Transpiration Efficiency Research Articles

Genetic Analysis of Transpiration Efficiency and its Relation to Grain Yield under Drought Stress Conditions in Bread Wheat

Genetic Analysis of Transpiration Efficiency and its Relation to Grain Yield under Drought Stress Conditions in Bread Wheat

Organic amendments enhance transpiration efficiency of corn plants via changes in soil microbial abundance and leaf hormones

Organic amendments enhance transpiration efficiency of corn plants via changes in soil microbial abundance and leaf hormones

Morfofisiologia de gravioleira sob estresse salino e aplicação de H2O2 na fase de pré-floração

ABSTRACT In the semi-arid region of the Brazilian Northeast, water sources generally have high levels of salts, standing out as one of the abiotic stresses that restrict the growth and development of plants. In this context, the objective of the present study was to evaluate the effects of foliar applications of hydrogen peroxide on the morphophysiology of soursop under salt stress in the pre-flowering phase. The experiment was carried out in a greenhouse, using a randomized block design and a 4 × 4 factorial arrangement, with four values of electrical conductivity of the irrigation water - ECw (0.8, 1.6, 2.4, and 3.2 dS m-1) and four concentrations of hydrogen peroxide - H2O2 (0, 10, 20, and 30 μM), with three replicates. An increase in water electrical conductivity from 0.8 dS m-1 reduced stomatal conductance, CO2 assimilation rate, instantaneous carboxylation efficiency, and leaf water saturation deficit. It inhibited the growth of soursop plants at 370 days after transplanting. Hydrogen peroxide at concentrations of up to 10 μM increased leaf transpiration and water use efficiency of soursop plants irrigated with 1.8 dS m-1 water in the pre-flowering phase.

NaCl stress, tissue specific Na+ and K+ up-take and their effect on growth and physiology of Helianthus annuus L. and Solanum lycopersicum L.

Salinity is one of the major abiotic stresses that can threat plant growth and yield. Helianthus annuus L. and Solanum lycopersicum L. are economically important crops and widely cultivated, but the uptake of Na+ and K+ during the NaCl stress in their above and below ground parts is not well-understood. The main objective of this study was to understand the response of leaf structure and function to different concentrations of NaCl and to understand the Na+ and K+ uptake in H. annuus and S. lycopersicum. Four different concentrations of NaCl (H. annuus; 50 mM, 100 mM, 150 mM, 200 mM, and S. lycopersicum; 25 mM, 50 mM, 75 mM, 100 mM) were applied. Plant Biomass and the leaf structure and function (leaf area, midrib length, secondary vein length, petiole diameter, photosynthesis, stomatal conductance, transpiration, and intrinsic water use efficiency) were studied. We found that the salinity concentration of more than 150 mM in H. annuus and 75 mM in S. lycopersicum significantly reduced the plant height and leaf performance. At the same time, the yield (seed and fruit weight) decreased at 100 mM and 50 mM of NaCl concentration of H. annuus and S. lycopersicum, respectively. Maximum Na+ and K+ were accumulated in roots and stem in H. annuus and roots and fruits in S., lycopersicu. At the same time, the minimum Na+ and K+ were detected in seeds of H. annuus and fruit and root of S. lycopersicum. The K+: Na+ showed variation in both crops. We conclude that the vegetative parts of Helianthus annuus can tolerate up to 150 mM and S. lycopersicum up to 75 mM of NaCl concentration. The concentration of Melatonin increases as the stress level increases as it acts to remove the stress. These findings can be helpful to cultivate the Helianthus annuus and S. lycopersicum in saline areas and can also be useful to cultivate other crops when the successive cultivation of both crops is practiced and Na+ is absorbed by the crop from the soil.

Numerical simulations on the performance of transpiration cooling implemented with perforated flat plates

Transpiration cooling is an effective method of protecting high-temperature components. However, this technology is currently not applicable to turbine blades because conventional sintered porous materials cannot precisely control the geometric parameters of the cooling channels and coolant outlets. In this study, numerical simulations using the conjugate heat transfer method were conducted to study the effects of hole diameter, injection ratio, and mainstream Reynolds number on the cooling performance of perforated flat plates. A novel optimisation method for the overall transpiration cooling efficiency that reduces coolant consumption through a nonuniform coolant allocation strategy was proposed. The effects of different pore diameters (0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm) on transpiration cooling were investigated numerically. The results revealed that the hole diameter had a marginal effect on the average cooling efficiency of transpiration cooling under the same coolant-injection ratio. With dense heat transfer occurring within the solid matrix, the influence of variations in the pore size was diminished. However, the nonuniformity of the cooling efficiency on the hot wall surface increased with increasing pore size. A double coolant chamber non-uniform injection was adopted for the 0.3 mm perforated plate. The results indicated that there is an optimum coolant allocation ratio for achieving the highest average cooling efficiency with a certain coolant.

