Photosynthetic Characteristics and Yield Response of Isatis indigotica to Regulated Deficit Irrigation in a Cold and Arid Environment

Deficit irrigation is an effective alternative to traditional irrigation, as it improves crop productivity and conserves water. However, crops may be sensitive to deficit irrigation-induced water stress at different periods. To access the effect of deficit irrigation on the growth, water consumption characteristics, yield, and quality of Isatis indigotica (woad), we performed a three-year (2017-2019) mulched drip irrigation field experiment. Woad plants were provided adequate water supply at the seedling stage but were subjected to mild (65–75% field water capacity FC), moderate (55–65% FC), and severe (45–55% FC) water deficit at the vegetative growth, fleshy root growth and fleshy root maturity stages, respectively; plants supplied with adequate water throughout the growth period served as a control (CK, 75–85% FC). The water consumption characteristics, agronomic traits, dry matter content and distribution, yield, and quality of these plants were measured at various growth stages. The results showed that the total water consumption in water deficit was significantly less than that in CK by 4.44–10.21% (P< 0.05). The dry matter content of plants treated with moderate (WT2 and WT5) and severe (WT3) water deficit was reduced by 12.83–28.75%. The economic yield of mild water deficit-treated plants was higher during vegetative growth (WT1) and fleshy root growth (WT4), while the water use efficiency of these plants was significantly increased by 7.84% and 6.92% at the two growth stages, respectively. Continuous mild water deficit (WT4) enhanced the contents of indigo, indirubin, (R,S)-goitrin, polysaccharides, and soluble proteins during vegetative growth and fleshy root growth, while moderate and severe water deficit were detrimental to the quality of woad plants. Thus, continuous mild water deficit during vegetative and fleshy root growth periods (WT4) is optimal for the cultivation of woad in the cold and cool irrigation district of the Hexi Oasis region.

Although regulated deficit irrigation may improve crop yields, little research has been conducted on the effects of water deficits on Isatis indigotica, a popular herbal medicine. Field experiments were conducted in 2016 and 2017 to study the effects of regulated deficit irrigation on the net photosynthetic rate, yield, water use efficiency (WUE), and quality of I. indigotica in northwest China. Plants at the vegetative and fleshy root growth stages were subjected to mild, moderate, and severe water deficits, and their photosynthetic physiological indexes, yield, and WUE were measured. Moderate and severe deficits, but not a mild deficit, significantly decreased the net photosynthetic rate and dry matter accumulation. The yield and WUE under mild deficit were markedly higher, reaching 8239.56 kg·ha−2 and 8390.80 kg·ha−2, respectively, in the vegetative stage and 24.11 kg·ha−2·mm−1 and 23.62 kg·ha−2·mm−1, respectively, in the fleshy root growth stage, while severe deficits significantly reduced yield and WUE. Mild and moderate deficits increased the content of (R,S)-goitrin, indirubin, and indigo, improving root quality, but severe deficits decreased these compounds. Therefore, a mild water deficit in the vegetative and fleshy root growth stages is optimal and can reduce water consumption and improve I. indigotica quality and WUE without reducing yield.

Quantitative analysis of tomato root water uptake and soil water utilization in the root zone under deficit irrigation is an important tool to improve agricultural water utilization efficiency. In this study, three different deficit irrigation levels were set at the flowering and fruit development stage (Stage I) and the fruit-ripening stage (Stage II), respectively. The Hydrus-1D model and field data were used to analyze the effects of deficit irrigation on tomato root growth, soil water uptake and utilization in the root zone. The results showed that deficit irrigation could reduce the total root length density of water-absorbed roots but increase the water-absorbed root length density of the underlying soil (30–60 cm). Moderate and severe water deficits at Stage II increased the water-absorbed root length density of the underlying soil by 0.10–6.26% and 2.12–11.71% compared with a mild water deficit. Considering tomato root growth, the Hydrus-1D model can improve the accuracy of soil moisture simulation. The main water absorption zone of tomato roots was 0–30 cm. Compared with full irrigation, the ratio of water absorption by the underlying root system (30–60 cm) to the total water absorption of the profile (0–60 cm) increased by 2.16–2.82% and 5.34–6.34% due to mild and moderate water deficits at Stage I. At Stage I and Stage II, a water deficit could reduce soil evaporation. T3 had the highest water use efficiency in two years, which was 24.07% (T9) and 20.47% (T8) higher than the lowest value, respectively. The optimal deficit irrigation scheme under this experiment condition is as follows: the soil water content was 70–90% θf (field capacity) at Stage I and was 40–60% θf at Stage II (T3).

