Regulation Of Water Loss Research Articles

A fatty acid synthase gene (FASN3) from the integument tissue of Rhodnius prolixus contributes to cuticle water loss regulation.

Fatty acid synthase is a multifunctional enzyme involved in the formation of fatty acids. Despite the role of fatty acids in cell signalling and energy metabolism, and as precursors to pheromones and hydrocarbons that waterproof the cuticle, the insect fatty acid synthases have been scarcely studied. Here we perform the molecular characterization of three fatty acid synthase genes (fatty acid synthase RPRC000123, RPRC000269 and RPRC002909) in the Chagas disease vector, Rhodnius prolixus. Gene expression screening by reverse transcription quantitative PCR showed that RPRC000123 and RPRC002909 are expressed almost exclusively in the integument tissue whilst RPRC000269 is mostly expressed in the fat body and also in several body organs. Phylogenetic analysis, together with gene expression results, showed that RPRC000269, RPRC002909 and RPRC000123 are orthologues of Drosophila melanogaster fatty acid synthase 1 (FASN1), FASN2 and FASN3 genes, respectively. After RNA interference-mediated knockdown of RPRC000123, insects died immediately after moulting to the next developmental stage. However, mortality was prevented by placing the insects under saturated humidity conditions, suggesting that dehydration might play a role in the insects' death. Lipid analyses in RPRC000123-silenced insects showed reduced amounts of integument fatty acids and methyl-branched hydrocarbons, compared to controls. These data support an important role for FASN3 in the biosynthesis of the precursors to hydrocarbons that waterproof the insect cuticle.

Genetic and morpho-physiological differentiation in a limpet population across an intertidal gradient

Marine organism adaptive capacity to different environmental conditions is a research priority to understand what conditions are important in structuring the spatial distribution of natural populations. In this context, this study evaluates whether potential differences in Siphonaria lessonii morphology (size and shell shape) and physiology (water loss regulation) at different shore heights are linked to genetically distinguishable individuals. To achieve this goal, we compared size-frequency distribution, morphometric, and genetic data (ISSR-PCR technique) of S. lessonii from the upper, middle and lower shore. We complemented these field samplings with laboratory experiments on water loss and mortality. Genetic analysis showed different genetic composition for individuals from the upper and lower shore. This pattern was accompanied by morpho-physiological variations: the upper shore had fewer small limpets, lower shell shape dispersion (with a morphotype characterized by a higher shell), and less water loss and mortality related to air exposure than the lower shore. The results reported herein support the idea that the extreme and unpredictable conditions of the upper shore may impose strong selection pressure on its inhabitants, leading to considerable morpho-physiological differentiation consistent with different genetic composition. This probably plays an important role in structuring the spatial distribution of natural S. lessonii populations with a possible effect on size-structure distribution.

Genetic and environmental influences on stomates of big bluestem (Andropogon gerardii)

Big bluestem (Andropogon gerardii) is a dominant C4 prairie grass that has wide distribution and several genetically distinct ecotypes. Many of the ecotypic adaptations are related to water availability in the native environment. Stomates facilitate photosynthetic gas exchange and regulate water loss from the plant. As such, stomatal size and density represent possible adaptations to conserve water. We hypothesized drought-tolerant ecotypes of big bluestem would have fewer or smaller stomates compared to more mesic ecotypes. Five ecotypes of big bluestem were planted in four common gardens from western Kansas to southern Illinois, USA to determine genetic and environmental influences on stomates. Leaves of all ecotypes of A. gerardii were largely hypostomatous and genetics was a greater influence than environment for stomatal size and density. The drought-tolerant Sand bluestem had larger stomates on abaxial surfaces of leaves, but a lower density compared to most other ecotypes. The most mesic Illinois ecotype and the Kaw cultivar had the greatest density of stomates on abaxial surfaces of leaves. Sand Bluestem had a greater density of stomates on adaxial surfaces of leaves compared to all other ecotypes. Gas exchange measures followed patterns of stomate distribution, where abaxial CO2 uptake rates were greater than adaxial CO2 uptake rates, although differences between leaf surfaces was more pronounced in stomatal density than in CO2 uptake. There were minor differences in size and density of stomates among sites that corresponded with precipitation, although these differences were minor, illustrating the genetic underpinnings of stomates in big bluestem. There is a genetic predisposition for drought-tolerant ecotypes to have fewer stomates, illustrating an evolutionary adaptation to drought tolerance in an important prairie species.

