Evaporative Water Loss Research Articles

Water‐based spent drilling mud regulates hydrophysical properties of coarse‐textured loessial soil

AbstractAmendment application is one of the effective measures used to remediate structural problems in coarse‐textured soils. However, the application of water‐based spent drilling mud (WBSM) as a potential amendment and its associated impacts on physical and hydraulic soil properties is not well‐studied. This research aimed to investigate the effect of the application of WBSM on basic hydrophysical properties of coarse‐textured loessial soil sampled from the Loess Plateau, China. Application of WBSM to repacked loessial soil at four application rates (0, 25.0, 50.0, 75.0 g kg−1, dry basis), denoted as control (H0), low (HDL), medium (HDM) and high (HDH), respectively, was used to investigate changes in soil bulk density (ρb), soil total porosity (ƒ), saturated hydraulic conductivity (Ks), relative gas diffusivity (Dp/Do), soil‐water retention and soil evaporation characteristics. The results showed that the soil ρb in HDL and HDM decreased by 4.0% and 5.5%, respectively, as compared to H0 (p < 0.05). Measured Ks changed to 36.7% (HWL), 12.2% (HWM) and 4.4% (HWH) as compared to H0 (5.56 cm d−1). The application of WBSM further decreased the percentage of soil pore sizes >30 μm, but increased the proportion of medium pore sizes (≥30–50 μm), micro pore sizes (≥0.3–5 μm) and extremely micro pore sizes (<0.3 μm), which was attributed to the clogging effect of the fine and clay particles contained in WBSM. Decline in Dp/Do, however, was observed with increasing WBSM, likely due to the increased pore tortuosity in fine‐grained soil. The van Genuchten soil‐water retention model parameters differed largely across the WBSM application rates, with increased soil available water‐holding capacity by 50.9%, 65.9% and 64.1% in HDL, HDM and HWH, respectively, as compared to H0. However, WBSM application also increased soil available water‐holding capacity and reduced evaporative water loss, which has useful implications for the management of coarse‐textured soils with a distinct water deficit in fragile ecosystems. Widespread use of WBSM to amend coarse‐textured soils requires further studies to evaluate the effects of WBSM amendments in field trials and its environmental consequences.Highlights Water‐based spent drilling mud (WBSM) altered the texture of loessial soil. WBSM increased soil total porosity and changed pore size distribution. WBSM affected the characteristics of soil water and gas transport. The soil water availability was improved by WBSM application.

Changes of soil water budget in the area covered by biological soil crusts in Mu Us sandy land, China

Exploring and quantifying the impacts of biological soil crusts on soil hydrological processes and soil water budget in semi-arid ecosystems can provide a theoretical basis for vegetation restoration and reconstruction in deserts. Based on continuous observation of soil water content in different types of areas covered by biological soil crusts (e.g., algae, moss) and bare sand in the Mu Us sandy land during the growing season (May to October) from 2018 to 2020, we examined the effects of biological soil crusts on soil water budget at a depth of 0-40 cm. Results showed that algae and moss crusts significantly reduced soil water supplement below 40 cm by rainfall and increased soil water evaporation loss, compared with that under bare sand. In the relatively wet year (2018), the amount of soil water expenditure (seepage+evaporation) covered by bare sand and the various types of biological soil crusts was less than that of rainfall, resulting in net soil water income. In the relative dry years (2019 and 2020), the amount of soil water expenditure covered by dominant algae and moss crusts was higher than that of rainfall, causing net soil water deficit, but opposite for bare sand. Biological soil crusts led to the imbalance of soil water budget of 0-40 cm depth and even soil water deficit in relatively dry years, which may lead to the succession of plant communities to be dominated by shallow-rooted plants in this area.

Linking xylem structure and function: the comparative method in from the cold.

This article is a Commentary on Savage et al. (2022), 235: 953–964.

