pearl millet (Pennisetum glaucum) contrasting for the transpiration response to vapour pressure deficit also differ in their dependence on the symplastic and apoplastic water transport pathways.

Genotypic differences in transpiration rate responses to high vapour pressure deficit (VPD) was earlier reported. Here we tested the hypothesis that this limitation could relate to different degrees of dependence on the apoplastic (spaces between cells), and symplastic water transport pathways (through cells via aquaporin-facilitated transport), which are known to have different hydraulic conductivities. The low transpiration rate (Tr) genotype PRLT 2/89/33 either restricted its transpiration under high VPD, or was more sensitive to VPD than H77/833-2, when grown hydroponically or in soil. The slope of the transpiration response to an ascending series of VPD was lower in whole plants than in de-rooted shoots. In addition, the transpiration response of detached leaves to moderately high VPD (2.67kPa), normalised against leaves exposed to constant VPD (1.27kPa), was similar in low and high Tr genotypes. This suggested that roots hydraulics were a substantial limitation to water flow in pearl millet, especially under high VPD. The dependence on the apoplastic and symplastic water transport pathways was investigated by assessing the transpiration response of plants treated with inhibitors specific to the AQP-mediated symplastic pathway (AgNO3 and H2O2) and to the apoplastic pathway (precipitates of Cu(Fe(CN)6) or Cu(CuFe(CN)6)). When CuSO4 alone was used, Cu ions caused an inhibition of transpiration in both genotypes and more so in H77/833-2. The transpiration of high Tr H77/833-2 was decreased more by AQP inhibitors under low VPD (1.8kPa) than in PRLT 2/89/33, whereas under high VPD (4.2kPa), the transpiration of PRLT 2/89/33 was decreased more by AQP inhibitors than in H77/833-2. The transpiration rate of detached leaves from H77/833-2 when treated with AgNO3 decreased more than in PRLT 2/89/33. Although the root hydraulic conductivity of both genotypes was similar, it decreased more upon the application of a symplastic inhibitor in H77/833-2. The transpiration of low Tr PRLT 2/89/33 was decreased more by apoplastic inhibitors under both low and high VPD. Then the hydraulic conductivity decreased more upon the application of an apoplastic inhibitor in PRLT 2/89/33. In conclusion, both pathways contributed to water transport, and their contribution varied with environmental conditions and genotypes. Roots were a main source of hydraulic limitation in these genotypes of pearl millet, although a leaf limitation was not excluded. The similarity between genotypes in root hydraulic conductivity under normal conditions also suggests changes in this conductivity upon changes in the evaporative demand. The low Tr genotype depended more on the apoplastic pathway for water transport, whereas the high Tr genotype depended on both pathway, may be by 'tuning-up' the symplastic pathway under high transpiration demand, very likely via the involvement of aquaporins.

Stomatal conductance increases with rising temperature

ABSTRACTStomatal conductance directly modifies plant water relations and photosynthesis. Many environmental factors affecting the stomatal conductance have been intensively studied but temperature has been largely neglected, even though it is one of the fastest changing environmental variables and it is rising due to climate change. In this study, we describe how stomata open when the temperature increases. Stomatal conductance increased by ca 40% in a broadleaf and a coniferous species, poplar (Populus deltoides x nigra) and loblolly pine (Pinus taeda) when temperature was increased by 10 °C, from 30 °C to 40 °C at a constant vapor pressure deficit of 1 kPa. The mechanism of regulating stomatal conductance by temperature was, at least partly, independent of other known mechanisms linked to water status and carbon metabolism. Stomatal conductance increased with rising temperature despite the decrease in leaf water potential, increase in transpiration, increase in intercellular CO2 concentration and was decoupled from photosynthesis. Increase in xylem and mesophyll hydraulic conductance coming from lower water viscosity may to some degree explain temperature dependent opening of stomata. The direct stomatal response to temperature allows plants to benefit from increased evaporative cooling during the heat waves and from lower stomatal limitations to photosynthesis but they may be jeopardized by faster depletion of soil water.