INDICATORS OF WATER EXCHANGE OF LEAVES OF OAK QUERCUS ROBUR L. AND QUERCUS RUBRA L. IN VARIOUS GROWING CONDITIONS IN THE NORTHERN SUBZONE OF THE STEPPE OF UKRAINE

Water metabolism indicators of leaves Q. robur and Q. rubra in artificial planting and trees at a distance from him wascompared . Found that the leaves Q. robur of separately growing trees is characterized by predominantly higher intensity of transpiration in all months of the study than Q. rubra. Planting both types in the vast majority of measurements of water evaporation is less significant than in the separately growing trees in a clearing. Noted that in September, the figures of evaporation of water is the highest relative to the previous time of measurement. Was observed the fall of this indicator in the hottest period of the day, as in July, indicating deterioration of the water loss regulation. The Q. robur leaf water deficit in plants of open space is bigger than in planting in all studied periods. In Q. rubra, the figure bigger in the planting. A comparison of leaves water deficit both species separately growing trees indicates that it is smaller in Q. rubra than in Q. robur, it is consistent with a more intense return of water by Q. robur leaves. But planting despite more intense transpiration and lower water-holding capacity from Q. robur has conversely situation. During all periods of the study water-storage capacity is higher in the Q. rubra leaves than in Q. robur. However, the relative turgescence in Q. robur leaves the highest in the plantations, in Q. rubra this figure the biggest in separately growing trees, which can be explained by the fact that this indicator depends not only from evaporation, but also to a large extent on the flow of water through the root system.

Can birds do it too? Evidence for convergence in evaporative water loss regulation for birds and mammals.

Birds have many physiological characteristics that are convergent with mammals. In the light of recent evidence that mammals can maintain a constant insensible evaporative water loss (EWL) over a range of perturbing environmental conditions, we hypothesized that birds might also regulate insensible EWL, reflecting this convergence. We found that budgerigars (Melopsittacus undulatus) maintain EWL constant over a range of relative humidities at three ambient temperatures. EWL, expressed as a function of water vapour pressure deficit, differed from a physical model where the water vapour pressure deficit between the animal and the ambient air is the driver of evaporation, indicating physiological control of EWL. Regulating EWL avoids thermoregulatory impacts of varied evaporative heat loss; changes in relative humidity had no effect on body temperature, metabolic rate or thermal conductance. Our findings that a small bird can regulate EWL are evidence that this is a common feature of convergently endothermic birds and mammals, and may therefore be a fundamental characteristic of endothermy.

Coordination of rooting depth and leaf hydraulic traits defines drought-related strategies in the campos rupestres, a tropical montane biodiversity hotspot

The survival and coexistence of plants in water-limited environments are related to their ability to coordinate water acquisition and regulation of water loss. To assess the coordination among below and aboveground hydraulic traits and the diversity of water-use strategies, we evaluated rooting depth and several leaf hydraulic traits of 15 species in campos rupestres, a seasonally-dry biodiversity hotspot in central Brazil. We assessed the depth of plant water acquisition by excavating roots and analyzing the stable isotope composition of hydrogen (δD) and oxygen (δ18O) in the xylem and soil water. We also measured mid-morning stomatal conductance, leaf-water potential at turgor loss point (ѰTLP) and pre-dawn leaf water potentials (ѰPD) during wet and dry seasons. We demonstrated that rooting depth is a good predictor of seasonal variations in stomatal conductance and ѰPD. Shallow-rooted plants had greater variation in stomatal conductance and ѰPD than deep-rooted plants. Woody plants with shallower roots also had lower ѰTLP than deep-rooted plants, revealing higher drought resistance. We demonstrate that shallow-rooted species, more exposed to variation in water availability, have mechanisms to confer drought resistance through turgor maintenance. Our results support the theory of hydrological niche segregation and its underlying trade-offs related to drought resistance.

Courageous or Compliant?

Courageous or Compliant?

Dehydration tolerance in relation to short day length in nonfed Amblyomma maculatum Koch, 1844 ticks (Acari: Ixodidae)

ABSTRACTTicks utilize a variety of strategies to mitigate water loss and enhance their off-host survival. This is the first report of a primarily tropical zone tick, the Gulf Coast tick Amblyomma maculatum, vector of Rickettsia parkeri, to regulate water loss by photoperiodic induction. Under short-day conditions (10 h:14 h L:D), water loss rates are decreased. This has a positive effect on survival by extending the time it takes to reach the dehydration tolerance limit. When cycled between long- and short-day conditions, the water loss rate drops and then returns to a faster rate after re-entering long-day conditions; this can occur quickly (within a day), multiple times, and in more than one life history stage. The decrease in water loss is more pronounced in immatures than adults. The percentage body water content, dehydration tolerance limit and critical equilibrium humidity are independent of photoperiodic changes. We conclude that any nonfed stage is adapted for survival by enhanced water conservation when the day length shortens.

