Impact Of Water Stress Research Articles

Global synthesis of the impact of droughts on crops’ water-use efficiency (WUE): Towards both high WUE and productivity

Increasing frequencies and intensities of drought associated with climate change are placing great strain on agricultural water availability and crop yields across the globe. Thus, numerous studies have examined factors affecting water-use efficiency (WUE, an important indicator of the balance between productivity and water availability), and ways to improve it. However, conflicting results have been obtained and WUE has generally only been improved at the expense of yield. Here, we performed a meta-analysis to examine the impact of water stress on WUE and identify crops and some water management strategies that could potentially increase both productivity and WUE under water stress. Overall, the meta-analysis of 80 peer-reviewed publications, including 792 observations, showed that crop WUE slightly improved under drought stress (LnRR++=0.015), but the results varied depending on crop type and drought treatments. Moreover, the results indicate that both WUE and yield can be improved under drought stress by identifying appropriate crops (potentially including manioc, canola, rose geranium, spearmint, peanut, wheat, pear-jujube, watermelon, tomato, spinach, and pepper) and water management regimes. Short drought duration (< 30 days) and deficit irrigation throughout the whole season rather than only during the vegetative or reproductive phase are more likely to improve WUE and yield concurrently. Our study is one of the first to analyze factors affecting WUE variation and identify ways to increase WUE and yield simultaneously under drought stress, based on a large set of data from all over the world. The findings may help efforts to formulate practical guidance for future agricultural production as climate change progresses.

Photosynthetical activity modelisation of olive trees growing under drought conditions

Predicting photosynthetic production in olive trees is a key feature in managing the effect of climate change on arid areas. Functional-structural plant modelling is a promising tool for achieving this goal. We used a photosynthetic sub-model that accounted for water and temperature stress and implemented it into LIGNUM model. We then conducted an experiment to validate the model at the leaf level using olive trees (Olea europaea) grown under various climatic condition. Then, we simulated photosynthetic production of three static olive tree models aged 1, 2, and 3 years. Results revealed a good fit between observed and predicted photosynthesis, with coefficient of determination (R2) values of 0.94 and 0.93 for Chemlali and Zarrazi cultivars, respectively. These results showed that the impact of water stress on photosynthetic production was marginal.

Assessments of gross primary productivity estimations with satellite data-driven models using eddy covariance observation sites over the northern hemisphere

The accurate quantification of gross primary productivity (GPP) has been a major challenge in global climate change research. Satellite data-driven models have been universally used as scientific tools for investigating the carbon cycle, including vegetation index (VI)-based models, light use efficiency (LUE) models, and process-based models. However, inconsistencies and uncertainties have been found in the GPP estimations from various models. The understanding of model behaviors under different climatic conditions remains unclear. In this study, three typical satellite data-driven models, namely, Moderate Resolution Imaging Spectroradiometer (MODIS) GPP (MOD17) model, Temperature and Greenness (TG) model and Boreal Ecosystem Productivity Simulator (BEPS), respectively, were compared to better understand discrepancies and uncertainties in GPP estimations at 119 northern eddy covariance (EC) sites. Due to the variations in climatic drivers of GPP, temperature, precipitation and incoming solar radiation were selected to describe climatic conditions. The results showed that BEPS and MOD17 exhibited similar performance in simulating GPP, with root-mean-square error (RMSE) values of 2.50 g C m−2 d−1 and 2.53 g C m−2 d−1, respectively, and performed slightly better than TG (RMSE = 2.98 g C m−2 d−1). Comparison between simulated GPP and EC GPP also revealed that model performance varied substantially among different vegetation types. The three models performed better for deciduous broadleaf forest, evergreen needleleaf forest, and mixed forest, in comparison to the results from evergreen broadleaf forest and crop. Specifically, all three models showed poor performance under the conditions of high temperature and low precipitation, revealing the models’ inability to characterize the impact of water stress on photosynthesis when drought occurs. Furthermore, our results indicated that GPP estimations from satellite data-driven models were also sensitive to remotely sensed data, suggesting that the high accuracy of remotely sensed data in describing vegetation canopy is important for carbon modeling. This study highlights the importance of understanding model behaviors in different vegetation types and climatic conditions, so that the model performances may be improved in future carbon cycle studies.

