Transpiration Efficiency Research Articles

Conservation tillage increases yield and precipitation use efficiency of wheat on the semi-arid Loess Plateau of China

Drought is a major limiting factor for rainfed spring wheat production on the semiarid Loess Plateau of China. Suitable tillage practices are important for improving precipitation use efficiency (PUE), which is the ratio of grain yield to annual precipitation. To obtain a better understanding of the effects of conservation tillage practices on PUE on the semiarid Loess Plateau, PUE was divided into five steps: precipitation storage efficiency, farmland water consumption rate, ratio of transpiration to evapotranspiration, crop transpiration efficiency, and harvest index. Six tillage practices were assessed in this paper, including conventional tillage with no straw (T), no-till with straw cover (NTS), no-till with no straw (NT), conventional tillage with straw incorporated (TS), conventional tillage with plastic mulch (TP), and no-till with plastic mulch (NTP), based on a long-term experiment initiated in 2001. The impact of tillage practices on soil quality, soil water storage, soil evaporation, biomass yield, and grain yield of spring wheat were monitored in 2015 and 2016. The results show that NTS improved soil quality and soil water storage before sowing. No-till with plastic mulch and NTS increased evapotranspiration but decreased evaporation, thus optimizing precipitation storage efficiency, the farmland water consumption rate, the ratio of transpiration to evapotranspiration, and crop transpiration efficiency, which gave rise to greater aboveground dry matter accumulation and more dry matter accumulation in grain. As a result, grain yield under NTS and NTP was significantly increased by 45 and 41 % compare to T, respectively, with corresponding improvements in PUE of 43 and 39 %. Therefore, both NTS and NTP have potential to substantially increase grain yield of spring wheat and PUE. However, for sustainable intensification in the long-run, NTS is the best combination of tillage and soil surface management for spring wheat production on the semi-arid Loess Plateau of China.

Mitigating drought stress in sesame by foliar application of salicylic acid, beeswax waste and licorice extract

This study evaluated the effects of salicylic acid (SA), beeswax waste extract (BWE) and licorice extract (LE) as novel biostimulants, on drought-induced oxidative stress on sesame. The treatments consisted of three drought stress conditions (full irrigation, 90 % field capacity (FC); moderate stress, 60 % FC; and severe stress, 30 % FC) together with four exogenous foliar applications (control, water; LE, 5000 ppm; BWE, 2000 ppm; and SA, 1.5 mM). Plants subjected to drought stress displayed significant reduction in plant height, leaf area index, biological and seed yield, chlorophyll a and b content, quantum efficiency of photosystem II (Fv/Fm), net photosynthetic rate (Pn), stomatal conductance (gs), transpiration (Tr) and water use efficiency (WUE). Drought stress stimulated Malondialdehyde (MDA), proline, protein and carotenoid contents, and catalase (CAT), ascorbate peroxidase (APX), Guaiacol peroxidase (GPX) and glutathione reductase (GR) activity, while the exogenous foliar application of substances mitigated the oxidative damages. The alleviated effect of BWE on drought stress was more effective than those of LE and SA. In conclusion, it could be recommended that the application of the natural substances may lead to overcoming the negative effects of drought stress by regulating osmoprotectants content and antioxidant defense system, increasing mineral nutrients in plant organs and adjusting photosynthesis systems; consequently, contributing to improving the sesame productivity.

Genetic variation for leaf carbon isotope discrimination and its association with transpiration efficiency in canola (Brassica napus).

Drought is a major constraint to canola production around the world. There is potential for improving crop performance in dry environments by selecting for transpiration efficiency (TE). In this work we investigated TE by studying its genetic association with carbon isotope discrimination (Δ) and other traits, e.g. specific leaf weight (SLW) and leaf chlorophyll content (SPAD). Among the 106 canola genotypes - including open-pollinated, hybrid, inbred types and cytoplasmic variants - tested in the field and glasshouse there was significant genotypic variation for TE, Δ, plant total dry weight, SLW and SPAD. Strong negative correlations were observed between TE and Δ (-0.52 to -0.76). Negative correlations between Δ and SLW or SPAD (-0.43 to -0.78) and smaller but significant positive correlations between TE and SLW or SPAD (0.23 to 0.30) suggested that photosynthetic capacity was, in part, underpinning the variation in TE. A cytoplasmic contribution to genetic variation in TE or Δ in canola was also observed with Triazine tolerant types having low TE and high Δ. This study showed that Δ has great potential for selecting canola germplasm with improved TE.