Effects of branch removal on water use of rain-fed jujube (Ziziphus jujuba Mill.) plantations in Chinese semiarid Loess Plateau region

As a drought tolerant plant, jujube (Ziziphus jujuba Mill.) is commonly planted in Chinese semiarid Loess Plateau Region under rain-fed conditions. To evaluated the effectiveness of branch removal to conserve water resources in rain-fed jujube plantations in the region, two degrees of branch removal treatments (T1–two main branches removed; T2–one main branch removed) were compared with control treatment (none of the three main branches removed) and the effects on water use in Jujube plantations were analyzed. Sap flow was monitored (using the Granier-type thermal dissipation probes) along with meteorological factors, soil water content, vessel diameter, crown projection area and leaf area index, with soil moisture condition divided into water stress and non-water stress. Results showed that branch removal was an efficient way of conserving water resources in jujube plantations. a) It improved soil water content by reducing water loss via total evapotranspiration (ET) during jujube growth period. Total ET values were 452, 463 and 478mm respectively for T1, T2 and the control treatments during jujube growth period in 2012; 408, 426 and 451mm respectively for T1, T2 and the control treatments during jujube growth period in 2013 and 374, 381 and 392mm respectively for T1, T2 and the control treatments during jujube growth period in 2014. b) Branch removal not only decreased transpiration per unit ground area (stand transpiration: Tg), but also increased the sensitivity of Tg to environmental variables. In contrast, the removal of two (out of three) branches increased transpiration per unit leaf area (leaf transpiration: Tl), making it less sensitive to soil water content. c) Treatment T1 significantly increased the sensitivity of canopy conductance (Gc) to vapor pressure deficit (VPD), which effect was not significant under T2. Isohydric regulation of water loss through Gc response to VPD was the same for the three treatments, regardless of the different tree canopy sizes and soil water conditions, but reference canopy conductance (Gcref: canopy conductance at VPD=1kPa) was treatment-specific. d) Branch removal improved the tolerant of jujube tree to negative water potential and xylem cavitation by decreasing average vessel lumen diameters. Compared with the control, both branch removal treatments (T1 and T2) resulted in a significant decrease in average vessel lumen diameter at 15mm below the cambium (40.74, 42.53 and 46.81μm respectively for T1, T2 and the control treatments). Similarly, T1 and T2 reduced mean vessel lumen diameter at 5mm below the cambium (43.20, 47.44 and 48.39μm respectively for T1, T2 and the control treatments). e) Branch removal significantly decreased the fresh fruit yield and water use efficiency except in 2013, during which differences were not significant. Fresh fruit yield values were 8082, 8964 and 11293kgha−1 respectively for T1, T2 and the control treatments in 2012; 5691, 5426 and 6000kgha−1 respectively for T1, T2 and the control treatments in 2013; 6804, 8341 and 10589kgha−1 respectively for T1, T2 and the control treatments in 2014. WUE values were 1.79, 1.94 and 2.36kgm−3 in 2012; 1.40, 1.28 and 1.33kgm−3 in 2013; 1.82, 2.19 and 2.70kgm−3 in 2014. T1 treatment was recommended in terms of improving soil water storage as well as maintaining a certain amount of productivity in jujube plantations in Chinese semiarid Loess Plateau Region. The result of the study is critical for the development of effective water management strategies in jujube plantations ensure that the fragile ecology of the Loess Plateau is sustained.

Skin barrier in atopic dermatitis: beyond filaggrin.

Atopic dermatitis is a chronic inflammatory skin disease with a complex pathogenesis, where changes in skin barrier and imbalance of the immune system are relevant factors. The skin forms a mechanic and immune barrier, regulating water loss from the internal to the external environment, and protecting the individual from external aggressions, such as microorganisms, ultraviolet radiation and physical trauma. Main components of the skin barrier are located in the outer layers of the epidermis (such as filaggrin), the proteins that form the tight junction (TJ) and components of the innate immune system. Recent data involving skin barrier reveal new information regarding its structure and its role in the mechanic-immunological defense; atopic dermatitis (AD) is an example of a disease related to dysfunctions associated with this complex.

