Nighttime Water Research Articles

Effects of atmospheric CO2 concentration on transpiration and leaf elongation responses to drought in Triticum aestivum, Lolium perenne and Festuca arundinacea.

Leaf elongation is vital for Poaceae species' productivity, influenced by atmospheric CO2 concentration ([CO2]) and climate-induced water availability changes. Although [CO2] mitigates the effects of drought on reducing transpiration per unit leaf area, it also increases total leaf area and water use. These complex interactions associated with leaf growth pose challenges in anticipating climate change effects. This study aims to assess [CO2] effects on leaf growth response to drought in perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinacea) and wheat (Triticum aestivum). Plants were cultivated in growth chambers with [CO2] at 200 or 800ppm. At leaf six to seven unfolding, half of the plants were subjected to severe drought treatment. Leaf elongation rate (LER) was measured daily, whereas plant transpiration was continuously recorded gravimetrically. Additionally, water-soluble carbohydrate (WSC) content along with water and osmotic potentials in the leaf growing zone were measured at drought onset, mid-drought and leaf growth cessation. Elevated [CO2] mitigated drought impacts on LER and delayed growth cessation across species. A positive correlation between LER and soil relative water content (SRWC) was observed. At the same SRWC, perennial grasses exhibited a higher LER with elevated [CO2], likely due to enhanced stomatal regulation. Despite stomatal closure and WSC accumulation, CO2 did not influence nighttime water potential or osmotic potential. The marked increase in leaf area across species resulted in similar (wheat and tall fescue) or higher (ryegrass) total water use by the experiment's end, under both watered and unwatered conditions. In conclusion, elevated [CO2] mitigates the adverse effects of drought on leaf elongation in three Poaceae species, due to its impact on plant transpiration. Overall, these findings provide valuable insights into CO2 and drought interactions that may help anticipate plant responses to climate change.

Personnel Detection in Dark Aquatic Environments Based on Infrared Thermal Imaging Technology and an Improved YOLOv5s Model.

This study presents a novel method for the nighttime detection of waterborne individuals using an enhanced YOLOv5s algorithm tailored for infrared thermal imaging. To address the unique challenges of nighttime water rescue operations, we have constructed a specialized dataset comprising 5736 thermal images collected from diverse aquatic environments. This dataset was further expanded through synthetic image generation using CycleGAN and a newly developed color gamut transformation technique, which significantly improves the data variance and model training effectiveness. Furthermore, we integrated the Convolutional Block Attention Module (CBAM) at the end of the last encoder's feedforward network. This integration maximizes the utilization of channel and spatial information to capture more intricate details in the feature maps. To decrease the computational demands of the network while maintaining model accuracy, Ghost convolution was employed, thereby boosting the inference speed as much as possible. Additionally, we applied hyperparameter evolution to refine the training parameters. The improved algorithm achieved an average detection accuracy of 85.49% on our proprietary dataset, significantly outperforming its predecessor, with a prediction speed of 23.51 FPS. The experimental outcomes demonstrate the proposed solution's high recognition capabilities and robustness, fulfilling the demands of intelligent lifesaving missions.

Study on indoor temperature and thermal performance of a novel solar coupled floor and Kang heating system

Coupled floor and Kang surface heating terminals have significant advantages in meeting the differentiated indoor thermal requirements of Northwest rural dwellings in winter. A novel solar coupling floor and Kang surface heating system is proposed, a mathematical analysis model of thermal performance is established, and experimental validation is carried out. The solar coupling floor and Kang surface heating systems can effectively meet the differing heating requirements of indoor and bedding thermal environment. The solar fraction can reach 59.4 %, showing good energy-saving capability. The solar coupled floor and Kang surface heating system were simulated and optimized. The more suitable scheme is a solar collector size of 7.0 m2 and a water tank capacity of 0.35 m3. This configuration better meets the differing heating requirements of indoor and bedding thermal environment when the nighttime water supplier temperature is inferior to the daytime water supplier temperature. The solar coupling floor and Kang surface heating system has a 20.4 % increase and can recover the payback period in 2.3 years compared with traditional solar heating system. The results of the study support the use of solar energy to enhance the indoor thermal demands of rural dwellings in Northwest China.