Variations in drought tolerance components and their association with yield components in finger millet (Eleusine coracana).

Finger millet has gained considerable attention worldwide due to its nutritional and health benefits. Being a rainfed crop of semiarid and arid regions, drought is one of the major constraints to its yield stabilisation. To address this, a set of 38 accessions of finger millet were evaluated in both field and mini-lysimeters under both well-watered (WW) and water-stressed (WS) conditions. The objectives of the study were to identify the range of variations for yield components, water-use (WU) and transpiration efficiency (TE) and to examine the potential of the mini-lysimeter system in assessing the genotypic performance in the field conditions. Approximately 2-fold variations in shoot biomass and ~9-fold variations in grain yield under WS conditions were observed. Reproductive growth was more sensitive to WS than the vegetative growth. Our results indicate that in addition to yield potential under WW conditions, WU followed by TE were the other two major contributors toward shoot biomass, whereas, HI followed by TE were the major contributors toward grain yield under WS. The close association between the yield components recorded in the field and in mini-lysimeters suggests that the lysimetric system has the great potential to reflect the genotypic performance under field conditions. Regression analyses suggest that HI explained almost all the variations in grain yield under WW conditions, whereas under WS treatment, next to HI, both TE and WU had also contributed significantly to grain yield. The absence of interrelationship between WU and TE suggests that both these components contribute independently toward the yield components under WW or WS conditions. The accessions with higher shoot biomass and grain yield extract much more water during the post-anthesis stages than the poor performers under WS. Results also suggests that higher WU contributed more towards shoot biomass and higher TE contributed more towards grain yield by improving the harvest index.

Physiological Response of Advanced Lines of Rice under Water Deficit in Campeche, Mexico

Yields of rice (Oryza sativa L.) respond to complex interactions between the genotype and the environment; rice has the particularity of being a semi-aquatic crop, and as a result of this, it presents lower adaptation to the limiting water content of soil and is extremely sensitive to stress from drought; therefore, it is the most important limiting factor in rice production. The objective of this study was to research the physiological response of rice genotypes to water stress. The grain yield and its components, leaf area and transpiration efficiency under irrigation (I) and drought (D) were evaluated in eight advanced lines from the nursery of the Latin American Fund for Irrigated Rice (Fondo Latinoamericano para Arroz de Riego, FLAR) and a control variety of rice. The experiment was established in Campeche, in the 2015 autumn-winter cycle. The grain yield and its components, as well as the leaf area were greater under irrigation conditions than under drought. The transpiration from the water stress was reduced and the plants under drought increased their transpiration efficiency. The genotypes P-V 2006 and P-V 2009 were identified, with genealogies FL05392-3P-12-2P-2P-M and FL08224-3P-2-1P-3P-M, respectively, as the most outstanding compared to the rest of the genotypes in the grain yield and its components, leaf area, total root biomass, and transpiration efficiency.

New approaches to enhance the water productivity in horticultural crops with special reference to Tamil Nadu

Water being a critical resource that is gradually diminishing, the need to increase Water Use Efficiency (WUE) becomes progressively more crucial. Limited success has been obtained so far through genetic approaches to modify complex traits such as transpiration efficiency. This is partly due to our limited understanding of the molecular basis and physiological mechanisms regulating WUE in stressed and non-stressed plants. There are various irrigation techniques to enhance the efficiency of the applied water to the crop. Improving irrigation techniques can directly affect WUE by increasing the yield per unit of water applied and reducing the amount of water loss. Major improvements could be obtained through management and innovative design of integrated water delivery and application schemes. Innovative decision support systems integrated by sensor networks to monitor soil and plant water status will help farmers to efficiently allocate limited water resources.