Evaporative water loss of 1.42 million global lakes

The evaporative loss from global lakes (natural and artificial) is a critical component of the terrestrial water and energy balance. However, the evaporation volume of these water bodies—from the spatial distribution to the long-term trend—is as of yet unknown. Here, using satellite observations and modeling tools, we quantified the evaporation volume from 1.42 million global lakes from 1985 to 2018. We find that the long-term average lake evaporation is 1500 ± 150 km3 year−1 and it has increased at a rate of 3.12 km3 year−1. The trend attributions include an increasing evaporation rate (58%), decreasing lake ice coverage (23%), and increasing lake surface area (19%). While only accounting for 5% of the global lake storage capacity, artificial lakes (i.e., reservoirs) contribute 16% to the evaporation volume. Our results underline the importance of using evaporation volume, rather than evaporation rate, as the primary index for assessing climatic impacts on lake systems.

Climate Drivers Contribute in Vegetation Greening Stalls of Arid Xinjiang, China: An Atmospheric Water Drying Effect

Xinjiang, an arid region of China, has experienced a substantial warming–wetting trend over the past five decades. However, climate change has affected vegetation growth/greening in arid Central Asia in unexpected ways due to complex ecological effects. We found a significant greening trend (consistent increase in the normalized difference vegetation index or NDVI) from 1982 to 1996, during the growing season; however, the NDVI consequently decreased and plateaued from 1997 to 2015, especially in naturally vegetated regions. Atmospheric vapor pressure deficit (VPD) is a critical driver of vegetation growth, is a direct measure of atmospheric aridity, and has increased sharply in recent decades. A partial correlation analysis indicated a significant relationship between growing season NDVI and VPD from 1997 to 2015. This implies that decreased VPD corresponds to increasing NDVI, and increasing VPD corresponds to a decrease and plateauing in the NDVI trend. Using the partial derivative equation method, our results suggest that the trend in growing season NDVI was affected primarily by increasing VPD (contributing 87.57%) from 1997 to 2015, especially in the grassland and desert biomes. Rising temperatures lead to a greater VPD, resulting in exacerbated evaporative water loss. Soil drought and atmospheric aridity limit plant stomatal conductance and could effectively lead to a decrease in the greening trend and increased vegetation mortality in arid Xinjiang. Our results emphasize the importance of VPD as a limiting factor of greening trends in arid regions. The influence of VPD on vegetation growth should be considered when evaluating arid ecosystem functioning under global warming.

Home is where the heat is: Thermoregulation of European bats inhabiting artificial roosts and the threat of heat waves

Abstract Anthropogenic land use changes, such as deforestation and commercial forestry, have substantially reduced natural roost sites for European bats. A common conservation solution is to provide artificial roosts (i.e. bat boxes), but there are concerns that these can become hotter than natural roosts in summer and could be death traps during heat waves. Nevertheless, females of several bat species form maternity colonies in these boxes, thus occupying hotter and more humid microclimates than solitarily roosting males. We tested if cooling efficiency and heat tolerance differ between sexes in European bats, and estimated the evaporative water requirements for bats living in bat boxes during hot summer days. We used indirect calorimetry and thermometry to quantify thermoregulation at high air temperatures (Ta) in four species of verspitilionid bats that regularly occupy artificial roosts. We measured resting metabolic heat production, evaporative water loss rates (EWL) and body temperature (Tb) at Ta between 28°C and 48°C during summer. We predicted that females have higher evaporative cooling efficiency (evaporative heat loss/metabolic heat production) than males, allowing them to reach their heat tolerance limit at higher Ta. We found no sex differences in maximum evaporative cooling efficiency, maximum Tb, and maximum Ta tolerated. However, the patterns of increasing EWL with Ta differed between sexes. Females tolerated higher Ta before increasing EWL than males and then rapidly increased EWL to higher values than males at the maximum Ta tolerated. These sex differences in heat dissipation strategies may reflect varying ecological and physiological constraints associated with different summer roosting habits. Synthesis and applications. Our study revealed that some small European bat species are already at risk of succumbing to lethal dehydration during present‐day heat waves, with daytime evaporative water requirements equivalent to ~30% of body mass in sun‐exposed boxes. For conservation managers working with common European bat species, particularly those in monoculture forests with woodcrete bat‐boxes, our physiologically informed recommendations include positioning boxes in diverse locations varying in aspect and sun exposure. This will ensure thermal heterogeneity of roost sites and provide a wide gradient of microclimate conditions, allowing for roost switching when necessary.