Water shortage and wastage are critical challenges to sustainable agricultural development, especially in arid and semiarid regions worldwide. Isatis indigotica (woad), as a traditional Chinese herb, was planted in a large area in a cold and arid environment of Hexi. Regulated deficit irrigation can reduce the growth of some vegetative organs by changing the accumulation and distribution of photosynthetic products in crops, thus increasing the economic yield of crops. In agricultural production, crop productivity may be improved by mulched drip irrigation and deficit irrigation. Hence, a field experiment was conducted to investigate the responses of photosynthesis, malondialdehyde, osmotic regulators, antioxidant enzyme activities, and the yield of woad to water deficit at different growth stages. The growth stage of woad was divided in four stages: seedling, vegetative growth, fleshy root growth, and fleshy root maturity. During vegetative growth, fleshy root growth, and fleshy root maturity, three water gradients were set for plants with mild (65-75% in field water capacity, FC), moderate (55-65% in FC), and severe (45-55% in FC) deficits, respectively. In contrast, an adequate water supply (75-85% in FC) during the growth period was designed as the control (CK). The net photosynthetic rate (Pn), transpiration rate, and stomatal conductance of woad significantly decreased (P< 0.05) by moderate and severe water deficits. Still, rehydration after the water deficit could produce a noticeable compensation effect. In contrast, malondialdehyde and proline accumulation significantly increased under moderate and severe water deficits. At the same time, the superoxide dismutase, peroxidase, and catalase all had high activities (increased significantly by 19.87-39.28%, 19.91-34.26%, and 10.63-16.13% compared with CK, respectively), but yields were substantially lower, compared to CK. Additionally, the net photosynthetic rate was negatively correlated with antioxidant enzyme activity. The economic yield of plants subjected to continuous mild water deficit during both vegetative and fleshy root growth was not significantly different from that in CK. Still, the water use efficiency improved significantly. Therefore, the continuous mild water deficit during vegetative and fleshy root growth could improve the physiological and biochemical mechanisms of the plant, representing an optimal irrigation strategy for woad in cold and arid areas.

Exploring the impacts of CO2 and soil water availability on the photosynthetic performance and water use efficiency of three green manure plants could provide theoretical basis for the adaptive management of grassland ecosystems under future climate change. An experiment was conducted in an artificial climate chamber with precisely controled CO2 concentrations of 400 (natural atmospheric) and 800 μmol·mol-1 (doubled), and four water treatments, 80% field water holding capacity (FC) (full irrigation control group), 55%-60% FC (mild water deficit), 35%-40% FC (moderate water deficit), &lt;35% FC (severe water deficit) to investigate the impacts of increasing CO2 concentration and water deficit on chlorophyll content, gas exchange variables, and water use efficiency (WUE) of oilseed rape (Brassica napus), white clover (Trifolium repens), and alfalfa (Medicago sativa). The results showed that under the same CO2 concentration, when soil moisture was less than 40% FC, the chlorophyll content and gas exchange parameters of three plants were significantly decreased. The treatment of 55%-60% FC did not alter the total chlorophyll content of three species, but reduced the photosynthetic rate (Pn) and transpiration rate (Tr) of white clover and alfalfa by 6%-25% and did not affect their WUE. Compared with atmospheric CO2 concentration, the doubled CO2 concentration significantly decreased the Pn of oilseed rape by 21.5% under the full irrigation treatment, increased the Pn of three species under mild water deficit, increased the Pn of oilseed rape and alfalfa under moderate water deficit, but only improved the Pn of alfalfa under severe water deficit. The doubled CO2 concentration significantly increased WUE of white clover and alfalfa under all water deficit conditions, but only increased WUE of oilseed rape under mild water deficit. Increasing CO2 concentration and water deficit significantly interacted to affect Pn of three species and the WUE of oilseed rape. In summary, the three species differed in their responses to doubled atmospheric CO2 concentration and different levels of water deficit. Our results suggested that elevated CO2 concentration could improve the adverse effects of mild water deficit on photosynthetic performance and WUE of three species, but only improve the photosynthetic performance of alfalfa under severe water deficit.