Leaf Conductance Study on Twelve (12) Genotypes of Sorghum [Sorghum bicolor (L.) Moench

Enhancing transpiration efficiency (TE), defined as biomass accumulation per unit water transpired, may be an effective approach to increasing sorghum yield in arid and semi-arid regions under drought conditions. Water use efficiency was compared among 12 sorghum cultivars collected from the ICRISAT Genebank and representing diverse origins. Plants were cultivated in a split plot experimental design using pots with two factors in 5 replications. An irrigation system with two levels: the "well water”, and “water stress” were applied. Plastic bags were used to wrap the pots after the phase of water saturation. Transpiration Efficiency (TE) was used to evaluate the performance of a genotype in water deficit conditions. The parameters such as leaf weight, stem weight and root weight were measured and the data were analyzed using the statistical software tool GenStat version 19. Leaf weight, stem weight and root weight varied significantly between genotypes under well water conditions while under water stress conditions only the stem weight measured was significantly different among the genotypes. Significant differences between genotypes for leaf canopy conductance were found. The leaf canopy conductance was weakly correlated to the stem weight and root weight in both well-watered and water stress conditions.

Nitrogen application modified the effect of deficit irrigation on tomato transpiration, and water use efficiency in different growth stages

Nitrogen (N) application affects the relationships between tomato transpiration (T), water use efficiency (WUE) and soil water content (SWC), and is important for practical agricultural management. This study investigated T (hourly, Th, and daily, TC) and WUE (leaf scale, WUEL, and plant scale, WUEP) differences of tomato grown in a solar greenhouse in response to different N and irrigation treatments. Three N application rates (0, 100 and 200 mg N kg−1 soil) were applied with four irrigation levels (full irrigation, Wck; and deficit irrigation, half amount of Wck, happened in different growth stage, W1, W2 and W3 respectively). Results showed that N application partly alleviated reductions in T associated with deficit irrigation, and it enhanced the promotion of deficit irrigation in WUEL. In tomato fruit late growth stage (stage 3), a balance is needed between irrigation and N application rate, higher N application can improve T and WUEL under higher irrigation water available. The positive effects of N2 and N3 on T were more pronounced when SWC was in the range of 0.19 − 0.22 cm3 cm−3 and 0.22 − 0.26 cm3 cm−3, respectively in this study. In tomato fruit early growth stage (stage 1), N application aggravated the reduction in WUEP due to deficit irrigation, while in tomato fruit middle and late growth stages (stage 2 and 3), N application enhanced the promotion of deficit irrigation on WUEP. Generally, in tomato early growth stage, there should be no water shortage and N excess; in fruit middle and late growth stages, more N can be applied along with the increase of SWC. This study proposes a prospect to implement integrative management of irrigation and N application during tomato growth, promoting transpiration and water use efficiency in a scientific way.

A Crop Simulation Model for Tef (Eragrostis tef (Zucc.) Trotter)

Tef is an Ethiopian staple grain that provides both food security and income for smallholders. As tef is nutritious and gluten free, it is also gaining popularity as a health food. A tef model was calibrated based on the Decision Support System for Agrotechnology Transfer’s (DSSAT) NWheat model and included parameter changes in phenology, photoperiod response, radiation use efficiency, and transpiration efficiency for both standard and elevated atmospheric CO2, based on published literature for tef and other C4 species. The new DSSAT-Tef model was compared with tef field experiments. DSSAT-Tef accurately simulated phenology and responded to changes in N supply and irrigation, but overestimated growth and occasionally yields. Simulation-observation comparisons resulted in an RMSE of 2.5 days for anthesis, 4.4 days for maturity, 2624 kg/ha (49.6%) for biomass, and 475 kg/ha (41.0%) for grain yield. Less data were available for N uptake, and the model simulated crop N uptake with an RMSE of 45 kg N/ha (46.2%) and 15 kg N/ha (37.3%) for grain N. While more data from contrasting environments are needed for further model testing, DSSAT-Tef can be used to assess the performance of crop management strategies, the suitability of tef for cultivation across growing environments, and food security.

Functional Dissection of the Chickpea (Cicer arietinum L.) Stay-Green Phenotype Associated with Molecular Variation at an Ortholog of Mendel's I Gene for Cotyledon Color: Implications for Crop Production and Carotenoid Biofortification.

