Impact Of Water Stress Research Articles

Melia azedarach plants show tolerance properties to water shortage treatment: An ecophysiological study

Candidate species for reforestation of areas prone to drought must combine water stress (WS) tolerance and economic or medicinal interest. Melia azedarach produces high quality timber and has insecticidal and medicinal properties. However, the impact of WS on M. azedarach has not yet been studied. Two-month old M. azedarach plants were exposed to WS during 20 days. After this period, plant's growth, water potential, photosynthetic performance and antioxidant capacity were evaluated. WS did not affect plants' growth, but induced stomatal closure, reduced net CO2 assimilation rate (A) and the intercellular CO2 availability in mesophyll (Ci). WS also reduced the photosynthetic efficiency of PSII but not the pigment levels. WS up-regulated the antioxidant enzymes and stimulated the production of antioxidant metabolites, preventing lipid peroxidation. Therefore, despite some repression of photosynthetic parameters by WS, they did not compromise plant growth, and plants increased their antioxidant capacity. Our data demonstrate that M. azedarach juvenile plants have the potential to acclimate to water shortage conditions, opening new perspectives to the use of this species in reforestation/afforestation programs of drought prone areas.

The impacts of water stress on phloem transport in Douglas-fir trees

Despite the critical role that phloem plays in a number of plant functional processes and the potential impact of water stress on phloem structural and phloem sap compositional characteristics, little research has been done to examine how water stress influences phloem transport. The objectives of this study were to develop a more accurate understanding of how water stress affects phloem transport in trees, both in terms of the short-term impacts of water stress on phloem sap composition and the longer-term impacts on sieve cell anatomical characteristics. Phloem sieve cell conductivity (kp) was evaluated along a gradient of tree height and xylem water potential in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees in order to evaluate the influence of water stress on phloem transport capacity. The Hagen-Poiseuille equation was used with measurements of sieve cell anatomical characteristics, water content of phloem sap, non-structural carbohydrate content of phloem sap and shoot water potential (Ψl) to evaluate impacts of water stress on kp. Based on regression analysis, for each 1 MPa decrease in mean midday Ψl, sieve cell lumen radius decreased by 2.63 µm MPa(-1). Although there was no significant trend in sucrose content with decreasing Ψl, glucose and fructose content increased significantly with water stress and sieve cell relative water content decreased by 13.5% MPa(-1), leading to a significant increase in sugar molar concentration of 0.46 mol l(-1) MPa(-1) and a significant increase in viscosity of 0.27 mPa s MPa(-1). Modeled kp was significantly influenced both by trends in viscosity as well as by water stress-related trends in sieve cell anatomy.

English

The impact of water stress on the growth, concentration of phytochemicals and antifungal potency of Bryophyllum pinnatum L. was investigated. Three weeks old seedlings were subjected to 3, 7 and 10 days water deficit regimes and a control (watered daily). Plant height, number of leaves, whole plant dry weight, net assimilation rate, leaf area ratio and relative growth rate were reduced by 6 to 50% as intervals of water deficit increased. Alkaloids, tannins, saponins and flavonoids were present in all plants and all but alkaloids increased with increase in intervals of water deficit. Alkaloid content decreased by 1.3 to 10.5% while the other phytochemicals increased by 12 to 206% in response to water deficit stress. Ethanolic extracts of plants from the four batches showed varying inhibition zones against Candida albicans. The inhibition zones decreased with increasing water deficit intervals corresponding with the decrease in alkaloid content. This research has revealed that water stress increases the tannin, saponin and flavonoid contents of Bryophyllum but decreases the alkaloid content.   Key words: Bryophyllum, water deficit, phytochemicals, inhibition zone.

