Instantaneous Water Use Efficiency Research Articles

Effects of CO2 concentration and soil water content on short-term water-use efficiency at whole-plant level

Uncovering the variations of short-term water-use efficiency (WUEp) at whole-plant level in response to CO2 concentration (Ca) and soil water content (SWC) can improve the understanding of plant survival strategies under climate change. In this study, Platycladus orientalis saplings were cultured in simulated climate chambers.There were totally 15 treatments, including Ca of 400 (C400), 600 (C600) and 800 (C800) μmol·mol-1 and SWC of 35%-45% field water holding capacity (FC), 50%-60%FC, 60%-70%FC, 70%-80%FC and 95%-100%FC. The WUEp was measured by mini-lysimeters, weighting method, and static assimilation chamber. The results showed that both daytime (0.12-1.87 mol·h-1) and nighttime transpiration rates (0.01-0.16 mol·h-1) at whole-plant level reached the maximum at C400×70%-80%FC, while the whole-plant daytime net photosynthetic rate (2.12-22.10 mmol·h-1) reached the maximum at C800×70%-80%FC. In contrast, nighttime respiration rate (0.84-4.41 mmol·h-1) increased with increasing SWC, but decreased with increasing of Ca, reaching the maximum at C400×95%-100%FC. For WUEp (5.37-24.35 mmol·mol-1), it reached the maximum at C800×50%-60%FC, indicating that plants could use less water and fixed more carbon by adjusting adaptation strategies under high Ca and drought conditions. In addition, leaf instantaneous water-use efficiency was a good predictor of WUEP when the canopy structure was similar.

Green Light Partial Replacement of Red and Blue Light Improved Drought Tolerance by Regulating Water Use Efficiency in Cucumber Seedlings

Light is one of the most important environmental signals in plant growth, development, and stress response. Green light has been proved to enhance plant defense against biotic and/or abiotic stress. To illustrate the effects of green light partially replaced red light and blue light on the plant under drought condition, cucumber (Cucumis sativus L. cv. Xinchun No. 4) seedlings were treated with short-term drought stress and were concomitantly exposed to four treatments, which were set up by adjusting the relative amount of green light as 0 (RB), 25 (RBG25), 50 (RBG50), and 75 (RBG75) μmol m−2 s−1, respectively, with a total photosynthetic photon flux density of 250 μmol m−2 s−1 and a fixed red-to-blue ratio of 4:1. The results showed that compared with RB, RBG50 significantly increased shoot fresh weight (FW) and dry weight (DW), root DW, plant height, stem diameter, leaf area, and leaf dry mass per unit area (LMA) by 10.61, 7.69, 66.13, 6.22, 10.02, 4.10, and 12.41%, respectively. Also, the addition of green light significantly increased the root volume and root tip number. Moreover, green light partial replacement of red light and blue light increased total water content, especially free water content, improved leaf water status, and alleviated water loss in plants caused by drought stress. Also, the addition of green light increased net photosynthetic rate (Pn), reduced both stomata conductance (gs) and transpiration rate (E), enhanced the intrinsic water-use efficiency (WUE) and instantaneous water-use efficiency (iWUE) of leaves, and increased the content of chlorophylls a and b. Green light substituting a proportion of blue and red light regulated stomatal aperture by significantly increasing abscisic acid (ABA) and γ-aminobutyric acid (GABA) content. In addition, the increase of GABA was resulted from the upregulation of Glutamate Decarboxylase 2 (CsGAD2). However, the relative electrolytic leakage and contents of malondialdehyde (MDA), superoxide anion (), and hydrogen peroxide (H2O2) vigorously decreased as the intensity of green light was added to the spectrum under drought. Conclusively, green light partially replaced red light and blue light and improved drought tolerance of cucumber seedlings by upregulating the expression of CsGAD2 gene and promoting the synthesis of GABA. The increase in GABA content further downregulated the expression of aluminum-activated malate transporter 9 (CsALMT9) gene, induced stomata to close, improved water utilization, and alleviated damage caused by drought. This study highlights a role of green light in plant physiological processes. Moreover, analyzing the function of green light on improving drought tolerance of plants could open alternative avenues for improving plant stress resilience.