“Stay-green” crop phenotypes have been shown to impact drought tolerance and nutritional content of several crops. We aimed to genetically describe and functionally dissect the particular stay-green phenomenon found in chickpeas with a green cotyledon color of mature dry seed and investigate its potential use for improvement of chickpea environmental adaptations and nutritional value. We examined 40 stay-green accessions and a set of 29 BC2F4-5 stay-green introgression lines using a stay-green donor parent ICC 16340 and two Indian elite cultivars (KAK2, JGK1) as recurrent parents. Genetic studies of segregating populations indicated that the green cotyledon trait is controlled by a single recessive gene that is invariantly associated with the delayed degreening (extended chlorophyll retention). We found that the chickpea ortholog of Mendel’s I locus of garden pea, encoding a SGR protein as very likely to underlie the persistently green cotyledon color phenotype of chickpea. Further sequence characterization of this chickpea ortholog CaStGR1 (CaStGR1, for carietinum stay-green gene 1) revealed the presence of five different molecular variants (alleles), each of which is likely a loss-of-function of the chickpea protein (CaStGR1) involved in chlorophyll catabolism. We tested the wild type and green cotyledon lines for components of adaptations to dry environments and traits linked to agronomic performance in different experimental systems and different levels of water availability. We found that the plant processes linked to disrupted CaStGR1 gene did not functionality affect transpiration efficiency or water usage. Photosynthetic pigments in grains, including provitaminogenic carotenoids important for human nutrition, were 2–3-fold higher in the stay-green type. Agronomic performance did not appear to be correlated with the presence/absence of the stay-green allele. We conclude that allelic variation in chickpea CaStGR1 does not compromise traits linked to environmental adaptation and agronomic performance, and is a promising genetic technology for biofortification of provitaminogenic carotenoids in chickpea.

Pepper Photosynthesis, Stomatal Conductance, Transpiration, and Water Use Efficiency Differ with Variety, Indigenous Habitat, and Species of Origin

The instantaneous photosynthetic rate (Pn), transpiration rate (E), and stomatal conductance (gS) were measured for 33 outdoor-grown Capsicum varieties (varying in species of origin and indigenous habitat) between 29 July and 22 Aug. 2017 using a portable gas exchange meter. Cuvette leaf temperature (Tleaf) and relative humidity (RH) were recorded at that same time. Pn differed from 3.6 to 3.7 for ‘Malawi Piquante’ and ‘Korean Long Green’ peppers to 16.3 μmol CO2/m2/s (fixed) for ‘Thai Hot’ peppers. The gS differed from 0.01 to 0.05 among 13 varieties to 0.28 mmol H2O/m2/s for ‘Thai Hot’ peppers. E differed from 0.43 to 0.59 among three varieties to 4.14 to 4.20 mmol H2O/m2/s for ‘CGN 22091’ and ‘Peruvian Purple’ peppers. Water use efficiency (WUE; Pn/E) varied from 2.92 to 3.43 among three varieties to 5.10 to 7.20 for 16 other varieties. C. annuum derived varieties had higher Pn (9.4 μmol CO2/m2/s fixed) than varieties derived from other species (4.5–8.6 μmol CO2/m2/s fixed). Varieties originating from dry climates had higher Pn (12.5 μmol CO2/m2/s fixed) than those originating from temperate or tropical climates (8.0–8.8 μmol CO2/m2/s fixed). Tleaf (27 to 33 °C) and RH (38% to 39% and 57% to 59%) differed among varieties. Pn was positively correlated with gS, E, and RH and was negatively correlated with WUE. We found that Capsicum Pn, E, and gS varied more than has been previously reported, and our data suggested that Pn, gS, and E data of outdoor-grown peppers should be used only when selecting parents for a breeding program (unless progeny is intended for greenhouse production).

Leaf Anatomical Modification in Drought of Rice Varieties (Oryza sativa L.)

