A meta-analysis highlights the cross-resistance of plants to drought and salt stresses from physiological, biochemical, and growth levels.

In nature, drought and salt stresses often occur simultaneously and affect plant growth at multiple levels. However, the mechanisms underlying plant responses to drought and salt stresses and their interactions are still not fully understood. We performed a meta-analysis to compare the effects of drought, salt, and combined stresses on plant physiological, biochemical, morphological and growth traits, analyze the different responses of C3 and C4 plants, as well as halophytes and non-halophytes, and identify the interactive effects on plants. There were numerous similarities in plant responses to drought, salt, and combined stresses. C4 plants had a more effective antioxidant defense system, and could better maintain above-ground growth. Halophytes could better maintain photosynthetic rate (Pn) and relative water content (RWC), and reduce growth as an adaptation strategy. The responses of most traits (Pn, RWC, chlorophyll content, soluble sugar content, H2O2 content, plant dry weight, etc.) to combined stress were less-than-additive, indicating cross-resistance rather than cross-sensitivity of plants to drought and salt stresses. These results are important to improve our understanding of drought and salt cross-resistance mechanisms and further induce resistance or screen-resistant varieties under stress combination.

Diversifying crop rotation increases food production, reduces net greenhouse gas emissions and improves soil health.

Global food production faces challenges in balancing the need for increased yields with environmental sustainability. This study presents a six-year field experiment in the North China Plain, demonstrating the benefits of diversifying traditional cereal monoculture (wheat-maize) with cash crops (sweet potato) and legumes (peanut and soybean). The diversified rotations increase equivalent yield by up to 38%, reduce N2O emissions by 39%, and improve the system's greenhouse gas balance by 88%. Furthermore, including legumes in crop rotations stimulates soil microbial activities, increases soil organic carbon stocks by 8%, and enhances soil health (indexed with the selected soil physiochemical and biological properties) by 45%. The large-scale adoption of diversified cropping systems in the North China Plain could increase cereal production by 32% when wheat-maize follows alternative crops in rotation and farmer income by 20% while benefiting the environment. This study provides an example of sustainable food production practices, emphasizing the significance of crop diversification for long-term agricultural resilience and soil health.

Elevated CO2 concentration increases maize growth under water deficit or soil salinity but with a higher risk of hydraulic failure.

Climate change presents a challenge for plants to acclimate their water relations under changing environmental conditions, and may increase the risks of hydraulic failure under stress. In this study, maize plants were acclimated to two different CO2 concentrations ([CO2]; 400 ppm and 700 ppm) while under either water stress (WS) or soil salinity (SS) treatments, and their growth and hydraulic traits were examined in detail. Both WS and SS inhibited growth and had significant impacts on hydraulic traits. In particular, the water potential at 50% loss of stem hydraulic conductance (P50) decreased by 1 MPa in both treatments at 400 ppm. When subjected to elevated [CO2], the plants under both WS and SS showed improved growth by 7-23%. Elevated [CO2] also significantly increased xylem vulnerability (measured as loss of conductivity with decreasing xylem pressure), resulting in smaller hydraulic safety margins. According to the plant desiccation model, the critical desiccation degree (time×vapor pressure deficit) that the plants could tolerate under drought was reduced by 43-64% under elevated [CO2]. In addition, sensitivity analysis showed that P50 was the most important trait in determining the critical desiccation degree. Thus, our results demonstrated that whilst elevated [CO2] benefited plant growth under WS or SS, it also interfered with hydraulic acclimation, thereby potentially placing the plants at a higher risk of hydraulic failure and increased mortality.

Response of soil respiration and carbon budget to irrigation quantity/quality and biochar addition in a mulched maize field under drip irrigation.

