Effect Of Vapor Pressure Deficit Research Articles

Effect of vapor pressure deficit on growth and water status in muskmelon and cucumber

Climatic warming and water shortages have become global environmental issues affecting agricultural production. The change of morphology and anatomical structures in plant organs can greatly affect plant growth. The study combined temperature and relative humidity to regulate vapor pressure deficit (VPD) to form low and high VPD environments (LVPD and HVPD, respectively) in two climate-controlled greenhouses. The effects of different VPD conditions on gas exchange parameters, dry matter, and leaf and stem anatomical structure parameters of muskmelon and cucumber were compared and studied. The results show that the background VPD conditions give different internal structure of muskmelon and cucumber, therefore it can improve the transport capacity of water to the leaf surface under LVPD conditions. At the same time, the stomatal closure induced by atmospheric drought stress is avoided and the gas exchange capacity of the leaf stomata is enhanced, thereby maintaining high photosynthetic rate. Thus, reducing VPD is the key to achieving high yield and productivity in greenhouse muskmelon and cucumber production.

Empirical evidence for resilience of tropical forest photosynthesis in a warmer world.

Tropical forests may be vulnerable to climate change1-3 if photosynthetic carbon uptake currently operates near a high temperature limit4-6. Predicting tropical forest function requires understanding the relative contributions of two mechanisms of high-temperature photosynthetic declines: stomatal limitation (H1), an indirect response due to temperature-associated changes in atmospheric vapour pressure deficit (VPD)7, and biochemical restrictions (H2), a direct temperature response8,9. Their relative control predicts different outcomes-H1 is expected to diminish with stomatal responses to future co-occurring elevated atmospheric [CO2], whereas H2 portends declining photosynthesis with increasing temperatures. Distinguishing the two mechanisms at high temperatures is therefore critical, but difficult because VPD is highly correlated with temperature in natural settings. We used a forest mesocosm to quantify the sensitivity of tropical gross ecosystem productivity (GEP) to future temperature regimes while constraining VPD by controlling humidity. We then analytically decoupled temperature and VPD effects under current climate with flux-tower-derived GEP trends in situ from four tropical forest sites. Both approaches showed consistent, negative sensitivity of GEP to VPD but little direct response to temperature. Importantly, in the mesocosm at low VPD, GEP persisted up to 38 °C, a temperature exceeding projections for tropical forests in 2100 (ref. 10). If elevated [CO2] mitigates VPD-induced stomatal limitation through enhanced water-use efficiency as hypothesized9,11, tropical forest photosynthesis may have a margin of resilience to future warming.

Growth stage-dependent responses of carbon fixation process of alpine grasslands to climate change over the Tibetan Plateau, China

Alpine grassland ecosystem on the Tibetan Plateau (TP) is highly sensitive to climate change and plays a critical role in terrestrial carbon cycle. However, the long-term responses of alpine grassland ecosystem carbon fluxes to climate change at different growth stages and their controlling mechanisms have not been well understood. In this study, we quantified the spatial and temporal variations of gross primary productivity (GPP) and net ecosystem productivity (NEP) of alpine grassland ecosystems from 1982 to 2015 based on an improved Biome-BGC model, and then we examined how different climate factors (i.e., soil moisture, temperature, vapor pressure deficit (VPD), and solar shortwave radiation) affected GPP and NEP dynamics at different growth stages (i.e., the early rapid growth, physiological maturity, and senescence stages) using partial correlation analysis. Furthermore, the relative contributions of different climate factors on GPP and NEP dynamics were also analyzed using path analysis model. The results showed that both GPP and NEP of alpine grassland ecosystems increased significantly during the past 34 years, and the responses of GPP and NEP to climate change and their dominant climate factors significantly varied at different growth stages. Specifically, temperature severely limited the productivity of most alpine grasslands at all growth stages, and soil moisture played an increasingly important role in vegetation carbon fixation before senescence stage, while the effects of VPD and solar shortwave radiation on vegetation carbon fixation were relatively weak. Our study suggested that a finer temporal scale (e.g., the growth stage basis) should be considered to reveal the complex relationships between climate change and the variations of ecosystem carbon fluxes, which could provide a new sight to understand the mechanisms of terrestrial ecosystem's responses to global climate change.

Atmospheric CO2 and VPD alter the diel oscillation of leaf elongation in perennial ryegrass: compensation of hydraulic limitation by stored-growth.