Each organ plant has been formed perfectly to support physiological processes in an unfavorable environmental condition. Rice (Oryza sativa L.) be included plants sensitive to drought conditions during a stage of growth and development. This will cause pressure (stress) resulting in a decrease in rate metabolism in leaf cells. Leaf anatomical characteristics are criteria that can be used to identify plants that are tolerant to drought. Anatomical response leaves in drought conditions inform the development of leaf photosynthetic parts carrying out changes in anatomical structure morphology includes changes in cell walls, organ size, changes in direction growth, including dropping leaves and enhancing the life cycle. The research aimed to determine the anatomic response leaves rice varieties (Oryza sativa L.) to drought stress. Five rice varieties used were given drought-stress treatment for 12 days. Identification leaf anatomical structures using microscopic slices of transverse was made according to the paraffin method. Changes in the anatomical structure of leaves of drought-stress have decreased bulliform cells increase in size, the thickness epidermis cells in an effort to retain the water content in cells, and reducing the size and total stomata with purpose process control flow of transpiration and water use efficiency.

Aboveground biomass, transpiration and water use efficiency in eucalypt plantation fertilized with KCl, NaCl and phonolite rock powder

Potassium has important physiological functions in eucalypt plantations, increasing their productivity when applied to soil via mineral fertilizers. There is interest in identifying alternative sources to KCl owing to its high cost and limited reserves. The aim of the study was to test the effect of replacing KCl with NaCl and phonolite rock powder. Two comparisons were made: (1) application of 283 kg ha−1 of KCl compared with that of 2125 kg ha−1 of phonolite rock powder (equivalent to 170 kg ha−1 of K2O in both treatments); (2) application of 139 kg ha−1 of NaCl compared with that of 183 kg ha−1 of KCl (equivalent to 2.33 kmol Na and K, respectively). Radial growth, soil water content, leaf water potential (Ψ), accumulated transpiration, stem volume and biomass increment, as well as water use efficiency (WUE) were evaluated. In the first comparison, both fertilizations presented equal values for all characteristics evaluated. In the second, the accumulated transpiration in trees fertilized with KCl was 17% higher than that in plants fertilized with NaCl. In contrast, the WUE was 20% higher in the trees fertilized with NaCl than in those fertilized with KCl, reflecting the lower water consumption for the same increment in stem volume and biomass. We conclude that phonolite rock powder and NaCl are possible substitutes for conventional K fertilization performed with KCl.

Evaluating the Effect of Groundwater Table on Summer Maize Growth Using the AquaCrop Model

Shallow groundwater has a great influence on crop growth. However, few studies have investigated the impact of different groundwater depth on crop growth. This paper mainly discusses the impact of the groundwater depth on summer maize growth and the groundwater contributions to summer maize evapotranspiration and yield via the AquaCrop crop growth model. Numerical simulation results showed that summer maize growth and soil water in the Shijin irrigation district were highly related to the groundwater depth. With the depletion of the groundwater, the crop coefficient, crop actual transpiration, crop yield and crop water-use efficiency tended to increase and then decrease. Considering the groundwater contribution, maize yield and water-use efficiency, the suitable groundwater table depth for summer maize growth in the Shijin irrigation district was 1.5 m, and the groundwater contribution was 58.8 % in this case. Thus, discussing the impact of groundwater on crop growth is highly pertinent, as it is important for arranging irrigation schedules.

Influence of plastic film mulch on maize water use efficiency in the Loess Plateau of China

Water is the main limiting factor for crop growth in dryland farming areas. Plastic film mulch (PM) is widely used to improve water use efficiency (WUE) and increase crop yield over conventional methods (no mulch, NM) in China. To get a better understanding about PM influence on water use process in the field, we defined WUETWI as the ratio of yield (Y) to the total water input (TWI), and divided WUETWI into 4 steps by means of a systematic and quantitative approach. The 4 steps included ratio of available soil water (SW) to TWI (SW0+P, where SW0 is available soil water at the sowing, P is seasonal precipitation), ratio of crop evapotranspiration (ETC) to SW, ratio of crop transpiration (T) to ETC and transpiration efficiency (WUET, Y/T). Three field experiments were conducted to analyze the influence of PM on soil moisture content, water consumption, and the grain yield of dryland spring maize (Zea mays L.). Results showed that, compared with NM, spring maize yield of PM was increased by 28.6%, and the WUETWI of PM was increased by 26.4% on average in the experiment 1. Since ETc with PM was slightly higher than that with NM, the ETC/SW was increased by 3.9%. In the experiment 2, the T/ETC with PM was 77.7% on average, 30.6% higher than that with NM; the Y/T increased by 13.6% from NM to PM. Precipitation storage efficiency increased linearly with the percentage of PM. Improved crop growth under PM led to higher crop biomass and higher leaf area index, which might result in higher transpiration rate. The T/ETC under PM was also increased.