BACKGROUND: Biochar addition strongly alters net carbon (C) balance in agroecosystems. However, the effects of biochar addition on net C balance of maize field under various irrigation water quantities and qualities remains unclear. Thus, a field experiment combining two irrigation levels of full (W1) and deficit irrigation (W2 = 1/2 W1), two water salinity levels of fresh (S0, 0.71 g L-1 ) and brackish water (S1, 4 g L-1 ), and two biochar addition rates of 0 t ha-1 (B0) and 60 t ha-1 (B1) was conducted to investigate soil carbon dioxide (CO2 ) emissions, maize C sequestration and C budget. RESULTS: Compared with W1, W2 reduced average cumulative CO2 emissions by 6.5% and 19.9% for 2020 and 2021, respectively. The average cumulative CO2 emissions under W1S1 treatments were 5.4% and 22.3% lower than W1S0 for 2020 and 2021, respectively, whereas W2S0 and W2S1 had similar cumulative CO2 emissions in both years. Biochar addition significantly increased cumulative CO2 emissions by 17.8-23.5% for all water and salt treatments in 2020, and reduced average cumulative CO2 emissions by 11.9% for W1 but enhanced it by 8.0% for W2 in 2021. Except for W2S1, biochar addition effectively increased total maize C sequestration by 6.9-14.8% for the other three treatments through ameliorating water and salt stress over the 2 years. Compared with W1S0, W1S1 did not affect net C sequestration, but W2 treatments significantly decreased it. Biochar addition increased net C sequestration by 39.47-43.65 t C ha-1 for four water and salt treatments for the 2 years. CONCLUSION: These findings demonstrate that biochar addition is an effective strategy to increase both crop C sequestration and soil C storage under suitable water-saving irrigation methods in arid regions with limited freshwater resources. © 2023 Society of Chemical Industry.

Agricultural transformation towards delivering deep carbon cuts in China's arid inland areas.

Since agriculture is a main source of global greenhouse gas (GHG) emissions, reducing agricultural GHG emissions is crucial for achieving global climate goals. Nevertheless, there has been a lack of thorough and systematic assessment of the spatiotemporal distribution of agricultural GHG emissions at the county level, considering many factors such as crop and livestock products, different processes and gases, and the impact of carbon fixation. Furthermore, the potential of comprehensive technical strategies to reduce GHG emissions remains uncertain. Considering the unique attributes of agricultural development in arid areas of northwest China, this study aimed to explore long-term changes in agricultural net GHG emissions by county, product group, process, and gas and quantify the future reduction potential based on the Agricultural System-induced GreenHouse Gases INVentory (ASGHG-INV) econometric model. The results showed increasing trends in carbon emissions (CE), carbon sequestration (CS), carbon footprint (CF), crop carbon footprint per unit area (CFCF), and crop carbon footprint per unit product (CPCF) in various regions from 1991 to 2019, while there was a decreasing trend in livestock carbon footprint per unit product (LPCF). Focus on reducing GHG emissions in the crop-sector should be in Shihezi, Alaer, and Liangzhou; those of the livestock-sector should be in Xinyuan, Yecheng, Liangzhou, and Gaotai. Scenario analysis indicated that agricultural transformation could substantially reduce GHG emissions in all regions. Reducing the loss of reactive nitrogen was shown to be the most effective single strategy for reducing crop emissions. A comprehensive scheme further integrating the optimization of nitrogen fertilizer management, increasing water-saving, manure application, and straw returning measures, and using biochar and inhibitors can decrease CE, CF, CFCF, and CPCF by 22.62-43.45%, 40.55-111.60%, 41.38-111.78%, and 43.33-111.32%, respectively, increase CS by 9.07-39.97%. Optimizing forage composition was the most influential strategy for reducing livestock GHG emissions. The integrated strategy of further using forage additives, breeding low-emission varieties, and optimizing fecal management can reduce CF and LPCF by 37.32-76.42% and 40.51-78.70%, respectively. This study's results can be a reference for developing more effective GHG emissions reduction and green transformation pathways for global dryland agriculture.

Integrated model simulates bigger, sweeter tomatoes under changing climate under reduced nitrogen and water input.

When simulating the response of fruit growth and quality to environmental factors and cultivation practices, the interactions between the mother plant and fruit need to be considered as a whole system. Here, we developed the integrative Tomato plant and fruit Growth and Fruit Sugar metabolism (TGFS) model by coupling equations describing the biophysical processes of leaf gas exchange, water transport, carbon allocation, organ growth and fruit sugar metabolism. The model also accounts for effects of soil nitrogen and atmospheric CO2 concentration on gaseous exchange of water and carbon by the leaf. With different nitrogen and water input values, TGFS performed well at simulating the dry mass of the tomato leaf, stem, root, and fruit, and the concentrations of soluble sugar and starch in fruit. TGFS simulations showed that increasing air temperature and CO2 concentration has positive effects on fruit growth, but not on sugar concentrations. Further model-based analyses of cultivation scenarios suggest that, in the context of climate change, decreasing N by 15%-25% and decreasing irrigation by 10%-20% relative to current levels would increase tomato fresh weight by 27.8%-36.4% while increasing soluble sugar concentration by up to 10%. TGFS provides a promising tool to optimise N and water inputs for sustainable high-quality tomatoes.

