Unlimited Water Supply Research Articles

Potential Evaporation and the Complementary Relationship

AbstractThe complementary relationship (CR) provides a framework for estimating land surface evaporation with basic meteorological observations by acknowledging the relationship between actual evaporation, apparent potential evaporation and potential evaporation (Epo). As a key variable in the CR, Epo estimates by conventional models have a long‐standing problem in practical applications. That is, the meteorological forcings (i.e., radiation and temperature) employed in conventional Epo models are observed under actual conditions that are generally not saturated. Hence, conventional Epo models do not conform to the original definition of Epo (i.e., the evaporation that would occur with an unlimited water supply). Here, we estimate Epo using the maximum evaporation approach (Epo_max) that does follow the original Epo definition. We find that adopting Epo_max considerably reduces the asymmetry of the CR compared to when the conventional Priestley‐Taylor Epo is used. We then employ Epo_max and develop a new physically based, calibration‐free CR model, which shows an overall good performance in estimating actual evaporation in 705 catchments at the mean annual scale and 64 flux sites at monthly and mean annual scales (R2 ranges from 0.73 to 0.75 and root‐mean‐squared error ranges from 9.8 to 18.8 W m−2).Both the 705 catchments and 64 flux sites cover a wide range of climates. More importantly, the use of Epo_max leads to a new physical interpretation of the CR.

Assessing the maximum potential cooling benefits of irrigation in Australia during the “Angry Summer” of 2012/2013

Recent studies using global climate models have suggested that irrigation, assuming unlimited water supply and that all crops can be irrigated, may be an option for regional cooling in southeast Australia. In this paper, using idealised simulations, we aim to quantify the maximum possible benefits of irrigation in southeast Australia during a record breaking summer. By limiting the amount of irrigation applied to the actual amount used, and only to areas which are equipped for it, our study provides much needed practical context on the maximum potential benefits of irrigation for southeast Australia. We conduct simulations with the Weather Research and Forecasting regional atmospheric model to investigate the sensitivity to both land surface models and irrigation parameters (start hour, duration and frequency). All simulations used the same total amount of irrigation water. Our results show that irrigation could potentially reduce the mean seasonal maximum temperature during the Angry summer of 2012/2013 by −1.44°C to −2.13°C over irrigated regions. Maximum possible cooling was achieved by applying irrigation during the middle of the day, over 4 h, with daily application. During early hours of the morning, increasing the number of hours that irrigation is on has little to no effect on maximum cooling, but longer duration of irrigation later during the day leads to larger cooling. Similar results were found when decreasing irrigation frequency. The amount of cooling was strongly dependent on the land surface model, with use of the CLM model resulting in 2.32 to 2.66 times more cooling as compared to the Noah and Noah-MP land surface models, highlighting the importance of using multiple land surface models. Our results also highlight that considering realistic irrigation volumes and equipped-areas leads to cooling benefits that are largely local, and studies using global models that do not take this into consideration are likely over-estimating the potential cooling benefits of irrigation.