We explored the effects of atmospheric CO2 concentration (Ca ) and vapor pressure deficit (VPD) on putative mechanisms controlling leaf elongation in perennial ryegrass. Plants were grown in stands at a Ca of 200, 400 or 800μmolmol-1 combined with high (1.17kPa) or low (0.59kPa) VPD during the 16h-day in well-watered conditions with reduced nitrogen supply. We measured day:night-variation of leaf elongation rate (LERday :LERnight ), final leaf length and width, epidermal cell number and length, stomatal conductance, transpiration, leaf water potential and water-soluble carbohydrates and osmotic potential in the leaf growth-and-differentiation zone (LGDZ). Daily mean LER or morphometric parameters did not differ between treatments, but LERnight strongly exceeded LERday , particularly at low Ca and high VPD. Across treatments LERday was negatively related to transpiration (R2 =0.75) and leaf water potential (R2 =0.81), while LERnight was independent of leaf water potential or turgor. Enhancement of LERnight over LERday was proportional to the turgor-change between day and night (R2 =0.93). LGDZ sugar concentration was high throughout diel cycles, providing no evidence of source limitation in any treatment. Our data indicate a mechanism of diel cycling between daytime hydraulic and night-time stored-growth controls of LER, buffering Ca and daytime VPD effects on leaf elongation.

Effects of Vapor Pressure Deficit and Potassium Supply on Root Morphology, Potassium Uptake, and Biomass Allocation of Tomato Seedlings

Atmospheric humidity, defined as the vapor pressure deficit (VPD), is an important factor affecting plant transpiration and nutritional status. Previous work has focused on the relationship between VPD and nitrogen metabolism; however, little is known about potassium (K) responses to VPD. Here, we investigated the effects of VPD and K supply on root morphology, potassium uptake, and plant growth with tomato (Solanum lycopersicum L., cv. Jinpeng). Experiments were conducted in greenhouses under low and high VPD conditions and featured three levels of K nutrient solution supply (2, 4, and 8 mmol/L). Characteristics of root morphology were significantly promoted by low VPD, including root length, root volume, root diameter, root surface area, number of fine roots, and proportion of fine roots, which combined were more conducive to the absorption of nutrients; low VPD reduced the transpiration rate, but the K accumulation by plants showed an increasing trend, indicating increased root morphology parameters could compensate for the impact of reduced transpiration-driven mass flow on K uptake. Meanwhile, higher biomass also promotes the accumulation of potassium. Photosynthesis is promoted due to increased potassium accumulation in the leaves, which in turn increases plant biomass, especially with moderate K supply. Furthermore, low VPD increases biomass allocation in leaves and reduces biomass allocation in stems but, in contrast, relatively more potassium is allocated to stems and roots but less to foliage. In summary, low VPD promotes K uptake by facilitating root system development in summer greenhouses. This result provides new knowledge for enhancing potassium utilization efficiency and reducing the use of chemical fertilizers.

Soil water deficit promotes the effect of atmospheric water deficit on solar-induced chlorophyll fluorescence

Solar-induced chlorophyll fluorescence (SIF) is a novel optical signal that has been successfully used to track plant dynamics with the influence of soil water deficit. However, the effect of atmospheric water deficit on SIF under the impact of soil water deficit still remains unclear. Here, continuous measurements of SIF (at 760 nm, F760) of winter wheat under different soil water deficit were collected with a self-developed system. Additionally, soil moisture and atmosphere parameters [including air temperature (Ta), relative air humidity (Rh), and photosynthetically active radiation at 400–700 nm (PAR)] were also synchronously collected by common commercial devices. Vapor pressure deficit (VPD) was calculated based on the measurements of Ta and Rh. The results showed that the driving effect of PAR on F760 was obvious as we expected. Additionally, such effects of PAR on AF760 (F760/PAR) and Fy760 (F760/L685, L685 was canopy radiance at 685 nm) still existed when the PAR influences were partially removed by the calculation of F760/PAR and F760/L685. Furthermore, the relationship of PAR with AF760 or Fy760 was observed to be strengthened under the situation of water deficit through the analysis of Pearson correlations. With the influence of PAR, the accelerative effect of VPD on SIF under soil water deficit was not always observed in our study. Nevertheless, when the effect of PAR was removed by using partial correlation, VPD showed much stronger correlation with SIF in soil water stressed plot than that in unstressed one both at diurnal and seasonal scales. These results revealed that soil water deficit might promote the effect of atmospheric water deficit on SIF. This study has great significance for the application of SIF in drought monitoring and health assessments in terrestrial ecosystem.