Meta-learning based infrared ship object detection model for generalization to unknown domains

Infrared images exhibit considerable variations in probability distributions, stemming from the utilization of distinct infrared sensors and the influence of diverse environmental conditions. The variations pose great challenges for deep learning models to detect ship objects and adapt to unseen maritime environments. To address the domain shift problem, we propose an end-to-end infrared ship object detection model based on meta-learning neural network to improve domain adaptation for target domain where data is not available at training phase. Different from existing domain generalization methods, the novelty of our model lies in the effective exploitation of meta-learning and domain adaptation, ensuring that the extracted domain-independent features are meaningful and domain-invariant at the semantic level. Firstly, a double gradient-based meta-learning algorithm is designed to solve the common optimal descent direction between different domains through two gradient updates in the inner and outer loops. The algorithm enables extraction of domain-invariant features from the pseudo-source and pseudo-target domain data. Secondly, a domain discriminator with dynamic-weighted gradient reversal layer (DWGRL) is designed to accurately classify domain-invariant features and provide additional global supervision information. Finally, a multi-scale feature aggregation method is proposed to improve the extraction of multi-scale domain-invariant features. It can effectively fuse local features at different scales and global features of targets. Extensive experimental results conducted in real nighttime water surface scenes demonstrate that the proposed model achieves very high detection accuracy on target domain data, even no target domain data was used during the training phase. Compared to the existing methods, our method not only improves the detection accuracy of infrared ships by 18%, but also exhibits the smallest standard deviation with a value of 0.93, indicating its superior generalization performance.

Assessing the feasibility of nighttime water harvesting from solar photovoltaic panels in a desert region

Photovoltaics has emerged as a crucial and progressively significant contributor to renewable energy generation. Nevertheless, its effectiveness is limited to daylight hours when sunlight is available. This research paper presents an approach to promote dual usage of solar panels beyond daytime operations to facilitate water production. An AWGPV (Atmospheric water generation on PV modules) system is built and operated for nearly a year. During this period, several prototypes were built to produce up to 2.5 L/panel per day without optimizing the energy consumed during direct cooling. A techno-economic assessment was done for the prototype AWGPV system. The prototype system consisting of 3 AWGPV panels connected to the grid was able to produce water at 33 USD cents per liter in Dubai, UAE. If the electricity for direct cooling is reduced, the cost of water can be reduced further. The results point to new avenues to explore methods for reducing the electricity consumption for cooling for achieving further cost reduction. A parameter n-MHI (night Moisture harvesting index) is introduced to evaluate the feasibility and energy demands of harvesting atmospheric moisture through direct cooling. Through a climate-based analysis of various locations, the global potential of this process is explored. The collected water can be used for dust cleaning of solar panels, agrophotovoltaic systems, and other applications where water and electricity generation needs to be decentralized.

Water supply telemetry data processing in apartment buildings

The digital transformation of construction and housing and utilities sector involves data-based management. The most accessible data is telemetry of electricity, gas, heat and water consumption. Despite the fact that not all apartment buildings are equipped with meters yet, it is necessary to think about methods for processing measurement data. Intelligent data processing methods are gaining wide popularity. The purpose of this study is the processing and analysis of water consumption telemetry data. The objective of the study is to determine the periods of nighttime water consumption using the clustering method. The data of apartment meters of hourly consumption of hot and cold water are investigated. The measurement period is 1 month. Intelligent cluster analysis was conducted based on the DBSCAN machine learning model (Density-based spatial clustering of applications with noise). Clustering objects are the hours of the day. As a result of the study, the hours of night consumption of cold and hot water were allocated, both in the whole month and separately on weekdays and Sundays. The conclusion is made about the benefits of using intelligent cluster analysis of water consumption telemetry data for effective management of water resources and equipment.

Night-time water relations and gas exchange in cut shoots of five boreal dwarf shrub species: impact of soil water availability.