Identifying the most promising agronomic adaptation strategies for the tomato growing systems in Southern Italy via simulation modeling

Abstract The main cultivation area of the Italian processing tomato is the Southern Capitanata plain. Here, the hardest agronomic challenge is the optimization of the irrigation water use, which is often inefficiently performed by farmers, who tend to over-irrigate. This could become unsustainable in the next years, given the negative impacts of climatic changes on groundwater availability and heat stress intensification. The aim of the study was to identify the most promising agronomic strategies to optimize tomato yield and water use in Capitanata, through a modeling study relying on an extensive dataset for model calibration and evaluation (22 data sets in 2005–2018). The TOMGRO simulation model was adapted to open-field growing conditions and was coupled with a soil model to reproduce the impact of water stress on yield and fruit quality. The new model, TomGro_field, was applied on the tomato cultivation area in Capitanata at 5 × 5 km spatial resolution using an ensemble of future climatic scenarios, resulting from the combination of four General Circulation Models, two extreme Representative Concentration Pathways and five 10-years time frames (2030–2070). Our results showed an overall negative impact of climate change on tomato yields (average decrease = 5–10%), which could be reversed by i) the implementation of deficit irrigation strategies based on the restitution of 60–70% of the crop evapotranspiration, ii) the adoption of varieties with longer cycle and iii) the anticipation of 1–2 weeks in transplanting dates. The corresponding irrigation amounts applied are around 360 mm, thus reinforcing that a rational water management could be realized. Our study provides agronomic indications to tomato growers and lays the basis for a bio-economic analysis to support policy makers in charge of promoting the sustainability of the tomato growing systems.

Nutritional and environmental effects on biological nitrogen fixation in soybean: A meta-analysis

Biological N2 fixation (BNF) and mineral soil absorption are complementary N sources for soybean growth. BNF is sensitive to nutrient and environmental conditions, though a comprehensive synthesis of the studies underlying these conclusions is currently lacking. Our objective was to conduct a meta-analysis of nutrient and environmental effects on BFN. Articles reporting manipulative treatments and BNF estimations were compiled, and data and metadata were extracted. N fertilization reduced BNF ∼70% relative to the unfertilized control in greenhouse experiments and ∼44% in field experiments. This effect was higher for vegetative than for reproductive stage applications. Fertilization with other nutrients stimulated BNF relative to the unfertilized treatments. Water stress reduced BNF 40% relative to the unstressed control. The negative impact of water stress was larger when stress was applied at vegetative (-70%) compared to reproductive (-30%) stages. Flooding reduced BNF by 40% relative to the non-flooded control with highest effect when applied during vegetative stage (-82%). Increased temperature reduced BNF nitrogenase activity. Carbon dioxide enrichment has a stimulatory effect on BNF. With the exception of N fertilization, soybean and Rhizobium fitness showed a high positive correlation across nutrients and environmental factors. This work summarizes for the first time the impact and relative response of BNF to different nutrient and environmental factors. Results showed an initial critical stage (i.e. vegetative stage) for BNF that is common to most environmental factors negatively affecting BNF. This suggests that common strategies might exist to increase BNF that are independent of the specific identity of the stressor. Also, the positive correlation between host and Rhizobium fitness suggest that strategies to increase BNF potential are the same that those required to increase crop performance. We observed publication bias for some variables, suggesting that effect sizes might be inflated compared to true effect sizes. The only way to solve this problem is to find venues for publication of no significant results when sound experimental approaches and reasonable statistical power can be proved.