Leaf gas exchange, photochemical responses and oxidative damages in assai (Euterpe oleracea Mart.) seedlings subjected to high temperature stress

In this work, we aimed to examine the magnitude of changes in leaf gas exchange, chlorophyll fluorescence, and antioxidant responses in assai (Euterpe oleracea Mart.) seedlings subjected for 14 days to different temperatures (28 °C, control treatment, and 36 and 40 °C, high-temperature stress). Exposure to 36 °C decreased stomatal conductance (gs), photochemical quenching (qL), and non- photochemical quenching (NPQ) by 27, 53, and 20%, respectively. Further, it increased the photosynthetically active radiation (PAR) fraction that was absorbed by photosystem (PS)-II-antenna (but neither used in photochemistry nor dissipated thermally) by 14%. Moreover, incubation of seedlings at 36 °C induced a 53% increase in ascorbate peroxidase (APX) activity and a 16% decrease in hydrogen peroxide (H2O2); however, there were neither photooxidative damages to the PS nor lipid peroxidation. In contrast, seedlings incubated at 40 °C exhibited significantly decreased net CO2 assimilation rate (93%), gs (83%), transpiration (75%), and water use efficiency (71%). The maximum efficiency of PS II photochemistry did not differ compared to control plants, but the actual quantum yield of PS II electron transport, qL, and NPQ were decreased by 74, 60 and 19%, respectively. At 40 °C, there was increased photorespiration and elevated superoxide dismutase and APX activities, but the seedlings exhibited increased lipid peroxidation and general chlorosis in the youngest leaves. Taken together, our findings support that assai seedlings were tolerant to 36 °C but very sensitive to 40 °C.

Rhizophagus irregularis MUCL 41833 Improves Phosphorus Uptake and Water Use Efficiency in Maize Plants During Recovery From Drought Stress.

Irregular precipitations are likely to affect maize production in the future. Arbuscular mycorrhizal fungi (AMF) have been reported to increase maize resistance to drought, but their role on the short-term inorganic phosphorus (Pi) uptake, leaf gas exchange parameters and water content during recovery after drought remains poorly understood. Here, we investigated these parameters in maize plants colonized or not by Rhizophagus irregularis MUCL 41833. The mycorrhizal (M) and non-mycorrhizal (NM) plants were grown for a 3-week period in a circulatory semi-hydroponic cultivation system and were submitted to well-, moderately-, or poorly-watered conditions (WW, MW, and PW, respectively), the two latter conditions corresponding to moderate and severe droughts. The plants were then watered at field capacity for 42 h with a Pi impoverished Hoagland nutrient solution and the dynamic of Pi depletion in the nutrient solution, corresponding to Pi uptake/immobilization by the maize-AMF associates, was evaluated at 0, 9, 21, and 42 h. The CO2 assimilation rate (A), stomatal conductance (gs), transpiration (E), and instantaneous water use efficiency (WUEi) were also assessed at 0 and 42 h of circulation. Plant biomass, plant water content, phosphorus concentration and content, and leaf relative water content were evaluated at harvest. During recovery, Pi uptake was significantly higher in M versus NM plants whatever the water regime (WR) applied before recovery. AMF did not affect leaf gas exchange parameters before recovery but modulated gs and E, and improved WUEi after 42 h of recovery. At harvest, no significant difference in dry biomass was found between M and NM plants but shoot fresh weight was significantly higher in M plants. This resulted in an increased shoot water content in M plants grown in the MW and PW treatments. Surprisingly, leaf relative water content was significantly lower in M plants when compared with NM plants. Finally, P content and concentration were significantly higher in roots but not in shoots of M plants. Our results suggested that AMF can play a role in drought resistance of maize plants by increasing the Pi uptake and WUEi during recovery after drought stress.