Recent findings suggest that drought may affect plants' daytime and night-time stomatal regulation differently. However, knowledge of night-time stomatal behaviour in dwarf shrubs growing in boreal ecosystems is lacking. We sampled cut shoots from dwarf shrub species to elucidate their capacity to transpire at night and the effect of drought on stomatal regulation. The shoots' water relations and gas exchange were measured under controlled conditions in a growth chamber. The studied species demonstrated considerable differences in their diurnal water use. The night-time water use percentage of daytime water use (NWU) reached up to 90% in Andromeda polifolia and Vaccinium uliginosum. In Rhododendron tomentosum, Vaccinium myrtillus and Chamaedaphne calyculata, the NWU was 62, 27 and 26%, respectively. The shoots of C. calyculata showed a significant increase (P < 0.001) in the transpiration rate (E) during the night. However, in R. tomentosum, a decrease (P < 0.05) in nightly E was observed. The shoot conductance (g) at the end of the night was lower than daytime g in all studied species, but the difference was not significant for V. uliginosum. Across the species, NWU was negatively related (P < 0.001) to the soil volumetric water content (SWC) in the plant habitat. However, daytime E and g were positively related (P < 0.05) to the habitat SWC. Only in V. myrtillus was night-time E higher (P < 0.05) in dry conditions than in wet conditions. Our results demonstrate high variability in diurnal water relations in dwarf shrubs, which can keep stomata open in the dark even when drought limits daytime g and E.

Nocturnal transpiration in field crops: Implications for temporal aggregation and diurnal weighing of vapor pressure deficit

Daytime transpiration is driven by evaporative demand (vapor pressure deficit, VPD) and radiative energy, dominantly accounting for daily transpiration (T). Recent modeling approaches recommend weighing VPD for diurnal cycle of T using radiation to predict T, as opposed to using daily mean VPD. This proposition requires field evaluation so that diurnal patterns of water use are represented fairly. In this research, hourly T was measured concurrently for irrigated maize, sorghum, and soybean in a dry sub-humid climate. Various VPD conditioning approaches available to the user that differed in measurement frequency, spectral sampling, and weighing strategies were evaluated to explain variance in T. The locally derived radiation-based weighing coefficient (Frac) showed substantial variability with mean estimates of 0.61 (annual) and 0.58 (growing season), which were lower than the classically recommended Tanner-Sinclair coefficient (0.75). The use of a constant Frac value for weighing VPD was suboptimal to dynamic weighing of VPD for each day, accounting for day-to-day variability. This is primarily because of considerable nighttime water use: Tn demonstrated values that were 6–16% of T across the three crops. Tn was driven by wind speed and VPD during nighttime hours. These field observations of Tn hold implications for (un)suitability of radiation-based weighing procedures, which assume no Tn. Diurnally weighted VPD was suboptimal to using daily mean VPD, as the former does not account for dark period-VPD. Additionally, reference evapotranspiration (ETo), the standardized metric of crop water use was either negative or zero for nocturnal periods when Tn ≠ 0, and thus, failed to appropriately represent Tn. A variable of transpiration, based on daily mean VPD and total daily radiation, was the most effective in explaining T variance in all crops. With increasing asymmetry between daytime and nighttime warming and aridity, it becomes increasingly important to appropriately precondition VPD data to predict T. Caution should be exercised while using radiation-weighted VPD in crops, environments and seasons with non-negligible Tn.

The overlooked non-rainfall water input sibling of fog and dew: Daily water vapor adsorption on a !Nara hummock in the Namib Sand Sea

The Namib Sand Sea is a hyper-arid coastal fog desert, with limited vegetation scattered across the extensive sand dunes. Minimal and unpredictable rainfall, along with proximity to the ocean, make non-rainfall water inputs (NRWIs), i.e. fog, dew and water vapor adsorption, an important part of the ecohydrology. We studied water accumulation across an elevated hummock formed around a !Nara (Acanthosicyos horridus) thicket in the Namib dunes during February 2020. Continuous measurements of temperature and relative humidity (RH) gradients between the soil and the air were complemented with three nights of intensive NRWI observations using 14 micro-lysimeters. While the overall objective was to study total NRWI accumulation, micro-lysimeter placement was designed to address additional questions about how NRWI accumulation was affected by hummock micro-topography and the position of the !Nara thicket. Water vapor adsorption was the primary form of NRWI, occurring nightly and accounting for at least half of the total water accumulation, even on nights with fog. This was confirmed by the measured water vapor pressure gradients between the air and the soil, which indicated nightly downward vapor fluxes. Actual vapor pressures in the air were similar on nights with and without fog, indicating fog was mostly determined by temperature. Soil RH was used as a proxy for soil water content and was found to be strongly correlated with air RH. Average nighttime air RH was correlated with total nighttime water accumulation with an R2 of 0.69–0.78. Average nighttime air RH was correlated with total nighttime water accumulation with a coefficient of determination (R2) of 0.69–0.78. Even though measurements were limited to the soil, comparison between micro-lysimeters placed on the hummock inside and outside the !Nara thicket indicated consistent, but not significant, lower water contents inside the thicket, suggesting interception of water vapor by the spines and stems of the !Nara. We conclude that water vapor adsorption, though not always appreciated as such, is a large contributor to total NRWI. The fact that water vapor adsorption was the primary NRWI in sand, which has a much lower surface area than most other soil types, and in a place where fog occurs regularly, has implications for deserts worldwide.