Cover crops enhance resource availability for soil microorganisms in a pecan orchard

Currently, there are substantial knowledge gaps on the impacts of cover crops on soil resources in tree cropping systems, wherein they are typically planted in interrow alleys and maintained for multiple years. While cover crops uptake soil nutrients and water, they can also prevent soil water evaporative losses and return nutrients to soils via decomposition of plant residues and stimulation of microbial nutrient cycling. This field sampling study examined variances in soil conditions across 5- and 7-year-old, cover cropped pecan orchards. We collected soil beneath cover crops and beneath adjacent trees, where soil was kept bare, to evaluate impacts of cover on the soil biota, nutrients, carbon, and their dynamics across a production season. We employed routine soil chemical analyses, phospholipid fatty acid (PLFA) analysis, and high throughput sequencing of 16 S rRNA genes and ITS regions for soils collected at four time points. We revealed that the cover cropped alley soils contained higher relative abundances of microbes that use labile soil substrates in resource rich conditions than did the tree row soils. Soil chemical analyses provided additional evidence that the cover crops did not deplete soil nutrients and reduce soil moisture, but rather, enhanced soil nutrient and moisture contents during many of the sampling time points. Notably, cover crop plant species correlated with soil nutrients and plant beneficial microbes, which may warrant consideration when selecting cover crop species. The tree row and cover cropped alley soils had different proportions of plant-beneficial mycorrhizal fungi. The tree rows supported higher numbers of ectomycorrhizal (ECM) fungi and alleys had higher relative abundances of arbuscular mycorrhizal (AM) fungi, suggesting potential benefits for tree species like pecan, which support dual colonization by AM and ECM Fungi. Altogether, the cover crops enhanced soil carbon, nutrients, and microbial populations in a pecan orchard and these impacts were frequently larger in a 7-year-old versus 5-year-old orchard.

Breathing in the Cold: Seasonal Changes in the Ventilatory Pattern in a Small Boreal Passerine Bird

Small passerine birds in the north need to take advantage of several behavioral and physiological mechanisms to maintain energy balance during the winter characterized by low food supply, low ambient temperatures, and short days. Here we test if the breathing pattern of a non-migratory species, the great tit (Parus major), show seasonal variation that could help the species keeping a positive energy balance in the winter. To this aim, we measured oxygen consumption and ventilatory variables (tidal volume and respiratory frequency) in summer- and winter-acclimatized great tits exposed to ambient temperatures between –15 and 30°C. Winter-acclimatized great tits had a higher resting metabolic rate and a different breathing pattern compared to the summer-acclimatized birds. During the winter the great tits utilized a breathing pattern, consisting of an increased respiratory frequency to tidal volume ratio compared to summer-acclimatized birds at all temperatures. The higher oxygen uptake and the altered breathing pattern in the winter-acclimatized tits resulted in a higher lung oxygen extraction. However, during acute cold exposure neither the winter- nor summer-acclimatized great tits increased the oxygen extraction at low ambient temperature. The higher lung oxygen extraction in the winter-acclimatized tits implies that the birds will save on the minute ventilation, which reduces the evaporative water loss through respiration. The daily water loss saved can be more than 1 g of water per day. This is a substantial saving corresponding to a saving in evaporative heat loss corresponding to between 4 and 8% of the resting metabolic rate. This might be significant in keeping an energy balance, and the altered breathing pattern in the winter, ensuring an increased oxygen extraction, may therefore represents an additional physiological mechanism making it possible for small passerine birds to survive the northern winter.