Thirst protects cottonmouths from infection

2022 has been an extraordinarily dry year for some regions of the planet. Rivers are running low, reservoirs are shrinking and animals are going thirsty. However, drought is a routine part of life for the cottonmouth (Agkistrodon conanti) population of Snake Key, off the Florida coast, USA. ‘The islands of the Cedar Keys are recently formed relic sand dunes and recent patterns of sea level rise in the northern Gulf of Mexico suggest the islands have been isolated from the mainland for 3500–4500 years’, says Mark Sandfoss from the University of Florida, USA. With access only to rainfall, the snakes often go thirsty. However, Sandfoss and Harvey Lillywhite, also from the University of Florida, had a hunch that the snakes may gain some benefit from their dehydrated lifestyle. ‘Recent studies have found that as reptiles become dehydrated, the ability of their immune system to protect them from disease improves’, says Sandfoss. Could the same hold true for the castaway cottonmouths?Sandfoss headed over to Snake Key in search of the marooned vipers. ‘They conceal themselves under vegetation but often gave themselves away by attempting a quick strike at a passing boot. This is both helpful and unsettling’, chuckles Sandfoss. He picked up each animal with a snake hook before securing it in a bucket and collecting a tiny blood sample, ‘which requires incredible trust in the person holding the venomous snake while I draw blood from the tail’, Sandfoss admits. With the blood sample in hand, he transported the snakes back to the lab where he offered them a drink to find out how dehydrated they were, weighing them to monitor their mass gain as they took on water to quench their thirst. In addition, François Brischoux (La Rochelle Université, France) checked the animals’ corticosterone levels – a hormone which usually rises when animals are thirsty – to find out how stressed they were.Sure enough, the Snake Key cottonmouths were more dehydrated (with a blood plasma concentration of 344.1 mosmol kg−1) and keener to drink than well-hydrated cottonmouths (309.1 mosmol kg−1 blood plasma concentration) from a nearby marshy wildlife reserve at Paynes Prairie, FL, USA. In addition, the thirsty Snake Key cottonmouths were more stressed than the Paynes Prairie snakes. Yet, when the team tested how well primed the snakes’ blood was to fight an infection, the island snakes were no better prepared than their mainland cousins. But would the snakes’ immunity alter as their thirst levels changed?This time, Sandfoss transported 17 snakes back to the lab (eight from Snake Key and nine from the mainland) providing the animals with an unlimited water supply to ensure that they were well hydrated before testing how their immune system attacked a fake infection. Then, he removed the reptiles’ water bowls until they had lost one-fifth of their body mass – they were thirsty, but not dangerously so – before rechecking the strength of their immune system. Finally, he returned their water bowls and allowed the animals to slake their thirst before retesting their immunity 48 h later.Both the thirsty Snake Key and mainland snakes produced powerful immune responses after losing 20% of their mass in water. Dehydration made the snakes more resistant to infection, although the strength of the snakes’ immune response returned rapidly to normal after a long drink. Even though the Snake Key snakes routinely experience thirst, they are no more immune to infection when deprived of water than their mainland cousins. And it is becoming increasingly essential that we understand how reptiles react when their waterholes dry up as climate patterns continue shifting and animals face greater environmental uncertainty.

On the Estimation of Potential Evaporation Under Wet and Dry Conditions

AbstractPotential evaporation (EP) is an important concept that has been extensively used in hydrology, climate, agriculture and many other relevant fields. However, EP estimates using conventional approaches generally do not conform with the underlying idea of EP, since meteorological forcing variables observed under real conditions are not necessarily equivalent to those over a hypothetical surface with an unlimited water supply. Here, we estimate EP using a recently developed ocean surface evaporation model (i.e., the maximum evaporation model) that explicitly acknowledges the inter‐dependence between evaporation, surface temperature (Ts) and radiation such that is able to recover radiation and Ts to a hypothetical wet surface. We first test the maximum evaporation model over land by validating its evaporation estimates with evaporation observations under unstressed conditions at 86 flux sites and found an overall good performance. We then apply the maximum evaporation model to the entire terrestrial surfaces under both wet and dry conditions to estimate EP. The mean annual (1979–2019) global land EP from the maximum evaporation model (EP_max) is 1,272 mm yr−1, which is 11.2% higher than that estimated using the widely adopted Priestley‐Taylor model (EP_PT). The difference between EP_max and EP_PT is negligible in humid regions or under wet conditions but becomes increasingly larger as the surface moisture availability decreases. This difference is primarily caused by increased net radiation (Rn) when restoring the dry surfaces to hypothetical wet surfaces, despite a lower Ts obtained under hypothetical wet conditions in the maximum evaporation model.