Nighttime transpiration: does it contribute to water stress in grape?

Climate change is driving the search for grapevine cultivars and/or rootstocks that use water more efficiently. Recently, there has been increasing attention on nighttime transpiration. The reasoning is simple. While daytime transpiration results from the necessity to have stomata open so the plant can take up carbon dioxide for photosynthesis, nighttime transpiration could be considered a “waste” of water since no photosynthesis occurs at night. So how significant is nighttime water use in grape, and does it serve some other purpose that benefits the vine?

Aerosols and Tides in the Martian Tropics During Southern Hemisphere Spring Equinox From Mars Climate Sounder Data

AbstractWe analyze Mars Climate Sounder temperature and aerosol data in the tropics, and use Fourier analysis at different local times to study atmospheric tides and their relation to the dust and water ice distributions. Our results reveal that Mars year (MY) 29 has large amplitude non‐migrating thermal tides during southern hemisphere spring equinox that are not observed at the same local time in any other year. The nighttime temperatures are the most perturbed compared to other years, with strong temperature inversions at 35–55 km altitude. The nighttime water ice cloud structure is strongly influenced by the eastward‐propagating diurnal Kelvin waves 1 and 2. Increased nighttime radiative cooling from regions of thicker clouds results in stronger downwelling above the clouds, leading to increased adiabatic warming and a strengthening of the temperature inversions. The temperatures and water ice clouds at 3:45 a.m. in MY29 more closely resemble those at 5:00 a.m. in other years, suggesting there was a shift in the phase of the diurnal tide. This phase shift, and the large amplitude non‐migrating thermal tides, appear to be related to early dust activity. Two early dust storms occurred in MY29 around the time there was upwelling over the tropics, associated with the Hadley circulation. This likely enabled the dust to be transported to higher altitudes where it has a larger radiative influence. The early dust activity in MY29 also increased the strength of the westward‐propagating non‐migrating thermal tides.

Biophysical control on nighttime sap flow in Salix psammophila in a semiarid shrubland ecosystem

The impact of extreme desert conditions on long-term nighttime sap flow dynamics in desert-dwelling shrubs is poorly understood. Based on heat-balance measurements in a semiarid area of northwest China, we investigated the nighttime sap flow (transpiration) dynamics in Salix psammophila as affected by changes in site biophysical variables over a six-year period (2012-2017). Nocturnally, sap flow rate per leaf area (Jsn) formed a positive linear relationship with air temperature (Ta), water vapor pressure deficit (VPD) and stomatal conductance (Gs), when Ta < 17 °C, VPD < 1 kPa, and Gs < 0.004 mol m−2 s−1, remaining unchanging or forming a negative linear relationship, when Ta, VPD and Gs were greater than these limits. This relationship was modified by soil water content (SWC) through its effects on Gs. The multiple regression model showed that together Ta, VPD and Gs explained 63% of the variation in Jsn. Seasonally, pairwise relationships between Ta and VPD and Gs and SWC explained 76 and 70% of the variation in Jsn during wet and dry years, respectively. Interannually, Ta and Gs were able to explain a significant portion of observed variation in Jsn, individually explaining about 74 and 83% of that variation. Interannual control on Jsn also varied with SWC, Ta and Gs explaining 84% of the variation. The diminished sensitivity of Jsn to both Ta and VPD and increased sensitivity to SWC during dry years, suggested that the shrubs had a physiological capacity to adapt to dry soil conditions. Daytime sap flow rates (Jsd) were significantly greater than those at night (i.e., Jsn), with an interannual mean difference of 0.15 ± 0.04 g cm−2 d−1 and coefficient of variation of 27%. In addition, Jsn formed a positive linear association with Jsd during the growing season. Mean Jsn contributed to the daily total sap flow (i.e., Jsn/Js24-h × 100) by 8-14% over the six years, with an interannual mean of 11%. Our findings underscore the importance of nighttime sap flow in S. psammophila and the importance of temperature and SWC in controlling nighttime water losses through transpiration. It is suggested that the proportion of nighttime sap flow could increase during plant acclimatization in response to increasing temperature and water shortages with future climate change.

