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Key message The history of the relationship between plant growth and water consumption is retraced by following the progression of scientific thought through the centuries: from a purely philosophical question, to conceptual and methodological developments, towards a research interest in plant functioning and the interaction with the environment. Context The relationship between plant growth and water consumption has for a long time occupied the minds of philosophers and natural scientists. The ratio between biomass accumulation and water consumption is known as water use efficiency and is widely relevant today in fields as diverse as plant improvement, forest ecology and climate change. Defined at scales varying from single leaf physiology to whole plants, it shows how botanical investigations changed through time, generally in tandem with developing disciplines and improving methods. The history started as a purely philosophical question by Greek philosophers of how plants grow, progressed through thought and actual experiments, towards an interest in the functioning of plants and the relationship to the environment. Aims This article retraces this history by following the progression of scientific questions posed through the centuries, and presents not only the main methodological and conceptual developments on biomass growth and transpiration but also the development of the carbon isotopic method of estimation. The history of research on photosynthesis is only touched briefly, but the development of research on transpiration and stomatal conductance is presented with more detail. Conclusion Research on water use efficiency, following a path from the whole plant to leaf-level functioning, was strongly involved in the historical development of the discipline of plant ecophysiology and is still a very active research field across nearly all levels of botanical research.

The film-forming antitranspirant, di-1-p-menthene, is able to reduce transpiration in a number of crops, potentially resulting in water savings and improved productivity. The success of the response is, however, dependent on genotype and environmental factors. We aimed to assess the efficacy of this natural terpene polymer on red raspberry (Rubus idaeus, L.) cv. Tulameen leaf water-use efficiency across a 25&ndash, 40 &deg, C temperature range under controlled conditions. The film reduced transpiration (E) and was most effective when applied to the lower leaf surface. Leaf net assimilation (A) and stomatal conductance (g) were also curtailed after the application of di-1-p-menthene, and as a consequence intrinsic transpiration efficiency (A/g) and instantaneous transpiration efficiency (ratio of net carbon fixation to water loss, A/E) did not improve. At 40 &deg, C, gas exchange of both treated and untreated leaves was minimal due to stomatal closure. The antitranspirant was effective at reducing water loss from berries, but only at the immature stages when transpiration rates were naturally high. Further studies are required to determine if the antitranspirant, di-1-p-menthene, will offer protection against dehydration across a range of temperatures and if productivity and berry composition will benefit.

© 2020 by the authors., The physiological performance of early-maturing nectarine trees in response to water deficits was studied during the postharvest period. Two deficit irrigation treatments were applied, moderate and severe, and these were compared with a control treatment (fully irrigated). Stem water potential and leaf gas exchange (net CO2 assimilation rate, ACO2; transpiration rate, E; and stomatal conductance, gs) were measured frequently. Drought avoidance mechanisms included a decrease in stomatal conductance, especially in the case of the severe deficit treatment, which also showed a strong dependence of ACO2 on gs. Intrinsic water-use efficiency (ACO2/gs) was more sensitive than instantaneous water-use efficiency (ACO2/E) as an indicator to detect water deficit situations in nectarine trees. However, in contrast to the results obtained for other deciduous fruit trees, a poor correlation was found between ACO2/E and ACO2/gs, despite the important relation between E and gs. ACO2/E was also weakly correlated with gs, although this relationship clearly improved when the vapor pressure deficit (VPD) was included, along with gs as the independent variable. This fact reveals that apart from stomatal closure, E depends on the boundary layer conductance (gb), which is mediated by VPD through changes in wind speed. This suggests low values of the decoupling coefficient for this water-resilient species., This research was supported by the Spanish Research Agency and co-financed by European Union FEDER funds (AEI/FEDER-UE, AGL2016-77282-C3-1R and PID2019-106226RB-C2-1) and “Fundación Séneca, Agencia de Ciencia y Tecnología” of the Region of Murcia under the Excellence Group Program (19903/GERM/15) projects.