Environmental influences on light response parameters of net carbon exchange in two rotation croplands on the North China Plain

The ecosystem light response parameters, i.e. apparent quantum yield (α), maximum rate of ecosystem gross photosynthesis (Amax), and daytime ecosystem respiration (Rd), are very important when estimating regional carbon budgets. But they are not well understood in double cropping systems. Here, continuous flux data were collected from two rotation croplands in Yucheng (YC) and in Luancheng (LC) to describe the among-year variations in α, Amax, and Rd, and to investigate variation mechanism on an annual scale. The three parameters exhibited marked fluctuations during the observation years. The annual α, Amax, and Rd ranged from 0.0022–0.0059 mg CO2 μmol photon−1, from 2.33–4.43 mg CO2 m−2 s−1, and from 0.19–0.47 mg CO2 m−2 s−1 at YC, and from 0.0016–0.0021 mg CO2 μmol photon−1, from 3.00–6.30 mg CO2 m−2 s−1, and from 0.06–0.19 mg CO2 m−2 s−1 at LC, respectively. Annual α and Rd declined significantly when vapor pressure deficit (VPD) exceeded 1.05 kPa and increased significantly when canopy conductance (gc) exceed 6.33 mm/s at YC, but changed slightly when VPD and gc exceeded 1.16 kPa and 7.77 mm/s at LC, respectively. The fact that the negative effects of VPD and gc on α and Rd at LC were not as significant as they were at YC may be attributed to different climate conditions and planting species. A negative relationship (R2 = 0.90 for YC and 0.89 for LC) existed between VPD and gc. Therefore, the VPD, through its negative effect on gc, inhibited α and Rd indirectly. Among-year Amax variation was mainly influenced by the annual mean surface soil temperature (Ts) of non-growing season of wheat significantly (R2 = 0.59, P < 0.01). Therefore, in future climate change scenarios, these environmental effects need to be included in carbon cycle models so that the accuracy of the carbon budget estimation can be improved.

Development of an In Vivo Sensor to Monitor the Effects of Vapour Pressure Deficit (VPD) Changes to Improve Water Productivity in Agriculture.

Environment, biodiversity and ecosystem services are essential to ensure food security and nutrition. Managing natural resources and mainstreaming biodiversity across agriculture sectors are keys towards a sustainable agriculture focused on resource efficiency. Vapour Pressure Deficit (VPD) is considered the main driving force of water movements in the plant vascular system, however the tools available to monitor this parameter are usually based on environmental monitoring. The driving motif of this paper is the development of an in-vivo sensor to monitor the effects of VPD changes in the plant. We have used an in vivo sensor, termed “bioristor”, to continuously monitor the changes occurring in the sap ion’s status when plants experience different VPD conditions and we observed a specific R (sensor response) trend in response to VPD. The possibility to directly monitor the physiological changes occurring in the plant in different VPD conditions, can be used to increase efficiency of the water management in controlled conditions thus achieving a more sustainable use of natural resources.

The role of ambient temperature and body mass on body temperature, standard metabolic rate and evaporative water loss in southern African anurans of different habitat specialisation.

Temperature and water availability are two of the most important variables affecting all aspects of an anuran’s key physiological processes such as body temperature (Tb), evaporative water loss (EWL) and standard metabolic rate (SMR). Since anurans display pronounced sexual dimorphism, evidence suggests that these processes are further influenced by other factors such as vapour pressure deficit (VPD), sex and body mass (Mb). However, a limited number of studies have tested the generality of these results across a wide range of ecologically relevant ambient temperatures (Ta), while taking habitat use into account. Thus, the aim of this study was to investigate the role of Ta on Tb, whole-animal EWL and whole-animal SMR in three wild caught African anuran species with different ecological specialisations: the principally aquatic African clawed frog (Xenopus laevis), stream-breeding common river frog (Amietia delalandii), and the largely terrestrial raucous toad (Sclerophrys capensis). Experiments were conducted at a range of test temperatures (5–35 °C, at 5 °C increments). We found that VPD better predicted rates of EWL than Ta in two of the three species considered. Moreover, we found that Tb, whole-animal EWL and whole-animal SMR increased with increasing Ta, while Tb increased with increasing Mb in A. delalandii and S. capensis but not in X. laevis. Whole-animal SMR increased with increasing Mb in S. capensis only. We did not find any significant effect of VPD, Mb or sex on whole-animal EWL within species. Lastly, Mb did not influence Tb, whole-animal SMR and EWL in the principally aquatic X. laevis. These results suggest that Mb may not have the same effect on key physiological variables, and that the influence of Mb may also depend on the species ecological specialisation. Thus, the generality of Mb as an important factor should be taken in the context of both physiology and species habitat specialisation.

