Vapor pressure deficit (VPD) is considered to be one of the major environmental factors influencing stomatal functions and photosynthesis, as well as plant growth in crop and horticultural plants. In ...the greenhouse cultivation, air temperature and relative air humidity are regulated by switching on/off the evaporative systems and opening/closing the roof windows, which causes VPD fluctuation. However, it remains unclear how VPD fluctuation affects photosynthetic and growth performance in plants. Here, we examined the effects of the VPD fluctuation on the photosynthetic and growth characteristics in lettuce (
L.). The parameters for gas exchange and chlorophyll fluorescence and biomass production were evaluated under the conditions of drastic (1.63 kPa for 6 min and 0.63 for 3 min) or moderate (1.32 kPa for 7 min and 0.86 kPa for 3 min) VPD fluctuation. The drastic VPD fluctuation induced gradual decrease in stomatal conductance and thus CO
assimilation rate during the measurements, while moderate VPD fluctuation caused no reduction of these parameters. Furthermore, data showed moderate VPD fluctuation maintained leaf expansion and the efficiency of CO
diffusion across leaf surface, resulting in enhanced plant growth compared with drastic VPD fluctuation. Taken together, fine regulation of VPD can be crucial for better plant growth by maintaining the photosynthetic performance in lettuce. The present work demonstrates the importance of VPD control during plant cultivation in plant factories and greenhouses.
In this work, the effect of low air relative humidity on the operation of a polymer electrolyte membrane fuel cell is investigated. An innovative method through performing in situ electrochemical ...impedance spectroscopy is utilised to quantify the effect of inlet air relative humidity at the cathode side on internal ionic resistances and output voltage of the fuel cell. In addition, algorithms are developed to analyse the electrochemical characteristics of the fuel cell. For the specific fuel cell stack used in this study, the membrane resistance drops by over 39 % and the cathode side charge transfer resistance decreases by 23 % after increasing the humidity from 30 % to 85 %, while the results of static operation also show an increase of ∼2.2 % in the voltage output after increasing the relative humidity from 30 % to 85 %. In dynamic operation, visible drying effects occur at < 50 % relative humidity, whereby the increase of the air side stoichiometry increases the drying effects. Furthermore, other parameters, such as hydrogen humidification, internal stack structure, and operating parameters like stoichiometry, pressure, and temperature affect the overall water balance. Therefore, the optimal humidification range must be determined by considering all these parameters to maximise the fuel cell performance and durability. The results of this study are used to develop a health management system to ensure sufficient humidification by continuously monitoring the fuel cell polarisation data and electrochemical impedance spectroscopy indicators.
•PEM Fuel cell inlet air relative humidity regulation using a passive humidifier with fuzzy logic control.•Using EIS characteristics to quantify the effect of air relative humidity on PEMFC performance.•Air RH affects PEMFC significantly depicted by mean cell voltage and internal resistances.•Electrochemical analyses using EIS oriented algorithms to develop a health management system.
•Local environment influenced regeneration dynamics of two Nothofagus species.•Differences in the environment influenced seedling survival but not emergence.•Transition from the germinated seed to ...the seedling showed the larger loss of individuals.•The ability of seedling survival was influenced by the ontogenetic state of the seedling.•Colder environments inside species natural ranges favored seedling performance.
A widely accepted paradigm in forest ecology proposes that patterns of relative abundance among mature forest trees are largely influenced by biotic and abiotic processes that operate most intensely during the earliest life-cycle stages. Therefore, traits expressed early in development such as germination and seedling establishment may be under strong selective pressure from the environment, and their adjustment to changing climates may ultimately influence species’ responses to global climate change. Here we used different environments established across altitude in an old-growth temperate Patagonian forest as a natural laboratory, and studied the Nothofagus obliqua and N. pumilio regeneration response – seedling emergence and survival –to different climatic scenarios, inside and outside their natural distribution range. These are two iconic species of sub-Antarctic forests, which co-exist in contrasting and non-overlapping thermal niches. Whereas N. obliqua is predominant in the warmer and lower environments at 650–850 m above sea level (a.s.l.), N. pumilio inhabits the colder and higher montane environments, above 1000 m a.s.l. By sowing germinated seeds of both species at different altitudes in the forest – 680, 930 and 1340 m a.s.l. – we were able to distinguish the environmental influence on seedling emergence from its influence on germination. Our results show that the local environment had a major effect on seedling survival, and a minor influence on emergence. Overall, regeneration of both species showed a temporal window of stronger environmental susceptibility, which comprised the process of emergence, and in the particular case of N. obliqua, the first month of post-emergence growth. Survival ability was influenced by the ontogenetic stage of the seedling, evidencing stronger environmental resistance and higher probability of survival after the first year of growth. Interestingly, we found inter-specific differences in survival dynamics and the final number of surviving seedlings, which may reflect species-specific physiological adaptations and tolerance to abiotic stress. However, the performance of both species was favored in relatively colder environments inside their natural ranges. This indicates that present climatic conditions in the lower zones of the gradient exert physiological constraints at seedling stage, even in N. obliqua, which shows high abundance of adult trees at these altitudes. Results reported here were consistent across two independent experiments and will be discussed in the context of forest regeneration in present and future climatic scenarios.