Mathematical Modelling of Crop Water Productivity for Processing Tomato

Crop water productivity models (CWPMs) are of great importance in evaluating different irrigation programs. The mean goal of the study was to evaluate the performance of the Jensen, Minhas, Blank, Stewart and Rao CWPMs in predicting fruit yield of processing tomato. Field experiments were conducted for two consecutive growing seasons. The soil water stress sensitivity indices of the CWPMs were determined using experimental data from the second crop growing season. Yields simulated by the CWPMs were compared with the experimental data for the first season. The sensitivity indices for the crop growth stages were taken into account as appropriate weights of the soil water sensitivity of the vegetative, flowering, yield formation and ripening stages of the processing tomato crop. The results give evidence that processing tomato is much more sensitive to soil water stress during flowering and yield formation stages whereas the adverse impact of water stress on yield is very limited at vegetative stage. The highest modelling efficiency (0.96) between field-measured and simulated yield by the model, the lowest arithmetic mean of errors (0.04), mean absolute deviation (0.07), mean square error (0.02), absolute percentage error (12.76), root mean square error (0.15) and coefficient of residual mass (0.05) were achieved by Minhas model and followed by Rao model based on same parameters of statistical analyses. Both the Minhas and the Rao models with their soil water stress sensitivity indices generated for the different growth stages obtained in this study are recommended for the processing tomato in the sub-humid environments.

Impact of regional tectonic and water stress on the seismicity in Ataturk Dam Basin: southeast of Turkey

The Ataturk Dam (AD) and Hydroelectric Power Plant (HPP), one of the biggest dams in Turkey, is located on a NE-SW axis between Adiyaman and Şanliurfa, in the southeastern part of Turkey. The construction of the AD and HPP began in 1983 and after starting the impoundment in 1990, HPP initiated electric power production in 1992. AD and HPP are located in a tectonically very active region that is, bounded by the East Anatolian Fault Zone (EAFZ) to the northwest, the Bozova Fault (BF) to the southwest and the Kalecik Fault to the southeast. According to instrumental records that have been collected inquiring all available catalogues from 1900 to January 30, 2018, 42 earthquakes were recorded with magnitudes greater than 4.0 in the dam basin and its close surroundings. The scientific community is discussing whether earthquakes may be induced by pressure variations of the water level. When earthquake reports from Turkey’s General Directorate of State Hydraulic Works (DSI) were examined, it was found that quite high seismic activity (1.2 ≤ M ≤ 5.2) had been recorded before the water retention in the basin. DSI, which is responsible for the dams in Turkey, has been following the seismic activity before and after water retention in the big dams since 1973 with its own local seismic network. The focal mechanism solutions of the earthquakes indicate that the tectonics of the region are controlled by right lateral strike-slip fault systems. Although the earthquakes which occurred in the region have been mostly connected with previously defined faults systems, recent earthquakes (2008 and 2017) have not been directly associated with any fault in the region. Thus, the question of whether there is a right lateral strike-slip fault buried in the region is raised. In this paper, we examine the characteristics of the tectonic structures in the region and their effect on the dam basin. We also discuss whether recent seismic series (2008 and 2017) could be connected with reservoir-induced or reservoir-triggered seismicity (RIS or RTS) or/are relevant to directly tectonic structures in a highly seismically active zone. A polygon of 20 km distance from the AD and HPP was selected as the study area. On the other hand, the issue of whether seasonal changes in the water level affect seismic activity in the dam, by comparing it to other examples in the world, are discussed. In conclusion, we propose a model that explains the tectonic structures that cause the seismic activity in the region. The obtained results indicate that the seismicity in the region occurs independently of the water load.

Oxygen and Hydrogen Isotopes in Human Hair and Tap Water: Modeling Relationships in a Modern Mexican Population