First use of triply labelled water analysis for energy expenditure measurements in mice

The doubly labelled water (DLW) method is widely used to determine energy expenditure. In this work, we demonstrate the addition of the third stable isotope, 17O, to turn it into triply labelled water (TLW), using the three isotopes measurement of optical spectrometry. We performed TLW (2H, 18O and17O) measurements for the analysis of the CO2 production (rCO2) of mice on different diets for the first time. Triply highly enriched water was injected into mice, and the isotope enrichments of the distilled blood samples of one initial and two finals were measured by an off-axis integrated cavity output spectroscopy instrument. We evaluated the impact of different calculation protocols and the values of evaporative water loss fraction. We found that the dilution space and turnover rates of 17O and 18O were equal for the same mice group, and that values of rCO2 calculated based on 18O–2H, or on 17O–2H agreed very well. This increases the reliability and redundancy of the measurements and it lowers the uncertainty in the calculated rCO2 to 3% when taking the average of two DLW methods. However, the TLW method overestimated the rCO2 compared to the indirect calorimetry measurements that we also performed, much more for the mice on a high-fat diet than for low-fat. We hypothesize an extra loss or exchange mechanism with a high fractionation for 2H to explain this difference.

A prenatal acoustic signal of heat affects thermoregulation capacities at adulthood in an arid-adapted bird

Understanding animal physiological adaptations for tolerating heat, and the causes of inter-individual variation, is key for predicting climate change impacts on biodiversity. Recently, a novel mechanism for transgenerational heat adaptation was identified in a desert-adapted bird, where parents acoustically signal hot conditions to embryos. Prenatal exposure to “heat-calls” adaptively alters zebra finch development and their thermal preferences in adulthood, suggesting a long-term shift towards a heat-adapted phenotype. However, whether such acoustic experience improves long-term thermoregulatory capacities is unknown. We measured metabolic rate (MR), evaporative water loss (EWL) and body temperature in adults exposed to a stepped profile of progressively higher air temperatures (Ta) between 27 and 44 °C. Remarkably, prenatal acoustic experience affected heat tolerance at adulthood, with heat-call exposed individuals more likely to reach the highest Ta in morning trials. This was despite MR and EWL reaching higher levels at the highest Ta in heat-call individuals, partly driven by a stronger metabolic effect of moderate activity. At lower Ta, however, heat-call exposed individuals had greater relative water economy, as expected. They also better recovered mass lost during morning trials. We therefore provide the first evidence that prenatal acoustic signals have long-term consequences for heat tolerance and physiological adaptation to heat.

Time changes everything: a multispecies analyses of temporal patterns in evaporative water loss.

Increasing trends in environmental temperatures and changes in the hydrological cycle caused by climate change are affecting organisms around the world. Water balance is an important feature of organisms as warmer and drier environments increase water vapour pressure deficit and cutaneous water loss. The aim of our study was to understand the hourly kinetics of losses under water-restricted conditions. In general, these kinetics are thought to be negligible, and values from water loss studies have often been summed or averaged for population and species comparisons. We compiled a cross-species data set of instantaneous water loss (EWLi) of lizards in which weight was recorded every hour for 12h (a period considered ecologically relevant for lizards) under standardized conditions with minimal disturbance. We statistically tested whether the duration of the experiment affected the values and found that the duration affected 83% of the data sets. In most cases, water loss was significantly higher during the first hour. This is likely a result of increased activity due to acclimation to the experimental conditions. However, as the experiment progressed, other temporal patterns of EWLi occurred that were not consistent between species. In addition, the average value and the first and last values of EWLi changed significantly for most species as the experiment progressed. These results suggest that the hourly kinetics of water loss should not be ignored, while experimental procedures in which EWL is recorded continuously rather than only at the beginning and end of the experiment should be used to find finer temporal variations.