Groundwater in Crisis? Addressing Groundwater Challenges in Michigan (USA) as a Template for the Great Lakes

Groundwater historically has been a critical but understudied, underfunded, and underappreciated natural resource, although recent challenges associated with both groundwater quantity and quality have raised its profile. This is particularly true in the Laurentian Great Lakes (LGL) region, where the rich abundance of surface water results in the perception of an unlimited water supply but limited attention on groundwater resources. As a consequence, groundwater management recommendations in the LGL have been severely constrained by our lack of information. To address this information gap, a virtual summit was held in June 2021 that included invited participants from local, state, and federal government entities, universities, non-governmental organizations, and private firms in the region. Both technical (e.g., hydrologists, geologists, ecologists) and policy experts were included, and participants were assigned to an agricultural, urban, or coastal wetland breakout group in advance, based on their expertise. The overall goals of this groundwater summit were fourfold: (1) inventory the key (grand) challenges facing groundwater in Michigan; (2) identify the knowledge gaps and scientific needs, as well as policy recommendations, associated with these challenges; (3) construct a set of conceptual models that elucidate these challenges; and (4) develop a list of (tractable) next steps that can be taken to address these challenges. Absent this type of information, the sustainability of this critical resource is imperiled.

Environmental heterogeneity and water availability shape the structure of phyllostomid bat assemblages (Mammalia: Chiroptera) in the northeastern Amazon forest

The relationship between environmental heterogeneity and species diversity has been one of the most studied patterns in ecology. However, some taxa and regions worldwide still lack studies to verify this relationship. Phyllostomidae is the most ecologically diverse family of mammals worldwide, encompassing a great proportion of the species of mammals and bats across the Amazon forest. Even though the Amazon seems to be a homogeneous landscape with an unlimited supply of water, it presents a high variation in vegetation types and proximity to large bodies of water. In our study, we have analyzed the relationship between environmental heterogeneity and proximity to large bodies of water in the structure of phyllostomid assemblages (Chao-estimated species richness and capture rates). We have found that an increase in landscape heterogeneity associated with large bodies of water and representative flooded forest increase species richness. In addition, more heterogeneous landscapes in the presence of water have presented a higher abundance of bats. Our findings might be related with the small niche widths of phyllostomids, which could have promoted specialization in some landscape features, while the presence of water could have promoted an increase in food availability (insects and fruits), leading to an increase in phyllostomid richness and abundance. This is important information for planning where to place protected areas in the northeastern portion of the Amazon, while taking into account the consequences of drought and deforestation close to water bodies on the local phyllostomid fauna, and the maintenance of the ecosystem services provided by a higher bat diversity.

Water use efficiency of sugar beet genotypes: A relationship between growth rates and water consumption

AbstractDrought stress restricts sugar beet growth and yield formation. For the development of adapted varieties, reasons for high water demand in certain growth periods and for genotypic differences in water use efficiency (WUE) were investigated. In 2019 and 2020, different drought stress periods were simulated in pot trials in the greenhouse with four sugar beet genotypes by reducing the water supply to 50% of the water holding capacity. With unlimited water supply, water consumption developed in parallel to the growth rate. This indicates that water demand is driven by growth rate. Therefore, early drought stress in the period with highest growth rate caused strongest yield reductions, which could not be compensated later in the season. Unlike sugar yield, water consumption differed among genotypes, resulting in genotypic differences in WUE. However, no relevant genotype by water supply interaction occurred, giving no indication for drought tolerance of the genotypes with high WUE. WUE is rather determined by the sugar yield potential of a genotype than by water supply. Therefore, sugar beet genotypes should be selected for their sugar yield potential when breeding for environments with varying water supply.

Development of Irrigation Regime of Limited and Unlimited Water Supply for Satisfactory Rice Yield

Rice is the staple food for majority of the population worldwide and is a water-consuming crop. Decreasing water availability due to climate change necessitates the development of water saving rice production technology. The objective of this study was to develop water management strategies for two contrast scenarios of water availability for improvement of rice yield with high water productivity. A pot experiment using different levels of water percentages for water management treatments in rice was conducted inside a greenhouse during the wet

Knockout of Auxin Response Factor SlARF4 Improves Tomato Resistance to Water Deficit.