This study investigated the relationship between 18O and 2H isotopes in samples of Mexican hair and drinking water. The purpose of this study was twofold: to quantify the relationship between isotopes in Mexican hair and tap water, in order to understand the impact of water stress and differing socioeconomic status on accurate predictions of drinking water; and to determine whether currently existing semimechanistic models can accurately represent the relationship between hair and tap water. This study used a subset of paired samples of human hair (n = 62) and tap water (n = 76). Isotope values in tap water ranged from –11.4‰ to –4.3‰ and –79.1‰ to –22.5‰, and in hair from +9.5‰ to +16.1‰ and –90.8‰ to –53.7‰, for δ18O and δ2H, respectively. The most depleted δ18O and δ2H hair values came from individuals in the state of Morelos. For modern Mexican populations, positive correlations between isotopes in hair and water were not significant, with correlation coefficients r = 0.61 (p = 0.05) and r = 0.60 (p = 0.06) for 18O and 2H, respectively. Error-in-variables regression yielded linear fits that were somewhat better for 2H relative to 18O: δ18Oh = 0.183 [±0.132] δ18Otw + 15.7 [±0.9]‰ (r2 = 0.23); δ2Hh = 0.181 [±0.076] δ2Htw – 64.0 [±3.0]‰ (r2 = 0.34). In short, data from this Mexican population did not exhibit the strong relationships between isotope values of 18O and 2H in tap water and hair that have been characteristic of other populations studied to date. Given the economic stratification of this region and the poor correlation between hair and water samples, the authors considered the possibility that l, the fraction of the diet derived from local sources, and fs, the fraction of nonexchangeable H in keratin that was fixed in vivo, are local rather than global parameters for this population. The authors estimated different values of l and fs for each location. Given the anticipated importance of the nonlocal dietary contribution, they treated the isotopic content of nonlocal food and the offset parameters for predicting isotopes in locally derived food as tuning parameters and compared the results with parameters based on the American supermarket diet. They found that, although O and H isotopes in water and hair maintained similar geographic distributions, O and H isotopes in tap water explained only a small part of the variation observed in hair samples. Compared to the standard American supermarket diet, the Mexican estimates for nonlocal diet and local diet offsets predicted regional distributions of l and fs that cleanly segregated urban areas from rural towns.

Genotypic, Developmental and Environmental Effects on the Rapidity of gs in Wheat: Impacts on Carbon Gain and Water-Use Efficiency.

Stomata are the primary gatekeepers for CO2 uptake for photosynthesis and water loss via transpiration and therefore play a central role in crop performance. Although stomatal conductance (gs) and assimilation rate (A) are often highly correlated, studies have demonstrated an uncoupling between A and gs that can result in sub-optimal physiological processes in dynamic light environments. Wheat (Triticum aestivum L.) is exposed to changes in irradiance due to leaf self-shading, moving clouds and shifting sun angle to which both A and gs respond. However, stomatal responses are generally an order of magnitude slower than photosynthetic responses, leading to non-synchronized A and gs responses that impact CO2 uptake and water use efficiency (iWUE). Here we phenotyped a panel of eight wheat cultivars (estimated to capture 80% of the single nucleotide polymorphism variation in North–West European bread wheat) for differences in the speed of stomatal responses (to changes in light intensity) and photosynthetic performance at different stages of development. The impact of water stress and elevated [CO2] on stomatal kinetics was also examined in a selected cultivar. Significant genotypic variation was reported for the time constant for stomatal opening (Ki, P = 0.038) and the time to reach 95% steady state A (P = 0.045). Slow gs opening responses limited A by ∼10% and slow closure reduced iWUE, with these impacts found to be greatest in cultivars Soissons, Alchemy and Xi19. A decrease in stomatal rapidity (and thus an increase in the limitation of photosynthesis) (P < 0.001) was found during the post-anthesis stage compared to the early booting stage. Reduced water availability triggered stomatal closure and asymmetric stomatal opening and closing responses, while elevated atmospheric [CO2] conditions reduced the time for stomatal opening during a low to high light transition, thus suggesting a major environmental effect on dynamic stomatal kinetics. We discuss these findings in terms of exploiting various traits to develop ideotypes for specific environments, and suggest that intraspecific variation in the rapidity of stomatal responses could provide a potential unexploited breeding target to optimize the physiological responses of wheat to dynamic field conditions.