In arid regions, deficit irrigation stands as an efficacious strategy for augmenting agricultural water conservation and fostering sustainable crop production. The Hexi Oasis, an irrigation zone situated in Northwest China, serves as a pivotal area to produce grain and cash crops. Nonetheless, due to the predominant conditions of low rainfall and high evaporation, the scarcity of irrigation water has emerged as a critical constraint affecting crop growth and yield in the area. In order to evaluate the effects of deficit irrigation on photosynthetic characteristics, yield, quality, and water use efficiency of sunflower, a two-year field experiment with under-mulched drip irrigation was conducted in the cold and arid environment of the Hexi Oasis region. Water deficits were implemented at sunflower seedling and maturity and consisted of three deficit levels: mild deficit (65-75% field capacity, FC), moderate deficit (55-65% FC), and severe deficit (45-55% FC). A total of six combined water deficit treatments were applied, using full irrigation (75-85% FC) throughout the entire crop-growing season as the control (CK). The results illustrated that water deficit engendered a decrease in leaf net photosynthetic rate, transpiration rate, and stomatal conductance of sunflower compared to CK, with the decrease becoming significant with the water deficit increasing. A mild water deficit, both at the seedling and maturity phases, precipitated a significant enhancement (p< 0.05) in leaf water use efficiency. Under mild water deficit, stomatal limitation emerged as the predominant factor inducing a reduction in the photosynthetic capacity of sunflower leaves, while as the water deficit escalated, non-stomatal limitation progressively assumed dominance. Moreover, a mild/moderate water deficit at seedling and a mild water deficit at maturity (WD1 and WD3) significantly improved sunflower seed quality under consistent yield conditions and significantly increased irrigation water use efficiency, with an average increase of 15.3% and 18.5% over the two years, respectively. Evaluations utilizing principal component analysis and membership function methods revealed that WD1 attained the highest comprehensive score. Consequently, a mild water deficit at both seedling and maturity (WD1) is advocated as the optimal deficit irrigation strategy for sunflower production within the cold and arid environment of Northwest China.

The monitoring of vine water status is of interest for irrigation management in order to improve water use while optimizing both berry yield and quality. Remote-sensing techniques might provide accurate, rapid, and non-destructive estimates of vine water status. The objective of this study was to test the capability of the reflectance-based water index (WI) and the photochemical reflectance index (PRI) to characterize Vitis vinifera L. cv. Xarel·lo water status under mild to moderate water deficits. The study was conducted at the leaf level in irrigated potted plants and at the plant level on five commercial rain-fed vineyards in 2009 and 2010. In potted plants, the reflectance indices PRI and WI closely tracked variation in the leaf-to-air temperature difference (ΔT) with r2 = 0.81 and r2 = 0.83, for WI and PRI, respectively (p &lt; 0.01). In addition, in potted plants, both PRI and WI showed significant relationships with light-use efficiency (LUE)—calculated as the ratio between net CO2 assimilation rate (An) and incident photosynthetic active radiation (PAR) at the leaf surface—with r2 = 0.92 and r2 = 0.74 for PRI and WI, respectively. At the canopy level, vine predawn water potential (Ψpd) was related to the canopy-to-air temperature difference (ΔTm) across years (r2 = 0.37, p &lt; 0.05). In the years of study, the relationships between PRI and WI showed variable degrees of correlation against Ψpd and ΔTm. Across years, PRI and WI showed significant relationships with Ψpd, with r2 = 0.41 and r2 = 0.37 (p &lt; 0.01), for WI and PRI, respectively. Indices formulated to account for variation in canopy structure (i.e., PRInorm and WInorm) showed similar degrees of correlation against Ψpd to their original formulations. In addition, PRI and WI were capable of differentiating (p &lt; 0.01) between mild (Ψpd &gt; −0.4 MPa) and moderate (Ψpd &lt; −0.4 MPa) water deficits, and a similar response was observed when PRInorm and WInorm—formulated to account for variation in canopy structure—were considered. Thus, at the leaf level, our result suggest that WI and PRI can be used to adequately predict the diurnal dynamics of stomatal aperture and transpiration. In addition, at the canopy level, PRI and WI effectively differentiated vines under mild water deficits from those experiencing moderate water deficits. Thus, our results show the capability of WI and PRI in characterizing vine water status under mild to moderate water deficits.

