Low Relative Air Humidity Research Articles

Low relative air humidity and increased stomatal density independently hamper growth in young Arabidopsis.

Stomatal pores in plant leaves mediate CO2 uptake for photosynthesis and water loss via transpiration. Altered stomatal density can affect plant photosynthetic capacity, water use efficiency, and growth, potentially providing either benefits or drawbacks depending on the environment. Here we explore, at different air humidity regimes, gas exchange, stomatal anatomy, and growth of Arabidopsis lines designed to combine increased stomatal density (epf1, epf2) with high stomatal sensitivity (ht1-2, cyp707a1/a3). We show that the stomatal density and sensitivity traits combine as expected: higher stomatal density increases stomatal conductance, whereas the effect is smaller in the high stomatal sensitivity mutant backgrounds than in the epf1epf2 double mutant. Growth under low air humidity increases plant stomatal ratio with relatively more stomata allocated to the adaxial epidermis. Low relative air humidity and high stomatal density both independently impair plant growth. Higher evaporative demand did not punish increased stomatal density, nor did inherently low stomatal conductance provide any protection against low relative humidity. We propose that the detrimental effects of high stomatal density on plant growth at a young age are related to the cost of producing stomata; future experiments need to test if high stomatal densities might pay off in later life stages.

Indoor environmental quality in schools: NOTECH solution vs. standard solution.

In many Danish schools, the indoor environmental quality (IEQ) is challenged and studies document a poor IEQ in a majority of existing schools. Municipalities cannot afford comprehensive renovations and expensive mechanical ventilation solutions, hence public schools often suffer from poor indoor environment conditions. This study tests a new façade based, demand-controlled ventilation solution called NOTECH in the renovation of school. The study tests NOTECH vs. existing mechanical ventilation solution, comparing performance of both solutions at Skovbrynet Skole in Denmark. The project investigates the effect of the NOTECH solution in a primary school classroom, comparing it to a similar classroom with conventional, mechanical ventilation. Methodically, indoor environmental quality and energy performance is monitored in the two identical classrooms during one school year 2018 - 2019. The results show that both systems keep the conditions within acceptable limits and CO2 levels below 1000 ppm, which is the requirement according to the Danish Building Regulations. In terms of costs, the NOTECH system has a lower overall cost than the mechanical ventilation system, with total estimated costs for installation, heating, electricity and maintenance amounting to approximately 35% of the mechanical system's costs. Finally, the results show that the NOTECH solution has a smaller embedded CO2 footprint for building materials, reducing the estimated carbon load by 95% compared to the mechanical ventilation solution. While the performance of the both systems complies to the Danish Building Regulations, the indoor environmental quality between systems differs significantly. Results showing a higher air-temperature and lower relative air-humidity in the classroom with mechanical ventilation during winter and lower CO 2 levels in the mechanically ventilated classroom during winter and summer. Costs for implementation, energy consumption for heating and CO 2 footprint for building materials are significantly lower for the NOTECH solution, compared to the mechanical solution.

What do vegetable farmers expect from climate services to adapt to climate change by 2060? A case study from the Parisian region

Climate services are an important tool providing information for many sectors to adapt to climate change. For agriculture, the impacts of climate change vary between regions and between crops, and farmers' needs for climate information are also determined by local context. The purpose of this paper is to identify the climate information needs of vegetable farmers, and to discuss these needs within the specific context of the Parisian region. Based on participatory workshops in three areas of the Parisian region, and using regional downscaled data from the French climate services, this study addresses the following question: what do vegetable farmers of a peri-urban area expect from climate services to adapt to climate change by 2060? Participatory workshops with agricultural expert allowed us to build a preliminary set of climate variables based on crops' vulnerability to high temperatures, mild temperature in winter, late frost, low relative air humidity, low precipitation, and climate extremes such as drought, heat waves and floods. Based on this set of variables climate projection on monthly, seasonal, and annual scales were provided to farmers for the near (2021–2040) and distant (2041–2060) future, as well as for past period (1990–2020) and discussed during 3 participatory workshops. Based on farmer’s feedbacks, we made a synthesis of climate information required by farmers which was validated and further discussed in a last round of workshops involving farmers and agricultural advisers. Three main findings emerge from this participatory study. Our first finding shows the need for both climate and non-climate information for vegetable farming adaptation. Specific needs include information on wind speed peaks and directions, soil moisture, climate analogous spaces (or sites), and urban planning regulations (constraining the possibility to build greenhouses or tunnels to adapt to climate change). Our second finding is that farmers expect from climate services to visualise a comprehensive climatic situation, that is, a whole conjunction of several inter-related variables, rather than precise and detailed variations of a single one. Seasonal and annual time scales seem to be the most relevant for farmers’ adaptation strategies (except for frost requiring more precise information). Our third finding is that these needs remain context-specific and depend on water access, the market demand (here Parisian), and the peri-urban location.