Partial root zone drying irrigation, planting methods and nitrogen fertilization influence on physiologic and agronomic parameters of winter wheat

The effectiveness of water-saving irrigation strategies such as partial root zone drying (PRD) should be explored to ensure food security as the availability of water for irrigation declines and population increases. PRD is easily performed by localized irrigation method; however very small percentage of irrigated area is under this irrigation method and main irrigation method is furrow irrigation that should be adapted to PRD. In this respect, present study was conducted to explore the effects of PRD in furrow irrigation strategies on physiological and agronomic behavior of winter wheat. The field experiment included two irrigation strategies (variable alternate furrow irrigation (VAFI) as PRD and ordinary furrow irrigation (OFI), two different planting method (in-furrow planting and on-ridge planting) and three nitrogen rates (0, 150, and 300 kg N ha−1) over 2015–2016 and 2016–2017. Results showed that decreasing leaf water potential (LWP) during the stem elongation stage resulted in increasing the sensitivity of winter wheat to water stress and yield reduction. The leaf photosynthesis rate (An) was not significantly lowered in VAFI (PRD) in comparison with that obtained in OFI. The VAFI strategy reduced the stomatal conductance (gs) about 12% and 7% in comparison with that obtained in OFI in the first and second year, respectively that were statistically significant. The lower slope of linear relationship between leaf transpiration efficiency (An/Tr) and vapor pressure deficit (VPD) in VAFI strategy indicated that with increasing VPD, leaf transpiration efficiency was higher than that obtained in OFI. As a consequence, VAFI strategy as PRD was effective in increasing An/Tr and can be an alternative irrigation management in winter wheat farms with limited water supplies. Although, in-furrow planting showed higher efficiency in increasing yield in comparison with that obtained in on-ridge planting, on-ridge planting showed higher effects on leaf transpiration efficiency. Furthermore, there was no significant difference between two application rates of nitrogen (150 kg N ha−1 and 300 kg N ha−1) for different parameters; therefore, application of 150 kg N ha−1 can be suggested as an effective rate to increase winter wheat yield. Consequently, in areas with scarce water and furrow irrigation, combination of VAFI, in-furrow planting and 150 kg N ha−1 is recommended to achieve optimum yield with possibility of saving water during the winter wheat growing season.

Stomatal response in soybean during drought improves leaf-scale and field-scale water use efficiencies

Diminishing water resources and an expected increase in frequency of extreme water stress events necessitate tools to diagnose and improve the drivers of variability in agronomic water use efficiency. The objective of this study was to determine if leaf-scale water use efficiency (measured as intrinsic water use efficiency and transpiration efficiency) is expressed at the field scale as yield or agronomic water use efficiency variability. We measured grain yield, total aboveground biomass, and carbon isotope discrimination and estimated evapotranspiration using a mass balance approach for field-grown Glycine max (soybean) over five years. We found that the high agronomic water use efficiency in years characterized by high vapor pressure deficit was caused by a large reduction in evapotranspiration and a relatively smaller reduction in yield. This has implications for developing drought tolerance in soybeans without compromising yield. We observed a positive relationship between transpiration efficiency and agronomic water use efficiency, with the leaf scale explaining 68% of the variability at the field scale. Through this analysis, we infer that increasing transpiration efficiency at the leaf scale will likely improve agronomic water use efficiency at the field scale in rain-fed soybean systems.

Additive effects of high growth rate and low transpiration rate drive differences in whole plant transpiration efficiency among black poplar genotypes

Poplar plantations, widely used for the production of woody biomass, might be at high risk from the climate change-induced increase in the frequency of drought periods. Therefore, selecting improved genotypes, which are highly productive but with a high water use efficiency (WUE), is becoming a major target. The use of automated weighing systems in controlled environments facilitates the estimation of cumulated water loss and whole plant transpiration efficiency (TE). Differences in TE and leaf level intrinsic WUE as well as the contribution of underlying ecophysiological traits were determined in three contrasting P. nigra genotypes. Strong differences in TE among the selected genotypes were congruent with differences in leaf level intrinsic WUE. Our data show that a high total leaf area was overcompensated by a low per leaf area transpiration rate, leading to higher TE in highly productive genotypes originating from cool locations. Nocturnal water loss was relatively low but contributed to variations in TE among genotypes. In response to drought, leaf level WUE increased but not TE, suggesting that carbon losses due to whole plant respiration could offset the drought-induced increase in intrinsic WUE.