CO2 capture and water use efficiency in Opuntia stricta (Haw.) at different seasons and evaluation times

The forage cactus Mexican Elephant Ear is widely incorporated into the animal productive chain of the northeast region of Brazil. However, there is a lack of studies on the physiological dynamics of this cactus. Therefore, this study was conducted at the Estação Experimental Prof. Ignácio Salcedo of the Instituto Nacional do Semiárido (INSA), in Campina Grande, State of Paraíba, Brazil. The aim of this study was to evaluate CO2 uptake and water-use efficiency levels in Opuntia stricta (Haw.) during different seasons and evaluation times. The treatments were distributed using a 24×2 factorial arrangement, which corresponded to the evaluation of gas exchange processes for 24 hours in the rainy (June) and dry (December) seasons. The evaluated parameters were stomatal conductance, transpiration and CO2 uptake rate, internal CO2 concentration, instantaneous water-use efficiency and intrinsic water-use efficiency. The results revealed that gas exchange in the forage cactus was more intense during the rainy season, with good stability, than the low exchange levels during the dry season. Regardless of the season, the CO2 uptake peaked between 24:00 and 02:00. In addition, this range of time is the most suitable to conduct analyses under field conditions.

Pre- and post-harvest evapotranspiration, carbon exchange and water use efficiency of a mature peach orchard in semi-arid climate

Better knowledge of the evapotranspiration and carbon exchange of fruit trees is needed to optimize the trade-off between water use and carbon assimilation and to better understand the role of agriculture in the biogeochemical cycles. In this work, we measured water and carbon fluxes with eddy covariance and transpiration with sap flow in a drip-irrigated peach orchard of 70% ground cover located in southern Spain for 2 years. The empirically measured crop coefficient (Kc) under good watering conditions in the summer ranged from 1 to 1.1. The daytime net ecosystem exchange (NEE) flux of the orchard averaged 30 g CO2 m2 day−1 during the period of maximum activity in July. The daytime ecosystem water use efficiency (WUE) of the orchard reached a minimum in late June, flattened around 4 g CO2 L−1 throughout the summer, and increased in autumn, but was unaffected by fruit removal or post-harvest irrigation reduction imposed by the farm (30% reduction). The response of instantaneous peach ecosystem WUE to VPD was also investigated. Both Kc, NEE, leaf water potential and stomatal conductance decreased sharply after harvest. Transpiration data from some purposely over-irrigated experimental trees demonstrated that the post-harvest alterations we found were not caused by fruit removal, but are result of mild water stress originated by the irrigation reduction. Hence, the often-observed alterations in water relations after harvest in well-watered trees were not observed in this experiment. This work adds insight on peach irrigation efficiency and on the contribution of orchards to agricultural carbon budgets.

Gas exchange in genotypes of Nopalea cochenillifera in different seasons and evaluations times

This study aimed to evaluate the gas exchanges in genotypes of Nopalea cochenillifera Salm-Dyck in different seasons and times of the day. The experiment was conducted with the varieties Miúda and Baiana at the Experimental Station Prof. Ignacio Salcedo, belonging to the National Semi-Arid Institute (INSA), in the municipality of Campina Grande, State of Paraíba, Brazil. The treatments were distributed in a 24 × 2 factorial arrangement, corresponding to gas exchange evaluations performed every hour for 24 hours in the rainy season (June) and in the drought season (December). Analyzed were stomatal conductance, transpiration rate, CO2 uptake, and internal CO2 concentration, besides instantaneous water-use efficiency, intrinsic water-use efficiency, and instantaneous carboxylation efficiency. In both drought and rainy seasons, variety Baiana presented higher gas exchange intensity than the variety Miúda. In the rainy season, gas exchanges are potentialized in both varieties evaluated. In this period, the peak of CO2 uptake occurs from 1:00 a.m. to 3:00 a.m. for the verity Baiana, and from11:00 p.m. to 2:00 a.m. for the variety Miúda, whereas, in the drought season, it occurs from 11:00 p.m. to 2:00 a.m. for both varieties, with these constituting the ideal intervals for measuring gas exchanges in the field.