Determination of soya grain strength, reduction and loss in storage and processing

This scientific article analyzes, that with an increase in soybean production, an important role is given to reducing the loss of soybean grain per harvester and from crushing, when the plants are harvested, and post-harvest processing of grain in the production of reproductive seeds. The studied climatic conditions of the Amur region during the soybean harvesting period (October) are characterized by low precipitation and low relative air humidity, it helps dry the plants. Identified, that under these conditions, soybeans and grain are losing strength and, under the influence of the working bodies of motovil and reaper, beans are pulled off or uncovered and grain losses are noted, a threshing and separation devices (MSU) of a grain harvester crush grain when milled, resulting in crop losses. Formulated in the process of scientific research, that the tensile strength or destructive load of soybean kernels by grade at humidity 6,5% change from 13.03 before 29.02 kg. Knowing the destructive load for soybean grain, proposal for Action, prevent destructive modes of operation for the working organs of the threshing and transporting devices of the combine. Based on the reliably obtained regression equation, the response surface is represented, determining the force of the action of the working bodies of the combine in the function of the changing speed from 8.0 before 20 m/s, mass of grain from 0.15 before 0.35 g., which in the September variety increases to 10 N.

System integration analysis of a zeolite 13x thermal energy storage

Nowadays a major energy transition aimed at cutting CO2 emissions has begun, with the ambitious goal of drastically reducing the dependence on fossil fuels and promoting the use of renewable energy sources. In this context, energy storage systems play a key role in ensuring a stable, secure and time-aligned energy availability. Open sorption thermal energy storages (TESs) can contribute to such transition, since they are simple and cheap devices able to provide a hot airflow with a high energy density and to store energy for long time. In this work, open sorption TES systems operated with Zeolite13X are investigated with a focus on the integration in practical applications. First, the experimental analysis and modelling of the sole TES system is described. Then, the integration of the TES at system level is carried out. The analysis evidences that a significant reduction of storage capacity occurs if air humidification is necessary before the adsorption process or afterwards to keep adequate indoor comfort conditions for the occupants. For the exemplary case study considered, an energy density of 150 kWhm−3 can drop to 40 kWhm−3 in case of complete compensation of the adsorbed water through a humidifier. This paper provides useful guidelines for evaluating the performance of a TES integrated system in terms of specific energy and efficiency. It also identifies applications involving high latent loads (e.g., swimming pools, locker rooms) or for which low relative air humidity is required (e.g. interior of vehicles to prevent condensation on windows) as particularly beneficial for using a TES system.

CO2 emissions from reed litter in the air and on the soil surface in the Yellow River Delta, China

The decay of litter in the air (that is, standing litter) and on the ground is an essential process of litter decomposition for many plant species. However, the contribution of standing litter to litter decomposition (e.g., CO2 emission) is still ambiguous, especially for non-leaf litter. In this study, we examined the CO2 emission from reed litter (Phragmites communis) in coastal wetlands in the Yellow River Delta (YRD), China. The results showed that the soil litter released more CO2 than the standing litter due to its rapid loss of labile organic carbon and high enzyme activities (that is, invertase and β-glucosidase). In contrast, cumulative CO2 emissions from standing litter were equivalent to 56%–70% of those on the soil surface, indicating that CO2 emissions from standing litter cannot be ignored. The sheath litter had the highest cumulative CO2 emission per unit of dry biomass among the three types of litter. Taking into account the biomass per unit area, the non-leaf litter (that is, culm and sheath) emitted more CO2 than leaf litter. On the daily scale, the litter released more CO2 at night than in the daytime, because low air temperature and high relative air humidity at night can help dew formation, accelerating CO2 emission at night. On the seasonal scale, air temperature and relative air humidity were positively related to CO2 emission, leading to rapid CO2 emission in summer and fall. The Q10 value of CO2 emission from standing litter (an average of 1.44) was lower than that of litter on the ground (an average of 2.16) due to a low residual rate of recalcitrant organic carbon in standing litter. Our findings highlight that standing litter decomposition should not be overlooked and suggest that more attention should be paid to the decay of non-leaf litter in the coastal wetland of the YRD.