•Dead outer bark (periderm) is a highly hygroscopic tissue•Reversible stem diameter variations (SDVs) are affected by bark hygroscopicity (Bhy)•Relative air humidity is closely related to SDVs of ...dead and living Scots pine trees•Bhy affects detection of environmental drivers of SDVs and radial stem growth
Time series of stem diameter variations (SDVs) recorded by dendrometers are composed of two components: (i) irreversible radial stem growth and (ii) reversible stem shrinking and swelling caused by dynamics in water storage in elastic tissues outside the cambium. However, SDVs measured over dead outer bark (periderm) could also be affected by absorption and evaporation of water from remaining dead bark layers after smoothing the stem surface to properly mount dendrometers. Therefore, the focus of this study was to determine the influence of hygroscopicity of a thin dead outer bark layer on the reversible component of dendrometer records of Scots pine (Pinus sylvestris) under field conditions. To accomplish this, SDVs deduced from dendrometers mounted over dead outer bark were compared among living and dead saplings and mature trees. Results revealed that dead trees showed high synchronicity in reversible daily SDVs compared to living trees throughout several growing seasons (mean Pearson correlation coefficient (r) = 0.844 among saplings and r = 0.902 among mature trees, respectively; P<0.001). Furthermore, diurnal and long-term SDVs closely followed changes in relative air humidity (RH) in living and dead trees. A multiple linear regression analysis of environmental influence on SDVs in dead and living trees revealed that the most important predictor of daily SDVs was RH (relative importance 64 %). Hence, results indicate that dendrometers mounted over dead outer bark with a thickness of <4 mm record hygroscopic shrinking and swelling of the bark tissue, which can amplify fluctuations in whole-tree water status. To conclude, hygroscopic processes must be taken into account when extracting intra-annual radial growth, determining environmental drivers of SDVs, and evaluating changes in tree water status from SDVs recorded by dendrometers, which were mounted over even thin dead outer bark layers.
The effect of considering cultivar differences in stomatal conductance (gs) on relative air humidity (RH)-related energy demand was addressed. We conducted six experiments in order to study the ...variation in evapotranspiration (ETc) of six pot rose cultivars, investigate the underlying processes and parameterise a gs-based ETc model. Several levels of crop ETc were realised by adjusting the growth environment. The commonly applied Ball–Woodrow–Berry gs-sub-model (BWB-model) in ETc models was validated under greenhouse conditions, and showed a close agreement between simulated and measured ETc. The validated model was incorporated into a greenhouse simulator. A scenario simulation study showed that selecting low-gs cultivars reduces energy demand (≤5.75%), depending on the RH set point. However, the BWB-model showed poor prediction quality at RH lower than 60% and a good fit at higher RH. Therefore, an attempt was made to improve model prediction: the in situ-obtained data were employed to adapt and extend either the BWB-model, or the Liu-extension with substrate water potential (Ψ; BWB-Liu-model). Both models were extended with stomatal density (Ds) or pore area. Although the modified BWB-Liu-model (considering Ds) allowed higher accuracy (R2 = 0.59), as compared to the basic version (R2 = 0.31), the typical lack of Ψ prediction in greenhouse models may be problematic for implementation into real-time climate control. The current study lays the basis for the development of cultivar specific cultivation strategies as well as improving the gs sub-model for dynamic climate conditions under low RH using model-based control systems.
•Relative air humidity control is a key but costly aspect of greenhouse climate.•Accurate estimation of evapotranspiration (ETc) is essential for relative air humidity regulation.•Six pot rose cultivars and several cultivation regimes were used.•ETc estimation was improved using cultivar-specific stomatal conductance parameters.•The use of low-stomatal conductance cultivars secures energy saving (2.5–5.75%).
•The effects of relative air humidity (RH) on Pakchoi growth under high temperature were investigated by fuzzy comprehensive evaluation.•Biomass peaked at 60% RH and leaf-air temperature difference ...peaked at 40% RH under high temperature. Excessively high or low RH caused a significant reduction in the production and intrinsic quality.•The RH of 60% was the appropriate for Pakchoi growth at high temperature.•The proper RH could reduce the leaf temperature, and maintained stomatal conductance, thereby maintaining the high net photosynthetic efficiency.