Auxin response factors (ARFs) play important roles in various plant physiological processes; however, knowledge of the exact role of ARFs in plant responses to water deficit is limited. In this study, SlARF4, a member of the ARF family, was functionally characterized under water deficit. Real-time fluorescence quantitative polymerase chain reaction (PCR) and β-glucuronidase (GUS) staining showed that water deficit and abscisic acid (ABA) treatment reduced the expression of SlARF4. SlARF4 was expressed in the vascular bundles and guard cells of tomato stomata. Loss of function of SlARF4 (arf4) by using Clustered Regularly Interspaced Short Palindromic Repeats/Cas 9 (CRISPR/Cas 9) technology enhanced plant resistance to water stress and rehydration ability. The arf4 mutant plants exhibited curly leaves and a thick stem. Malondialdehyde content was significantly lower in arf4 mutants than in wildtype plants under water stress; furthermore, arf4 mutants showed higher content of antioxidant substances, superoxide dismutase, actual photochemical efficiency of photosystem II (PSII), and catalase activities. Stomatal and vascular bundle morphology was changed in arf4 mutants. We identified 628 differentially expressed genes specifically expressed under water deficit in arf4 mutants; six of these genes, including ABA signaling pathway-related genes, were differentially expressed between the wildtype and arf4 mutants under water deficit and unlimited water supply. Auxin responsive element (AuxRE) elements were found in these genes’ promoters indicating that SlARF4 participates in ABA signaling pathways by regulating the expression of SlABI5/ABF and SCL3, thereby influencing stomatal morphology and vascular bundle development and ultimately improving plant resistance to water deficit.

Reassessing the Role of Potassium in Tomato Grown with Water Shortages

Potassium (K) is closely related to plant water uptake and use and affects key processes in assimilation and growth. The aim of this work was to find out to what extent K supply and enhanced compartmentation might improve water use and productivity when tomato plants suffered from periods of water stress. Yield, water traits, gas exchange, photosynthetic rate and biomass partition were determined. When plants suffered dehydration, increasing K supply was associated with reduction in stomatal conductance and increased water contents, but failed to protect photosynthetic rate. Potassium supplements increased shoot growth, fruit setting and yield under water stress. However, increasing the K supply could not counteract the great yield reduction under drought. A transgenic tomato line with enhanced K uptake into vacuoles and able to reach higher plant K contents, still showed poor yield performance under water stress and had lower K use efficiency than the control plants. With unlimited water supply (hydroponics), plants grown in low-K showed greater root hydraulic conductivity than at higher K availability and stomatal conductance was not associated with leaf K concentration. In conclusion, increasing K supply and tissue content improved some physiological features related to drought tolerance but did not overcome yield restrictions imposed by water stress.

Understanding topography-driven groundwater flow using fully-coupled surface-water and groundwater modeling

Numerical models with spatially-varying head as top boundary conditions were used in previous studies to understand topography-driven groundwater flow. The head boundary conditions could cause artifacts of extremely large, but unrealistic recharge rates owing to unlimited supply of water. This study adopted a fully-coupled surface–subsurface hydrologic modeling approach to simulate transient topography-driven groundwater flow and also surface-water flow under homogeneous and isotropic settings. Two 100-year climate datasets and five hydraulic conductivities (K, 0.01–100 m/d) were tested in numerical experiments. In the base case with a wet climate (annual precipitation 1696 mm/y) and K of 1 m/d, groundwater head at two different locations close to both lateral boundaries fluctuates only within 5.1 m and 9.6 m, respectively, during the 100-year period. Despite the local water table fluctuations caused by the variability in the climatic record, large-scale groundwater flow systems can be assumed in dynamic equilibrium provided stationary climate. Long-term average exchange fluxes are spatially constant and limited by precipitation infiltration when surface water is absent, whereas they vary from positive to negative values (i.e., recharge to discharge) spatially when surface water is present. Sensitivity analysis suggests that wetter climate and smaller K lead to more inundation of the land surface, stronger hierarchical nesting of groundwater flow systems and more variable exchange fluxes. Overall, our first fully-coupled modeling of topography-driven groundwater flow implies that attention must be paid to causality between head and flow, and climatic record as boundary conditions may be more appropriate due to its relaxed manner.