Vegetation fires along the Czech rail network

BackgroundIn the past, fires around railways were often associated with steam locomotives. Although steam locomotives have disappeared from everyday rail traffic, fires still occur. A vegetation fire near Bzenec (Czech Republic) on 21 June 2018 affected, for example, 124,110 m2 of forest and grassland. The investigation revealed that the fire was caused by a spark from a passing train. In this study, we analyzed vegetation fires that occurred near Czech railway lines between 2011 and 2019 to investigate their temporal pattern and relation to weather conditions or to identify the most hazardous locations.ResultsFires were concentrated mainly between March and August in the afternoon. They are also more likely to occur during periods of high air temperature, low rainfall, low relative air humidity, and low wind speed. Using the KDE+ method, we identified 186 hotspots, which contained 510 vegetation fires and represented only 0.3% of the length of the entire Czech rail network. Spatial analysis revealed that there are more than 4 times higher odds that a vegetation fire occurs near an electrified railway line than near a non-electrified line or that additional 10 freight trains per 24 h increases the odds by 5%.ConclusionsAs the results show, vegetation fires near railway lines are still relatively common phenomenon, mainly due to favorable weather conditions. Grassy areas with dry or dead vegetation are particularly at risk. These areas can be ignited, for example, by sparks from the brakes of railway vehicles. Due to global warming, vegetation fires can be expected to occur more frequently in the future. The identified hotspots can thus be used to reduce the risk of fires, for example by managing the surrounding vegetation.

Phylloplane Biodiversity and Activity in the City at Different Distances from the Traffic Pollution Source.

The phylloplane is an integrated part of green infrastructure which interacts with plant health. Taxonomic characterization of the phylloplane with the aim to link it to ecosystem functioning under anthropogenic pressure is not sufficient because only active microorganisms drive biochemical processes. Activity of the phylloplane remains largely overlooked. We aimed to study the interactions among the biological characteristics of the phylloplane: taxonomic diversity, functional diversity and activity, and the pollution grade. Leaves of Betula pendula were sampled in Moscow at increasing distances from the road. For determination of phylloplane activity and functional diversity, a MicroResp tool was utilized. Taxonomic diversity of the phylloplane was assessed with a combination of microorganism cultivation and molecular techniques. Increase of anthropogenic load resulted in higher microbial respiration and lower DNA amount, which could be viewed as relative inefficiency of phylloplane functioning in comparison to less contaminated areas. Taxonomic diversity declined with road vicinity, similar to the functional diversity pattern. The content of Zn in leaf dust better explained the variation in phylloplane activity and the amount of DNA. Functional diversity was linked to variation in nutrient content. The fraction of pathogenic fungi of the phylloplane was not correlated with any of the studied elements, while it was significantly high at the roadsides. The bacterial classes Gammaproteobacteria and Cytophagia, as well as the Dothideomycetes class of fungi, are exposed to the maximal effect of distance from the highway. This study demonstrated the sensitivity of the phylloplane to road vicinity, which combines the effects of contaminants (mainly Zn according to this study) and potential stressful air microclimatic conditions (e.g., low relative air humidity, high temperature, and UV level). Microbial activity and taxonomic diversity of the phylloplane could be considered as an additional tool for bioindication.

Influenza A virus hemagglutinin prevents extensive membrane damage upon dehydration

While the molecular mechanisms of virus infectivity are rather well known, the detailed consequences of environmental factors on virus biophysical properties are poorly understood. Seasonal influenza outbreaks are usually connected to the low winter temperature, but also to the low relative air humidity. Indeed, transmission rates increase in cold regions during winter. While low temperature must slow degradation processes, the role of low humidity is not clear. We studied the effect of relative humidity on a model of Influenza A H1N1 virus envelope, a supported lipid bilayer containing the surface glycoprotein hemagglutinin (HA), which is present in the viral envelope in very high density. For complete cycles of hydration, dehydration and rehydration, we evaluate the membrane properties in terms of structure and dynamics, which we assess by combining confocal fluorescence microscopy, raster image correlation spectroscopy, line-scan fluorescence correlation spectroscopy and atomic force microscopy. Our findings indicate that the presence of HA prevents macroscopic membrane damage after dehydration. Without HA, fast membrane disruption is followed by irreversible loss of lipid and protein mobility. Although our model is principally limited by the membrane composition, the macroscopic effects of HA under dehydration stress reveal new insights on the stability of the virus at low relative humidity.