Downscaling Crop Water Sensitivity Index Using Monotone Piecewise Cubic Interpolation

Crop-water production functions quantitatively describe the relationship between crop yield and field evapotranspiration. The crop water sensitivity indexes of crop-water production functions, a key factor for optimizing irrigation scheduling in case of water scarcity, are usually obtained from field experiments or other sources for crop growth stages, while their values in shorter intervals are preferred for practical irrigation scheduling. We proposed a method to downscale the sensitivity index from growth stages to shorter intervals by monotone piecewise cubic interpolation of the cumulative sensitivity index curve. This method was used to estimate sensitivity indexes in irrigation intervals of about 10 d for corn and wheat in central Shanxi Province of China. Results showed that the downscaled sensitivity index could reflect the impact of water stress on crop growth both at different growth stages and within each stage. Scenario analysis of water stress at a single growth stage of wheat showed the rationality of downscaling water sensitivity index from growth stages to shorter intervals through interpolation of cumulative sensitivity index, and this proposed downscaling method was superior to the traditional linear downscaling method.

Postharvest salicylic acid treatment reduces storage rots in water-stressed but not unstressed sugarbeet roots

Exogenous application of salicylic acid (SA) reduces storage rots in a number of postharvest crops. SA's ability to protect sugarbeet (Beta vulgaris L.) taproots from common storage rot pathogens, however, is unknown. To determine the potential of SA to reduce storage losses caused by three common causal organisms of sugarbeet storage rot, freshly harvested roots were treated with 0.01, 0.1, 1.0 or 10mM SA, inoculated with Botrytis cinerea, Penicillium claviforme, or Phoma betae, and evaluated for the severity of rot symptoms after incubation at 20°C and 90% relative humidity. Roots were obtained from plants that received sufficient water or were water-stressed prior to harvest. Roots from water-stressed plants were included since water-stress increases sugarbeet root susceptibility to storage rot and SA mitigates drought effects in other plant species. SA at concentrations of 0.01–10mM had no effect on the severity of storage rot caused by B. cinerea, P. claviforme, or P. betae in roots from plants that received sufficient water prior to harvest. However, SA at these same concentrations reduced the severity of rot symptoms for all three pathogens in roots from plants that were water stressed before harvest. For water-stressed roots, all concentrations of SA produced statistically equivalent reductions in the weight of rotted tissue for each pathogen, and on average, SA reduced rot severity due to B. cinerea, P. claviforme, and P. betae by 54, 45, and 58%, respectively. SA reduced rot from all three pathogens by reducing lesion size, but did not affect the incidence of infection. The ability of SA to reduce rot severity in water-stressed roots, but not in roots that received sufficient water before harvest suggests that SA alleviated the negative impact of water stress but did not directly protect sugarbeet roots against storage rots.

Impact of emerging clean vehicle system on water stress

While clean vehicles (i.e., vehicles powered by alternative fuels other than fossil fuels) offer great potential to reduce greenhouse gas emissions from gasoline-based vehicles, the associated impact on water resources has not yet been fully assessed. This research provides a systematic evaluation of the impact of a fully implemented clean vehicle system on national and state-level water demand and water stress. On the national level, based on existing policies, transitioning the current gasoline-based transportation into one with clean vehicles will increase national annual water consumption by 1950–2810 billion gallons of water, depending on the market penetration of electric vehicles. On the state level, variances of water efficiency in producing different fuels are significant. The fuel choice for clean vehicle development is especially crucial for minimizing water stress increase in states with already high water stress, high travel demands, and significant variations in water efficiency in producing different alternative fuels. Current development of clean vehicle infrastructure, however, has not reflected these state-level variations. This study takes an optimization approach to further evaluate impacts on state-level water stress from a fully implemented clean vehicle system and identified potential roles (fuel producer or consumer) states may play in real world clean vehicle development scenario. With an objective of minimizing overall water stress impact, our optimization model aims to provide an analytical framework to better assess impacts on state-level water resources due to clean vehicle deployment.