Combination of suitable planting density and nitrogen rate for high yield maize and their source-sink relationship in Northwest China.

BACKGROUND: Increasing crop yield per unit area by increasing planting density is essential to ensure food security. However, the optimal combination of planting density and nitrogen (N) application for high-yielding maize and its source-sink characteristics need to be more clearly understood. RESULTS: A 2-year field experiment was conducted combining three planting densities (D1: 70 000 plants ha-1 ; D2: 100 000 plants ha-1 ; D3: 130 000 plants ha-1 ) and three nitrogen rates (N1: 150 kg hm-2 ; N2: 350 kg hm-2 ; N3: 450 kg hm-2 ). The results showed that increasing planting density significantly increased leaf area index and grain yield but negatively affected ear traits. The Richards model was used to fit the dynamic changes of dry matter accumulation of maize under different treatments, and the fitting results were good. Increasing planting density increased population yield while limiting the development of individual plants, bringing the period of rapid dry matter accumulation to an early end and accelerating leaf senescence. An appropriate nitrogen rate could prolong the period of rapid accumulation of dry matter in maize, and increase the 100-kernel weight. Increasing planting density enhanced post-silking dry matter accumulation to a lesser extent, and the source-sink relationship of the maize population gradually developed from sink limitation to source limitation with increasing planting density. CONCLUSION: The decrease in yield due to the insufficient source strength to meet the sink demand at too high densities was the reason that limited further improvement of the optimal planting density. An appropriate nitrogen rate facilitated the realization of yield potential at high density. © 2023 Society of Chemical Industry.

Salinity-specific stomatal conductance model parameters are reduced by stomatal saturation conductance and area via leaf nitrogen.

Modeling stomatal behavior is necessary for accurate stomatal simulation and predicting the terrestrial water­carbon cycle. Although the Ball-Berry and Medlyn stomatal conductance (gs) models have been widely used, variations and the drivers of their key slope parameters (m and g1) remain poorly understood under salinity stress. We measured leaf gas exchange, physiological and biochemical traits, soil water content and electrical conductivity of saturation extract (ECe), and fitted slope parameters of two genotypes of maize growing in two water and two salinity levels. We found m was different between the genotypes, but no difference in g1. Salinity stress reduced m and g1, saturated stomatal conductance (gsat), the fraction of leaf epidermis area allocation to stomata (fs), and leaf nitrogen (N) content, and increased ECe, but no marked decrease in slope parameters under drought. Both m and g1 were positively correlated with gsat, fs, and leaf N content, and negatively correlated with ECe in the same fashion among the two genotypes. Salinity stress altered m and g1 by modulating gsat and fs via leaf N content. The prediction accuracy of gs was improved using salinity-specific slope parameters, with root mean square error (RMSE) being decreased from 0.056 to 0.046 and 0.066 to 0.025 mol m-2 s-1 for the Ball-Berry and Medlyn models, respectively. This study provides a modeling approach to improving the simulation of stomatal conductance under salinity.

Three-dimensional linkage between meteorological drought and vegetation drought across China.

Advance knowledge of the linkage between meteorological drought and vegetation drought is relevant for the risk of droughts and the impacts on vegetation health. This study employs a 3-dimensional clustering identification method to capture drought events and their characteristics (i.e., drought severity, intensity, area, center, and trajectory) in vegetated regions of China during 1982-2018. The probability of vegetation droughts, triggered by different types of drought events, is investigated by using a K-means trajectory clustering method and copula with the vegetation health index (VHI). Moreover, the impacts of moisture deficit and high temperature caused by drought on vegetation are examined with the vegetation condition index (VCI) and temperature condition index (TCI). The analysis has identified a total of 93 drought events in 1982-2018. The drought occurrences have become more concentrated in space along the time and droughts frequently occur in spring and summer. Drought events are categorized into three types, and droughts in type 1 lead to vegetation droughts with larger area, droughts in type 2 lead to vegetation droughts with stronger intensity, droughts in type 3 pose the least threat to vegetation. Additionally, the impacts of moisture deficit and high temperature have significant seasonal difference and contradictory trends over time. For example, grassland is most sensitive to moisture deficit in summer, while forest is the most sensitive to moisture deficit in spring and winter. The complex response of vegetation to drought is resulted from the combined effects of moisture and heat stress and different regional climate and vegetation types.