SPREAD AND HARMFULNESS OF THE THRIPS TABACI LIND IN APPLE PLANTATIONS OF THE KRASNODAR TERRITORY

The results of daily phytosanitary monitoring of fruit plantations and literature data on biology, ecology, harmfulness of tobacco thrips (Thrips tabaci Lind.) are presented. In the apple agrocenoses of the Kuban and Black Sea zones of Krasnodar Territory, an increase in the harmfulness of representatives of the order Thysanoptera is observed. An increase in the number of tobacco thrips was noted, which led to a decrease in the quality of fruits. In the growing season of 2018, isolated symptoms of fruit damage by phytophagous were noted, in the growing season of 2019, fruit damage reached up to 2 %, in 2020 — 5-30 %. It was revealed that during the flowering period the number of T. tabaci Lind was 1-2 specimens per inflorescence; at the end of flowering, the amount of the pest increased by 5 times. High temperatures and lack of precipitation led to an outbreak of the pest population; in the first decade of June, 15 to 40 individuals were fixed per leaf. A high degree of damage to the tops of shoots, leaves and fruits was observed, the tissue in the feeding places of the pest was deformed, discolored, acquiring the appearance of whitish spots, which grew during the growth and ripening of fruits. It is known that the intensive development of thrips takes place in dry and hot years; the optimum temperature for the development of T. tabaci Lind is +25 °C. As a result of our monitoring, it was revealed that the maximum amount of the pest was observed during the period when high temperatures and low relative air humidity were noted — June and early July. The greatest number of the pest was found in areas bordering the fields of grain and tilled crops, while the number of phytophages at the time of registration reached 45 individuals per leaf and more. It should be noted that when the air temperature rises above +35 °C, the development of the phytophage stops, and the mortality rate of all stages sharply increases. To ensure a stable phytosanitary situation in fruit agrocenoses and prevent loss of fruit quality from damage by thrips, it is necessary to develop a set of measures to control the number of pests.

Incorporating cultivar-specific stomatal traits into stomatal conductance models improves the estimation of evapotranspiration enhancing greenhouse climate management

The effect of considering cultivar differences in stomatal conductance (g s ) on relative air humidity (RH)-related energy demand was addressed. We conducted six experiments in order to study the variation in evapotranspiration (ET c ) of six pot rose cultivars, investigate the underlying processes and parameterise a g s -based ET c model. Several levels of crop ET c were realised by adjusting the growth environment. The commonly applied Ball–Woodrow–Berry g s -sub-model (BWB-model) in ET c models was validated under greenhouse conditions, and showed a close agreement between simulated and measured ET c . The validated model was incorporated into a greenhouse simulator. A scenario simulation study showed that selecting low-g s 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 (D s ) or pore area. Although the modified BWB-Liu-model (considering D s ) allowed higher accuracy (R 2 = 0.59), as compared to the basic version (R 2 = 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 g s 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 (ET c ) is essential for relative air humidity regulation. • Six pot rose cultivars and several cultivation regimes were used. • ET c estimation was improved using cultivar-specific stomatal conductance parameters. • The use of low-stomatal conductance cultivars secures energy saving (2.5–5.75%).

The Influence of Work Environment Factors on the OcularSurface in a One-Year Follow-Up Prospective Clinical Study.

The purpose of this study was to assess the effect of environmental working conditions on the symptoms and signs of dry eye disease and to examine whether and how those conditions impact the ocular surface. Methods: This single-center, prospective clinical study with a 1-year follow-up included 150 patients. The following parameters were evaluated: non-invasive keratograph break-up time (NIKBUT), tear meniscus height (TMH), and conjunctival and limbal hyperemia. We also performed staining of the surface of the eye for simulated fluorescein images, Schirmer’s test I, assessment of Meibomian gland dysfunction (MGD), and an Ocular Surface Disease Index (OSDI) questionnaire. Results: In the OW (office workers) group, in people working >4 h at the computer, the NIKBUT before work and the Schirmer test results were statistically significantly lower than in people working <4 h. The conjunctival hyperemia result before work was statistically significantly higher for people working >4 h at a computer in both groups and after work in the MW (medical workers) group. Low relative air humidity in the building and air-conditioned rooms negatively affects the tear film, causing the symptoms of dry eye disease. At the 1-year follow-up, there was a statistically significant reduction in conjunctival and limbal hyperemia in the OW group as well as a statistically significant reduction in TMH at the first examination before and after work, and in the second examination after 1 year in both groups. Conclusions: Environmental factors such as reduced relative air humidity, increased air temperature, and decreased illumination have a negative impact on the ocular surface.