Drought tolerance assessment of citron watermelon (Citrullus lanatus var. citroides (L.H. Bailey) Mansf. ex Greb.) accessions based on morphological and physiological traits

Long-term cultivation of citron watermelon under water-constrained environments in sub-Saharan Africa resulted in the selection and domestication of highly tolerant genotypes. However, information on the magnitude of variation for drought tolerance in citron watermelon is limited for the effective selection of suitable genotypes for breeding. The objective of this study was to determine variation for drought tolerance among South African citron watermelon landrace accessions for selection and use as genetic stock for drought-tolerance breeding in this crop and closely-related cucurbit crops. Forty genetically differentiated citron watermelon accessions were grown under non-stress (NS) and drought-stress (DS) conditions under glasshouse environment. Data of physiological (i.e., leaf gas exchange and chlorophyll fluorescence parameters) and morphological traits (i.e., shoot and root system architecture traits, and fruit yield) were collected and subjected to various parametric statistical analyses. The accessions varied significantly for assessed traits under both NS and DS conditions which aided classification into five groups, namely; A (highly drought-tolerant), B (drought-tolerant), C (moderate drought-tolerant), D (drought-sensitive) and E (highly drought-sensitive). Drought-tolerant genotypes produced more fruit yield with less water compared with drought-sensitive genotypes. Several physiological and morphological parameters correlated with fruit yield under DS condition namely: instantaneous water-use efficiency (r = 0.97), leaf dry weight (r = 0.77), total root length (r = 0.46) and root dry weight (r = 0.48). The following accessions, namely: WWM-46, WWM-68, WWM-41(A), WWM-15, WWM-64, WWM-57, WWM-47, WWM-37(2), WWM-79, WWM-05 and WWM-50) were identified as highly drought-tolerant and recommended for drought-tolerance breeding in this crop or related cucurbit crops such as sweet dessert watermelon.

Profiling of Water-Use Efficiency in Switchgrass (Panicum virgatum L.) and the Relationship with Cadmium Accumulation

Planting bioenergy crops with high water-use efficiency (WUE) on heavy metal-polluted land is a good practice for biomass production and phytoremediation. Switchgrass (Panicum virgatum L.), a C4 perennial bioenergy grass, is native to the United States. The relationship between the WUE and Cd accumulation of switchgrass has seldom been studied. Here, the WUE and Cd accumulation characteristics of 14 high-biomass switchgrass cultivars were investigated under Cd stress by hydroponic culture. The main results showed that Cd inhibited the instantaneous WUE in switchgrass seedlings and that the inhibition rate was more significant in the upland types than in the lowland types of switchgrass. A positive correlation was found between relative WUE and Cd accumulation in roots and shoots. The relative expression level of stomatal control-related genes (ERECTA and EPF1) in lowland cultivars with high WUE was higher than in upland cultivars with low WUE, both in control and Cd treatment conditions. The results suggest that it would be possible to further select and cultivate switchgrass with high WUE and a high capacity for Cd accumulation for phytoremediation in Cd-contaminated land.

Effects of Magnetized, Chelated Iron Foliage Treatments on Foliar Physiology, Plant Growth and Drought Tolerance for Two Legume Species

A greenhouse study was conducted to determine the effects of foliar applications of magnetized, chelated liquid iron fertilizer for increasing the drought tolerance of two legumes. Study objectives were to determine the drought tolerance effects of four treatments on foliar gas exchange, soil moisture, and plant growth for velvet bean (Mucuns pruriens) and soybean (Gylcine max) plants. The four foliage treatments included applications with chelated liquid iron fertilizer (2.5 and 5%) with a conventional boom sprayer, with and without magnets in the spray lines. Physiological measurements were collected before foliar treatments and again after a 24-day deficit irrigation schedule. Physicochemical water properties were measured for each of the foliar treatments. Photosynthesis rates were 5.98, 2.04 and 3.19 µmol/m2/s for the control, non-magnetized and magnetized fertilizer treatments (2.5%), respectively, after completing the deficit irrigation schedule. Instantaneous water use efficiency (IWUE) was 0.60, 0.28 and 1.02 for the control, non-magnetized and magnetized fertilizer treatments (2.5%), respectively, after completing the deficit irrigation schedule. Photosynthesis and IWUE increased 56 and 263% for the magnetized fertilizer treatment (2.5%) compared to the non-magnetized foliar treatment, when averaged across both legume species. Photosynthesis and IWUE increased as electrical conductivity increased and oxidation reduction potential (ORP) decreased in absolute terms. A single foliar application resulted in aberrant physiological responses that are contrary to very widely held plant defense theories involving abiotic stressors. The single application improved the photosynthesis and water use efficiency for water stressed legumes emphasizing the need to better understand the relationships between water quality, plant bioenergetics, and stress physiology. Improved drought tolerance in row crops such as dry beans and soybeans, with a single magnetized fertilizer application, would be cost effective and easily adapted into current cropping systems. Interactions among physicochemical water properties, bioenergetics, plant metabolism, and crop stress physiology need to be further investigated in order to improve the quality of irrigation water to enhance drought tolerance of field crops.