Vapour pressure deficit: The hidden driver behind plant morphofunctional traits in controlled environments

AbstractCurrently, climate change is threatening farming opportunities to feed a growing population, making necessary the implementation of worldwide cultivable lands, also through the improvement of highly intensified cropping systems such as greenhouses and indoor growing modules. To ameliorate plant performance and reach the potential yield in controlled environment, these systems should be based on the fine control of all microclimatic factors among which vapour pressure deficit (VPD) plays a major role. VPD represents a driver for transpiration in plants, and it is crucial in inducing specific plant structure and physiological behaviour. VPD changes with relative air humidity and temperature, and through its control it is possible to regulate the entire evaporative demand of an indoor cultivation. Therefore, VPD control becomes critical to improve plant growth and productivity. The regulation of VPD in controlled environment should be managed dynamically because VPD can modulate morphophysiological processes in plants, which adapt to the new environmental conditions and in turn, modify the environment itself, thus requiring the continuous update of VPD according to phenological phases. The aim of this review is to report VPD effects on plant growth and physiological processes as carbon metabolism and water use efficiency in controlled environments. Available information about the wide variety of VPD effects on different plant traits and species is summarised, considering the structure‐mediated regulation of water fluxes in plant. Towards the goal of optimising cultivation strategies in protected agriculture, the importance of considering possible interaction between VPD and other microclimatic factors is highlighted. Finally, future research areas, which should be explored further, based on needed synergies among different expertise from biological and horticultural fields, are identified and discussed.

Maize yield under a changing climate: The hidden role of vapor pressure deficit

Temperatures over the next century are expected to rise to levels detrimental to crop growth and yield. As the atmosphere warms without additional water vapor input, vapor pressure deficit (VPD) increases as well. Increased temperatures and accompanied elevated VPD levels can both lead to negative impacts on crop yield. The independent importance of VPD, however, is often neglected or conflated with that from temperature due to a tight correlation between the two climate factors. We used a coupled process-based crop (MAIZSIM) and soil (2DSOIL) model to gain a mechanistic understanding of the independent roles temperature and VPD play in crop yield projections, as well as their interactions with rising CO2 levels and changing precipitation patterns. We found that by separating out the VPD effect from rising temperatures, VPD increases had a greater negative impact on yield (12.9 ± 1.8%, increase in VPD associated with 2 °C warming) compared to that from warming (8.5 ± 1.4%, the direct effect of 2 °C warming). The negative impact of these two factors varied with precipitation levels and influenced yield through separate mechanisms. Warmer temperatures caused yield loss mainly through shortening the growing season, while elevated VPD increased water loss and triggered several water stress responses such as reduced photosynthetic rates, lowered leaf area development, and shortened growing season length. Elevated CO2 concentrations partially alleviated yield loss under warming or increased VPD conditions through water savings, but the impact level varied with precipitation levels and was most pronounced under drier conditions. These results demonstrate the key role VPD plays in crop growth and yield, displaying a magnitude of impact comparative to temperature and CO2. A mechanistic understanding of the function of VPD and its relation with other climate factors and management practices is critical to improving crop yield projections under a changing climate.

Coordination between vapor pressure deficit and CO2 on the regulation of photosynthesis and productivity in greenhouse tomato production

The high vapor pressure deficit (VPD) in some arid and semi-arid climates creates undesirable conditions for the growth of tomato plants (Solanum lycopersicum L., cv. Jinpeng). The global CO2 concentration ([CO2]) has also risen in recent years to levels above 400 μmol·mol−1. However, the coordinated effect of VPD and [CO2] on tomato plant growth remains unclear, especially at VPDs of 5–6 kPa or even higher that are extremely detrimental to plant growth. Here, we explore the interaction of VPD and [CO2] on plant water status, stomatal characteristics, and gas exchange parameters in summer greenhouses in a semi-arid area. Plants were grown in four adjacent glass greenhouses with different environmental conditions: (i) high VPD + low [CO2] representing natural/control conditions; (ii) high VPD + high [CO2] representing enriched CO2; (iii) low VPD + low [CO2] representing reduced VPD; and (iv) low VPD + high [CO2] representing reduced VPD and enriched CO2. Reducing the VPD alleviated the water stress of the plant and increased the gas exchange area of the leaf, which was beneficial to the entry of CO2 into the leaf. At this time, the increase of [CO2] was more beneficial to promote the photosynthetic rate and then improve the water use efficiency and yield.