Formation characteristics of watermelon seed productivity under intercropping

Characteristics of watermelon seed formation in intercropping were studied. Different growing methods of watermelon seeds depending on its interaction with intercrops (sugar maize and common bean) and their planting schemes in melon fields were investigated. The developed elements of the watermelon seed growing technology reduced the impact of high temperatures on this melon crop (the number of fruits with sunburn decreased by 7.1 % compared to control). The results of phenological observations and analysis of yield components, seed productivity and quality of Favoryt watermelon variety in the intercropping with sugar maize and common bean were presented. It was established that the developed elements of the watermelon growing technology in intercropping under high temperatures and low relative air humidity in the Northern Steppe of Ukraine increased of watermelon yield and the full-value seed formation. It was found that intercropping of watermelon with sweet corn under proper cultivation gave positive results (watermelon seed yield gain by 12.4 % and 0.7 t/ha ears of sweet maize in milky-wax ripeness were received additionally), and with common bean (watermelon seed yield gain by 8.9 % and additional 75 kg/ha of beans). Methods and planting schemes of watermelon and intercrops were established: sugar maize in the rows of watermelon according to scheme 2.8 x 1 m, common bean in the rows of watermelon according to scheme 1.4 x 0.5 m. It was found that under intercropping of watermelon with sweet maize the full-value seed yield per one fruit increased up to 88.5 %, and with common bean – to 84.9 %. Key words: watermelon, sugar maize, common bean, intercropping, seed yield.

Climatic determinants of lowland rice development

AbstractAccurate modelling of plant development is the basis for any assessment of climate change impact on crop yields. Most rice models simulate development (phenology) based on temperature and photoperiod, but often the reliability of these models is reduced beyond the environment they were calibrated for. In our study, we tested the effects of relative air humidity and solar radiation on leaf appearance rate in greenhouse experiments and analysed data sets from field studies conducted in two extremely different rice‐growing environments in Nepal and Senegal. We also analysed environmental effects on duration to flowering of one popular IRRI material (IR64) for eight different sites covering the entire temperature range where rice is widely cultivated. Both low relative air humidity and low solar radiation significantly decreased leaf appearance rate. Mean air temperature explained 81% of the variation in duration to flowering across sites, which was furthermore significantly influenced by relative air humidity. Across all sites, a simple linear regression approach including mean air temperature and mean relative humidity in the calculation of duration to flowering led to a root mean square error (RMSE) of 10 days, which was slightly lower than the RMSE of 11 days achieved with an automated calibration tool for parameter optimization of cardinal temperatures and photoperiod sensitivity. Parameter optimization for individual sites led to a much smaller prediction error, but also to large differences in cardinal temperatures between sites, mainly lower optimum temperatures for the cooler sites. To increase the predictive power of phenological models outside their calibration range and especially in climate change scenarios, a more mechanistic modelling approach is needed. A starting point could be including relative air humidity and radiation in the simulation procedure of crop development, and presumably, a closer link between growth and development procedures could help to increase the robustness of phenological models.

Stomatal conductance bears no correlation with transpiration rate in wheat during their diurnal variation under high air humidity.

A good understanding of the response of photosynthesis rate (PN) and transpiration rate (Tr) to stomatal alteration during the diurnal variations is important to cumulative photosynthetic production and water loss of crops. Six wheat genotypes were studied for 2 years with pot cultivation in rain-shelter. Among different genotypes, stomatal conductance (gs) was significantly correlated with both PN and Tr. But for each genotype, though gs was significantly correlated with PN regardless of relative air humidity (RH) status and it was also significantly correlated with Tr under lower RH (LRH, 15.4%) and moderate RH (MRH, 28.3%), it was not correlated with Tr under higher RH (HRH, 36.7%) during the diurnal changes. The conditional correlation between gs and Tr of wheat evoked new thinking on the relationships among gs, PN and Tr. Path analysis was further carried out to clarify the correlations of gs with the four atmospheric factors, that of Tr with gs and the four factors and the direct and indirect effects of the factors, during their diurnal dynamic variation. The effects of these factors on gs or Tr were related to RH. All the four factors had a much higher correlation with gs under HRH than that under LRH and MRH. Air temperature (T) had a rather higher direct effect than RH and photosynthetically active radiation (PAR). Also, the other factors had a much higher indirect effect on gs through vapor pressure deficit (VPD) and T. Transpiration rate was highly correlated with gs under LRH and MRH, with gs having a higher direct effect on it. In comparison, Tr was not correlated with gs under HRH but highly correlated with the atmospheric factors, with T, RH, and PAR having a higher indirect effect through VPD.