Short day exposure suppresses water loss rate in the lone star tick Amblyomma americanum and blacklegged tick Ixodes scapularis (Acari: Ixodidae)

ABSTRACTWe report that all non-fed stages of the lone star tick Amblyomma americanum and blacklegged tick Ixodes scapularis have reduced water loss by exposure to short days. This reduction in water loss is more pronounced in larvae and nymphs than in adults. Impressive was the rapid response: all non-fed stages could transition quickly, losing water fast (long day), then slow (short day), and back to fast (long day), with only a single day exposure to short or long day conditions. Short days did not improve the tick’s dehydration tolerance limit. Ticks under short days were capable of absorbing water vapour, so their ability to rehydrate by water vapour absorption is not inhibited by change in photoperiod. Our conclusion is that a short-day-induced temporary quiescence helps to regulate water loss that applies to any non-fed stage for overwintering. The shallow nature of this quiescence implies that ticks could easily become active at any time and re-enter quiescence.

Water transport properties of seven woody species from the semi-arid Mu Us Sandy Land, China

Maintenance of water transport is very important for plant growth and survival. We studied seven woody species that inhabit the semi-arid Mu Us Sandy Land, China, to understand their strategies for maintaining hydraulic function. We evaluated water transport properties, including cavitation resistance, hydraulic recovery, and water loss regulation by stomatal control, which are associated with xylem structural and leaf physiological traits. We also discussed the water-use characteristics of these species by comparing them with those of species in other regions. Species with tracheids had higher levels of xylem resistance to cavitation and a smaller midday transpiration rate than the other species studied. Although species with vessels were less resistant to cavitation, some recovered hydraulic conductivity within 12 h of rehydration. Species with xylem tracheids could maintain their hydraulic function through resistance to cavitation and by relaxing xylem tension. Although species with vessels had less resistant xylem, they could maintain hydraulic function through hydraulic recovery even when xylem dysfunction occurred. Additionally, the species studied here were less resistant to cavitation than species in semi-arid environments, and equally or less resistant than species in humid environments. Rather than allow hydraulic dysfunction due to drought-induced dehydration, they may develop water absorption systems to avoid or recover quickly from hydraulic dysfunction. Thus, not only stem cavitation resistance to drought but also stem–root coordination should be considered when selecting plants for the revegetation of arid regions.

Flag Leaf Photosynthesis and Stomatal Function of Grain Sorghum as Influenced by Changing Photosynthetic Photon Flux Densities

Photosynthesis (A) and stomatal function research in grain sorghum (Sorghum bicolor (L.) Moench) is limited compared to other crops. Flag leaves from three plants of two hybrids, grown with added N-fertilizer of 0.0, 112, and 224 kg ha−1 near Elizabeth, MS, were measured for A and stomatal functions at growth stages GS6 and GS7. A Li-Cor LI-6400XT set at 355 µmol [CO2], a flow rate of 500 µmol s−1, and a 6400-02 LED light source were used to collect data. Light levels were initially set at 2200 µmol m−2 s−1 indicated photosynthetic photon flux density (PPFD), A was allowed to stabilize, data was recorded, indicated PPFD level was reduced by 200 µmol m−2 s−1, and the process was repeated to a level of 200 µmol m−2 s−1. At GS6 all data were unaffected by N-fertility, hybrids, or years. Data on Ci at GS6 indicated A declines faster with decreasing PPFD than gs. Intrinsic water use efficiency (IWUE) data supports prior research showing stomata function more to regulate water loss and only marginally limit A. Nitrogen fertility was null on A and stomatal functions and minimal on yield; thus no attempt was made to correlate yield with these data.

Water balance attributes for off-host survival in larvae of the winter tick (Dermacentor albipictus; Acari: Ixodidae) from wild moose

ABSTRACTTo explore how the one-host tick Dermacentor albipictus survives off-host, we determined water balance characteristics of eggs and larvae. In contrast to eggs, larvae lost water fast, absorbed water vapour and died from a low amount of water loss. Placing mated females under near water-saturated conditions yielded larvae that absorbed and survived only at high relative humidities. We observed larvae forming clusters. Water loss rate of larvae decreased as group size increased. In response to day length, larvae lost water slower under long day than short day conditions. Larvae could switch quickly between fast water loss rate (short day) and slow water loss rate (long day) within a day, independent of the photoperiodic experience of the egg or mother. Long day exposure had no effect on water relations, incubation and survival of eggs. We conclude that eggs are modified for water conservation. Larvae survive by having a water balance maternal effect; i.e. capacity for water vapour absorption in the larva is determined by the relative humidity experienced by the mother. Larvae regulate water loss behaviourally through larval clustering and summer quiescence. Understanding these water balance attributes and effects of desiccation on egg and larval survival during summer are important to better predict the potential population impacts of winter ticks on moose.