Relative Water Economy Is a Useful Index of Aridity Tolerance for Australian Poephiline Finches

We evaluate if the iconic Australian Zebra Finch (Taeniopygia guttata) has a unique physiology or if its metabolic, thermal and hygric physiology are similar to other Australian poephiline finches, by comparing it with three other species, the arid-habitat Painted Finch (Emblema pictum) and the mesic-habitat Double-barred (Taeniopygia bichenovii) and Red-browed (Neochmia temporalis) Finches. All physiological variables responded to ambient temperature as expected. There were no species differences for any of the standard physiological variables, consistent with the hypotheses that birds are pre-adapted to arid habitats, the recent development of Australian deserts has limited opportunity for physiological adaptation, and all four species share similar behavioural and ecological traits. Nevertheless, the ambient temperature where metabolic water production equals evaporative water loss (point of relative water economy) was highest for the Zebra (19.1 °C), lower for Double-barred (16.4 °C) and Painted (15.2 °C) and lowest for Red-Browed (4.1 °C) Finches, corresponding with their general patterns of habitat aridity. The point of relative water economy may be a sensitive index for assessing a species’ tolerance of aridity because it integrates individual physiological variables. We conclude that the Zebra Finch is not a physiological outlier amongst Australian finches, but is at the end of a continuum of aridity tolerance for the four study species.

Effects of common tillage practices on soil moisture retention within a crop rooting zone in a sandy loam soil

Several reports states that global warming is likely to be about 1.0 ℃ above pre-industrial conditions and may even reach 1.5 ℃ between 2030 and 2052. It is therefore envisaged that as a result, climate change will intensify and rainfed arable conditions will become more unpredictable particularly in semi-arid conditions like those of Botswana due to increased heat stress resulting due to evaporative soil water losses. Considering this, several countries have therefore been experimenting with different climate smart technologies with a view to find suitable ones for arable crop production. A study was carried out at Botswana University of Agriculture & Natural Resources (BUAN) fields in 2014 to investigate the effects of different common tillage methods practiced in Botswana and how they influenced the resultant soil moisture retention. A Completely Randomized Block Design field study comprising Mouldboard ploughing, Disc ploughing, Chisel ploughing all at 200 mm depth and a no-till control were compared. During the study, soil moisture content measurements for each tillage method were taken during different sampling dates. The results showed that the no-till method retained more soil moisture when compared to the other 3 tillage methods. It retained 10%, 20% and 29% more moisture than the Disc, Chisel and Mouldboard ploughing respectively.

Impact of Spartina alterniflora invasion on evapotranspiration water loss in Phragmites australis dominated coastal wetlands of east China

A comparative analysis of co-existing invasive and native wetland plants is a practical approach to exploring exotic plant invasiveness. Spartina alterniflora is an invasive C4 grass, prevalent in China's coastal wetlands and other parts of the world, posing a risk to the hydrological cycle. While the crop coefficient Kc and evaporative water loss of the invasive S. alterniflora are still considerably unexplored, we utilized field measurements and a modeling technique to evaluate water loss to Evapotranspiration ET in marshes with S. alterniflora and P. australis. Changes in surface resistance, canopy height, and the technique used to calculate net radiation from incoming solar radiation have all been shown to influence the Penman–Monteith methodology for estimating ET. Overall, S. alterniflora surpassed P. australis in leaf area index LAI, ET, crop coefficient Kc, peak net photosynthetic rate, and growing season. Daily ET values in both plants ranged from 0.98 to 6.35 mm/day and 1.91 to 8.16 mm/day during the monitoring period. According to regression analysis, the key driving factors of ET from both plant communities throughout the growing season are net radiation, soil moisture, relative humidity, air temperature, and surface temperature. These findings highlight the necessity of precisely determining these parameters based on site-specific data instead of depending on empirical models developed mainly for crops and forests. Given the mean ET rates found in this study, S. alterniflora invasion in China currently accounts for ~4.3 × 106 m3 day−1 of water loss to ET, posing a severe threat to the availability of water resources in China's wetlands. Our findings contribute to a better understanding of the link between plant invasiveness and water loss in wetlands, offering stakeholders a benchmark for achieving future goals and plans related to the utilization of wetland water resources worldwide.

Small Alpine Marsupials Regulate Evaporative Water Loss, Suggesting a Thermoregulatory Role Rather than a Water Conservation Role.