Resposta fotossintética de umbuzeiro ao deficit de pressão de vapor

Abstract The objective of this work was to evaluate the photosynthetic response to vapor pressure deficit (VPD) in umbu (Spondias tuberosa) tree accessions. The experiment was carried out in a completely randomized design in a 5×7×2 factorial arrangement (five umbu accessions – BRS-68, EPAMIG-05, BGU-61, BGU-75, and BGU-50 –, seven evaluation times, and two reading times – at 8 a.m. and 2 p.m.) in split-split plots in time. Leaf temperature increased with air temperature. The variation of stomatal conductance and transpiration with the VPD was not significant. Net photosynthesis rate, carboxylation efficiency, and instantaneous water-use efficiency decreased with increasing VPD in all accessions, except in BRS-68, whose rates remained positive.

Leaf- and ecosystem-scale water use efficiency and their controlling factors of a kiwifruit orchard in the humid region of Southwest China

Understanding the characteristics of water use efficiency (WUE) and its controlling factors in the agricultural ecosystem can help us better understand the coupled process between water use and carbon assimilation spatially. The characteristics of the leaf- and ecosystem-level water, carbon and WUE variations as well as their drivers in a kiwifruit orchard were systematically analyzed during the growing seasons of 2018–2020. The results showed that leaf transpiration rate (Tr), net photosynthetic rate (Pn) and instantaneous WUE (WUEi) in exposed leaves were 2.25–2.77, 8.32–9.44 and 2.53–3.77 times higher than those of shaded leaves. Tr and Pn were significantly affected by photosynthetic active radiation (PAR) and stomatal conductance (gs). Air temperature (Ta), leaf water vapor deficit (VPDl) and stomatal conductance (gs) affected WUEi through leaf water consumption, while PAR affected WUEi through leaf photosynthetic process. Averaged evapotranspiration (ET), gross primary productivity (GPP) and ecosystem WUE (eWUE) were 551.30 ± 75.92 kg H2O m-2, 1475.37.59 ± 201.25 g C m-2 and 2.68 ± 0.04 g C kg−1 H2O, respectively. Global total radiation (Rg), Ta and VPD were the dominant climatic factors affecting ET and GPP, while Rg and wind speed (U2) were significantly correlated with eWUE (p < 0.01). WUEu, defined as the ratio of Pn·VPDl0.5 and Tr, could be considered as an effective indicator quantifying the coupled relationship between Tr and Pn·VPDl0.5 at the leaf scale. The coupled relationship between ET and GPP was strengthened after incorporating the effect of VPD on GPP due to reduced time lags among GPP, ET and VPD at the ecosystem scale. Rg, Ta, U2 and VPD contributed to greater effects through ET than that of GPP on eWUE, while the differences between them were reduced after incorporating VPD on GPP, which may be the source of the dependence of iWUE (GPP·VPD/ET) and uWUE (GPP·VPD/ET) on environmental conditions. This study enriches the scarce literature on what drives multi-scale water and carbon in a humid orchard and contributes to improving the understanding of the coupled process of water and carbon incorporating the effect of VPD at leaf and ecosystem scales.