Major latex protein-like protein 43 (MLP43) functions as a positive regulator during abscisic acid responses and confers drought tolerance in Arabidopsis thaliana.

Drought stress is one of the disadvantageous environmental conditions for plant growth and reproduction. Given the importance of abscisic acid (ABA) to plant growth and abiotic stress responses, identification of novel components involved in ABA signalling transduction is critical. In this study, we screened numerous Arabidopsis thaliana mutants by seed germination assay and identified a mutant mlp43 (major latex protein-like 43) with decreased ABA sensitivity in seed germination. The mlp43 mutant was sensitive to drought stress while the MLP43-overexpressed transgenic plants were drought tolerant. The tissue-specific expression pattern analysis showed that MLP43 was predominantly expressed in cotyledons, primary roots and apical meristems, and a subcellular localization study indicated that MLP43 was localized in the nucleus and cytoplasm. Physiological and biochemical analyses indicated that MLP43 functioned as a positive regulator in ABA- and drought-stress responses in Arabidopsis through regulating water loss efficiency, electrolyte leakage, ROS levels, and as well as ABA-responsive gene expression. Moreover, metabolite profiling analysis indicated that MLP43 could modulate the production of primary metabolites under drought stress conditions. Reconstitution of ABA signalling components in Arabidopsis protoplasts indicated that MLP43 was involved in ABA signalling transduction and acted upstream of SnRK2s by directly interacting with SnRK2.6 and ABF1 in a yeast two-hybrid assay. Moreover, ABA and drought stress down-regulated MLP43 expression as a negative feedback loop regulation to the performance of MLP43 in ABA and drought stress responses. Therefore, this study provided new insights for interpretation of physiological and molecular mechanisms of Arabidopsis MLP43 mediating ABA signalling transduction and drought stress responses.

Stomatal patchiness of field-grown sultana leaves: Diurnal changes and light effects

Unirrigated, field-grown Sultana vines were used to study diurnal changes of stomatal patchiness under the natural ambient conditions of South Australia. Non-homogenous aperture of stomata (patchiness) was determined by an infiltration technique and by counting infiltrated patches. Stomatal conductance was linearly related to the number of patches with open stomata (r 2 = 0.622). Both parameters increased in the early morning (maxima at 8 a.m.) and decreased thereafter. In the afternoon stomatal conductance and the number of patches with open stomata remained at a low level. When dark adapted leaves were exposed to sun light (900 -1000 mu mol quanta . m -2 . s -1 ) the number of patches with open stomata increased from 23 to 143 cm -2 within 15 min, indicating that besides several stress factors light induces non-homogenous stomatal opening. It is assumed that stomatal action of single patches is autonomous, i.e. stomata of single patches will regulate water loss and CO 2 uptake according to local changes of ambient and endogenous conditions.

EARLY SENESCENCE1 Encodes a SCAR-LIKE PROTEIN2 That Affects Water Loss in Rice.

The global problem of drought threatens agricultural production and constrains the development of sustainable agricultural practices. In plants, excessive water loss causes drought stress and induces early senescence. In this study, we isolated a rice (Oryza sativa) mutant, designated as early senescence1 (es1), which exhibits early leaf senescence. The es1-1 leaves undergo water loss at the seedling stage (as reflected by whitening of the leaf margin and wilting) and display early senescence at the three-leaf stage. We used map-based cloning to identify ES1, which encodes a SCAR-LIKE PROTEIN2, a component of the suppressor of cAMP receptor/Wiskott-Aldrich syndrome protein family verprolin-homologous complex involved in actin polymerization and function. The es1-1 mutants exhibited significantly higher stomatal density. This resulted in excessive water loss and accelerated water flow in es1-1, also enhancing the water absorption capacity of the roots and the water transport capacity of the stems as well as promoting the in vivo enrichment of metal ions cotransported with water. The expression of ES1 is higher in the leaves and leaf sheaths than in other tissues, consistent with its role in controlling water loss from leaves. GREEN FLUORESCENT PROTEIN-ES1 fusion proteins were ubiquitously distributed in the cytoplasm of plant cells. Collectively, our data suggest that ES1 is important for regulating water loss in rice.