AbstractWe show here that evaporative water loss (EWL) is constant over a wide range of ambient relative humidity for two species of small, mesic habitat dasyurid marsupials (Antechinus agilis and Antechinus swainsonii) below thermoneutrality (20°C) and within thermoneutrality (30°C). This independence of EWL from the water vapor pressure deficit between the animal and its environment indicates that EWL is physiologically controlled by both species. The magnitude of this control of EWL was similar to that of two other small marsupials from more arid habitats, which combined with the observation that there were no effects of relative humidity on body temperature or metabolic rate, suggests that control of EWL is a consequence of precise thermoregulation to maintain heat balance rather than a water-conserving strategy at low relative humidities. The antechinus appear to manipulate cutaneous EWL rather than respiratory EWL to control their total EWL by modifying their cutaneous resistance and/or skin temperature. We propose that there is a continuum between enhanced thermoregulatory EWL at high ambient temperature and so-called insensible EWL at and below thermoneutrality.

Keeping your cool: thermoregulatory performance and plasticity in desert cricetid rodents.

Small mammals in hot deserts often avoid heat via nocturnality and fossoriality, and are thought to have a limited capacity to dissipate heat using evaporative cooling. Research to date has focused on thermoregulatory responses to air temperatures (Ta) below body temperature (Tb). Consequently, the thermoregulatory performance of small mammals exposed to high Ta is poorly understood, particularly responses across geographic and seasonal scales. We quantified the seasonal thermoregulatory performance of four cricetid rodents (Neotoma albigula, Neotoma lepida, Peromyscus eremicus, Peromyscus crinitus) exposed to high Ta, at four sites in the Mojave Desert. We measured metabolism, evaporative water loss and Tb using flow-through respirometry. When exposed to Ta≥Tb, rodents showed steep increases in Tb, copious salivation and limited evaporative heat dissipation. Most individuals were only capable of maintaining Ta-Tb gradients of ∼1°, resulting in heat tolerance limits (HTLs) in the range Ta=43-45°C. All species exhibited a thermoneutral Tb of ∼35-36°C, and Tb increased to maximal levels of ∼43°C. Metabolic rates and rates of evaporative water loss increased steeply in all species as Ta approached Tb. We also observed significant increases in resting metabolism and evaporative water loss from summer to winter at Ta within and above the thermoneutral zone. In contrast, we found few differences in the thermoregulatory performance within species across sites. Our results suggest that cricetid rodents have a limited physiological capacity to cope with environmental temperatures that exceed Tb and that a rapidly warming environment may increasingly constrain their nocturnal activity.

Nature-Inspired Superhydrophobic Sand Mulches Increase Agricultural Productivity and Water-Use Efficiency in Arid Regions

Excessive evaporative loss of water from the topsoil in arid-land agriculture is compensated via irrigation that exploits massive freshwater resources. The cumulative effects of decades of unsustainable freshwater withdrawals in many arid regions are now threatening food–water security. While plastic mulches can reduce evaporation from the topsoil, their cost and nonbiodegradability limit their utility. In response, we report on biodegradable superhydrophobic sand (SHS), a bioinspired enhancement of common sand with a nanoscale wax coating. When SHS was applied as a 5–10 mm-thick mulch over the soil, evaporation was reduced by 56–78% and soil moisture increased by 25–45%, which benefited the development of crops. Multiyear field trials with tomato (Solanum lycopersicum), barley (Hordeum vulgare), and wheat (Triticum aestivum) under normal irrigation demonstrated that SHS mulch application enhanced yields by 17–73%. Under brackish water irrigation (5500 ppm NaCl), SHS mulching produced 53–208% higher fruit and grain yields for tomato and barley crops, respectively. SHS application did not affect the soil–root–rhizosphere microbial communities as evidenced by 16S rRNA gene analysis. The rhizospheric environments were dominated by an assemblage of diverse bacterial communities, such as Gammaproteobacteria, Alphaproteobacteria, and Bacteroidetes, followed by Firmicutes, Gemmatimonadetes, and Actinobacteria, which could be responsible for the degradation of paraffin wax on the SHS. Thus, SHS technology should benefit irrigated agriculture and city-greening efforts in arid regions under the constraint of high water-use efficiency.