Water stress impact on young seedling growth of Acacia arabica

Drought is the major constraint in arid regions throughout the world and identification of drought-resistant plants is therefore of crucial importance. Since young seedling stage is especially sensitive to water stress, the present work analyzed the physiological behavior of seedling from Acacia arabica issued from a dry area, grown under controlled environmental conditions and subjected to progressive soil drying. Although soil gravimetric water content (g H2O g-1 soil dry weight) dropped from 80 % to less than 35 %, most plants remained alive until the end of the water stress. Seedlings were able to efficiently close their stomata to reduce water losses and accumulated high amounts of proline. Despite osmotic adjustment, turgor pressure decreased in stressed plants and could explain the stress-induced inhibition of plant growth. Decrease in net photosynthesis was related to stress-induced decrease in stomatal conductance and not to any impact on chlorophyll concentration or fluorescence-related parameter: both PSII efficiency and photochemical quenching remained unaffected by water stress while drought-induced increase in non-photochemical quenching should be regarded as a strategy to avoid over-energisation of the photosynthetic apparatus. Instantaneous water use efficiency increased in stressed plants comparative to controls. Oxidative stress estimated by malondialdehyde concentration was recorded only at the end of the treatment, suggesting that stressed plants remained able to cope with reactive oxygen species. Water stress induced an increase in anthocyanins, while aglycone flavonols decreased. Those compounds were not involved in the management of oxidative stress. It is concluded that A. arabica is a promising drought-resistant plant species for rehabilitation of dry areas. © 2013 Franciszek Gorski Institute of Plant Physiology, Polish Academy of Sciences, Krakow.

Structural Uncertainty in Model-Simulated Trends of Global Gross Primary Production

Projected changes in the frequency and severity of droughts as a result of increase in greenhouse gases have a significant impact on the role of vegetation in regulating the global carbon cycle. Drought effect on vegetation Gross Primary Production (GPP) is usually modeled as a function of Vapor Pressure Deficit (VPD) and/or soil moisture. Climate projections suggest a strong likelihood of increasing trend in VPD, while regional changes in precipitation are less certain. This difference in projections between VPD and precipitation can cause considerable discrepancies in the predictions of vegetation behavior depending on how ecosystem models represent the drought effect. In this study, we scrutinized the model responses to drought using the 30-year record of Global Inventory Modeling and Mapping Studies (GIMMS) 3g Normalized Difference Vegetation Index (NDVI) dataset. A diagnostic ecosystem model, Terrestrial Observation and Prediction System (TOPS), was used to estimate global GPP from 1982 to 2009 under nine different experimental simulations. The control run of global GPP increased until 2000, but stayed constant after 2000. Among the simulations with single climate constraint (temperature, VPD, rainfall and solar radiation), only the VPD-driven simulation showed a decrease in 2000s, while the other scenarios simulated an increase in GPP. The diverging responses in 2000s can be attributed to the difference in the representation of the impact of water stress on vegetation in models, i.e., using VPD and/or precipitation. Spatial map of trend in simulated GPP using GIMMS 3g data is consistent with the GPP driven by soil moisture than the GPP driven by VPD, confirming the need for a soil moisture constraint in modeling global GPP.

Adapting to water scarcity: constraints and opportunities for improving irrigation management in Khorezm, Uzbekistan

Like many irrigation schemes in Central Asia, the one in Khorezm faces a two-fold challenge: on the one side, the severe problems inherited from the past need to be remedied and on the other side, the rising supply–demand gap driven by sharpening competition for water and climate change must be dealt with. Located in the lower part of the Amu Darya basin, Khorezm irrigation and drainage scheme is particularly vulnerable to supply–demand gaps. Promising solutions towards adaptation comprise modified strategies of land and water use towards higher efficiency and flexibility in combination with measures to lessen the constraints of the system itself, which was initially designed for the management of a few, large and uniform production units and not for many diverse and small units. Solutions consist of flexible, modeling-based approaches, re-arranging institutional settings and establishing economic incentive systems. Flexible modeling allows an integrated use of surface and groundwater resources avoiding or minimizing the impact of water stress on yield. Institutional settings strengthen the position of water users via improved participation and transparency of processes in Water Consumers Associations (WCAs). Economic measures support sustainable resource use strategies and improve the functioning of WCAs. The findings could be extrapolated to other regions of Central Asia with similar conditions and challenges.