Evapotranspiration and yield components of soybean

Observation was conducted to determine the impact of water deprivation under flowering on the yield components of soybean at Keszthely, in the growing seasons between 2017 and 2018. The soybean represents an artificial ecosystem in this study. Three water levels designated as full watering in traditionally operated evapotranspirometer (ET), water withdrawal under crop flowering in modified evapotranspirometer (RO), and rainfed (P) crops were used. In RO treatments, the crops received half of the water based on the amount of unlimited water supply. Irrespective of variety, the highest water uses were obtained in ET, while the lowest ones were observed in RO over both growing seasons. Surprisingly, in spite of different variety standards provided by the crop breeders, and irrespective to water supply, no significant impact in actual evapotranspiration rate, ETa, between the two varieties was observed. Significant impact in soybean water losses between the treatments was observed in RO as compared to the evapotranspiration of crops with unlimited watering.

Experimental Investigations on the Performance of a Single Slope Solar Still Coupled with Shallow Solar Pond under Malaysian Conditions

Water is important to life. Deprived of water, humans can only survive for a few days. Oceans offer unlimited supply of water but it could not be ingested by humans on account of its high salt content. Desalination using fossil fuels as an energy source is expensive and may harm the environment. On the other hand, solar energy which is renewable and environmentally friendly can be used as a cheaper alternative. This paper aims to investigate the performance of a single slope solar still coupled with shallow solar pond of different design parameters under Malaysian conditions. Results showed that the performance of stills coupled with shallow solar pond is better than the ones without. The active still with the steepest condenser tilt angle (20o) yielded the highest productivity of 119 ml of water as compared to the 3o tilt angle passive still (8.5 ml).

Determining the influence of irrigation efficiency improvement on water use and consumption by conceptually considering hydrological pathways

Improving irrigation efficiency is widely believed to be a promising opportunity for large water savings. However, more and more voices have been raised against this idea in recent years. This study investigated the impacts of irrigation efficiency improvement on water use and consumption by combining an agro-economic model with the conceptualization of hydrological pathways. The investigation was conducted under two different conditions, i.e., Case 1: unlimited water supply and restricted irrigatable land, and Case 2: limited water supply and unrestricted irrigatable land. At the scale of the WUU, we found that the water uses could be reduced significantly after improving irrigation efficiency, while the water consumptions would be of similar magnitudes for different irrigation techniques under the condition of Case 1. However, in the condition of Case 2, the water uses would be inelastic to the enhanced irrigation efficiency; and the water consumption would increase slightly if the fixed cost ratio is high. At the scale of the irrigation system, the reductions in water use, as a result of efficiency improvement, would be more and more insignificant in response to increasing water cost ratios and numbers of WUUs under the condition of Case 1. In contrast, the water uses would increase, although with small magnitudes, when the fixed cost ratios and the number of reuse cycles are relatively high under the condition of Case 2. This study demonstrated that alternative restrictions on water supply and irrigatable land could effectively constrain water use and consumption after modernizing the irrigation systems. The sensitivity of the major assumptions, and the uncertainties and limitations have been revealed and discussed, along with some implications for agricultural water managements. The findings can shed some light on the lively debate regarding the effectiveness of technological water saving measures.