The effect of blue light on stomatal oscillations and leaf turgor pressure in banana leaves.

Stomatal oscillations are cyclic opening and closing of stomata, presumed to initiate from hydraulic mismatch between leaf water supply and transpiration rate. To test this assumption, mismatches between water supply and transpiration were induced using manipulations of vapour pressure deficit (VPD) and light spectrum in banana (Musa acuminata). Simultaneous measurements of gas exchange with changes in leaf turgor pressure were used to describe the hydraulic mismatches. An increase of VPD above a certain threshold caused stomatal oscillations with variable amplitudes. Oscillations in leaf turgor pressure were synchronized with stomatal oscillations and balanced only when transpiration equaled water supply. Surprisingly, changing the light spectrum from red and blue to red alone at constant VPD also induced stomatal oscillations - while the addition of blue (10%) to red light only ended oscillations. Blue light is known to induce stomatal opening and thus should increase the hydraulic mismatch, reduce the VPD threshold for oscillations and increase the oscillation amplitude. Unexpectedly, blue light reduced oscillation amplitude, increased VPD threshold and reduced turgor pressure loss. These results suggest that additionally, to the known effect of blue light on the hydroactive opening response of stomata, it can also effect stomatal movement by increased xylem-epidermis water supply.

Predictability of keeping quality of strawberry batches

Postharvest life of strawberries is largely limited by Botrytis cinerea infection. It is assumed that there are two factors influencing the batch keeping quality: the Botrytis pressure and the resistance of the strawberry to infection. The latter factor will be discussed in this article. A colour model is presented that describes the development of red colour and anti-fungal function of individual strawberries over time. The model was fitted to colour data from strawberries grown at two different nutrient densities (EC) and stored per batch at 5, 10 or 16 °C and constant vapour pressure deficit after harvest. A batch was defined as all strawberries from one EC and one harvest. Spoilage per batch was recorded daily during storage. The fitted initial spoilage per batch was found to relate to the fitted average amount of precursor of both the colour and the anti-fungal compounds. Batch keeping quality could be derived from the initial batch colour distributions for the low nutrient batches. Also, batch keeping quality correlated highly with the time between harvest dates for the low EC batches. An explanation for the ability to link colour distributions to keeping quality without having to use a term describing the pH is presented from pigment HPLC measurements of sub-batches. Indications that the colour distributions of high EC batches may be subject to substantial co-pigmentation are presented. For a practical implementation of predicting keeping quality of batches additional research is needed, especially regarding different Botrytis pressures between greenhouses.

Influence of temperature and vapor pressure deficit on the rate of predation by the predatory mite, Amblyseius cucumeris, on Frankliniella occidentalis

AbstractThe influence of temperature and vapor pressure deficit (VPD) on the rate of predation by the predatory mite, Amblyseius cucumeris (Oudemans) on Frankliniella occidentalis (Pergande) was determined under controlled laboratory conditions. The survival of first instars of F. occidentalis was initially determined by themselves. Then the number of first instars that were killed by a single female adult of A. cucumeris was determined for the same density of thrips. The differences in the mortality between the two experiments were used to calculate the rate of predation by A. cucumeris under a range of temperature and VPD regimes. Rate of predation was expressed as the number of thrips killed per h to account for the different time periods that the trials lasted. A quadratic model was fitted to the data. At a constant temperature, the rate of predation decreased with increasing VPD for VPDs ≤ 1.24 to 1.44 kPa. Above these VPDs, the rate of predation started to increase again. At a constant VPD, the rate of predation decreased slightly at the lower temperatures and increased at the higher temperatures. The rate of change was dependent upon the VPD. By using the quadratic model, the rate of predation can be predicted for the range of hygrothermal conditions that would be encountered in the greenhouse. The optimal condition for maximum rate of predation by A. cucumeris on first instars of F. occidentalis in the greenhouse is a VPD ≤ 0.75 kPa at the recommended production temperatures and VPDs (17 to 25°C and ≤ 1.5 kPa).