Closing the irrigation water productivity gap to alleviate water shortage in an endorheic basin.

Closing the irrigation water productivity (IWP) gap is an effective approach to alleviating water deficits and ensuring food security. However, few studies have attempted to quantify the IWP gap and the potential benefits of closing it. This study adopted the Heihe River Basin, the second-largest inland basin in China, as a typical study area. The aims of this study were to: (1) assess the positive achievements and potential risks triggered by the Heihe Ecological Water Diversion Project (EWDP) according to multi-source and multi-scale measured data; (2) analyze potential approaches to improve the IWP and quantify the potential benefits that can be achieved by closing its IWP gap. The results of this study indicated that the EWDP effectively reallocated surface water resources, replenished groundwater in the lower reaches, and facilitated the recovery of oases and economic development in the downstream regions. However, this project has indirectly led to an imbalance in the groundwater resource between the middle and lower reaches, resulting in decline in groundwater levels and degradation of local vegetation in the midstream regions. In addition, the expansion of cultivated land in the midstream and downstream oases has resulted in the deterioration of farmland environment. The water transfer resulted in a deceleration in the growth of IWP from 2.44 % to 1.15 %, and the existing IWP gap was 1.43 kg/m3 between 1984 and 2017. This study predicted a future increase in the IWP to 2.01 kg/m3 with a reduction in the gap to 0.45 kg/m3 while maintaining food production. The potential for conserving water in the Heihe agricultural region can reach 552 million m3 by reducing the planting area by 10 %, improving irrigation water use efficiency by 20 %, maintaining existing agricultural film inputs, and reducing fertilizer application by 10 %. Following the research recommendations can greatly alleviate the agricultural water shortage and over-extraction of groundwater in the middle reaches and ensure meeting ecological water demand in the lower reaches. This study can act as a reference for sustainable management of an endorheic basin.

The trade-offs between resistance and resilience of forage stay robust with varied growth potentials under different soil water and salt stress.

Water shortage and soil salinization are important factors restricting crop production worldwide. To conduct accurate yield prediction and reasonable crop layout, more attention should be paid to the performances of crop resistance and resilience under water and salt stress and their trade-off relationships. Here, we set different water (full irrigation, W0; moderate deficit irrigation, W1; and severe deficit irrigation, W2) and salt (S0, S1, S2, S3, S4, S5, and S6, representing 0 ‰, 1 ‰, 2 ‰, 3 ‰, 4 ‰, 5 ‰, and 6 ‰ salt in soil) treatments. Together with relevant studies, we analyzed the performances of forage resistance (Rt) and resilience (Rs) and their relationships under varied water and salt stress. The results indicated that logarithmic Rt (lg(Rt), the same as lg(Rs)) and the distribution of lg(Rs) were affected by water and salt stress, however, the relationships of lg(Rs)-lg(Rt) stayed stable with the constant slopes (k) and declined intercepts (m) as stress intensified. The physiological mechanisms and trade-offs for fixed species remained robust while the growth potentials varied under stress, which were closely related to stomatal regulations. Forage with larger |k| was suitable for fully irrigated regions to achieve higher yields, while regions with detrimental water and salt conditions should select cultivars with smaller |k| to ensure production. This study laid the groundwork for the estimation of the perennial forage adaptation and stability, and the method of long-term yield prediction and cultivar management under soil water and salt stress.

Plasticity in stomatal behaviour across a gradient of water supply is consistent among field-grown maize inbred lines with varying stomatal patterning.

Stomata regulate leaf CO2 assimilation (A) and water loss. The Ball-Berry and Medlyn models predict stomatal conductance (gs ) with a slope parameter (m or g1 ) that reflects the sensitivity of gs to A, atmospheric CO2  and humidity, and is inversely related to water use efficiency (WUE). This study addressed knowledge gaps about what the values of m and g1 are in C4 crops under field conditions, as well as how they vary among genotypes and with drought stress. Four inbred maize genotypes were unexpectedly consistent in how m and g1 decreased as water supply decreased. This was despite genotypic variation in stomatal patterning, A and gs . m and g1 were strongly correlated with soil water content, moderately correlated with predawn leaf water potential (Ψpd ), but not correlated with midday leaf water potential (Ψmd ). This implied that m and g1 respond to long-term water supply more than short-term drought stress. The conserved nature of m and g1 across anatomically diverse genotypes and water supplies suggests there is flexibility in structure-function relationships underpinning WUE. This evidence can guide the simulation of maize gs across a range of water supply in the primary maize growing region and inform efforts to improve WUE.