Hemp (Cannabis sativa L.) is a multi-purpose industrial species, which is valued as a low-input crop suited to marginal environments. However, research on the water stress resistance and water use efficiency of hemp cultivars is scarce. Three lab-scale experiments were carried out to test 26 commercial European hemp cultivars under osmotic stress at germination (experiment 1) and on plantlets at vegetative stage (experiment 2); and to calculate transpiration efficiency (TE) under well-watered conditions (experiment 3). Eight parameters were analysed: maximum germination percentage, lag time and germination homogeneity in experiment 1; maximum quantum yield of PSII (Fv/Fm), performance index, relative water content and proline content in experiment 2; TE in experiment 3. Osmotic stress application significantly affected all parameters in experiments 1 and 2, and responses to water stress differed significantly among cultivars for all parameters, except proline content. Considering all parameters except proline content, a principal component analysis was carried out for ranking the cultivars. The cultivars 'Carmaleonte', 'Codimono', 'Futura 75' and Santhica '70' ranked the highest, while cultivars 'Bialobrzeskie', 'Ermes' and 'Finola' had the worst performances for all traits.

Khon Kaen Agriculture Journal, 47, 1, 159-168

In water-scarce environments, water conservation is a means to increase agricultural production and preserve the environment. Water conservation can be approached at different scales with different objectives. Water productivity (the ratio between crop production and water use or water consumption) is increased by reducing non-beneficial use and by regulating water applications as to reduce transpiration in smaller proportion than yield. Water productivity can also be modified through other agronomical practices and breeding. The consumptive use coefficient (consumptive use to supply ratio) can be enhanced through various engineering solutions that reduce the use of irrigation water and energy although they do not necessarily reduce consumptive use. Therefore, engineering solutions for water conservation at farm level do not imply basin-scale water conservation. However, agronomical solutions such as regulated deficit irrigation are directly linked to basin water conservation because they goal is to reduce transpiration with little or no yield penalty. Optimising water productivity is a plausible goal in some situations; however, in others it clashes with profit maximization, food production and food security. Concerning breeding, past evidence shows that except for very harsh environments, selection for greater transpiration efficiency, evaluated physiologically as the ratio of photosynthetic assimilation versus transpiration or indirectly through the stable carbon isotope signature of plant dry matter, may have a negative effect by limiting yield potential as well as productivity under a wide range of water stress conditions., Contribution of J.L. Araus was supported in part by the Spanish Project AGL2013-44147-R.

As a supplemental practice to land consolidation projects, subsurface drainage systems have been installed in paddy fields to allow for crop diversification and to improve the overall productivity of paddy soils. The HYDRUS (2D/3D) model was applied to investigate the combined effects of different subsurface drainage systems and water management strategies on water balance, groundwater table, transpiration efficiency, and water use efficiency in paddy fields. Field experiments were conducted during four rice growing seasons (2011, 2012, 2014, and 2015) at the subsurface-drained paddies of the Sari Agricultural Sciences and Natural Resources University in northern Iran. Midseason drainage (MSD) management was applied in 2011 and 2012, while alternate wetting and drying (AWD) management was adopted in 2014 and 2015. The model performance was evaluated using the model efficiency (EF), root mean square error (RMSE), normalized root mean square error (NRMSE), and mean bias error (MBE) measures. The model had strong predictive capabilities for simulating the mid-drain water table depth for both water managements. Under MSD and AWD, daily evapotranspiration rates varied from 4.9 to 6.2 mm d−1 and 4.9 to 5.9 mm d−1, respectively. Drainage losses were higher under AWD than MSD, while the reverse order occurred for percolation losses. Compared with MSD, AWD improved the transpiration and water use efficiency of rice in the presence of subsurface drainage. Being capable of describing complex effects of AWD and MSD strategies in subsurface-drained paddy fields, the HYDRUS (2D/3D) model can serve as a practical tool for optimizing water productivity in these fields.