Determining the effect of water deficit during vegetative growth periods on grain yield will provide reasonable strategy for water-saving management of winter wheat (Triticum aestivum L.). Pot experiment was conducted using winter wheat cultivar (Yangmai16) to investigate the effects of water deficit during vegetative periods on post-anthesis photosynthetic capacity and the relationship with grain yield formation during the growing season of 2013–2014. Water deficit consisted of moderate (leaf water potential of −1.20 to −1.40 MPa) and severe (leaf water potential of −1.80 to −2.20 MPa) levels during tillering and jointing growth stages, respectively. Moderate water deficit during tillering significantly increased grain yield through an enhanced yield capacity per stem and moderate water deficit during jointing resulted in similar grain yields as compared to control, while severe water deficit during both periods significantly reduced grain yield due to strong reduction in number of spikes as compared to control. Moderate or severe water deficit during tillering had no effect on flag leaf area but reduced it significantly when it occurred during jointing. Water deficit treatments during jointing and tillering increased net photosynthetic rate (P n) of flag leaves, the treatment during jointing being the most stimulatory. The maximum photochemical efficiency of Photosystem II, actual photochemical efficiency, the maximum carboxylation rate and photosynthetic electron transport rate increased in ways similar to P n in response to water deficit but non-photochemical quenching decreased. We conclude that improved photosynthetic capacity by moderate water deficit during vegetative growth period highly contributes to grain yield, especially during tillering period, while grain yield decreased by the limitation of leaf area and spikes under severe water deficit.

Responses of grapevine vegetative growth components to mild, medium and severe soil water deficits were used to identify simple and sensitive indicators for early diagnosis of water stress. Soil water deficit was characterised as the fraction of transpirable soil water (FTSW) remaining in a water-depleted rootzone. Growth components included the number of emerged leaves on first (Ist) and second (IInd) order lateral branches, the leaf area and internode length of each phytomer of Ist order lateral branches, and the frequency of IInd order lateral branching. These components were measured in a greenhouse on Shiraz (syn. Syrah) grapevines, over a 38-day period of stabilised soil water regimes. Leaf emergence rate, final leaf area and final internode length of lateral branches I were relatively insensitive to mild and medium water deficits. They only decreased in response to severe water deficits. The frequency of IInd order lateral branching showed a similar trend, but was inhibited at severe water deficits. The leaf emergence rate of lateral branches II was highly sensitive to FTSW, and decreased even in response to mild water deficits. Because measurement of leaf emergence rate is a time consuming process, further analysis of the data was undertaken to identify a simpler but similarly effective indicator of cumulative water deficit. Accordingly, we established that the final length of lateral branches I was sensitive to medium water deficits, while the final ratio of the number of leaves on lateral branches II to the number of leaves on lateral branches I, was sensitive to even mild water deficits. Both of these composite indicators (derived variables) were relatively easy to measure and showed potential as early indicators of water deficits. They were more sensitive to FTSW than was predawn leaf water potential. Moreover, the final ratio of the number of leaves on lateral branches II to the number of leaves on lateral branches I was even more sensitive to FTSW than was stomatal conductance.