Nighttime transpiration represents a negligible part of water loss and does not increase the risk of water stress in grapevine.

Nighttime transpiration has been previously reported as a significant source of water loss in many species; however, there is a need to determine if this trait plays a key role in the response to drought. This study aimed to determine the magnitude, regulation and relative contribution to whole plant water‐use, of nighttime stomatal conductance (g night) and transpiration (E night) in grapevine (Vitis vinifera L.). Our results showed that nighttime water loss was relatively low compared to daytime transpiration, and that decreases in soil and plant water potentials were mainly explained by daytime stomatal conductance (g day) and transpiration (E day). Contrary to E day, E night did not respond to VPD and possible effects of an innate circadian regulation were observed. Plants with higher g night also exhibited higher daytime transpiration and carbon assimilation at midday, and total leaf area, suggesting that increased g night may be linked with daytime behaviors that promote productivity. Modeling simulations indicated that g night was not a significant factor in reaching critical hydraulic thresholds under scenarios of either extreme drought, or time to 20% of soil relative water content. Overall, this study suggests that g night is not significant in exacerbating the risk of water stress and hydraulic failure in grapevine.

Spatiotemporal Dynamics and Environmental Controlling Factors of the Lake Tana Water Hyacinth in Ethiopia

The largest freshwater lake in Ethiopia, Lake Tana, has faced ecological disaster due to water hyacinth (Eichhornia crassipes) infestation. The water hyacinth is a threat not only to the ecology but also to the socioeconomic development of the region and cultural value of the lake, which is registered as a UNESCO reserve. This study aims to map the spatiotemporal dynamics of the water hyacinth using high-resolution PlanetScope satellite images and assesses the major environmental variables that relate to the weed spatial coverage dynamics for the period August 2017 to July 2018. The plausible environmental factors studied affecting the weed dynamics include lake level, water and air temperature, and turbidity. Water temperature and turbidity were estimated from the moderate resolution imaging spectroradiometer (MODIS) satellite image and the water level was estimated using Jason-1 altimetry data while the air temperature was obtained from the nearby meteorological station at Bahir Dar station. The results indicated that water hyacinth coverage was increasing at a rate of 14 ha/day from August to November of 2017. On the other hand, the coverage reduced at a rate of 6 ha/day from December 2017 to June 2018. However, the length of shoreline infestation increased significantly from 4.3 km in August 2017 to 23.4 km in April 2018. Lake level and night-time water temperatures were strongly correlated with water hyacinth spatial coverage (p &lt; 0.05). A drop in the lake water level resulted in a considerable reduction of the infested area, which is also related to decreasing nutrient levels in the water. The water hyacinth expansion dynamics could be altered by treating the nutrient-rich runoff with best management practices along the wetland and in the lake watershed landscape.

Biophysical controls on nocturnal sap flow in plantation forests in a semi-arid region of northern China

Recent studies have recognized the importance of nocturnal sap flow (Qn) in affecting forest carbon and water budgets and responses to climate change at stand, regional, and global scales. However, biophysical controls on Qn are not fully understood, and their implications for land surface and vegetation models are unclear. We measured growing season sap flow of two widely distributed afforestation species, Pinus tabuliformis and Acer truncatum, in a middle-aged and a young monoculture forest stand, respectively, in a semi-arid mountainous area of northern China. We found a convergence in Qn between the two species and in the proportion of Qn to the total sap flow (12.2–15.0%) across species and ages. Total growing season Qn was higher for middle-aged stands than for young stands because of larger diameters at breast height of older stands. Nighttime vapor pressure deficit (VPDn) influence on Qn of young stands was soil moisture dependent. Nighttime wind speed indirectly controlled Qn through enhancing VPDn in young stands and directly promoted Qn in middle-aged stands with relatively low tree densities. For each species, both increased and decreased soil water content were able to promote Qn in stands with relatively dry soils, which might be due to enhanced nighttime water recharge for capacitance refilling and for avoiding hydraulic failure under prolonged water stress, respectively. Total effects of these three environmental factors explained less than 55% of the Qn variations. This study highlights uncertain physiological influences of VPDn on nighttime stomatal water loss, the nighttime water loss induced by wind, region-specific patterns of nighttime water recharge, and the importance of biotic controls on Qn. Our findings help to improve the existing VPD-based method for partitioning nighttime transpiration and water recharge at tree and stand levels, and suggest the importance of incorporating nocturnal sap flow into large-scale models.