Abiotic stresses such as, drought, heat, salinity, and flooding threaten global food security. Crop genetic improvement with increased resilience to abiotic stresses is a critical component of crop breeding strategies. Wheat is an important cereal crop and a staple food source globally. Enhanced drought tolerance in wheat is critical for sustainable food production and global food security. Recent advances in drought tolerance research have uncovered many key genes and transcription regulators governing morpho-physiological traits. Genes controlling root architecture and stomatal development play an important role in soil moisture extraction and its retention, and therefore have been targets of molecular breeding strategies for improving drought tolerance. In this systematic review, we have summarized evidence of beneficial contributions of root and stomatal traits to plant adaptation to drought stress. Specifically, we discuss a few key genes such as, DRO1 in rice and ERECTA in Arabidopsis and rice that were identified to be the enhancers of drought tolerance via regulation of root traits and transpiration efficiency. Additionally, we highlight several transcription factor families, such as, ERF (ethylene response factors), DREB (dehydration responsive element binding), ZFP (zinc finger proteins), WRKY, and MYB that were identified to be both positive and negative regulators of drought responses in wheat, rice, maize, and/or Arabidopsis. The overall aim of this review is to provide an overview of candidate genes that have been identified as regulators of drought response in plants. The lack of a reference genome sequence for wheat and non-transgenic approaches for manipulation of gene functions in wheat in the past had impeded high-resolution interrogation of functional elements, including genes and QTLs, and their application in cultivar improvement. The recent developments in wheat genomics and reverse genetics, including the availability of a gold-standard reference genome sequence and advent of genome editing technologies, are expected to aid in deciphering of the functional roles of genes and regulatory networks underlying adaptive phenological traits, and utilizing the outcomes of such studies in developing drought tolerant cultivars.

Highlight Genotypic variation in both average stomatal conductance operating levels and photosynthesis rates for given conductance levels make important contributions to the variation in intrinsic transpiration efficiency in diverse sugarcane-related germplasm., Sugarcane, derived from the hybridization of Saccharum officinarum×Saccharum spontaneum, is a vegetative crop in which the final yield is highly driven by culm biomass production. Cane yield under irrigated or rain-fed conditions could be improved by developing genotypes with leaves that have high intrinsic transpiration efficiency, TEi (CO2 assimilation/stomatal conductance), provided this is not offset by negative impacts from reduced conductance and growth rates. This study was conducted to partition genotypic variation in TEi among a sample of diverse clones from the Chinese collection of sugarcane-related germplasm into that due to variation in stomatal conductance versus that due to variation in photosynthetic capacity. A secondary goal was to define protocols for optimized larger-scale screening of germplasm collections. Genotypic variation in TEi was attributed to significant variation in both stomatal and photosynthetic components. A number of genotypes were found to possess high TEi as a result of high photosynthetic capacity. This trait combination is expected to be of significant breeding value. It was determined that a small number of observations (16) is sufficient for efficiently screening TEi in larger populations of sugarcane genotypes The research methodology and results reported are encouraging in supporting a larger-scale screening and introgression of high transpiration efficiency in sugarcane breeding. However, further research is required to quantify narrow sense heritability as well as the leaf-to-field translational potential of genotypic variation in transpiration efficiency-related traits observed in this study.

The majority of world almond acreage is grown under rainfed conditions but most of the production is obtained under irrigation. Increased water scarcity is reducing water availability for irrigation thus the need to characterize the responses of almond to water deficits. Several works have defined well the stomatal closure in almond leaves under water deficits, but the behavior at the canopy level is not well understood. A field experiment was conducted in an almond (cv. Guara) orchard in Córdoba (Spain) under four different levels of irrigation supply to investigate the responses of almond tree transpiration (T) and transpiration efficiency (TE) to water stress. Stem water potential (Ψx), whole tree transpiration (T) and leaf gas-exchange were periodically measured throughout the 2013 growing season. Tree T decreased linearly as midday Ψx decreased below a threshold value of about −1.1 MPa, and declined to about 50% of the Control value when midday Ψx reached −1.6 MPa. The quick decline in T in response to the lowering of ψx suggests a high sensitivity of almond T to water deficits. The instantaneous transpiration efficiency (TE) of almond leaves was unaffected by water and varied essentially with vapor pressure deficits. On a daily scale, the leaf TE of stressed trees followed the same pattern as in the non-stressed trees. Then, contrary to the behavior observed in olive and citrus, there were no instantaneous or daily TE increments in almond trees in response to water deficits., The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Competitiveness [project AGL2012-35196 and project AGL2015-66141-R] and of Junta de Andalucia [project P12-AGR-2521].