The slope of assimilation rate against stomatal conductance should not be used as a measure of water use efficiency or stomatal control over assimilation

Quantifying water use efficiency, and the impact of stomata on CO2 uptake are pivotal in physiology and efforts to improve crop yields. Although tempting, relying on regression slopes from assimilation-stomatal conductance plots to estimate water use efficiency or stomatal control over assimilation is erroneous. Through numerical simulations, I substantiate this assertion. I propose the term ‘instantaneous transpiration efficiency’ for the assimilation-to-transpiration ratio to avoid confusion with ‘intrinsic water use efficiency’ which refers to the assimilation-to-stomatal conductance ratio, and recommend to compute both metrics for each gas exchange data point.

Water deficit and potassium affect carbon isotope composition in cassava bulk leaf material and extracted carbohydrates.

Cassava (Manihot esculenta Crantz) is an important root crop, which despite its drought tolerance suffers considerable yield losses under water deficit. One strategy to increase crop yields under water deficit is improving the crop's transpiration efficiency, which could be achieved by variety selection and potassium application. We assessed carbon isotope composition in bulk leaf material and extracted carbohydrates (soluble sugar, starch, and cellulose) of selected leaves one month after inducing water deficit to estimate transpiration efficiency and storage root biomass under varying conditions in a greenhouse experiment. A local and improved variety were grown in sand, supplied with nutrient solution with two potassium levels (1.44 vs. 0.04 mM K+) and were subjected to water deficit five months after planting. Potassium application and selection of the improved variety both increased transpiration efficiency of the roots with 58% and 85% respectively. Only in the improved variety were 13C ratios affected by potassium application (up to - 1.8‰ in δ13C of soluble sugar) and water deficit (up to + 0.6‰ in δ13C of starch and soluble sugar). These data revealed a shift in substrate away from transitory starch for cellulose synthesis in young leaves of the improved variety under potassium deficit. Bulk δ13C of leaves that had fully developed prior to water deficit were the best proxies for storage root biomass (r = - 0.62, r = - 0.70) and transpiration efficiency (r = - 0.68, r = - 0.58) for the local and improved variety respectively, making laborious extractions redundant. Results obtained from the youngest fully developed leaf, commonly used as a diagnostic leaf, were complicated by remobilized assimilates in the improved variety, making them less suitable for carbon isotope analysis. This study highlights the potential of carbon isotope composition to assess transpiration efficiency and yield, depending on the chosen sampling strategy as well as to unravel carbon allocation processes.

Safflower (Carthamus tinctorius L.) crop adaptation to residual moisture stress: conserved water use and canopy temperature modulation are better adaptive mechanisms.

Oilseeds with high productivity and tolerance to various environmental stresses are in high demand in the food and industrial sectors. Safflower, grown under residual moisture in the semi-arid tropics, is adapted to moisture stress at certain levels. However, a substantial reduction in soil moisture has a significant impact on its productivity. Therefore, assessing genetic variation for water use efficiency traits like transpiration efficiency (TE), water uptake, and canopy temperature depression (CTD) is essential for enhancing crop adaptation to drought. The response of safflower genotypes (n = 12) to progressive soil moisture depletion was studied in terms of water uptake, TE, and CTD under a series of pot and field experiments. The normalised transpiration rate (NTR) in relation to the fraction of transpirable soil water (FTSW) varied significantly among genotypes. The genotypes A-1, Bhima, GMU-2347, and CO-1 had higher NTR-FTSW threshold values of 0.79 (R2 = 0.92), 0.74 (R2 = 0.96), 0.71 (R2 = 0.96), and 0.71 (R2 = 0.91), respectively, whereas GMU-2644 had the lowest 0.38 (R2 = 0.93). TE was high in genotype GMU-2347, indicating that it could produce maximum biomass per unit of water transpired. At both the vegetative and reproductive stages, significant positive relationships between TE, SPAD chlorophyll metre reading (SCMR) (p < 0.01) and CTD (p < 0.01) were observed under field conditions by linear regression. The genotypes with high FTSW-NTR thresholds, high SCMR, and low CTD may be useful clues in identifying a genotype's ability to adapt to moisture stress. The findings showed that the safflower genotypes A-1, Bhima, GMU-2347, and CO-1 exhibited an early decline and regulated water uptake by conserving it for later growth stages under progressive soil water depletion.