The Effect of Aeration on River Water Receiving Industrial Discharges to Its Quality and Toxicity

Citarum River in West Java Province was an important river that supported more than 25 million people in the region. It was considered highly polluted by many sources of wastes. This study was aimed to evaluate the effect of aeration process on river water quality and toxicity in Citarum tributary receiving industrial wastes as river restoration alternative. Three types of aeration methods namely mechanical, hydraulic, and diffused air were studied in laboratory scale. Water quality parameters analyzed were TSS, TDS, COD, nitrate, phosphate, nitrite, phenol, and acute toxicity LC50 96 hrs on Daphnia magna was tested to obtain TUa value. Results showed TUa of water samples collected at daytime was 0.467±0.12, whereas night time water samples resulted higher toxicity of TUa 1.36±0.3. Aeration of daytime river water by diffuser, mechanical aeration, and cascade aeration, reduced toxicity to TUa of 0.01±0.002, 0.08±0.04, and 0.30±0.2 respectively. On the other hand, aeration for night time river water samples still posed higher acute toxicity showing TUa respectively of 0.13±0.02, 0.44±0.13, and 1.04±0.13. These showed that aeration type has different capacity in lowering water toxicity and improving water quality. Study suggested that contaminated river water quality and toxicity could be improved by aeration processes.

Sap flow and responses to meteorological about the Larix principis-rupprechtii plantation in Gansu Xinlong mountain, northwestern China

The transpiration of trees plays a decisive role in the water balance of forest stands and in water yields from forested catchments, especially an artificial forest planted for the purpose of soil and water conservation in semiarid mountain ecosystem regions. For proper management of watershed ecosystems, quantification of water use, sensitivity and adaptation for artificial forest is needed. This study were monitored the sap flow for Larix principis-rupprechtii plantation by thermal dissipation probes (TDP), analyzed the correlation between the sap flow and the meteorological factors on daily and seasonal scale, and upscaled stand transpiration from individual sap flow measurements. Within a daily timescale, the net radiation (Ra), air temperature (AT), air humidity (AH), vapor pressure deficit (VPD) and wind speed (WS) showed a significantly positive correlation with sap flow velocity in day-time, but in the night-time sap flow had no significant correlation. Within a monthly timescale, the Ra, AT, WS, and VPD showed a significantly positive correlation with stand water use, whereas precipitation (Pr) showed a significantly negative correlation with stand water use. Our results also showed that the daily transpiration of L. principis-rupprechtii continued to increase with the increase of net radiation (Ra), until the late stages of growth season (except rainy and cloudy days), and the sap flow velocity showed an obvious hysteresis response to meteorological factors to alleviate plant water stress from June to October, while there was no significant correlation between day-time and night-time water use during the stage of germination and rapid growth in May. Besides, due to the relatively low temperature, the water consumption of forest stands was only about 151.05 mm during the whole growing season, and there was no obvious ‘noon break’ phenomenon in the whole growing season. These results indicated that L. principis-rupprechtii could manage the water consumption conservatively, and were appropriate for afforestation in the mountains ecosystem with high altitude and low temperature.