Changes in leaf characteristics and grain yield of soybean (Glycine max L.) in response to shading and water stress

Some leaf characteristics and yield of soybean were investigated under different light interception (25, 65 and 100% of sun light) and irrigation treatments (I1, I2, I3, I4 for irrigation after 60, 90, 120 and 150 mm evaporation from class A pan, respectively) in 2011. The experiment was arranged as split plot based on randomized complete block design in three replicates. Membrane stability index decreased with increasing shading. However, leaf water potential, relative water content and leaf area index under all irrigation treatments increased as light interception decreased. This trend was improved as water availability decreased. Specific leaf weight significantly decreased with increasing shading under I1 and I2, but it was statistically similar for all light interceptions under I3. In contrast, specific leaf weight was increased as shading increased under I4. In general, specific leaf weight decreased with increasing water deficit. Increasing shade stress decreased grain yield per unit area under I1 and I2, but improved grain yield under I3 and I4, which is directly related with changes in leaf water potential, relative water content and leaf area index under these conditions. Therefore, shading can reduce the impact of water stresses on soybean plant performance in the field.

Impact of Irrigation Water Stress and Plant Population on Water Productivity and Maize Yield

Field investigation was conducted on effect of water deficit and plant populations on maize during kharif (2009) season in a split plot design with irrigation as main plot treatments and plant population as sub plot treatments. The irrigation treatments such as normal irrigation water requirement (0.8 IW/CPE ratio) (500 mm) (I1), 75 % of irrigation water requirement (0.6 IW/CPE ratio) (375 mm) (I2), 50 % of irrigation water requirement (0.4 IW/CPE ratio) (250 mm) (I3), with a normal spacing (60x20cm) (80,000 plants ha-1) (S1), narrow spacing (30x30cm) (1,06,666 plants ha-1 ) (S2) and reduced narrow spacing (45x20cm) (1,11,111 plants ha-1 ) (S3) were followed. Higher water productivity was observed in 50 % irrigation water requirement followed by 75% of water requirement. Yield increment was registered in narrow spacing than normal spacing. Narrow planting increased the yield by 5 %, 6 %, 13 % over the normal spacing in 50 %, 75% and normal water requirement.

Resilience of physiological attributes of wheat (Triticum aestivum L.) to abiotic stresses

Water stress and high temperature variability are the major constraints for wheat crop productivity and food security in the context of climate change. Impact of high temperature and water stress at anthesis stage of spring wheat was studied through field experiments conducted during 2008 to 2009 and 2009 to 2010. Five wheat varieties of diverse origin namely Tatara, National Agricultural Research Centre (NARC)-2009, Sehar-2006, SKD-1 and F-Sarhad were sown in randomized complete block design (RCBD) replicated four times. Physiological parameters that is, net photosynthesis (An), transpiration rate (E), SPAD chlorophyll contents and prolines were recorded at anthesis stage. The results indicated reduction of An and increased E due to high temperature and moisture stresses. Among genotypes, maximum photosynthetic rate was recorded for Tatara (30.52 μ mole/m2/s) followed by NARC-2009. The E recorded maximum in Sehar-2006 (2.80 mole/m2/s) which had low photosynthetic activity whereas minimum E observed in Tatara (2.27 μ mole/m2/s) followed by NARC-2009. Maximum SPAD value observed in Tatara (53.17) followed by NARC-2009 (49.00) where as Sehar-2006 (37.17) depicted less chlorophyll contents and ultimately reduced photosynthesis and productivity. The highest proline contents were recorded in Tatara (59.69 µg g-1) followed by NARC-2009 (55.05 µg g-1) as compared to SKD-1 (46.27 µg g-1) and F-Sarhad (50.58) which might be due to genetic potential and physiological adaptability of Tatara cultivars against stress conditions. Water stress and high temperature at anthesis led to reduction in photosynthesis resulting reduced biomass and limited yield. Therefore, genotypes having better physiological performance under biotic stresses need to be considered for cultivation under changing environment. Since Tatara performed best in our study, it is recommended for cultivation under high temperature and moisture stresses. The values of all physiological attributes (An and E) were higher during first year (2008 to 2009) as compared to second year (2009 to 2010) which was due to relatively high temperature and low moisture availability during the second year. Key words: Temperature, water stress, photosynthesis, transpiration, proline, SPAD chlorophyll, anthesis, wheat.