Mild water and salt stress improve water use efficiency by decreasing stomatal conductance via osmotic adjustment in field maize.

Water and salt stress often occur simultaneously in heavily irrigated arid agricultural areas, yet they are usually studied in isolation. To understand the physiological bases of water use efficiency (WUE) of field-grown maize (Zea mays) at multi-scales under combined water and salt stress, we investigated the joint effects of water and salt stress on physiology, growth, yield, and WUE of two genotypes (XY335 and ZD958). We measured leaf stomatal conductance (gs), net photosynthesis rate (A) and hydraulic traits, whole-plant growth and water use (ET), and final biomass and grain yield. Leaf osmotic adjustment was a key trait of the physiological differences between XY335 and ZD958 under water and salt stress. Although the responses of the two genotypes were different, mild water and salt stress improved intrinsic water use efficiency (iWUE = A/gs) by (i) decreasing gsvia increasing osmotic adjustment and hydraulic resistance, and (ii) declining A via increasing stomatal limitations rather than reducing photosynthetic capacity. Joint water and salt stress had a synergistic effect on reproductive growth and grain formation of maize. Mild water and salt stress reduced ET, stabilized grain yield, and improved grain WUE via declining gs, maintaining photosynthetic capacity, and improving harvest index. Collectively, our study provides a novel insight into the physiological mechanisms of WUE and demonstrates an approach for the efficient management of water and salt by using a growth stage-based deficit irrigation strategy or/and selecting genotypes with strong osmotic adjustment capacity and high harvest index.

SUGAR Model-Assisted Analysis of Carbon Allocation and Transformation in Tomato Fruit Under Different Water Along With Potassium Conditions.

Carbohydrate concentrations in fruit are closely related to the availability of water and mineral nutrients. Water stress and minerals alter the assimilation, operation, and distribution of carbohydrates, thereby affecting the fruit quality. The SUGAR model was used to investigate the carbon balance in tomato fruit during different growth stages when available water was varied and potassium added. Further, we quantitatively studied the distribution of photoassimilates such as structural carbohydrates, soluble sugars, and starch in fruit and evaluated their response to water and potassium supply. The results revealed that the carbon allocation and transformation dynamically changed during the all growth stages; in fact, variation in carbon content showed similar trends for different water along with potassium treatments, carbon allocation during the early development stages was mainly to starch and structural carbon compounds. The relative rate of carbon conversion of soluble sugars to structural carbon compounds (k 3) and of soluble sugars to starch (k 5m ) peaked during the initial stage and then dropped during fruit growth and development stages. Carbon was primarily allocated as soluble sugars and starch was converted to soluble sugars at fruit maturation. k 3(t) and k 5m (t) approached zero at the end of the growth stage, mainly due to sugar accumulation. Potassium application can significantly raise carbon flows imported (C supply ) from the phloem into the fruit and thus increased carbon allocation to soluble sugars over the entire growth period. Potassium addition during the fruit maturation stage decreased the content of starch and other carbon compounds. Water deficit regulated carbon allocation and increased soluble sugar content but reduced structural carbon content, thereby improving fruit quality.

Fruit water content as an indication of sugar metabolism improves simulation of carbohydrate accumulation in tomato fruit.

Although fleshy fruit is mainly made up of water, little is known about the impact of its water status on sugar metabolism and its composition. In order to verify whether fruit water status is an important driver of carbohydrate composition in tomato fruit, an adaptation of the SUGAR model proposed previously by M. Génard and M. Souty was used. Two versions of the model, with or without integrating the influence of fruit water content on carbohydrate metabolism, were proposed and then assessed with the data sets from two genotypes, Levovil and Cervil, grown under different conditions. The results showed that, for both genotypes, soluble sugars and starch were better fitted by the model when the effects of water content on carbohydrate metabolism were taken into consideration. Water content might play a regulatory role in the carbon metabolism from sugars to compounds other than sugars and starch in Cervil fruit, and from sugars to starch in Levovil fruit. While water content influences tomato fruit carbohydrate concentrations by both metabolism and dilution/dehydration effects in the early developmental stage, it is mainly by dilution/dehydration effects in the late stage. The possible mechanisms underlying the effect of the fruit water content on carbohydrate metabolism are also discussed.