PHYTOPHTHORA RAMORUM FOLIAR INFECTION REDUCES LEAF-LEVEL PRODUCTIVITY IN TANOAK AND CALIFORNIA BAY: A PILOT STUDY FROM REDWOOD NATIONAL PARK

Woody plant infections of the pathogenic oomycete Phytophthora ramorum Werres, DeCock, & Manin'tVeld have brought an uncertainty to the future of western forests. Two understory hardwoods, tanoak (Notholithocarpus densiflorus (Hook. and Arn.) Manos, C.H.Cannon, and S.Oh) and California bay (Umbellularia californica (Hook. & Arn.) Nutt.), are commonly infected with P. ramorum leaf infection, the nonfatal foliar form of this pathogen. As the fatal bole infection form of this pathogen is most commonly studied, comparatively little research has been conducted on the nonfatal foliar infection form. This study measured physiological characteristics (midday water potential, stomatal conductance, net photosynthesis, and water-use efficiency) of healthy and infected foliage from tanoak and California bay trees in Redwood National Park to determine the effects P. ramorum foliar infection on leaf-level productivity. For both species, midday water potential, stomatal conductance, and net photosynthesis were all lower in infected samples compared to healthy samples. There was no significant difference in instantaneous water-use efficiency between infected and healthy foliage. Results suggest that P. ramorum leaf infection can lower leaf-level productivity and water status. Further research on the subject is still needed to better support informed management decisions in infected forests and to predict the long-term effects of P. ramorum leaf infections across a diverse suite of host species in the Pacific Northwest.

Potato Response to Drought Stress: Physiological and Growth Basis.

Drought poses a major challenge to the production of potatoes worldwide. Climate change is predicted to further aggravate this challenge by intensifying potato crop exposure to increased drought severity and frequency. There is an ongoing effort to adapt our production systems of potatoes through the development of drought-tolerant cultivars that are appropriately engineered for the changing environment. The breeding of drought-tolerant cultivars can be approached through the identification of drought-related physiological and biochemical traits and their deployment in new potato cultivars. Thus, the main objective of this study was to develop a method to identify and characterize the drought-tolerant potato genotypes and the related key traits. To achieve this objective, first we studied 56 potato genotypes including 54 cultivars and 2 advanced breeding lines to assess drought tolerance in terms of tuber yield in the greenhouse experiment. Drought differentially reduced tuber yield in all genotypes. Based on their capacity to maintain percent tuber yield under drought relative to their well-watered controls, potato genotypes differed in their ability to tolerate drought. We then selected six genotypes, Bannock Russet, Nipigon, Onaway, Denali, Fundy, and Russet Norkotah, with distinct yield responses to drought to further examine the physiological and biochemical traits governing drought tolerance. The drought-induced reduction in tuber yield was only 15–20% for Bannock Russet and Nipigon, 44–47% for Onaway and Denali, and 83–91% for Fundy and Russet Norkotah. The tolerant genotypes, Bannock Russet and Nipigon, exhibited about a 2–3-fold increase in instantaneous water-use efficiency (WUE) under drought as compared with their well-watered controls. This stimulation was about 1.8–2-fold for moderately tolerant genotypes, Onaway and Denali, and only 1.5-fold for sensitive genotypes, Fundy, and Russet Norkotah. The differential stimulation of instantaneous WUE of tolerant and moderately tolerant genotypes vs. sensitive genotypes was accounted for by the differential suppression of the rates of photosynthesis, stomatal conductance, and transpiration rates across genotypes. Potato genotypes varied in their response to leaf protein content under drought. We suggest that the rates of photosynthesis, instantaneous WUE, and leaf protein content can be used as the selection criteria for the drought-tolerant potato genotypes.

Effects of exposure of the leaf abaxial surface to direct solar radiation on the leaf anatomical traits and photosynthesis of soybean (Glycine max L.) in dryland farming systems

The frequent occurrence of monsoon winds usually leads to the formation of inverted soybean leaves. However, the effect of leaf inversion on photosynthetic capacity remains unclear. The responses of leaf anatomical traits, chlorophyll fluorescence induction kinetics parameters, photosynthetic capacity, and nonstructural carbohydrates of fully expanded leaves to inversion of leaves in two soybean cultivars were studied. Leaf inversion decreased the stomatal size and thickness of developed leaves. The net photosynthetic rate was significantly reduced under leaf inversion, which resulted from reduced excitation energy trapping and electron transport of PSII reaction center. Leaf inversion increased leaf temperature 10 d after leaf inversion but reduced the instantaneous water-use efficiency compared to normally oriented leaves. Due to the decreased light-saturated net photosynthetic rate, the soluble sugars of light-sensitive cultivar decreased significantly. In summary, leaf inversion deactivated the PS&#x2161; reaction centers, reduced photosynthesis and nonstructural carbohydrates in upper canopy soybean leaves.