Water use efficiency and its influencing factors of Platycladus orientalis plantation in Beijing mountains area, China.

Water use efficiency (WUE) is an important index to evaluate plant drought resistance. Studying the dynamics of WUE and its influencing factors can provide reference for the vegetation restoration in Beijing mountainous area. We measured WUE of Platycladus orientalis in growing season and investigated the influence of meteorological factors, soil factors, and atmospheric CO2 concentration on WUE, based on the stable carbon isotope techniques. The results showed that: 1) The short-term WUE decreased and then increased in the growing season, with minimum value (2.69 mmol·mol-1) in July and maximum value (13.88 mmol·mol-1) in October. 2) The vapor pressure deficit (VPD) had the most significant impacts on WUE, followed by air temperature (Ta), soil moisture (Ms), relative humidity (RH), and atmospheric CO2 concentration (Ca), explaining 89.7% of the total variance. Solar radiation (Ra) and wind speed (Ws) had no impacts on WUE. 3) VPD and Ta are the most two important factors influencing short-term WUE, explaining 53.9% of the total variance. The effects of VPD on short-term WUE was higher than that of Ta. Ms and RH were the second important factors of the short-term WUE, explaining 25.4% of the total variance. The effects of Ms on short-term WUE was higher than that of RH. Ca had little effect on the short-term WUE and could explain 10.3% of the total variance.

Beyond soil water potential: An expanded view on isohydricity including land-atmosphere interactions and phenology.

Over the past decade, the concept of isohydry or anisohydry, which describes the link between soil water potential (ΨS ), leaf water potential (ΨL ), and stomatal conductance (gs ), has soared in popularity. However, its utility has recently been questioned, and a surprising lack of coordination between the dynamics of ΨL and gs across biomes has been reported. Here, we offer a more expanded view of the isohydricity concept that considers effects of vapour pressure deficit (VPD) and leaf area index (AL ) on the apparent sensitivities of ΨL and gs to drought. After validating the model with tree- and ecosystem-scale data, we find that within a site, isohydricity is a strong predictor of limitations to stomatal function, though variation in VPD and leaf area, among other factors, can challenge its diagnosis. Across sites, the theory predicts that the degree of isohydricity is a good predictor of the sensitivity of gs to declining soil water in the absence of confounding effects from other drivers. However, if VPD effects are significant, they alone are sufficient to decouple the dynamics of ΨL and gs entirely. We conclude with a set of practical recommendations for future applications of the isohydricity framework within and across sites.

Energy exchange between the atmosphere and a subalpine meadow in the Qilian Mountains, northwest China

Understanding energy exchange between the atmosphere and the Earth’s surface is crucial. We observed the patterns of energy exchange between the atmosphere and a subalpine meadow in the Qilian Mountains, northwest China over the period of 2014 to 2016. Annual variations in energy exchange in study area exhibited drastic differences during time periods of frozen soil and non-frozen soil. Specifically, more than 80% and 28% of net radiation (Rn) were converted to sensible heat (H) during the frozen and non-frozen soil periods, respectively, whereas approximately 17% and 35% of Rn were converted to latent heat (LE) during the frozen and non-frozen soil periods, respectively. The non-frozen soil period was divided into the pre-growth period, the growth period, and the post-growth period. The high Bowe ratio (β) values of the pre-growth period were 4.34, 3.60, and 8.39 in 2014, 2015 and 2016, respectively. In general, rapid increases in Rn during this period increased the values of H, LE, and soil heat flux (G). The growth period was defined by a low β value that fluctuated between 0.3 and 0.4. The average β values for the post-growth period during 2014, 2015, and 2016 were 1.49, 3.12, and 2.37, respectively. The high decoupling coefficient (Ω) for the growth period indicated that the contribution of Rn to LE was greater than that of vapor pressure deficit (VPD). The small value of Ω during the other periods indicated that the effect of VPD on LE dominated that of other factors. The seasonal patterns of energy exchange showed that vegetation phenology is the major factor that affects energy partitioning significantly in the alpine meadow ecosystem in the Qilian Mountains. The annual energy partitioning in the same ecosystem over 3 years was not constant, and climate may be the main factor that influences interannual variations in energy exchange.