Water balance and tree water use dynamics in remnant urban reserves

During the expansion of urban areas, small natural reserves have often been left intact within the built environment as central elements of biodiversity conservation, ecological connectivity, landscape sustainability, and quality of life of urban dwellers. Consequently, the surrounding urbanized landscape may impact the environmental conditions of these reserves (e.g., high temperatures, low moisture conditions), resulting in the need for extensive maintenance. This study presents an estimation of the water balance over two years (2017–2018) in three small urban reserves (between 2 and 30 ha) within the Greater Melbourne metropolitan area in Australia, for the purpose of understanding tree water use. Measurements of micrometeorological variables, soil moisture content profiles, water-table levels, sap flow velocities, and stem diameter variations were used to quantify the water sources of tree transpiration in these reserves. Results revealed that, despite the urban surroundings and the climate variations, these reserves have enough water to sustain tree transpiration. In two of the three reserves, groundwater was pivotal in sustaining transpiration rates; specifically, groundwater was estimated to contribute about 30–40% of the total transpiration amount during the driest periods of the year. Groundwater also played an essential role during nights with temperatures above 25 °C, helping trees to maintain night-time water use from 3 to 16% of the daily water use. In the third reserve, the presence of a shallow layer of heavy clay supplied water to the trees, which were able to maintain relatively constant transpiration rates throughout the year. These results demonstrate the importance of understanding the water regime of each urban reserve in order to support government authorities in preserving these ecosystems.

Variability in temperature-independent transpiration responses to evaporative demand correlate with nighttime water use and its circadian control across diverse wheat populations.

Nocturnal transpiration, through its circadian control, plays a role in modulating daytime transpiration response to increasing evaporative demand, to potentially enable drought tolerance in wheat. Limiting plant transpiration rate (TR) in response to increasing vapor pressure deficit (VPD) has been suggested to enable drought tolerance through water conservation. However, there is very little information on the extent of diversity of TR response curves to "true" VPD (i.e., independent from temperature). Furthermore, new evidence indicate that water-saving could operate by modulating nocturnal TR (TRN), and that this response might be coupled to daytime gas exchange. Based on 3years of experimental data on a diverse group of 77 genotypes from 25 countries and 5 continents, a first goal of this study was to characterize the functional diversity in daytime TR responses to VPD and TRN in wheat. A second objective was to test the hypothesis that these traits could be coupled through the circadian clock. Using a new gravimetric phenotyping platform that allowed for independent temperature and VPD control, we identified three and fourfold variation in daytime and nighttime responses, respectively. In addition, TRN was found to be positively correlated with slopes of daytime TR responses to VPD, and we identified pre-dawn variation in TRN that likely mediated this relationship. Furthermore, pre-dawn increase in TRN positively correlated with the year of release among drought-tolerant Australian cultivars and with the VPD threshold at which they initiated water-saving. Overall, the study indicates a substantial diversity in TR responses to VPD that could be leveraged to enhance fitness under water-limited environments, and that TRN and its circadian control may play an important role in the expression of water-saving.

Potential involvement of root auxins in drought tolerance by modulating nocturnal and daytime water use in wheat.

The ability of wheat genotypes to save water by reducing their transpiration rate (TR) at times of the day with high vapour pressure deficit (VPD) has been linked to increasing yields in terminal drought environments. Further, recent evidence shows that reducing nocturnal transpiration (TRN) could amplify water saving. Previous research indicates that such traits involve a root-based hydraulic limitation, but the contribution of hormones, particularly auxin and abscisic acid (ABA), has not been explored to explain the shoot-root link. In this investigation, based on physiological, genetic and molecular evidence gathered on a mapping population, we hypothesized that root auxin accumulation regulates whole-plant water use during both times of the day. Eight double-haploid lines were selected from a mapping population descending from two parents with contrasting water-saving strategies and root hydraulic properties. These spanned the entire range of slopes of TR responses to VPD and TRN encountered in the population. We examined daytime/night-time auxin and ABA contents in the roots and the leaves in relation to hydraulic traits that included whole-plant TR, plant hydraulic conductance (KPlant), slopes of TR responses to VPD and leaf-level anatomical traits. Root auxin levels were consistently genotype-dependent in this group irrespective of experiments and times of the day. Daytime root auxin concentrations were found to be strongly and negatively correlated with daytime TR, KPlant and the slope of TR response to VPD. Night-time root auxin levels significantly and negatively correlated with TRN. In addition, daytime and night-time leaf auxin and ABA concentrations did not correlate with any of the examined traits. The above results indicate that accumulation of auxin in the root system reduces daytime and night-time water use and modulates plant hydraulic properties to enable the expression of water-saving traits that have been associated with enhanced yields under drought.