Changes in groundwater irrigation withdrawals due to climate change in Kansas

Warming temperatures increase the evapotranspiration demand of crops, leading to an increase in irrigation and exacerbating water scarcity. Previous research relies on models of irrigation water requirements to understand the potential impacts of climate change, but these models have significant uncertainty and ignore the risk-averse behavior of irrigators. Here we develop regression models to estimate how changes in vapor pressure deficit and precipitation affect groundwater withdrawals for corn, soybeans, and wheat using well-level data from the Kansas portion of the High Plains Aquifer. Withdrawals are expected to increase for all three crops, with the largest increase for soybeans. Even after accounting for the CO2 improvements in transpiration efficiency, we find that total withdrawals are expected to increase by 5.9% (7.6%) by mid-century under RCP 4.5 (8.5). The increase in withdrawals is expected to accelerate the decline in aquifer water levels and is therefore important to consider when projecting future aquifer conditions.

Inoculation with Azospirillum brasilense Strains AbV5 and AbV6 Increases Nutrition, Chlorophyll, and Leaf Yield of Hydroponic Lettuce.

Inoculation with Azospirillum brasilense has promisingly increased plant yield and nutrient acquisition. The study aimed to estimate the dose of A. brasilense that increases yield, gas exchange, nutrition, and foliar nitrate reduction. The research was carried out in a greenhouse at Ilha Solteira, in a hydroponic system in randomized blocks with four replicates. The treatments consisted of doses of inoculation with A. brasilense strains AbV5 and AbV6 via nutrient solution (0, 8, 16, 32, and 64 mL 100 L-1). Inoculation with A. brasilense at calculated doses between 20 and 44 mL provided the highest fresh and dry mass of shoots and roots, number of leaves, and leaf yield. In addition, the calculated doses of inoculation with A. brasilense increased the accumulation of N, P, K, Ca, Mg, S, B, Fe, Mn, and Zn in shoots and roots, except the accumulation of Ca in roots. It also increased cell membrane integrity index (15%), relative water content (13%), net photosynthesis rate (85%), intracellular CO2 concentration (15%), total chlorophyll (46%), stomatal conductance (56%), transpiration (15%), and water use efficiency (59%). Hence, inoculation with A. brasilense at doses between 20 and 44 mL 100 L-1 is considered the best approach for increasing the growth, yield, accumulation of nutrients, and gas exchange of hydroponically grown iceberg lettuce.

Physiological responses of oregano under different water management and application of fermented bokashi compost

Growing conditions such as water supply and soil fertility influence oregano morphological development and physiological responses. Our study aimed to analyse the physiological responses of oregano plants grown under different water conditions and bokashi application rates. The experiment was carried out in a greenhouse under a randomized block design and a 3 x 4 factorial scheme. Treatments encompassed three water replacement levels (60, 80, and 100% crop evapotranspiration - ETc) and four bokashi rates (0, 100, 200, and 300 g m-2), with five replications each. Oregano seedlings were transplanted and grown in a spacing of 0.3 m between plants and 1 m between bed rows. After 60 days, treatments were evaluated for photosynthetic rate (A), stomatal conductance (Gs), internal CO2 rate (Ci), transpiration (E), and water-use efficiency (WUE). Data underwent variance analysis by F-teste, multivariate analysis, and Pearson's linear correlation. Oregano physiological responses were significantly influenced by water replacement level and the application rate of fermented bokashi compost. The multivariate analysis allowed us to analyse the interaction effect between water replacement level and bokashi rate on photosynthesis, stomatal conductance, internal CO2, and transpiration.