Leaf Emergence on Potato Stems in Relation to Thermal Time

AbstractFor simulation of foliar development of potato plants (Solanum tuberosum L.), it is necessary to quantify the responses of leaf emergence to major environmental factors. This study was conducted to determine the relationship of leaf emergence on potato stems to growing degreedays (GDD) under varied temperature patterns over different growth periods. In each of two duplicate experiments in controlled environments, potato plants were grown for 63 d after transplanting of tissue culture plantlets into 20‐L pots containing peat‐vermiculite mix. Four treatments were maintained, involving two constant temperatures of 17 and 22°C and two changed temperatures of 17‐22‐17 and 22‐17‐22°C over three 21‐d periods under constant vapor pressure deficit of 0.60 kPa and photosynthetic photon flux density of 430 µmol m−2 s−1 for a 14‐h photoperiod. The first period was the first 21 d of plant growth after transplanting, the second 21‐d period coincided with plant enlargement and tuber initiation, and the third period coincided with tuber enlargement. Leaf numbers on main stems and uppermost apical branches were recorded every 2 to 3 d during the course of the experiments. This leaf number increased linearly with accumulated GDD over the whole experiment duration for each of the four treatments, whether the temperature was constant or changed. The phyllochron in GDD per leaf (6°C base temperature) was lowest at constant 17°C (19.2 GDD), highest at constant 22°C (22.8 GDD), and intermediate at the changed temperatures ( ≈21.3 GDD). Detailed analysis of the leaf emergence rates during each of the three 21‐d periods indicates that the phyllochron at either 17 or 22°C was also slightly lower during the second 21‐d period than during the first and third 21‐d periods. The total leaf number increased with increasing total GDD among the treatments, primarily from varied leaf number on apical branches. The data suggest that a constant phyllochron for a given growth location and calendar time may provide sufficient accuracy for predicting leaf emergence on potato stems in the field environment.

Phasic Temperature Change Patterns Affect Growth and Tuberization in Potatoes

This study determined the responses of potato (Solanum tuberosum L., cv. Norland) plants to various patterns of air temperature changes over different growth periods (phasic temperature changes). In each of two experiments under controlled environments, eight treatments of temperature changes were carried out in two growth rooms maintained at 17 and 22C and a constant vapor pressure deficit of 0.60 kPa and 14-hour photoperiod. Plants were grown for 63 days after transplanting of tissue culture plantlets in 20-liter pots containing peat-vermiculite mix. Temperature changes were imposed on days 21 and 42, which were essentially at the beginning of tuber initiation and tuber enlargement, respectively, for this cultivar. Plants were moved between two temperature rooms to obtain eight temperature change patterns: 17-17-17, 17-17-22, 17-22-17, 22-17-17, 17-22-22, 22-17-22, 22-22-17, and 22-22-22C over three 21-day growth periods. At harvest on day 63, total plant dry weight was higher for the treatments beginning with 22C than for those beginning with 17C, with highest biomass obtained at 22-22-17 and 22-17-17C. Shoot dry weight increased with temperature increases from 17-17-17 to 22-22-22C during the three growth periods. Tuber dry weight was highest with 22-17-17C, and lowest with 17-17-22 and 17-22-22C. With 22-17-17C, both dry weights of stolons and roots were lowest. Total tuber number and number of small tubers (<2.5 cm) were highest with 17-17-17 and 17-17-22C, and lowest with 17-22-22 and 22-22-22C, whereas number of medium tubers (2.5-5.0 cm) was highest with 22-17-22C, and number of large tubers (>5.0 cm) was highest with 22-17-17C. This study indicates that tuber development of potatoes is optimized with a phasic pattern of high temperature during early growth and low temperature during later growth.