Composting process and odor emission varied in windrow and trough composting system under different air humidity conditions

To comprehensively investigate the effect of different air humidity conditions on the performance and odor emission in composting technology, a full-scale experiment was conducted simultaneously in the regions with low air relative humidity (Kunming) and high relative air humidity (Xishuangbanna), Yunnan province. The results showed that: In the regions with low relative air humidity, similar performances were found on organic matter degradation and germination index values in windrow and trough composting. Windrow composting got lower H2S emission, but higher NH3 release comparing with trough composting. Windrow composting was more susceptible to high relative air humidity. The degradation rate and germination index were 22% and 28% lower than those in trough composting. Therefore, the trough composting was recommended in the areas with high relative air humidity, while suitable NH3 mitigation measure should be considered.

The effect of air flow on drying fodder on drying systems

Drying grass fodder in Europe’s Alpine countries is becoming increasingly important due to positive effects on the fatty acid composition of milk. A proper approach and technology of fodder drying can raise its quality to the level of grass silage. In principle, drying fodder means extracting water from fodder by means of ventilation – the air, the key to the speed of drying. Besides low relative air humidity, its flow rate through the fodder is also important. In the literature, the lower- and upper-bound limits of air flow rates can be found, with a difference of 85 % between the two. The article describes a test, measuring energy consumption and the efficiency of drying at a low air flow, often used in practice, and a high air flow. It was found that a high air flow results in 38 % higher energy consumption per kilogramme of extracted water, compared to a low air flow. The executed test has proved that drying at a higher air flow will not have a proportionally greater effect.

Low air humidity during cultivation promotes stomatal closure ability in rose

In greenhouse horticulture, evaporative demand varies between seasons. For instance, plants are typically exposed to low relative air humidity (RH) during summer, whereas elevated RH prevails in winter. Since high RH during cultivation impairs stomatal functioning, some opposite changes might be expected, when plants are subjected to long-term low RH. To investigate this, Rosa hybrida ‘Pasadena’ was cultivated at 40, 60 or 90% RH. Plant performance, transpiration, stomatal closing ability and anatomy were recorded. As RH increased from 40 to 60% as well as from 60 to 90%, plants showed larger leaf area and thinner leaves. Plant water loss was mainly determined by ambient RH in the growing environment, with stomatal conductance (gs) being of secondary importance. With increasing RH, plant transpiration declined at growth environment. Larger stomata were found at 90% RH, as compared to 40 or 60%. Stomatal physiology was considerably affected by 90% RH, including reduced gs oscillations within the photoperiod, attenuated opening response following dark/light transition, as well as reduced closing response upon darkening. The plants cultivated at 90% RH had a reduced ability to control water loss upon water deprivation, compared to those grown at 60%. In contrast, cultivation at 40% RH resulted in stomata, which were much more responsive to water stress, compared to 60% RH-grown plants. This superiority was dual: lower transpiration rate combined with less severe leaf drying to induce stomatal closure. In conclusion, low RH during cultivation, which is typical during summer, leads to thicker leaves with very responsive stomata.

Impact of Water Availability on Responses of Cucumis sativus Plants to a Short-Term Daily Temperature Drop

Impact of relative air humidity (RAH) and watering mode on responses of cucumber (Cucumis sativus L.) plants to a daily short-term (2 h) temperature decrease to 10oC (DROP treatment) was investigated. Plants were grown at comparably high (80%) or low (30%) RAH under conditions of normal watering or in the mode of artificially created “periodic drought.” It was found that RAH and watering mode exhibit strong quantitative and qualitative influence on plant responses to DROP treatment. Under high RAH, DROP treatment exhibits significant morphogenetic effect increasing plant biomass and compactness. Under the conditions of low RAH, effects of DROP treatment on plant compactness were leveled due to strong morphogenetic effect of the RAH itself and significant decrease in DROP-treated plant biomass under “drought”. Watering mode influenced on the effect of DROP treatment in a different manner depending on RAH. At high RAH, DROP treatment, together with “drought,” led to increase in plant compactness as well as their chilling tolerance. Besides, these plants became more tolerant to water stress induced by low temperature (4°C). At low RAH, no increase in compactness of DROP-treated plants was observed.

Fuzzy comprehensive evaluation of the effects of relative air humidity on the morpho-physiological traits of Pakchoi (Brassica chinensis L.) under high temperature

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.