Interannual variation in gross ecosystem production and evapotranspiration in a temperate semiarid grassland undergoing vegetation recovery

Carbon gains (gross ecosystem production, GEP) and water losses (evapotranspiration, ET) are critical for assessing vegetation recovery potential in drylands. However, large uncertainties remain regarding the controlling factors that regulate GEP and ET in semiarid grasslands, especially during periods of vegetation re-establishment and succession. Using the eddy-covariance technique, we assessed the interannual variability and key biophysical controls of carbon (C) and water vapor (H2O) fluxes in a semiarid grassland ecosystem in northern China from 2012 to 2020. After years of being subjected to heavy grazing and with a recent ban, the shrub-to-herb ratio at the site increased from 0.5 in 2014 to 0.63 in 2020. Associated with decreasing soil water availability (∼4.0% year−1), canopy transpiration and light use efficiency also decreased at rates of about 3.3% and 6.2% year−1, respectively. Multi-year means of GEP and ET were 166.6 ± 20.1 g C m−2 (mean ± SD) and 190.2 ± 21.8 mm, respectively. Interannual variability in GEP was mostly driven by variation in summer GEP, which for the most part was limited by mid-summer air temperature (Ta), particularly when exceeding the plants’ optimal temperature for photosynthesis. Interannual variability in ET was predominantly caused by variation in spring ET, which was mostly affected by spring vapor pressure deficit (VPD) and associated reductions in canopy stomatal conductance. Synchronous changes in GEP and ET resulted in a relatively stable annual water use efficiency (WUE) of 0.97 ± 0.13 g C kg−1 H2O. This stability is indicative of the shrubs’ capabilities to acclimate to arid conditions. Our results suggest that temperature and atmospheric aridity have important roles in regulating C gains and H2O losses in recovering dryland vegetation, respectively. Future increases in climatic variability anticipated with global climate change may augment the regional transition from grass to shrub cover.

Quantifying outdoor cooling effects of vertical greening system on mean radiant temperature

Energy flux of Vertical Greening System (VGS) is crucial for understanding of heat exchange processes by optimizing the cooling performance in outdoor thermal comfort, thereby mitigating heat stress through the transpiration. To understand the potential cooling effect of VGS, we quantify the Mean Radiant Temperature (MRT) of VGS by analyzing radiation flux and evaluating cooling efficiency, defined as the ratio of the cooling effect provided by the VGS to the energy input necessary to achieve that effect to quantify the effectiveness of VGS. The VGS showed a decrease in net radiation by 120 W/ m2, resulting in a decline in MRT by 3.02 °C compared to the wall. Furthermore, we found that the cooling efficiency of transpiration in VGS was 7.38 times more effective than evaporation from soil without plants. These findings suggest that VGS has the potential to significantly reduce heat stress and serve as an efficient strategy in urban areas.

Transpiration efficiency of lucerne under unlimited soil water conditions during the first growing season

Lucerne production is regarded as requiring high water inputs, making it necessary to understand its transpiration efficiency, especially in countries with water scarcity such as South Africa. The resurgent opportunities in the local lucerne markets prompted the publication of this short communication. The objective of this study was to quantify the transpiration efficiency of lucerne for different cutting periods during its first growing season. The study was conducted in a semi-arid area at Kenilworth Experimental Farm, University of the Free State, South Africa. Thirty field lysimeters of 1 800 mm diameter and 2 000 mm depth were arranged in two parallel rows and filled respectively with Clovelly and Bainsvlei soil types for the experiment. Surface drip irrigation was applied weekly and sub-irrigation applied daily to maintain a constant water table. The mean above-ground biomass production over 30-day cutting periods was 511 g m−2. A mean transpiration efficiency of 2.81 g m−2 mm−1 and a mean transpiration efficiency coefficient of 2.85 g kPa mm−1 were derived for the growing season. Both variables declined as the growing season progressed. Future work should ascertain the physiological and environmental factors that influence the declining trend in transpiration efficiency over the season.