Water use efficiency and evapotranspiration partitioning for three typical ecosystems in the Heihe River Basin, northwestern China

It is crucial to improve water use efficiency (WUE) and the transpiration fraction of evapotranspiration (T/ET) for water conservation in arid regions. As a link between carbon and water cycling, WUE is defined as the ratio of gross primary productivity (GPP) and ET at the ecosystem scale. By incorporating the effect of vapor pressure deficit (VPD) on WUE, two underlying WUE (uWUE) formulations, i.e. a potential uWUE (uWUEp = GPP·VPD0.5/T) and an apparent uWUE (uWUEa = GPP·VPD0.5/ET), were proposed recently. Both uWUEp and uWUEa can be estimated from eddy covariance measurements, and the ratio of uWUEa and uWUEp was then used to estimate T/ET. This new method for ET partitioning was applied to three typical ecosystems in the Heihe River Basin. Growing season T/ET at the Daman site (0.63) was higher than that at the Arou and Huyanglin sites (0.55) due to the application of plastic film mulching. The effect of leaf area index (LAI) on seasonal variations in T/ET was strong for Arou (R2 = 0.74) and Daman (R2 = 0.76) sites, but weak for Huyanglin (R2 = 0.44) site. Daily T/ET derived using the uWUE method agreed with that using the isotope and lysimeter/eddy covariance methods during the peak growth season at the Daman site. The estimated T using the uWUE method showed consistent seasonal and diurnal patterns and magnitudes with that using the sap flow method at the Huyanglin site. In addition, the uWUE method can estimate ecosystem T/ET without scaling issues, and can effectively capture T/ET variations in relation to LAI changes and the abrupt T/ET changes in response to individual irrigation events. These advantages make the uWUE method effective for ET partitioning at the ecosystem scale, and can be used for water resources management by predicting seasonal pattern of actual plant water requirements to support irrigation strategies in arid regions.

Impact of heat-wave at high and low VPD on photosynthetic components of wheat and their recovery

Indirect effects of high temperature through increased vapor pressure deficit (VPD) are vital but often ignored in climate impact studies. We investigated the direct (via heat) and indirect (via VPD) effects of a post-anthesis applied high temperature episode on biochemical and diffusional components of photosynthesis in two wheat cultivars. Plants were exposed to a five-day episode of hot humid (HH: 36 °C; 1.96 kPa) or hot dry (HD: 36 °C; 3.92 kPa) climate, including normal climate (NC: 24 °C; 1.49 kPa VPD) as control. The capacity and sensitivity of different photosynthetic components that included diffusional and biochemical processes was investigated both during the stress and after six-days of recovery under NC. The results showed that, regardless of VPD, photosynthetic capacity under high temperature was largely impaired by biochemical limitations while the diffusional limitations were relatively insignificant. The processes involved in CO2-use (i.e. in vivo carboxylation efficiency and Vcmax) presented higher sensitivity than the processes involved in light-use (PSII efficiency, quantum yield and chlorophyll content index). Maximum photosynthetic capacity under high temperature was primarily restricted by limitations to RuBP-regeneration. Effects of higher VPD through diffusional limitations (stomatal and mesophyll conductance) were potentially insignificant. The effects of VPD through changes in transpiration were observed under HH, where significantly higher gs and increase in gs (and transpiration) over time due to acclimation led to drought, because the irrigation amounts per day remained same over the stress period. Resultantly, the photosynthesis under HH was co-limited by both RuBP-carboxylation and RuBP-regeneration. Irrespective of VPD, the after-effects of heat-wave were either non-existent or potentially insignificant, as most of the photosynthetic and related parameters recovered to their respective control. The results indicated that the effect of VPD through changes in soil moisture dynamics is an important confounding variable to consider in climate-impact studies. Higher sensitivity of CO2-use suggested that even moderately high temperature-episodes might limit photosynthetic capacity and hence crop productivity, thus reiterating the need to develop crop cultivars with greater tolerance to high temperatures.