Nitrogen nutrition effects on triticale photosynthesis and assimilate translocation under late-season water stress conditions

In this study, photosynthesis and assimilate translocation and their contribution to improving grain yield and harvest index (HI) of triticale under different N sources and irrigation regimes in an arid climate were evaluated. There were two levels of water regimes: normal irrigation (IRN) and deficit irrigation (cutting irrigation after anthesis stage - IRD). Four N sources: Azospirillum brasilense (Bio), Azospirillum brasilense + 75 kg N ha−1 as urea (Bio + N75), 150 kg N ha−1 as urea (N150) and control unfertilized (N0) plots were used. Results showed the highest net photosynthesis rate (Pn ) was observed in Bio + N75 (24 and 20 µmol CO2 m−2 s−1 at the milking and soft dough stages, respectively) under IRN. The IRD decreased Pn in all N sources, however, the highest reduction was observed in N150 and the lowest in Bio and Bio + N75 treatments. Similar trends were observed in other photosynthetic traits and assimilate remobilization, except for the instantaneous water use efficiency (IWUE), which increased by IRD when bio-fertilizer was applied. The highest grain yield was found by N150 under IRN, which was not significantly different from Bio + N75 treatment. In contrast, application of Bio + N75 resulted in the highest grain yield compared to the other N sources under IRD. Overall, since the lowest reduction in photosynthetic traits, assimilate remobilization, and grain yield of triticale under IRD conditions occurred when bio-fertilizer was applied, this N fertilizer regime could be recommended for the arid areas where water shortage occurs frequently.

Azospirillum baldaniorum Sp245 Induces Physiological Responses to Alleviate the Adverse Effects of Drought Stress in Purple Basil.

Azospirillum spp. are plant growth-promoting rhizobacteria (PGPR) that exert beneficial effects on plant growth and yield of agronomically important plant species. The aim of this study was to investigate the effects of a root treatment with Azospirillum baldaniorum Sp245 on hormones in xylem sap and physiological performance in purple basil (Ocimum basilicum L. cv. Red Rubin) plants grown under well-watered conditions and after removing water. Treatments with A. baldaniorum Sp245 included inoculation with viable cells (1·107 CFU mL–1) and addition of two doses of filtered culture supernatants (non-diluted 1·108 CFU mL–1, and diluted 1:1). Photosynthetic activity, endogenous level of hormones in xylem sap (salicylic acid, jasmonic acid, and abscisic acid), leaf pigments, leaf water potential, water-use efficiency (WUE), and drought tolerance were determined. Fluorescence and gas exchange parameters, as well as leaf water potential, showed that the highest dose of filtered culture supernatant improved both photosynthetic performance and leaf water status during water removal, associated with an increase in total pigments. Moreover, gas exchange analysis and carbon isotope discrimination found this bacterial treatment to be the most effective in inducing an increase of intrinsic and instantaneous WUE during water stress. We hypothesize that the benefits of bacterial treatments based on A. baldaniorum Sp245 are strongly correlated with the synthesis of phytohormones and the induction of plant-stress tolerance in purple basil.

Ploidy influences wheat mesophyll cell geometry, packing and leaf function.

Leaf function is influenced by leaf structure, which is itself related not only to the spatial arrangement of constituent mesophyll cells, but also their size and shape. In this study, we used confocal microscopy to image leaves of Triticum genotypes varying in ploidy level to extract 3D information on individual mesophyll cell size and geometry. Combined with X‐ray Computed Tomography and gas exchange analysis, the effect of changes in wheat mesophyll cell geometry upon leaf structure and function were investigated. Mesophyll cell size and shape were found to have changed during the course of wheat evolution. An unexpected linear relationship between mesophyll cell surface area and volume was discovered, suggesting anisotropic scaling of mesophyll cell geometry with increasing ploidy. Altered mesophyll cell size and shape were demonstrated to be associated with changes in mesophyll tissue architecture. Under experimental growth conditions, CO2 assimilation did not vary with ploidy, but stomatal conductance was lower in hexaploid plants, conferring a greater instantaneous water‐use efficiency. We propose that as wheat mesophyll cells have become larger with increased ploidy, this has been accompanied by changes in cell geometry and packing which limit water loss while maintaining carbon assimilation.