Gas exchange and leaf area requirement in tall ‘Prata’ banana

The objective of this study was to evaluate the gas exchange and leaf area requirement for yield of six tall ‘Prata’ banana genotypes, under semi-arid conditions. The genotypes ‘Pacovan’ (AAB), ‘Pacovan Ken’ (AAAB), ‘Preciosa’ (AAAB), ‘Japira’ (AAAB), ‘PV79-34’ (AAAB) and ‘Garantida’ (AAAB) (four tetraploid hybrids and one triploid cultivar) were evaluated in two cycles, arranged in a completely randomized design in a factorial scheme, with five replicates and four usable plants per plot. For the physiological characteristics, a 6 x 12 x 2 factorial arrangement was adopted, with six genotypes, 12 evaluation periods and two reading times in each period, arranged in a completely randomized design. Of the 12 phytotechnical characteristics measured, seven were influenced by the interaction between the factors cultivar and cycle. Internal CO2 concentration, net photosynthesis rate, instantaneous water use efficiency, carboxylation efficiency and quantum efficiency of photosynthesis recorded in banana leaves are higher in the morning, favored by higher stomatal conductance and lower leaf temperature resulting from the meteorological conditions, while transpiration and intrinsic water use efficiency increase in the afternoon. The hybrid ‘PV79-34’ has higher yield and production efficiency per unit of leaf area, associated with high transpiration, compared to the tall ‘Prata’ banana cultivars.

Physiological responses to subsoil manuring in crop species across high and medium rainfall regions

Poorly-structured dense clay subsoils are widespread in dryland cropping regions in south-eastern Australia. They limit nutrient and water uptake from the subsoil which can limit grain yields. Recent research has shown that ameliorating subsoils with organic amendments can improve yields on these soils but the mechanisms underpinning this response remain unclear. Thus, different subsoil amelioration practices were imposed once at the high- and medium-rainfall sites followed with different crop sequences from 2018 to 2020. Both sites had poorly-structured sodic clay subsoils. The four experimental treatments assessed were 1) unamended control, 2) deep-banded gypsum, 3) chicken manure pellets applied to the topsoil, and (4) deep-banded in the subsoil. Compared to the control, both manure treatments significantly (p < 0.05) increased greenness in the upper leaves (SPAD readings), the green leaf area, and green leaf duration, and thereby delayed canopy senescence. The manures generally increased leaf N concentrations at anthesis, and at mid grain fill in all cereal crops, but not in faba bean. The manures also increased photosynthetic rates and instantaneous transpiration efficiencies (ITEs) in upper leaves of both cereal and faba bean crops, during grain or pod fill, but not in very dry years. Only one site and year combination, i.e. Tatyoon in 2018, showed an increase in grain yield. Despite the favourable effects of manures on crop canopies, unfavourable seasonal (rainfall) conditions were considered to be the major factor that limited yield increases by manured crops. Manuring in the medium-rainfall regions is likely ineffective in terms of crop productivity improvement.

Water replenishment to maize under heat stress improves canopy temperature and grain filling traits during the reproductive stage

The occurrence of heat often exacerbates drought stress by increasing atmospheric vapor pressure deficit and decreasing transpiration efficiency. Water replenishment to increase soil water content (SWC) could be an effective measure for improving crop resilience in heat. However, field observational evidence and the underlying mechanism for the mitigation were still limited. For this, two widely adopted maize hybrids (ZD958 and XY335) were planted in 2019 and 2020 in North China Plain with three growth environments during the reproductive stage: Normal field conditions (NC), High-temperature episodes (HT) and High-temperature together with elevating SWC (HT-W). Averagely, high temperature reduced grain yield by 21.6-65.1% in HT treatment compared with NC treatment. In HT-W treatment, grain yield was improved by 11.8-13.5% while SWC was elevated by 27.6–51.5% in 0–80 cm soil profile compared with HT treatment. In HT-W treatment, water replenishment to maize under heat stress improved canopy temperature and grain filling traits. The daily maximum canopy temperature was reduced by 1.0–3.1 °C. The effective grain-filling period (Pf) was extended by 1.0–1.6 days and the mean grain-filling rate (Gmean) was increased by 8.2%-10.5%. The improvement of Gmean and Pf for ZD958 was greater than XY335. Furthermore, the significant correlations between SWC in 0–20 cm soil profile and Gmean, and between SWC in 40–80 cm soil profile and Pf for both hybrids were observed. As a result, the fresh weight, volume, and water content of the grain were significantly improved in HT-W treatment compared with HT treatment. Overall, per unit increase in SWC (0–80 cm) decreased the daily maximum canopy temperature by 0.3 °C, increased dry matter accumulation by 1.5%, and grain yield by 2.1%. The information obtained from this study will be helpful to develop efficient management to protect against heat stress in the field.

Network feature-based phenotyping of leaf venation robustly reconstructs the latent space.