Intercomparison of Model-Estimated Potential Evapotranspiration on the Tibetan Plateau during 1981–2010

Abstract Potential evapotranspiration (PET), the maximum evapotranspiration rate under unlimited water supply, reflects the capacity for transpiration flow and plant primary production. Numerous models have been developed to quantify PET, but there are still large uncertainties in PET estimations. In this study, the authors conducted spatially explicit estimations of daily PET from 1981 to 2010 for eight different land-cover types on the Tibetan Plateau by applying three types of PET models including a combination model (Penman–Monteith), a radiation-based model (Priestley–Taylor), and a temperature-based model (Thornthwaite). This study found that the PET estimated by Thornthwaite model (PETT) was lower than those estimated by Priestley–Taylor (PETPT) and Penman–Monteith models (PETPM). Penman–Monteith model gave the highest estimates of PET on annual and daily scales. The mean annual PET for the whole plateau estimated by these three models varied from 675.1 to 700.5 mm yr−1, and daily PET varied from 1.33 to 1.92 mm day−1. The spatial pattern of PETT did not agree with the PETPT and PETPM, while the latter two agreed well with each other. Because of different model structures and dominant meteorological drivers, the interannual variability of PET varied significantly among the models. PETPT and PETPM showed a transition around 1993 since the dominant meteorological drivers were different before and after 1993. These disagreements among different models suggested that PET models with different algorithms should be used with caution. This study provided a validation to assist those undertaking PET estimations on the Tibetan Plateau.

Water relations and photosynthetic water use efficiency as indicators of slow climate change effects on trees in a tropical mountain forest in South Ecuador

The effects of an increasing moisture on trees of the tropical species-rich mountain rain forest in the South Ecuadorian Andes was investigated, using the daily total water consumption (TWC) and the instantaneous water use efficiency (WUE, ratio of photosynthetic CO2 uptake per water loss by transpiration) as ecophysiological indicators. Two canopy and one sub-canopy tree species, (Vismia tomentosa, Clusiaceae, an as of yet unknown Lauracee, and Spirotheca rosea, Bombacaceae) were the experimental objects. Seasonal changes as well as a long-term (18 months) trend of increasing precipitation caused an inverse reaction of the TWC of the trees. Because of a rather unlimited water supply to the trees from a permanently high water content of the soil, transpiration followed mainly the atmospheric demand of water vapor, and increasing moisture hence reduced water loss by transpiration. It was hypothesized that in spite of the reduction in transpiratory water loss photosynthetic carbon acquisition would be not or less affected due to an increase in water use efficiency. Concomitant measurements of photosynthetic net CO2 uptake showed the expected increase of WUE in V. tomentosa and S. rosea, but no clear reaction of the Lauracee. Accompanying measurements of stem extension growth confirmed an undiminished growth of V. tomentosa and S. rosea but showed also suspended growth of the Lauracee during the wettest months. While TWC can be continuously monitored with the heat dissipation technique, WUE is determined by leaf porometry in campaigns for which access to the canopy is required. Simultaneous recordings of the gas exchange of leaves at 4 different positions in the crown of one of the experimental trees (V. tomentosa) showed the usability of the trait WUE in combination with the total daily water consumption as indicator set for assessing the response of trees to a subtly changing climate. However, not all tree species appear as likewise useful indicator trees.

Effects of hydropeaking waves’ offsets on growth performances of juvenile Salix species

Hydropower production and other human activities change the natural flow regime of rivers (e.g., hydropeaking effects), in turn, impacting the riparian environment. Here we present an experiment conceived to investigate the response of forced offsets in water table dynamics on the temperate floodplain riparian vegetation species of Salix viminalis. Three specific water level regimes, simulating daily hydropeaking effects in terms of daily water table variations and offsets, were applied to three batteries of Salix cuttings growing outdoors in plastic pots. All pots initially were provided the same unlimited water supply. Then the dynamics were changed to include 90-cm daily oscillations of water table. The transitory responses of the cuttings were quantified with measurements of continuous sap flow and water potential. We regularly monitored growth parameters, leaf water potential, and gas exchange measurements, and took pictures of each plant. At the end of the experiment, all cuttings were removed and the biomass, from both above and below ground, analyzed. The 3D root structure was investigated using high-resolution computed tomography. Our results showed a clear link between root distribution and water regime. The strong offset of water table dynamics was followed by root system adjustment and plant adaptation to the new conditions. Macroscopic effects in terms of growth parameters corresponded with water pressure and transpiration measurements, strengthening our interpretation of the results. Daily hydropeaking offset appeared to have only a minor impact on the development and photosynthesis of S. viminalis cuttings, and can probably be neglected in real cases of dam regulation. On the other hand, weekly periodicity (e.g., weekend periods of dryness) could have harsher impacts, and should be evaluated in future studies.