Effects of water-nitrogen coupling on photosynthetic characteristics, yield, water and nitrogen use efficiency for mountain apple trees under surge-root irrigation in Northern Shaanxi area of China.

Taking 7-year-old apple trees (Hanfu) as the test material, an experiment with three irrigation levels including high water (W1, 85%-100%θf, θf was the field water holding capacity), medium water (W2, 70%-85%θf) and low water (W3, 55%-70%θf), and three nitrogen application levels, high (N1, 600 kg·hm-2), medium (N2, 400 kg·hm-2) and low (N3, 200 kg·hm-2), was conducted to investigate the effects of water and nitrogen coupling on photosynthetic characteristics, yield and water and nitrogen utilization of apple trees in mountainous areas under surge-root irrigation (SRI). The results showed that the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), intercellular CO2 concentration (Ci), leaf instantaneous water use efficiency (WUEi) of apple trees leaves decreased with decreasing nitrogen application rates under the same irrigation amount, but Ci increased. Under the same nitrogen application rate, foliar Pn, Tr, gs and WUEi decreased with decreasing irrigation amount, but Ci increased. The daily average values of Pn and Tr under W1N1 treatment were the largest, while W2N2 treatment had the largest WUEi. Apple yield, irrigation water use efficiency (IWUE) and nitrogen partial productivity (NPFP) were significantly affected by irrigation and nitrogen application. The W2N2 treatment had the highest yield (26761 kg·hm-2). IWUE increased significantly with the decreasing irrigation and the increasing nitrogen application, while NPFP increased significantly with the increases of irrigation and the decreases of nitrogen application. Results of the regression analysis showed that the combination of irrigation and nitrogen application was closest to W2N2 treatment when yield and IWUE got the optimal solution. Therefore, W2N2 treatment was the best combination mode of water and nitrogen application for apple under SRI in Northern Shaanxi mountain area.

Effects of biochar amendment and reduced irrigation on growth, physiology, water-use efficiency and nutrients uptake of tobacco (Nicotiana tabacum L.) on two different soil types

Biochar has shown beneficial effects in agricultural production, yet the combined effects of biochar and reduced irrigation on crop growth and water-use efficiency (WUE) in diverse soil types have not been fully explored. A split-root pot experiment was conducted to investigate the effects of addition of 2% softwood (SWB) and wheat straw biochar (WSB) on growth, physiology, WUE and nutrients uptake of tobacco (Nicotiana tabacum L.) plants grown in a Ferrosol and an Anthrosol, respectively, under three irrigation treatments. The plants were either irrigated daily to 90% of water-holding capacity (FI), or irrigated with 70% volume of water used for FI to the whole root-zone (DI) or alternately to half root-zone (PRD). The results showed that plants grown in Anthrosol possessed greater leaf gas exchange rates, dry biomass and WUE while lower nutrients content compared to those grown in Ferrosol. Despite a negative effect on plant N content and WUE, WSB addition increased water-holding capacity, consequently improved leaf gas exchange, water uptake, biomass and K content resulting in an improved in the leaf quality of tobacco as exemplified by an increased leaf K content and a more appropriate N to K stoichiometric ratio. However, these effects were not evident upon SWB addition. Moreover, these responses to biochar addition were stronger in Ferrosol than in Anthrosol might be associated with its lower pH. Compared to FI, PRD slightly reduced photosynthetic rate but significantly decreased stomatal conductance, transpiration rate and leaf area, leading to a significant increase in intrinsic, instantaneous and plant WUE. Additionally, PRD was superior over DI in improving yield, WUE, N uptake under a same irrigation volume. It was concluded that WSB combined with PRD could be a promising practice to synergistically improve tobacco yield, quality and WUE by improving soil hydro-physical properties and nutrients bioavailability.