Water use efficiency of a rice paddy field in Liaohe Delta, Northeast China

Water use efficiency (WUE) of rice paddy fields is very important because of the increasing demand for crop production and increasing scarcity of water for irrigation. The seasonal dynamics of WUE and their environmental controls were determined in a rice paddy field in Liaohe Delta, Northeast China, based on 2-year period (2013–2014) eddy-covariance flux and meteorological measurements. The annual and growing-season ecosystem water use efficiency (eWUE) of the paddy field were 1.00gCkg−1 H2O and 1.35gCkg−1 H2O (two-year average), respectively. The seasonal variation of eWUE showed an asymmetric single-peak curve. The leaf area index (LAI) was the dominant regulator of evapotranspiration-based WUE; however, the VPD was the most important controlling factor of transpiration-based WUE. The significant positive control of LAI on evapotranspiration-based WUE was likely caused by its strong regulation of the ratio of transpiration (TR) to evapotranspiration (ET). The residual WUE (calculated from the WUE subtracted from the modeled WUE using the relationship between the WUE and LAI) was negatively correlated with net radiation (Rn). The WUE was generally higher under cloudy conditions than under clear conditions. Based on a comparison of the four WUE indicators, the separation of ET to TR and soil evaporation (ES), as well as the incorporation of the nonlinear effect of vapor pressure deficit (VPD) on WUE, would both greatly improve the performances of WUE indicators in rice paddy fields.

Low vapour pressure deficit affects nitrogen nutrition and foliar metabolites in silver birch.

Air humidity indicated as vapour pressure deficit (VPD) is directly related to transpiration and stomatal function of plants. We studied the effects of VPD and nitrogen (N) supply on leaf metabolites, plant growth, and mineral nutrition with young micropropagated silver birches (Betula pendula Roth.) in a growth chamber experiment. Plants that were grown under low VPD for 26 d had higher biomass, larger stem diameter, more leaves, fewer fallen leaves, and larger total leaf area than plants that were grown under high VPD. Initially, low VPD increased height growth rate and stomatal conductance; however, the effect was transient and the differences between low and high VPD plants became smaller with time. Metabolic adjustment to low VPD reflected N deficiency. The concentrations of N, iron, chlorophyll, amino acids, and soluble carbohydrates were lower and the levels of starch, quercetin glycosides, and raffinose were higher in the leaves that had developed under low VPD compared with high VPD. Additional N supply did not fully overcome the negative effect of low VPD on nutrient status but it diminished the effects of low VPD on leaf metabolism. Thus, with high N supply, the glutamine to glutamate ratio and starch production under low VPD became comparable with the levels under high VPD. The present study demonstrates that low VPD affects carbon and nutrient homeostasis and modifies N allocation of plants.

Environmental and physiological effects on grouping of drought-tolerant and susceptible rice varieties related to rice (Oryza sativa) root hydraulics under drought.

Background and Aims Root hydraulic limitations (i.e. intra-plant restrictions to water movement) may be related to crop performance under drought, and groupings in the hydraulic function of drought-tolerant and drought-susceptible rice (Oryza sativa) varieties have been previously reported. This study aimed to better understand the environmental and physiological relationships with rice root hydraulics under drought. Methods Xylem sap bleeding rates in the field (gsap g-1shoot) were measured on seasonal and diurnal time frames, during which time environmental conditions were monitored and physiological measurements were conducted. Complementary experiments on the effects of vapour pressure deficit (VPD) on root hydraulic conductivity and on transpiration rates of de-rooted tillers were conducted in growth chambers. Key Results The diurnal effects on bleeding rate were more closely related to irradiance than VPD, and VPD effects on root hydraulic conductivity measured on 21-day-old plants were due to effects on plant growth including root surface area, maximum root depth and root:shoot ratio. Leaf osmotic potential was related to the grouping of drought-tolerant and drought-susceptible varieties in rice root hydraulics, and these groupings were independent of differences in phenology. Low single-tiller bleeding rates were observed under high evapo-transpirational demand, higher bleeding rates were observed at more negative leaf osmotic potentials in drought-susceptible varieties, and drought-tolerant and susceptible varieties differed in the VPD-induced increase in transpiration rates of de-rooted tillers. Low root suberin amounts in some of the drought-susceptible varieties may have resulted in higher ion transport, as evidenced by higher sap K+ concentration and higher bleeding rates in those varieties. Conclusions These results provide evidence of the environmental effects on shoots that can influence root hydraulics. The consistent groupings of drought-tolerant and susceptible varieties suggest that traits affecting plant osmotic status may regulate root hydraulic response to drought in rice.