With increasing demand for food and energy, there is a great need for improving sugarcane productivity. New cultivars and management strategies can be assessed using process-based crop models. Information on cultivars needs to be updated frequently, but it is still limited in most crop models. Therefore, it is important to identify possible candidates for varietal parameterization and calibration. Because sensitivity analysis is computationally expensive, we used a less expensive emulator-based approach to conduct a global sensitivity analysis using the apsimr package and GEM-SA software. We studied the sensitivity of four yield outputs of the APSIM-Sugar model to 13 parameters in rainfed and irrigated conditions in Japan and Sri Lanka. Unlike previous studies, our aim was to give comprehensive insights into the variation in sensitivity due to variation in climate. The results confirmed distinct variation of parameter influence between climates and between management conditions. We identify possible candidates for parameterization and calibration of new cultivars for APSIM-Sugar under different environments, and show the effect of variation in climate on variation in parameter influence under different management conditions. It was confirmed that both radiation use efficiency and transpiration efficiency were sensitive and have to be examined to use new cultivars, though these are not listed as cultivar parameters.

The opening and closing of plant stomata regulates the global water, carbon and energy cycles. Biophysical feedbacks on climate are highly dependent on transpiration, which is mediated by vegetation phenology and plant responses to stress conditions. Here, we explore the potential of satellite observations of solar-induced chlorophyll fluorescence (SIF)—normalized by photosynthetically-active radiation (PAR)—to diagnose the ratio of transpiration to potential evaporation (‘transpiration efficiency’, τ). This potential is validated at 25 eddy-covariance sites from seven biomes worldwide. The skill of the state-of-the-art land surface models (LSMs) from the eartH2Observe project to estimate τ is also contrasted against eddy-covariance data. Despite its relatively coarse (0.5°) resolution, SIF/PAR estimates, based on data from the Global Ozone Monitoring Experiment 2 (GOME-2) and the Clouds and Earth’s Radiant Energy System (CERES), correlate to the in situ τ significantly (average inter-site correlation of 0.59), with higher correlations during growing seasons (0.64) compared to decaying periods (0.53). In addition, the skill to diagnose the variability of in situ τ demonstrated by all LSMs is on average lower, indicating the potential of SIF data to constrain the formulations of transpiration in global models via, e.g., data assimilation. Overall, SIF/PAR estimates successfully capture the effect of phenological changes and environmental stress on natural ecosystem transpiration, adequately reflecting the timing of this variability without complex parameterizations.

International audience; High water use efficiency (WUE) can be achieved by coordination of biomass accumulation and water consumption. WUE is physiologically and genetically linked to carbon isotope discrimination (CID) in leaves of plants. A population of 148 recombinant inbred lines (RILs) of sunflower derived from a cross between XRQ and PSC8 lines was studied to identify quantitative trait loci (QTL) controlling WUE and CID, and to compare QTL associated with these traits in different drought scenarios. We conducted greenhouse experiments in 2011 and 2012 by using 100 balances which provided a daily measurement of water transpired, and we determined WUE, CID, biomass and cumulative water transpired by plants. Wide phenotypic variability, significant genotypic effects, and significant negative correlations between WUE and CID were observed in both experiments. A total of nine QTL controlling WUE and eight controlling CID were identified across the two experiments. A QTL for phenotypic response controlling WUE and CID was also significantly identified. The QTL for WUE were specific to the drought scenarios, whereas the QTL for CID were independent of the drought scenarios and could be found in all the experiments. Our results showed that the stable genomic regions controlling CID were located on the linkage groups 06 and 13 (LG06 and LG13). Three QTL for CID were co-localized with the QTL for WUE, biomass and cumulative water transpired. We found that CID and WUE are highly correlated and have common genetic control. Interestingly, the genetic control of these traits showed an interaction with the environment (between the two drought scenarios and control conditions). Our results open a way for breeding higher WUE by using CID and marker-assisted approaches and therefore help to maintain the stability of sunflower crop production.