Future Changes in the Surface Water Balance over Western Canada Using the CanESM5 (CMIP6) Ensemble for the Shared Socioeconomic Pathways 5 Scenario

The Prairie provinces of Canada have about 80% of Canada’s agricultural land and contribute to more than 90% of the nation’s wheat and canola production. A future change in the surface water balance over this region could seriously affect Canada’s agro-economy. In this study, we examined 25 ensemble members of historical (1975 to 2005), near future (2021–2050), far future (2050–2080), and end of the century (2080–2100) simulations of the Canadian Earth System Model version 5 (CanESM5) from the Coupled Model Intercomparison Project Phase 6 (CMIP6). A comprehensive analysis of a new Net Water Balance Index (NWBI) indicates an increased growing season dryness despite increased total precipitation over the Prairie provinces. Evapotranspiration increases by 100–300 mm with a 10–20% increase in moisture loss due to transpiration. Total evaporation decreases by 15–20% as the fractional contribution of evaporation from soil decreases by 20–25%. Total evaporation from vegetation increases by 10–15%. These changes in the surface water balance suggest enhanced plant productivity when soil moisture is sufficient, but evaporative water loss that exceeds precipitation in most years.

Potassium regulates diel leaf growth of Brassica napus by coordinating the rhythmic carbon supply and water balance.

Carbon and water are two main factors limiting leaf expansion. Restriction of leaf growth by low availability of carbon or water is among the earliest visible effects of potassium (K) deficiency. It is not known how K is involved in regulating the rhythmic supply of these two substrates, which differ remarkably across the day-night cycle, affecting leaf expansion. We investigated the effects of different K regimes on the time courses of leaf expansion, carbon assimilation, carbohydrates, and hydraulic properties of Brassica napus. Potassium supply increased leaf area, predominantly by promoting night-time leaf expansion (>60%), which was mainly associated with increased availability of carbohydrates from photosynthetic carbon fixation and import from old leaves rather than improvement of leaf hydraulics. However, sufficient K improved leaf hydraulic conductance to balance diurnal evaporative water loss and increase the osmotic contribution of water-soluble carbohydrates, thereby maintaining leaf turgor and increasing the daytime expansion rate. The results also indicated an ontogenetic role of K in modifying the amplitude of circadian expansion; almost 80% of the increase in leaf area occurred before the area reached 66.9% of the mature size. Our data provide mechanistic insight into K-mediated diel coordination of rhythmic carbon supply and water balance in leaf expansion.

Meet You at the Local Watering Hole? No Use of an Artificial Water Resource, and Evidence of Dehydration in Hibernating Bats in the Prairies

While torpid, small hibernators experience negative water balance due to evaporative water loss. The use of humid hibernacula and ability to drink during periodic arousals allows most hibernators to manage this deficit over the course of a winter. Some populations of big brown bats (Eptesicus fuscus) hibernate in relatively dry rock-crevices that do not contain free standing water. We monitored the winter behaviour and physiology of one such population in the Canadian prairies. Due to the semi-arid climate, we hypothesized that these bats would experience relatively high evaporative water loss and make frequent mid-winter flights to find water. We measured serum ion concentrations and hematocrit to assess level of dehydration in bats captured during winter. We also provided a heated water tank enriched in deuterium (2H) and used stable isotope analysis to test for elevated hydrogen isotope ratios (2H/1H; herein δ2H) in the blood of bats to determine if individuals drank from the tank. We also used passive acoustic monitoring, video surveillance, and passive integrated transponder (PIT) tags to determine if bats visited the heated water tank. We found evidence of hypertonic dehydration (elevated hematocrit and concentrations of some serum ions) in bats as winter progressed. Blood δ2H of bats was similar to that of water on the landscape, and acoustic and video surveillance did not indicate any visits by bats to the water tank. Post-arousal dehydration is not uncommon in hibernators, which agrees with our observation that the water tank did not represent a water resource, despite it being the only open (not frozen) water available. It is unknown whether bats may exploit frozen sources of water (e.g., snow) to supplement metabolic water produced from fat catabolism.