Divergent forcing of water use efficiency from aridity in two meadows of the Mongolian Plateau

The future climate change predicts higher drought risks in deteriorating the functions and services of dryland ecosystems. Interpreting the sensitivity of ecosystem water use efficiency (WUE) to aridity could provide important environmental implications to water conservation and carbon budgets of drylands. The effects of temporal aridity changes on WUE in semi-arid ecosystems, particularly in meadow steppes, have been poorly investigated. In this study, we used eddy-covariance data from two representative temperate meadows on Mongolian Plateau, Changling (2007-2015, China) and Bayan (2014-2018, Mongolia), to understand the inter- and intra-annual changes of WUE by evaporative fraction (EF), as well as the climatic and biotic controls on gross ecosystem production (GEP), evapotranspiration (ET) and partitioned evaporation (T) and transpiration (E). Results showed that the response of annual WUE to EF was positive in Changling meadow with dry atmosphere but insignificant in Bayan with cold climate; the contrasting WUEs were driven by divergent GEP and ET responses to EF in two meadows. Monthly T/ET increased linearly with EF in both meadows, but logarithmically with leaf area index (LAI). Bayan and Changling meadows had a similar instantaneous WUE (WUEp, GEP/T) that were insensitive to EF change. We also found that the frequency of growing season precipitation affected WUE at both sites. We conclude that contrasting GEP responses to EF determined the meadow WUE variations. The magnitude and changes in transpiration and evaporation provide further insights on the biophysical regulations (i.e., LAI) of ecosystem water use and WUEp. This study indicated that differences in ecosystem water yield, soil water status and sensitivities of GEP and ET partitioning jointly contributed to the divergent WUE at the two meadow steppes in this semi-arid region.

Determining optimal deficit irrigation and fertilization to increase mango yield, quality, and WUE in a dry hot environment based on TOPSIS

Rational application of water and fertilizer management practices can not only improve mango (Mangifera indica L.) yield and quality but also improve irrigation water-use efficiency (IWUE). However, few studies have addressed the use of water and fertilizer management practices in hot, dry environments with the aim of achieving relatively favorable levels of these parameters concurrently. We used the technique for order preference by similarity to an ideal solution (TOPSIS) method to identify optimal water and fertilizer management practices that resulted in high fruit yields and high IWUE in Southwest China. A randomized block design study with four irrigation levels [full irrigation throughout the growth period (FI), regulated deficit irrigation during flowering (RDIFS), regulated deficit irrigation during fruit expansion (RDIES), and regulated deficit irrigation at maturity (RDIMS)] and three fertilization levels [FH, a water-soluble compound fertilizer (N:P2O5:K2O = 12:8:40) applied at 129.0 kg ha−1; FM, 103.2 kg ha−1; and FL, 77.4 kg ha−1] was implemented in 2018 and 2019 to investigate these relationships. The net photosynthesis rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) of mango under the different water deficit treatments were significantly lower than those under the FI treatment with the same fertilization conditions, but the instantaneous water-use efficiency (WUEi) of the leaves increased. The fresh fruit yield, solids:acid ratio (SOAR), sugar:acid ratio (SUAR), and IWUE under the RDIFS treatment were significantly lower than those under the FI treatment at the same fertilization rates. Averaged over all fertilization rates, the fruit yield under RDIES was 8.6–22.3% lower than that under FI in both years, but the IWUE significantly increased from 3.7% to 18.6%. Compared with the FI treatment, the RDIMS treatment had no significant effect on fruit yield but significantly increased the IWUE (35.5–44.7%), total sugar (TS) content (3.7–8.5%), and carotenoid content (CC) (1.5–13.1%) in both years. At the same irrigation level, the Pn, Gs and Tr increased with an increasing fertilization rate, while the fruit yield, IWUE, TS, and vitamin C (VC) content of fresh fruit first decreased but then increased with increasing fertilization rate. IWUE was more closely related to photosynthesis characteristics at the flowering stage than at the mature stage, but fruit quality was more closely related to photosynthesis characteristics at the mature stage than at the flowering stage. Compared with the FIFH treatment, the RDIMSFM treatment significantly increased the fruit yield by 10.1% and 6.6% in 2018 and 2019, respectively, and increased the IWUE by 28.1% and 35.6%, respectively. On the basis of the TOPSIS method, the multi-target optimum scheduling of mango was achieved under the RDIMSFM treatment. The identified optimum combination of water and fertilizer can provide a scientific basis for irrigation and fertilization optimization and management in the hot, dry environment of Southwest China.