Despite substantial variation in leaf vein architectures among angiosperms, a typical hierarchical network pattern is shared within clades. Functional demands (e.g., hydraulic conductivity, transpiration efficiency, and tolerance to damage and blockage) constrain the network structure of leaf venation, generating a biased distribution in the morphospace. Although network structures and their diversity are crucial for understanding angiosperm venation, previous studies have relied on simple morphological measurements (e.g., length, diameter, branching angles, and areole area) and their derived statistics to quantify phenotypes. To better understand the morphological diversities and constraints on leaf vein networks, we developed a simple, high-throughput phenotyping workflow for the quantification of vein networks and identified leaf venation-specific morphospace patterns. The proposed method involves four processes: leaf image acquisition using a feasible system, leaf vein segmentation based on a deep neural network model, network extraction as an undirected graph, and network feature calculation. To demonstrate the proposed method, we applied it to images of non-chemically treated leaves of five species for classification based on network features alone, with an accuracy of 90.6%. By dimensionality reduction, a one-dimensional morphospace, along which venation shows variation in loopiness, was identified for both untreated and cleared leaf images. Because the one-dimensional distribution patterns align with the Pareto front that optimizes transport efficiency, construction cost, and robustness to damage, as predicted by the earlier theoretical study, our findings suggested that venation patterns are determined by a functional trade-off. The proposed network feature-based method is a useful morphological descriptor, providing a quantitative representation of the topological aspects of venation and enabling inverse mapping to leaf vein structures. Accordingly, our approach is promising for analyses of the functional and structural properties of veins.

The Roles of Net Photosynthetic Rate and Transpiration Efficiency on Economic Yield of Jerusalem artichoke (Helianthus tuberosus L.) Genotypes under Different Drought Durations during the Terminal Growth Stages

Knowledge of the influence of different drought durations during the terminal growth stages on net photosynthetic rate (Pn), transpiration rate (Tr), transpiration efficiency (TE), and tuber fresh weight (economic yield) is relatively limited in Jerusalem artichoke. Our aim was to examine the effect of different drought durations during the terminal growth stages on Pn, Tr, TE, and economic yield in Jerusalem artichoke genotypes with different ranges of drought tolerance. A two-year field experiment was established in the northeast of Thailand. A split-plot design replicated four times was used. Three water treatments, optimal conditions (SD0), short-drought (SD1), and long-drought (SD2) durations during the terminal growth stages, were arranged as main plots. Six genotypes (HEL256, JA37, HEL253, JA4, JA60, and JA125) are subplots. Different durations of drought in SD1 and SD2 reduced Pn, Tr, and economic yield, while drought stress during the terminal growth stages increased TE in whole genotypes over SD0 treatments. Drought-tolerant genotypes JA125 and JA4 exhibited high Pn, medium TE, and low economic yield reduction under SD2. Utilization of these superior parents in breeding could lead to the generation of new progenies with high economic yield productivity and drought tolerance during the long drought duration during the terminal growth stage. In addition, high SPAD chlorophyll meter readings (SCMR) in SD1 and SD2 and low specific leaf area (SLA) in SD1 could be used as indirect selection traits to survey high Pn genotypes in Jerusalem artichoke. Consequently, these indirect selection traits may allow for speedy breeding programs in Jerusalem artichokes.

Plant size directly correlates with water use efficiency in Arabidopsis.

Plant transpiration is a fundamental process that determines plant water use efficiency (WUE), thermoregulation, nutrition, and growth. How transpiration impacts on such essential physiological aspects and how the environment modulates these effects are fundamental questions about which little is known. We investigated the genetic and environmental factors underlying natural variation in plant transpiration and water use efficiency in a population of natural Arabidopsis thaliana accessions grown under homogeneous conditions. As expected, we observed large variation of total transpiration capacity, transpiration per surface unit, and WUE among A. thaliana accessions. Despite the variation of stomatal density and ABA content in the population, WUE did not correlate with any of these parameters. On the contrary, a surprising direct correlation was found between WUE and projected leaf area, with bigger plants displaying a more efficient use of water. Importantly, genome-wide association studies further supported our observations through the identification of several loci involved in WUE variation, mutations in which caused a simultaneous reduction in plant size and a decrease in WUE. Altogether, our results strongly suggest that, although WUE depends on many parameters, plant size is an adaptive trait with respect to water use in A. thaliana.