Changes in yield and nutritive value of red clover (Trifolium pratense L.) and Festulolium (Festulolium braunii (K. Richt) A. Camus) under drought stress

The aim of the research was to assess the impact of water stress on the yield and content of basic nutrients in the biomass of Trifolium pratense and Festulolium braunii cultivated in pure stand and in mixture. A pot experiment was carried out in 2012–2014, at two levels of soil moisture: well-watered and drought stress. The study showed that stress significantly reduced the dry matter yield (DMY), the most in T. pratense, followed by mixture, and F. braunii. The effect of drought stress on the nutritive value was considerable less pronounced than the influence on DMY. No significant influence of water deficit on crude protein, crude fibre and crude ash contents was found, but only on water-soluble carbohydrate and crude fat content in one year of the study. It was found, that under drought stress T. pratense is more suitable for cultivation in the mixture with F. braunii than in pure stand, due to a lower reduction of DMY and no adverse effect of water deficiency on yield quality.

Interactive effect of temperature and water stress on physiological and biochemical processes in soybean.

Drought and heat stress are important abiotic stress restricting plant growth, while the two stresses often occur at the same time in nature and little is known about when these stresses occur in combination. Therefore, attempts were made to understand the impact of water stress imposed under different temperature conditions on photosynthesis, chlorophyll fluorescence, antioxidant enzymes, lipid peroxidation, chlorophyll, proline, free amino acid, epicuticular wax content and seed yield. Soybean genotype EC 538828 was grown under greenhouse conditions at day/night temperatures of 30/22, 34/24, 38/26 and 42/28°C. At each temperature, pots were divided into two sets, one set was unstressed while second was subjected to water stress at reproductive stage (beginning of seed fill). High temperature significantly declined the rate of photosynthesis, stomatal conductance, water use efficiency, Fv/Fm ratio, photochemical quenching, PhiPSII, electron transport rate, ascorbic acid, total free amino acids, chlorophyll content and seed yield. As against this with increase in temperature from 30/22 to 42/28°C intercellular CO2, transpiration rate, vapor pressure deficit, non photochemical quenching, proline content, SOD, POD, APX, GR, MDA and epicuticular wax content were increased. Water stress when imposed at different temperature further aggravated the effects of temperature, and the combination of water stress and high temperature had more detrimental effect.

Ecosystem Productivity and Water Stress in Tropical East Africa: A Case Study of the 2010–2011 Drought

Characterizing the spatiotemporal patterns of ecosystem responses to drought is important in understanding the impact of water stress on tropical ecosystems and projecting future land cover transitions in the East African tropics. Through the analysis of satellite measurements of solar-induced chlorophyll fluorescence (SIF) and the normalized difference vegetation index (NDVI), soil moisture, rainfall, and reanalysis data, here we characterize the 2010–2011 drought in tropical East Africa. The 2010–2011 drought included the consecutive failure of rainy seasons in October–November–December 2010 and March–April–May 2011 and extended further east and south compared with previous regional droughts. During 2010–2011, SIF, a proxy of ecosystem productivity, showed a concomitant decline (~32% lower gross primary productivity, or GPP, based on an empirical SIF–GPP relationship, as compared to the long-term average) with water stress, expressed by lower precipitation and soil moisture. Both SIF and NDVI showed a negative response to drought, and SIF captured the response to soil moisture with a lag of 16 days, even if it had lower spatial resolution and much smaller energy compared with NDVI, suggesting that SIF can also serve as an early indicator of drought in the future. This work demonstrates the unique characteristics of the 2010–2011 East African drought and the ability of SIF and NDVI to track the levels of water stress during the drought.