Impact of Temperature and Water Stress on Growth Yield and Related Biochemical Parameters of Okra

The main aim of this research is to compare the physical and biochemical parameters of okra when subjected to heat and water stress and to determine how heat shock or water deficit, either individually or in combination, affect the growth and yield of okra species. Experiments were conducted in three growing seasons in the low country wet zone as a replicated trial. The plants were grown in pots under temperature-controlled polytunnels. Main plot included two different wetting applications (no water stress, 50 % water stress from the field capacity) and sub plots contained 3 different temperature regimes (34 °C maximum temperature polytunnel / 32 °C maximum temperature polytunnel / ambient temperature). Individual water stress showed highly significant effect on growth, and yield parameters of okra. High yield reduction was shown in the water stressed plants. Further temperature stress has especially affected the pod quality parameters such as fibre and pectin content. Harvesting time of okra under ambient temperature was not suitable for the high temperature conditions due to rapid pod growth rate and break down of the calcium pectate, 5 to 6 days after full blooming. Results indicated that okra has high yield when it is grown under high temperature environment with no water stress. Therefore by maintaining irrigation at field capacity level even at high temperature stress conditions, it is possible to achieve a good yield by harvesting okra pods 5 to 6 days after full blooming without significant yield reduction. Tropical Agricultural Research Vol. 23 (1): 77-83 (2011) DOI: http://dx.doi.org/10.4038/tar.v23i1.4634

Influence of potassium fertilization, water and salt stress, and their interference on rheological soil parameters in planted containers

Rheological parameters of an artificial mixture of soil and quartz sand were analyzed with regard to potassium (K) fertilization, water and salt stress (via sodium). The examinations were part of a plant container experiment where originally plants were subjected to the factors mentioned beforehand. While for the plants, K fertilization had a positive impact on water use efficiency and could compensate partly for the negative impact of salinity and water stress, the soil itself showed no clear impact of K fertilization on maximum shear stress during an amplitude sweep test in oscillatory modus. Instead, the impact was overridden by the coarse substrate and the other influencing factors water and salt stress as well as the state of drainage in which the samples were measured. The results show a destabilizing effect of sodium, while the water stress caused no significant additional aggregation in the soil because of the coarse and thus rapidly drained substrate. However, homogenization revealed structure development during the plant experiment. It can be assumed, that in less coarse soil material the impact of the considered factors K fertilization, water and salt stress is more pronounced.

Modulation of chlorophyll biosynthesis by water stress in rice seedlings during chloroplast biogenesis*

To understand the impact of water stress on the greening process, water stress was applied to 6-day-old etiolated seedlings of a drought-sensitive cultivar of rice (Oryza sativa), Pusa Basmati-1 by immersing their roots in 40 mm polyethylene glycol (PEG) 6000 (-0.69 MPa) or 50 mm PEG 6000 (-1.03 MPa) dissolved in half-strength Murashige and Skoog (MS)-nutrient-solution, 16 h prior to transfer to cool-white-fluorescent + incandescent light. Chlorophyll (Chl) accumulation substantially declined in developing water-stressed seedlings. Reduced Chl synthesis was due to decreased accumulation of chlorophyll biosynthetic intermediates, that is, glutamate-1-semialdehyde (GSA), 5-aminolevulinic acid, Mg-protoporphyrin IX monomethylester and protochlorophyllide. Although 5-aminolevulinic acid synthesis decreased, the gene expression and protein abundance of the enzyme responsible for its synthesis, GSA aminotransferase, increased, suggesting its crucial role in the greening process in stressful environment. The biochemical activities of Chl biosynthetic enzymes, that is, 5-aminolevulinic acid dehydratase, porphobilinogen deaminase, coproporphyrinogen III oxidase, porphyrinogen IX oxidase, Mg-chelatase and protochlorophyllide oxidoreductase, were down-regulated due to their reduced protein abundance/gene expression in water-stressed seedlings. Down-regulation of protochlorophyllide oxidoreductase resulted in impaired Shibata shift. Our results demonstrate that reduced synthesis of early intermediates, that is, GSA and 5-aminolevulinic acid, could modulate the gene expression of later enzymes of Chl biosynthesis pathway.