Wheat productivity is commonly limited by a lack of water in rain-fed farming systems. Given this limitation and the variability in rainfall across the season, an increase in crop transpiration efficiency (TE), i.e. more crop per drop, could assist in improving crop productivity. But have breeders already selected indirectly for traits related to TE over the last decades? Fifteen Australian elite wheat varieties released between 1973 and 2012 were grown in a recently-developed greenhouse platform for TE phenotyping. Genotypes were chosen for their wide adoption and narrow phenological range. When grown in irrigated pots at normal field density, no significant change in total plant biomass was observed in respect to the year of release. However, the biomass partitioning among organs changed in recent cultivars, with more biomass allocated to the stems and heads, less to the leaves, and with no substantial change for the roots. Cumulated transpiration up to flowering was also reduced with the year of variety release, and overall, a slight increase in TE was observed in modern cultivars. Given the range of genetic variability observed in TE across a wider range of lines and the relatively high heritability of this trait reported in the literature, we believe that additional progress can be made to improve TE. Combining this rapid phenotyping method with speed breeding technologies could assist breeders to prepare for the future with the development of lines that produce more crop per drop.

To simulate cropping systems, crop models must not only give reliable predictions of yield across a wide range of environmental conditions, they must also quantify water and nutrient use well, so that the status of the soil at maturity is a good representation of the starting conditions for the next cropping sequence. To assess the suitability for this task a range of crop models, currently used in Australia, were tested. The models differed in their design objectives, complexity and structure and were (i) tested on diverse, independent data sets from a wide range of environments and (ii) model components were further evaluated with one detailed data set from a semi-arid environment. All models were coded into the cropping systems shell APSIM, which provides a common soil water and nitrogen balance. Crop development was input, thus differences between simulations were caused entirely by difference in simulating crop growth. Under nitrogen non-limiting conditions between 73 and 85% of the observed kernel yield variation across environments was explained by the models. This ranged from 51 to 77% under varying nitrogen supply. Water and nitrogen effects on leaf area index were predicted poorly by all models resulting in erroneous predictions of dry matter accumulation and water use. When measured light interception was used as input, most models improved in their prediction of dry matter and yield. This test highlighted a range of compensating errors in all modelling approaches. Time course and final amount of water extraction was simulated well by two models, while others left up to 25% of potentially available soil water in the profile. Kernel nitrogen percentage was predicted poorly by all models due to its sensitivity to small dry matter changes. Yield and dry matter could be estimated adequately for a range of environmental conditions using the general concepts of radiation use efficiency and transpiration efficiency. However, leaf area and kernel nitrogen dynamics need to be improved to achieve better estimates of water and nitrogen use if such models are to be use to evaluate cropping systems.

To understand the physiological basis of genetic variation and resulting quantitative trait loci (QTLs) for photosynthesis in a rice (Oryza sativa L.) introgression line population, 13 lines were studied under drought and well-watered conditions, at flowering and grain filling. Simultaneous gas exchange and chlorophyll fluorescence measurements were conducted at various levels of incident irradiance and ambient CO(2) to estimate parameters of a model that dissects photosynthesis into stomatal conductance (g(s)), mesophyll conductance (g(m)), electron transport capacity (J(max)), and Rubisco carboxylation capacity (V(cmax)). Significant genetic variation in these parameters was found, although drought and leaf age accounted for larger proportions of the total variation. Genetic variation in light-saturated photosynthesis and transpiration efficiency (TE) were mainly associated with variation in g(s) and g(m). One previously mapped major QTL of photosynthesis was associated with variation in g(s) and g(m), but also in J(max) and V(cmax) at flowering. Thus, g(s) and g(m), which were demonstrated in the literature to be responsible for environmental variation in photosynthesis, were found also to be associated with genetic variation in photosynthesis. Furthermore, relationships between these parameters and leaf nitrogen or dry matter per unit area, which were previously found across environmental treatments, were shown to be valid for variation across genotypes. Finally, the extent to which photosynthesis rate and TE can be improved was evaluated. Virtual ideotypes were estimated to have 17.0% higher photosynthesis and 25.1% higher TE compared with the best genotype investigated. This analysis using introgression lines highlights possibilities of improving both photosynthesis and TE within the same genetic background.