Transport efficiency through uniformity: organization of veins and stomata in angiosperm leaves.

Leaves of vascular plants use specific tissues to irrigate the lamina (veins) and to regulate water loss (stomata), to approach homeostasis in leaf hydration during photosynthesis. As both tissues come with attendant costs, it would be expected that the synthesis and spacing of leaf veins and stomata should be coordinated in a way that maximizes benefit to the plant. We propose an innovative geoprocessing method based on image editing and a geographic information system to study the quantitative relationships between vein and stomatal spatial patterns on leaves collected from 31 angiosperm species from different biomes. The number of stomata within each areole was linearly related to the length of the looping vein contour. As a consequence of the presence of free-ending veinlets, the minimum mean distance of stomata from the nearest veins was invariant with areole size in most of the species, and species with smaller distances carried a higher density of stomata. Uniformity of spatial patterning was consistent within leaves and species. Our results demonstrate the existence of an optimal spatial organization of veins and stomata, and suggest their interplay as a key feature for achieving a constant mesophyll hydraulic resistance throughout the leaf.

Fertilization increases sensitivity of canopy stomatal conductance and transpiration to throughfall reduction in an 8-year-old loblolly pine plantation

Loblolly pine (Pinus taeda L.) is the most important plantation species in the southeastern United States and therefore reductions in productivity associated with climate change may have significant economic impacts. To better understand the potential impact of drought on loblolly pine productivity, we studied the combined effects of reduced water availability and soil fertility on transpiration and canopy stomatal conductance (GS) over one year in an 8-year-old loblolly pine plantation by applying a throughfall treatment (ambient versus an approximate 30% reduction in throughfall) and a fertilization treatment (no fertilization versus one-time fertilization with N, P, K and micronutrients). We hypothesized that stomatal behavior would regulate water loss under a throughfall reduction treatment and the response would be greater under fertilization, due to an increase in leaf area index. Significant interactions between treatments indicated lower average monthly transpiration per unit ground area (EG) and per unit leaf area (EL), lower whole-plant hydraulic conductance, and lower average monthly midday GS in response to throughfall reduction only in the fertilized treatment, most likely due to increases in the leaf-to-sapwood area ratio in addition to isohydric regulation of water loss. In the throughfall reduction treatment but not the ambient throughfall treatment, reference GS (at vapor pressure deficit=1kPa, GSref) was significantly related to soil relative extractable water (REW) to a 0.6m soil depth, and sensitivity of GSref to REW was greater when combined with fertilization. These results indicate that the influence of drought on canopy-level processes of loblolly pine will be greater with fertilization.

Ecophysiology of Acacia species in wet–dry tropical plantations

Selected tropical Acacia species are used extensively for short-rotation plantation forestry in many parts of Asia and, to a limited degree, in Australia. We explored leaf-level photosynthetic activity and leaf water potential (Ψleaf) of three field-grown Acacia tree species (aged between 7 and 18 months) in contrasting wet–dry tropical plantations in southern Vietnam and northern Australia. Light-saturated photosynthetic rate (A1500) declined throughout the morning and early afternoon in the dry season; in the wet season, levels remained high and relatively constant throughout most of the day. Maximum daily A1500 at 09:00 ranged from 22.2 μmol m−2 s−1 in the wet to 10.4 μmol m−2 s−1 in the dry season. At both locations, trees were able to extract soil water such that pre-dawn leaf water potential (Ψpd) remained>−1.5 MPa even at the end of the dry season. Stomatal conductance to water vapour (gs) did not respond to decreasing Ψleaf during the wet season but was sensitive to changes in Ψleaf in the dry season. Species comparisons of the relationships between A1500 and Ψleaf revealed different strategies to balance carbon uptake and water loss in a wet–dry environment. Acacia crassicarpa and A. mangium regulated Ψleaf to a greater extent than the A. mangium×A. auriculiformis hybrid such that ∆Ψleaf (determined as Ψpd−midday Ψleaf) was unaffected by season. This result suggests that the hydraulic regulation of tree water status varies amongst young tropical Acacia species. From a management perspective, for Acacia species that tend to strongly regulate water loss in environments with an extended dry season, overall productivity at the end of a rotation may be less than for species that prioritise carbon gain.