Influence of climatic and nutritional factors on yeast population dynamics in the phyllosphere of wheat

The role of saprophytic phyllosphere yeasts in removing aphid honeydew and other nutrients from wheat leaves was evaluated in growth cabinet experiments at different temperatures and relative humidities. Population densities of both pink and white yeasts (Sporobolomyces roseus and Cryptococcus laurentii, respectively) increased between 12 and 24°C, if nutrients were supplied. White yeast numbers increased rapidly at a constant vapor pressure deficit (VPD) of 0.10 kPa and alternating VPDs of 0.10 and 0.61 kPa (each 12 hours per day) but decreased at a constant VPD of 0.61 kPa. In growth cabinet experiments with aphids on wheat plants, the amount of aphid honeydew on the leaves was lower when yeast population densities were high. Addition of amino acids to leaves with honeydew had no effect on yeast population density or the rate of honeydew consumption. This indicated that low concentrations of amino acids in aphid honeydew are not a limiting factor for honeydew consumption by the yeasts. The naturally occurring saprophytes efficiently removed fructose, sucrose, and melezitose from the phyllosphere of field-grown wheat plants.

Effect of vapor pressure deficit on photosynthesis of rice leaves with reference to light and CO2 utilization efficiency.

In our previous studies on diurnal courses of photosynthesis, transpiration and diffusive conductance of the leaf in the rice plants grown in the paddy field, it was recoginized that the photosynthetic rate decreased with the decreasse of diffusive conductance due to high vapor pressure deficit under sufficient light intensity in the fine midday. It has been pointed out that water stress affects photosynthetic rate through the decrease of both CO2 supply to mesophyll through stomata and photosynthetic activity in mesophyll. This study was conducted to examine whether high vapor pressure deficit reduced photosynthetic activity by measuring light and CO2 utilization efficiencies at low quantum flux density and CO2 concentration under different vapor pressure deficit, respectively. The results were as follows : 1) Transpiration rate increased rapidly, and photosynthetic rate, diffusive conductance and intercellular CO2 concentration (Ci) decreased gradually with changing vapor pressure deficit from low to high (Figs. 1 and 2). 2) Light utilization efficiency, which was shown by the degree of inclination of light dependent straight line of photosynthesis under low quantum flux density, decreased under high vapor pressure deficit (Figs. 3 and 4). And also CO2 utilization efficiency, shown by the degree of inclination of the straight line expressing the relation between photosynthetic rate and low intercellular CO2 concentration, decreased under high vapor pressure deficit (Figs. 5, 6 and 7). As light and CO2 utilization efficiencies were thought to indicate photochemical and carboxylation activity of photosynthesis, respectively, it was suggested that not only diffusive conductance but also photosynthetic activity related to photochemical and carboxylation activities were affected by high vapor pressure deficit. 3) Intercellular CO2 concentration decreased with the decrease of photosynthetic rate and diffusive conductance under high vapor pressure deficit (Fig. 1). Furthermore, it was found that the degree of inclination of the straight line, expressing the relation between ambient CO2 and intercellular CO2 concentrations, was smaller under high vapor pressure deficit than that under low vapor pressure deficit (Fig. 9). These facts indicated that the decreasing of diffusive conductance was more effective on the decrease of photosynthesis under high vapor pressure deficit than the decreasing of photosynthetic activity. 4) The three following equations were obtained on the basis of the relation between intercellular CO2 concentration and photosynthetic rate (Fig. 6) and on the fact that transpiration rate was proportional to diffusive conductance under constant vapor pressure deficit. In this case, GAASTRA's concept was also considered. P=(44.99×C)/(C+0.377) Ci=(350×C+18.86)/(C+0.377) T=3.43×C The figure (Fig.8) drawn by using these equations showed that the relations between diffusive conductance (C) and photosynthetic rate (P) and between diffusive conductance and intercellular CO2 concentration (Ci) were hyperbollic, while the relation between diffusive conductance and transpiration rate (T) was linear. Thus, if diffusive conductance were decreased without decreasing the photosynthetic activity in mesophyll, water use efficiency (photosynthetic rate to transpiration rate ratio) could be increased.