Improved Management Alleviating Impact of Water Stress on Yield Decline of Tropical Aerobic Rice

Yield decline is the major concern in tropical aerobic rice (Oryza sativa L.). Both biotic and abiotic factors were responsible for this phenomenon. No analytical information on actual causes was reported taking into account of responses of root to water stress conditions. In a field experiment at the Central Rice Research Institute, India during 2009 and 2010, five rice genotypes were grown under two soil water conditions, aerobic and semi‐aerobic condition, for better understanding of yield penalty vis‐à‐vis yield stability. Results showed aerobic condition significantly inhibited structural development of root and caused significant variation in biochemical root traits accounting for higher concentration of hydrogen peroxide (24.6%) and proline (20%), and lower concentration of total soluble protein (20%) that resulted in 17% yield decline than semi‐aerobic condition. Applying supplementary irrigation at semi‐aerobic condition achieved 21% more grain yield compared with aerobic condition due to 21%, 8.3, and 10.4% more root biomass, root volume, and root/shoot ratio, respectively. Interaction of genotypes with soil water conditions revealed that at aerobic condition, better performance could be expected in ‘Apo’(4.0 t ha−1) and ‘IR 74371‐3‐1‐1’ (3.80 t ha−1) with less yield decline (7.0–9.5%); supplementary irrigation enhanced their grain yield (4.3–4.4 t ha−1) at semi‐aerobic condition. Therefore, detrimental impact of physical and biochemical root traits’ changes on yield decline in aerobic rice could be alleviated with supplementary irrigation at critical growth stages under semi‐aerobic condition without compromising with water productivity.

Characterization of Crop Canopies and Water Stress Related Phenomena using Microwave Remote Sensing Methods: A Review

In this paper we reviewed the use of microwave remote sensing methods for characterizing crop canopies and vegetation water stress related phenomena. Our analysis includes both active and passive systems that are ground‐based, airborne, or spaceborne. Most of the published results that have examined crop canopy characterization and water stress have used active microwave systems. In general, quantifying the effect of dynamic vegetation properties, and water stress related processes in particular, on the measured microwave signals can still benefit from improved models and more observational data. Integrated data sets providing information on both soil status and plant status are lacking, which has hampered the development and validation of mathematical models. There is a need to link three‐dimensional functional, structural crop models with radiative transfer models to better understand the effect of environmental and related physiological processes on microwave signals and to better quantify the impact of water stress on microwave signals. Such modeling approaches should incorporate both passive and active microwave methods. Studies that combine different sensor technologies that cover the full spectral range from optical to microwave have the potential to move forward our knowledge of the status of crop canopies and particularly water related stress phenomena. Assimilation of remotely sensed properties, such as backscattering coefficient or brightness temperature, in terms of estimating biophysical crop properties using mathematical models is also an unexplored avenue.