Currently, the world is facing a serious agricultural water crisis, which also affects grassland areas. Alfalfa, a key perennial forage legume, consumes about 10% of China’s pastoral irrigation water. Reducing irrigation generally results in a loss of hay yield, but the effects on alfalfa quality and its relationship to water use are less clear. In this study, we explore alfalfa quality under different irrigation deficits and its relationship to water use in the Hexi Corridor of China. Alfalfa water use, quality yield (relative feeding value yield (RFVyield) and crude protein yield (CPyield)), and quality water use efficiency (relative feeding value water use efficiency (WUERFV) and crude protein water use efficiency (WUECP)) were measured in a field experiment. Alfalfa quality showed a negative correlation with the irrigation quota (the determination coefficient for relative feeding value was 0.375 and for crude protein was 0.289). There was a positive correlation between quality yield and irrigation quota (the determination coefficient for RFVyield was 0.570 and for CPyield was 0.631). The higher irrigation quota increased quality yield, which compensated for its negative effects on alfalfa quality. The mild and moderate water deficit treatments showed lower WUERFV than both the severe and no water deficit treatments. Moderate or mild water deficit is recommended to be used for one-year-old alfalfa treatment. No water deficit is beneficial to improve the quality water use efficiency of two-year-old alfalfa.

Effect of water deficits on pomegranate tree performance and fruit quality – A review

To better understand the adaptation mechanisms of the photosynthetic apparatus of cotton plants to water deficit conditions, the influence of water deficit on photosynthesis, chlorophyll a fluorescence and the activities of antioxidant systems were determined simultaneously in Gossypium hirsutum L. cv. Xinluzao 45 (upland cotton) and Gossypium barbadense L. cv. Xinhai 21 (pima cotton). Water deficit decreased photosynthesis in both cotton species, but did not decrease chlorophyll content or induce any sustained photoinhibition in either cotton species. Water deficit increased ETR/4-AG, where ETR/4 estimates the linear photosynthetic electron flux and AG is the gross rate of carbon assimilation. The increase in ETR/4-AG, which represents an increase in photorespiration and alternative electron fluxes, was particularly pronounced in Xinluzao 45. In Xinluzao 45, water deficit increased the activities of antioxidative enzymes, as well as the contents of reactive oxygen species (ROS), which are related to the Mehler reaction. In contrast, moderate water deficit particularly increased non-photochemical quenching (NPQ) in Xinhai 21. Our results suggest that Xinluzao 45 relied on enhanced electron transport such as photorespiration and the Mehler reaction to dissipate excess light energy under mild and moderate water deficit. Xinhai 21 used enhanced photorespiration for light energy utilisation under mild water deficit but, when subjected to moderate water deficit, possessed a high capacity for dissipating excess light energy via heat dissipation.

Regulated deficit irrigation improved fruit quality and water use efficiency of pear-jujube trees

The changes of soil ecological environment caused by different degrees of water deficit will affect the sustainable planting of soil, so it is of great significance to explore moderate water deficit and maintain a good ecological environment with sustainable soil. In this study, the effects of water stress on soil nutrients, microorganisms and enzyme activities of Isatis indigotica in Hexi corridor were studied by Mulched Drip Irrigation. The results showed that it was beneficial to the absorption and utilization of available phosphorus and available potassium in the soil of the root of Isatis indigotica by mild water deficit, increased the number of fungi and actinomycetes in the soil, and did not affect the activity of urease in the soil from 0 to 20cm. It was resulted in slow absorption of available phosphorus and available potassium in the soil and significantly decreased soil urease activity by severe water deficit, but it did not affect the number of fungi and actinomycetes. Therefore, mild water deficit is helpful to improve the utilization of soil nutrients and soil enzyme activity. This study provided a theoretical basis for the standardized planting of Isatis indigotica in northwest arid region on the basis of efficient water saving.

Exogenous abscisic acid coordinating leaf senescence and transport of assimilates into wheat grains under drought stress by regulating hormones homeostasis