Drying Rates of Intact Burley Tobacco Plant Components

ABSTRACT DRYING rates of the lamina, midrib, and stalk of intact burley tobacco plants were determined at temperatures and relative humidities of 16 C, 70%; 24 C, 70%; and 32 C, 70% during test 1, at 16 C, 51%; 24 C, 70%; and 32 C, 83% during test 2, and at 27 C, 70%; 27 C, 80%; and 27 C, 90% during test 3. Air velocity was held constant at 4.6 m/min. The environmental conditions were designed to determine drying rates at constant humidity and varying temperature during test 1, at constant vapor pressure deficit and varying temperature during test 2 and at constant temperature and varying relative humidity during test 3. The results showed that the stalk is an important contributor of moisture to the environment during curing. The average time required for the lamina, midrib and stalk to lose half their moisture was 4.4, 8.7, and 38.3 days, respectively.

Corn Earworm:1 Effects of Temperature Variation on a Colony2, 3

Under a constant vapor pressure deficit of 8.41 mm Hg, a holding temperature of 30.0°C produced the most rapid development of the corn earworm, Heliothis zea (Boddie). However, oviposition and fertility were greater when the larvae and pupae were held at lower temperatures. Under constant temperature conditions, adults held at 25.6° and 22.2°C were both more fecund and more fertile than those held at 28.9° and 18.9°C. Incorporation of this high temperature (28.9°C) into a fluctuating temperature regimen had no measurable effects on egg production and hatch. A high temperature of 32.2°C in a variable temperature regimen lowered egg hatch for one group of adults but had no effect on an apparently healthier group.

Effect of Temperature, Vapour-Pressure Deficit and Irradiance on Transpiration Rates of Maize, Paspalum, Westerwolds and Perennial Ryegrasses, Peas, White Clover and Lucerne

Rates of water use [g H2O (g dry wt leaf)-1 h-1] of young plants of maize, paspalum, perennial ryegrass, Westerwolds ryegrass, peas, white clover and lucerne were measured during the day under controlled climate conditions with ample water available to the plant. Plants were grown and observations made with day/night temperatures of 32.5/27.5°C, 27.5/22.5°, 22.5/17.5°, and 17.5/12.5°C with a day/night vapour pressure deficit (VPD) of the air of 10/2mbar. Water use measurements were also made at 27.5/22.5° and 17.5/12.5°C under day/night VPD regimes of 5/2 and 15/2 mbar. Irradiance during the 12-h day was 170 W m-2 (400-700 nm). Further water use determinations were made at the four temperature regimes under 10/2 mbar VPD and an irradiance of 60 W m-2 (400-700 nm). For a given species, transpiration rates increased with temperature at constant VPD under both irradiance environments, by factors ranging from 1.4 to 2.3. Transpiration rates of maize and paspalum (C4) were lower at a given temperature than were the rates of the C3 species, while lucerne and clover had the highest rates. Water use by lucerne was 2.5 to 3.5 times that of maize. Transpiration rates of maize and paspalum were lower under 60 W m-2 than under 170 W m-2 but irradiance had little effect on transpiration rate of the C3 species. Though transpiration rate generally increased with increasing VPD, the difference in rates between plants at 5 mbar and 10 mbar VPD was much greater than between 10 mbar and 15 mbar. The physiological adaption of different species to their growth environment is discussed, and the implications of the results with reference to water loss by young, single-spaced plants in the field is outlined.

Studies on the water economy of some Australian frogs.

The rate of evaporative water loss of several species of frog found in Australia and their ability to survive at high temperatures were studied at various temperatures in both dry and in humid air, and at constant vapour pressure deficit. The species studied were: Bufonidae, Bufo marinus (L.); Leptodactylidae, Crinia signifera Girard, Pseudophryne bibroni Gunther, Limnodynastes tasmaniensis Gunther, L. dorsalis (Gray), L. ornatus (Gray), Neobatrachus pictus Peters, N. centralis (Parker); Hylidae, Hyla ewingi (Dumeril & Bibron) and H. rubella Gray. To a certain extent, the trend for increased adaptation to terrestrial conditions follows the trend for reduced water loss. The rate of water uptake after dehydration is greatest in the burrowing frogs inhabiting arid and semi-arid regions. Survival at high temperatures in dry air was found to be a good criterion for judging the degree of adaptation of these frogs to life in arid regions.