Responses of water accumulation and solute metabolism in tomato fruit to water scarcity and implications for main fruit quality variables.

Fruit is important for human health, and applying deficit irrigation in fruit production is a strategy to regulate fruit quality and support environmental sustainability. Responses of different fruit quality variables to deficit irrigation have been widely documented, and much progress has been made in understanding the mechanisms of these responses. We review the effects of water shortage on fruit water accumulation considering water transport from the parent plant into the fruit determined by hydraulic properties of the pathway (including xylem water transport and transmembrane water transport regulated by aquaporins) and the driving force for water movement. We discuss water relations and solute metabolism that affect the main fruit quality variables (e.g. size, flavour, nutrition, and firmness) at the cellular level under water shortage. We also summarize the most recent advances in the understanding of responses of the main fruit quality variables to water shortage, considering the effects of variety, the severity of water deficit imposed, and the developmental stage of the fruit. We finally identify knowledge gaps and suggest avenues for future research. This review provides new insights into the stress physiology of fleshy fruit, which will be beneficial for the sustainable production of high-quality fruit under deficit irrigation.

Elevated [CO2 ] alleviates the impacts of water deficit on xylem anatomy and hydraulic properties of maize stems.

Plants can modify xylem anatomy and hydraulic properties to adjust to water status. Elevated [CO2 ] can increase plant water potential via reduced stomatal conductance and water loss. This raises the question of whether elevated [CO2 ], which thus improves plant water status, will reduce the impacts of soil water deficit on xylem anatomy and hydraulic properties of plants. To analyse the impacts of water and [CO2 ] on maize stem xylem anatomy and hydraulic properties, we exposed potted maize plants to varying [CO2 ] levels (400, 700, 900, and 1,200 ppm) and water levels (full irrigation and deficit irrigation). Results showed that at current [CO2 ], vessel diameter, vessel roundness, stem cross-section area, specific hydraulic conductivity, and vulnerability to embolism decreased under deficit irrigation; yet, these impacts of deficit irrigation were reduced at elevated [CO2 ]. Across all treatments, midday stem water potential was tightly correlated with xylem traits and displayed similar responses. A distinct trade-off between efficiency and safety in stem xylem water transportation in response to water deficit was observed at current [CO2 ] but not observed at elevated [CO2 ]. The results of this study enhance our knowledge of plant hydraulic acclimation under future climate environments and provide insights into trade-offs in xylem structure and function.

Interactive Regimes of Reduced Irrigation and Salt Stress Depressed Tomato Water Use Efficiency at Leaf and Plant Scales by Affecting Leaf Physiology and Stem Sap Flow.

Interactive effects of reduced irrigation and salt stress on leaf physiological parameters, biomass accumulation, and water use efficiency (WUE) of tomato plants at leaf and whole plant scales were investigated in a field experiment during 2016 and a greenhouse experiment during 2017. Experiment utilized two irrigation regimes (full, 2/3 of full irrigation) and four soil salt regimes (0, 0.3, 0.6, 0.9% in 2016 season; and 0, 0.2, 0.3, 0.4% in 2017 season). Three salts, sodium chloride, magnesium sulfate, and calcium sulfate (mass ratio of 2:2:1), were homogeneously mixed with soil prior to packing into containers (0.024 m3). Li-COR 6400 was used to measure tomato leaf physiological parameters. Instantaneous water use efficiency (WUEins, µmol mmol-1) and intrinsic water use efficiency (WUEint, µmol mol-1) were determined at leaf scale, yield water use efficiency (WUEY, g L-1), and dry biomass water use efficiency (WUEDM, g L-1) were determined at whole plant scale. Plants irrigated with 2/3 of full irrigation with zero soil-salt treatment had higher dry biomass and yield per plant, resulting in the highest WUEDM and WUEY at whole plant scale. Increasing soil salinity decreased dry biomass and yield, leading to greater decreases in whole plant WUEDM and WUEY under both irrigation treatments. At full irrigation, no decreases in stomatal conductance (gs, mol m-2 s-1) and slight increase in photosynthetic rate (Pn, µmol m-2 s-1) led to higher WUEint at leaf scale during both years. Under full and reduced irrigation, increasing soil salt content decreased Pn and transpiration rate (Tr, mmol m-2 s-1) and led to reductions in WUEins at the leaf scale. However, compared to full irrigation, reduced irrigation improved WUEins with a significant decline in Tr in no salt and 0.3% soil-salt treatments during both years. For soil salt content of 0.6%, stomatal limitation due to salt stress resulted in higher WUEint, but soil salt content of 0.9% decreased WUEint due to non-stomatal limitation. Soil salt content significantly decreased sap flow, with the maximum variation of daily sap flow per plant of 7.96-31.37 g/h in 2016 and 12.52-36.02 g h-1 in 2017. Sap flow rate was linearly related to air temperature (Ta, °C), solar radiation (Rs, W m-2), and vapor pressure deficit (VPD, kPa). These results advance knowledge on tomato response to abiotic stresses and could improve management of tomato production in water- and salt-stressed areas.