The Brassica species occupies a large portion of the world's economically important cultivated crops. These include vegetables, oilseeds, condiments, and forages. These crops are grown globally under a wide range of climatic conditions. With current concerns for food and energy security, expanded use of crop products, and environmental stewardship, there is a pressing need to improve yield through greater efficiency of resource utilization. Water availability is the most limiting factor to crop productivity and with the predicted scarcity, due to climate change and increased nonagricultural demand, improving water use efficiency (WUE) in crop production is an imperative. Consequently, increased carbon assimilation per unit of water used by Brassica crops must not only be realized but this carbon must also be efficiently partitioned into the harvested product. Thus, these plants need to be equipped with the genetic capacity to extract more water from the soil under water-limited conditions, fix more carbon, and transpire less water. There is natural genetic variability for WUE and this can be used for screening germplasm to identify better genotypes. Evaporative demand is the driving force for water loss and WUE can be improved by increasing transpiration efficiency (TE), alteration in crop phenology, increased carbon fixation, and increased harvest index (HI) by greater partitioning of assimilates into harvestable product. Modification of root architecture, leaf morphology, and stomata conductance are important targets for developing cultivars with improved WUE. Drought tolerance is closely associated with WUE and factors contributing to maintenance of metabolic function under water-limited conditions contribute to improved WUE. Studies on Arabidopsis have contributed to significant advances in our understanding of WUE and drought tolerance. The use of genetic engineering and genomic tools has allowed for the incorporation of identified genetic factors for improving WUE and drought tolerance traits and will be vital to the development of new Brassica cultivars. The carbon fixation machinery, a vital component in yield, will require adjustments to deal with anticipated water deficits in order to take advantage of increases in atmospheric carbon dioxide as a result of climate change. Manipulation of assimilate partitioning and selection of genotypes with capacity to store water-soluble carbohydrates in stems that can be remobilized to harvestable structures are targets for improving WUE. To maintain high yields of Brassica crops with economic use of water will require substantial increases in our understanding of the biological processes associated with growth under water-limited conditions. The availability of potential gene targets from the present and future discoveries including rapid advances coming from application of genomic technologies may provide a valuable resource base for development of superior WUE Brassica crops in the coming years.

This study compared the performance of four models to estimate the daily evapotranspiration (ET) in the greenhouse. The studied models were De Villele model (ETDV), Penman-Monteith model (ETPM), Stanghellini model (ETST) and finally Takakura (ETTK) transpiration model, based on heat balance equation of the crop canopy. The study was conducted during two tomato cropping seasons (2012 and 2013) under two greenhouses types (Monospan and Canarian), at INRA Melk Zhar Experiment Station (Agadir, Morocco). ETST and ETPM models correctly simulated tomato transpiration for both measured values and daily gain of the tomato stem (MC/DG) in the Monospan greenhouse (R² = 0,55 and 0,62). Similarly, we have reached a satisfactory relationship between the Eff-TR (the efficiency of plant transpiration) and the ratio MC/DG using the ETST model under Monospan and Canarian greenhouses (R² = 0,67; 0,58) respectively. The study identified critical thresholds or water status baselines of tomato: water comfort (0,40 0,46 and Eff-TR > 90%). In addition, the comparison of means according to yield level identified three groups of ET models; ETST (318 T/ha)> ETTK (272 t/ha)> ~ ETDV~ETPM (236-249 t/ha).

Despite recent progress in genetics, genomics, and phenotyping, trait selection is limited by our ability to predict genotype x environment interactions, and to identify impactful traits for target environments. Here, we combined crop modelling, physiology, genetics, and breeding to identify relevant traits to increase wheat yields in the target environments of the Australian wheatbelt, develop high-throughput phenotyping methods for relevant traits, and identify their underlying genetic controls. Better transpiration efficiency (i.e., ‘more crop per drop’) and its components were identified as traits of interest and used as an example to illustrate how integrating modelling, phenotyping, and genetics can be used to improve crop adaptation. We anticipate that such an approach can enhance the efficiency of breeding programmes to increase productivity in target environments in current and future climates.