Evaluation of Water Stress Impact on the Parameter Values in Stomatal Conductance Models Using Tower Flux Measurement of a Boreal Aspen Forest

Abstract The impact of water stress on plant stomatal conductance (g) has been widely studied but with little consensus as to the processes governing its responses. The photosynthesis-driven stomatal conductance models usually employ constant model parameters and attribute the decrease of g from water stress to the reduction of leaf photosynthesis. This has been challenged by studies showing that the model parameter values decrease when the plant is under water stress. In this study, the impact of plant water stress on the parameter values in stomatal conductance models is evaluated using the approach recently developed by S. Wang et al. and the tower flux measurements at a Canadian boreal aspen forest. Results show that the slope parameter (α) in the stomatal conductance models decreases substantially with the development of plant water stress. The magnitude of this reduction is dependent on how plant water stress is represented. Overall, the relative reduction of α from its maximum value is 28% when soil water content decreases from 0.38 to 0.18 m3 m−3, and is 38% when Bowen ratio increases from 0.25 to 3.5. Equations for α correction to account for water stress impacts are proposed. Further studies on different ecosystems are necessary to quantify the parameter variations with water stress among different climate regions and plant species.

Effects of salinity on microbial tolerance to drying and rewetting

Soil salinity and fluctuations in soil matric potential are stressors for soil microorganisms which, in turn, may affect soil organic matter turnover. In response to salinity and low soil water content, many microorganisms accumulate osmolytes. Therefore, it is conceivable that microorganisms in saline soils are more tolerant to drying and rewetting (DRW) stress than those in non-saline soils. An experiment was carried out with three different salinity levels: electrical conductivity (EC1:5) 0, 2 and 4 dS m−1 (EC0, EC2, EC4), and two water treatments: a constantly moist control or two DRW cycles. Respiration as an indicator of microbial activity was measured throughout the 59 days of incubation. At the end of the second dry period (day 35) and at the end of the following moist incubation (day 59), microbial biomass and microbial community structure were determined by phospholipid fatty acid (PLFA) analysis. Increasing salinity decreased microbial activity but did not affect its resistance to DRW. On day 59, cumulative respiration decreased in the order EC0 > EC2 > EC4 with no differences between water treatments. Fungal biomass was negatively affected by salinity at the end of the experiment, while bacterial biomass was unaffected. Microbial community structure in moist treatments differed between salinity levels, with EC4 influencing microbial community structure earlier than EC2. The resistance of microbial communities to DRW stress was salt level dependent; only beyond a critical salinity level adaptation to salt stress was able to reduce the impact of water stress on microbial community structure.

Impact of water stress on citrus yield

Water shortage is becoming a severe problem in arid and semi-arid regions worldwide, reducing the availability of agricultural land and water resources. Deficit irrigation strategies can improve water-use efficiency and the sustainability of agro-ecosystems, although it is important to model the effects on yield loss due to irrigation water restrictions. This work estimates the water production function in citrus trees, determining the relationship between plant water stress and yield depression, as well as establishing a mathematical model for each phenological stage considered (flowering, fruit growth and ripening), and for the entire productive process. For three consecutive years (2006–2008), four regulated deficit irrigation treatments plus a control (100% crop water evapotranspiration (ETC)) were implemented in 13-year-old citrus trees (Citrus sinensis L. Osb. cv. Navelina). Different water production functions were determined for each phenological stage, establishing the relationship between the irrigation water stress and crop yield. Our results show that the fruit growth and flowering stages were the most sensitive periods in relation to irrigation water deficit and yield loss. Water stress close to 50% of ETC during the flowering stage would impose a yield loss of up to 20%, whereas this same water stress level during the fruit growth or ripening stages would result in yield losses of nearly 10% and 6%, respectively. The adjustment with cross terms (r 2 = 0.87) estimated the yield loss with good accuracy, being very similar to data measured in each study season. Consequently, the combined effect of deficit irrigation in different stages would be an additive–multiplicative model, considering that the effect of water stress in previous periods determined the crop yield response. Our model indicated that the crop water production function under deficit irrigation programmes would have a quasi-linear relation for water deficits below to 40% ETC. The previous model functions did not enable us to establish an accurate relationship when the water stress was applied in different phenological stages. Thus, this new interpretation is valuable to improve our knowledge and predict the impact of regulated deficit irrigation and have potential application in precision water stress and sustainable irrigation scheduling for citrus.