Coelacanths

Coelacanths

The Effect of Prolonged Physical Activity Performed during Extreme Caloric Deprivation on Cardiac Function

BackgroundEndurance exercise may induce transient cardiac dysfunction. Data regarding the effect of caloric restriction on cardiac function is limited. We studied the effect of physical activity performed during extreme caloric deprivation on cardiac function.MethodsThirty-nine healthy male soldiers (mean age 20±0.3 years) were studied during a field training exercise lasted 85–103 hours, with negligible food intake and unlimited water supply. Anthropometric measurements, echocardiographic examinations and blood and urine tests were performed before and after the training exercise.ResultsBaseline VO2 max was 59±5.5 ml/kg/min. Participants' mean weight reduction was 5.7±0.9 kg. There was an increase in plasma urea (11.6±2.6 to 15.8±3.8 mmol/L, p<0.001) and urine osmolarity (692±212 to 1094±140 mmol/kg, p<0.001) and a decrease in sodium levels (140.5±1.0 to 136.6±2.1 mmol/L, p<0.001) at the end of the study. Significant alterations in diastolic parameters included a decrease in mitral E wave (93.6 to 83.5 cm/s; p = 0.003), without change in E/A and E/E′ ratios, and an increase in iso-volumic relaxation time (73.9 to 82.9 ms, p = 0.006). There was no change in left or right ventricular systolic function, or pulmonary arterial pressure. Brain natriuretic peptide (BNP) levels were significantly reduced post-training (median 9 to 0 pg/ml, p<0.001). There was no elevation in Troponin T or CRP levels. On multivariate analysis, BNP reduction correlated with sodium levels and weight reduction (R = 0.8, p<0.001).ConclusionsExposure to prolonged physical activity performed under caloric deprivation resulted in minor alterations of left ventricular diastolic function. BNP levels were significantly reduced due to negative water and sodium balance.

Diurnal patterns of water use in Eucalyptus victrix indicate pronounced desiccation-rehydration cycles despite unlimited water supply

Knowledge about nocturnal transpiration (E(night)) of trees is increasing and its impact on regional water and carbon balance has been recognized. Most of this knowledge has been generated in temperate or equatorial regions. Yet, little is known about E(night) and tree water use (Q) in semi-arid regions. We investigated the influence of atmospheric conditions on daytime (Q(day)) and nighttime water transport (Q(night)) of Eucalyptus victrix L.A.S. Johnson & K.D. Hill growing over shallow groundwater (not >1.5 m in depth) in semi-arid tropical Australia. We recorded Q(day) and Q(night) at different tree heights in conjunction with measurements of stomatal conductance (g(s)) and partitioned E(night) from refilling processes. Q of average-sized trees (200-400 mm diameter) was 1000-3000 l month(-1), but increased exponentially with diameter such that large trees (>500 mm diameter) used up to 8000 l month(-1). Q was remarkably stable across seasons. Water flux densities (J(s)) varied significantly at different tree heights during day and night. We show that g(s) remained significantly different from zero and E(night) was always greater than zero due to vapor pressure deficits (D) that remained >1.5 kPa at night throughout the year. Q(night) reached a maximum of 50% of Q(day) and was >0.03 mm h(-1) averaged across seasons. Refilling began during afternoon hours and continued well into the night. Q(night) eventually stabilized and closely tracked D(night). Coupling of Q(night) and D(night) was particularly strong during the wet season (R2 = 0.95). We suggest that these trees have developed the capacity to withstand a pronounced desiccation-rehydration cycle in a semi-arid environment. Such a cycle has important implications for local and regional hydrological budgets of semi-arid landscapes, as large nighttime water fluxes must be included in any accounting.