This study was conducted to investigate the effects of relative air humidity (RH) on morphological and physiological traits of Pakchoi (Brassica chinensis L.) under high temperature. Pakchoi was planted in climate chambers at 35/28 °C, day / night temperature, and the RH levels were 20%, 40%, 60%, 80%, and 95%. Most growth parameters peaked at 40–60% RH under high temperature. Biomass, leaf area, net photosynthetic rate (Pn), soluble sugar, and vitamin C were the highest at 60% RH, whereas total chlorophyll content, transpiration rate, and leaf air temperature were the highest at 40% RH. Superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were the highest at 80% RH. All the above properties showed the lowest value at 95% RH. Malondialdehyde (MDA) peaked at 95% RH, and severe chlorosis was observed simultaneously. Based on our fuzzy comprehensive evaluation, the fuzzy value of production and intrinsic quality was the highest at 60% RH and lowest at 95% RH. RH does affect the temperature difference between leaf and air from the change of transpiration. Excessively high or low RH caused a significant reduction in biomass production and intrinsic quality. We found that 60% RH was the optimum level for growth of Pakchoi at high temperature. With 95% RH, the Pakchoi was damaged under high temperature; Pn, SOD, CAT, and POD activities were the lowest; and MDA content was the highest. Results suggested that proper RH level could reduce leaf temperature and maintain stomatal conductance, thereby maintaining the high yield of Pakchoi via higher photosynthetic efficiency at high temperature.
Stomatal pores close rapidly in response to low-air-humidity-induced leaf-to-air vapor pressure difference (VPD) increases, thereby reducing excessive water loss. The hydroactive signal-transduction ...mechanisms mediating high VPD-induced stomatal closure remain largely unknown. The kinetics of stomatal high-VPD responses were investigated by using time-resolved gas-exchange analyses of higher-order mutants in guard-cell signal-transduction branches. We show that the slow-type anion channel SLAC1 plays a relatively more substantial role than the rapid-type anion channel ALMT12/QUAC1 in stomatal VPD signaling. VPD-induced stomatal closure is not affected in
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double mutants that completely disrupt stomatal CO
signaling, indicating that VPD signaling is independent of the early CO
signal-transduction pathway. Calcium imaging shows that osmotic stress causes cytoplasmic Ca
transients in guard cells. Nevertheless,
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Ca
-permeable channel quintuple,
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-channel double,
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-channel double,
-channel single,
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-channel double,
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-channel double,
kinase quintuple,
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quintuple, and
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double mutants showed wild-type-like stomatal VPD responses. A B3-family Raf-like mitogen-activated protein (MAP)-kinase kinase kinase, M3Kδ5/RAF6, activates the OST1/SnRK2.6 kinase in plant cells. Interestingly, B3 Raf-kinase
and
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(
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) quadruple mutants, but not a 14-gene
mutant including osmotic stress-linked B4-family Raf-kinases, exhibited slowed high-VPD responses, suggesting that B3-family Raf-kinases play an important role in stomatal VPD signaling. Moreover, high VPD-induced stomatal closure was impaired in receptor-like pseudokinase GUARD CELL HYDROGEN PEROXIDE-RESISTANT1 (GHR1) mutant alleles. Notably, the classical transient "wrong-way" VPD response was absent in
mutant alleles. These findings reveal genes and signaling mechanisms in the elusive high VPD-induced stomatal closing response pathway.
The absorption of scale model materials is generally measured in a scaled reverberation chamber, with frequency scaled according to the scale factor. Moreover, the acoustic absorption of the chamber ...needs to be reduced, especially the absorption of air. It depends not only on the volume of the chamber, but also on the air parameters: pressure, temperature and relative humidity. Most frequently, in order to reduce the air absorption, the air inside the model is dried or replaced with dry nitrogen, or a digital air absorption compensation is used. Air-drying methods are time consuming and require specialised equipment; digital compensation may in turn result in errors, hence the question arises whether scaling the air absorption is really necessary to achieve good accuracy of the sound absorption coefficient measurements. In order to answer this question, the authors firstly ran a theoretical analysis of the issue based on ISO 9613-1 formulas describing air acoustic absorption. Based on this analysis, the influence of particular air parameters on the total air absorption in the model reverberation chamber, Aair (m2), was examined, together with the possibilities of scaling down the Aair values. This indicated, that the Aair may be scaled by manipulating temperature or relative air humidity. For the needs of the study, the relative air humidity was chosen, as it was used by the predecessors and may be easily manipulated. In the next step, the experimental studies of sound absorption coefficient measurements were conducted in a 1:8 scale reverberation chamber for representative specimens at different relative air humidity values (3–45%). The gathered data was then statistically analysed. The results showed that the influence of relative air humidity on the accuracy of sound absorption coefficient measurements in model tests is negligible and therefore such measurements can be performed in the ambient air humidity of the test room. As a consequence, a conclusion was drawn that the Aair value does not need to be scaled. Moreover, an attempt was made to identify the cause of the inaccuracy of the measurements – the analysis indicated that the values of the intensity attenuation coefficient m calculated according to ISO 9613-1, at model frequencies are not sufficiently accurate.
Leaf abscisic acid concentration mediates the growth environment-induced effects on both the control of water loss during desiccation and the restoration of water uptake upon re-watering.
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