Effects of irrigation on water and energy balances in the Heihe River basin using VIC model under different irrigation scenarios.

Investigations of the water and energy balance in large river basins is one of the most important and contemporary issues, which is helpful to guide agricultural production and regional water resource management. Traditionally, water and energy balance have been assessed by field-scale experiments. However, it is not easy to find the effective ways for a whole region using limited observed data from on-farm experiments. In our study, the effects of irrigation water on surface water and energy balance fluxes are examined by employing the Variable Infiltration Capacity (VIC) model and irrigation scheme, for the upper and middle reaches of the Heihe River Basin in Northwest China. The model simulations are calibrated and validated using both streamflow records at a gauge station and eddy covariance observations at two stations. Besides, three irrigation scenarios are set as full irrigation, 90% and 75% of irrigation water requirement (IWR). The results showed the infiltration curve parameter (b) and the thickness of lower soil moisture layer (d2) are the most sensitive model parameters. Long-term irrigation activities lead to a greater evapotranspiration (or latent heat). With considering local irrigation water-using coefficient for the period 2001-2010 of 0.527, the total IWR is about 2.81 × 109 m3/year (the net IWR is about 1.48 × 109 m3/year). Compared with the no-irrigation baseline, the increase in latent heat flux (about 4.45 W/m2) or the significant decrease in Bowen Ratio (about 1.05) due to full irrigation activities is accompanied by a decrease in annual average surface temperature (about 0.076 °C) for the middle reaches of the Heihe River basin during the 10-year period.

Untangling the effects of shallow groundwater and deficit irrigation on irrigation water productivity in arid region: New conceptual model.

Water scarcity and salt stress are two main limitations for agricultural production. Groundwater evapotranspiration (ETg) with upward salt movement plays an important role in crop water use and water productivity in arid regions, and it can compensate the impact of deficit irrigation on crop production. Thus, comprehensive impacts of shallow groundwater and deficit irrigation on crop water use results in an improvement of irrigation water productivity (IWP). However, it is difficult to quantify the effects of groundwater and deficit irrigation on IWP. In this study, we built an IWP evaluation model coupled with a water and salt balance model and a crop yield estimation model. As a valuable tool of IWP simulation, the calibrated model was used to investigate the coupling response of sunflower IWP to irrigation water depths (IWDs), groundwater table depth (GTDs) and groundwater salinities (GSs). A total of 210 scenarios were run in which five irrigation water depths (IWDs) and seven groundwater table depths (GTDs) and six groundwater salinities (GSs) were used. Results indicate that increasing GS clearly increases the negative effect on a crop's actual evapotranspiration (ETa) as salt accumulation in root zone. When GS is low (0.5-1g/L), increasing GTD produces more positive effect than negative effect. In regard to relatively high GS (2-5g/L), the negative effect of shallow-saline groundwater reaches a maximum at 2m GTD. Additionally, the salt concentration in the root zone maximizes its value at 2.0m GTD. In most cases, increasing GTD and GS reduces the benefits of irrigation water and IWP. The IWP increases with decreasing irrigation water. Overall, in arid regions, capillary rise of shallow groundwater can compensate for the lack of irrigation water and improve IWP. By improving irrigation schedules and taking advantages of shallow saline groundwater, we can obtain higher IWP.