Evaluating Growth, Yield, and Water Use Efficiency of African and Commercial Ginger Species in South Africa

Ginger species play an important economic role as medicinal plants, food flavourings, and dietary supplements. Products from ginger, including oil and fresh and dried rhizomes can be used to treat malaria, asthma, headaches, and act as anti-inflammatory and anti-microbial agents. The cultivation of wild plant species can alleviate the pressure from harvesting from the wild. Under cultivation, the major constraints on crop yield and quality are water availability and plant nutrition. Therefore, the impact of water stress on commercial and African ginger was assessed in the rain shelter study. Irrigation treatments were based on the maximum allowable depletion (MAD) levels of plant available water in the root zone (T1: 20–25% MAD, the control; T2: 40–45% MAD; T3: 60–65% MAD; T4: 80–85% MAD). As water stress decreased, the plant height and number of stems per plant of both plant species were positively affected. The number of open stomata was higher for well-watered and less stressed treatments in both ginger species. Higher fresh and dry rhizome yields were recorded for commercial ginger at all water treatments as compared to those from African ginger. In general, water use efficiency (WUE) of fresh and dry rhizome yield was higher for commercial ginger as compared to the indigenous African ginger, while moderately stressed treatments generally resulted in the highest WUE for both species.

Fortified fertilizer application in wheat (Triticum aestivum L.) grown under water stress condition

Abstract Water stress is a major threat against wheat growth. The effects of induced stress can be reduced after by fortified fertilizer treated by Plant Growth Promoting Bacteria (PGPB). With the objective to combat the water stress, two different experiments under net house and field condition were conducted. Three different states of fertilizer [F0: Control (no fertilizer application); F1: PGPB-coated fertilizer (urea and phosphorous) &F2: uncoated fertilizer (urea and phosphorous)]. In a pot experiment, wheat plants were applied fertilizer in raised and well-watered (60 percent of field capacity) and water stressed (40 percent of field capacity) conditions in soil filled pots. In experiment-II (field study), similar treatments of fertilizer were revised, but well-watered and water stress treatments/plots were irrigated for 60 seconds and 30 seconds respectively. At maturity plants were harvested and various morphological (number of tillers/plant, number of spikelet/spike, number of grains/spike, weight of grains, biological yield, economic yield and harvest index) and biochemical parameters (leaf nitrogen, phosphorous & potassium contents) of crop were recorded. Leaf chlorophyll and relative water contents of crop were also measured 60 days after sowing. In this study, it was demonstrated that the water stress adversely affected all the above mentioned parameters. The PGPB coated fertilizer application in wheat significantly increased (p<0.01 for pot and p<0.05 for field study) morphological and biochemical parameters in the presence and absence of water stress both under net house and field conditions. We can conclude from these findings that application of PGPB coated fertilizer is valuable strategy to mitigate the water stress impact on wheat with improved yield. Keywords: Coated fertilizer; Un-coated fertilizer; PGPB; Chlorophyll; Harvest inde http://dx.doi.org/10.19045/bspab.2019.80037

Grapevine trunk diseases under thermal and water stresses.

Heat and water stresses, individually or combined, affect both the plant (development, physiology, and production) and the pathogens (growth, morphology, dissemination, distribution, and virulence). The grapevine response to combined abiotic and biotic stresses is complex and cannot be inferred from the response to each single stress. Several factors might impact the response and the recovery of the grapevine, such as the intensity, duration, and timing of the stresses. In the heat/water stress-GTDs-grapevine interaction, the nature of the pathogens, and the host, i.e., the nature of the rootstock, the cultivar and the clone, has a great importance. This review highlights the lack of studies investigating the response to combined stresses, in particular molecular studies, and the misreading of the relationship between rootstock and scion in the relationship GTDs/abiotic stresses. Grapevine trunk diseases (GTDs) are one of the biggest threats to vineyard sustainability in the next 30years. Although many treatments and practices are used to manage GTDs, there has been an increase in the prevalence of these diseases due to several factors such as vineyard intensification, aging vineyards, or nursery practices. The ban of efficient treatments, i.e., sodium arsenite, carbendazim, and benomyl, in the early 2000s may be partly responsible for the fast spread of these diseases. However, GTD-associated fungi can act as endophytes for several years on, or inside the vine until the appearance of the first symptoms. This prompted several researchers to hypothesise that abiotic conditions, especially thermal and water stresses, were involved in the initiation of GTD symptoms. Unfortunately, the frequency of these abiotic conditions occurring is likely to increase according to the recent consensus scenario of climate change, especially in wine-growing areas. In this article, following a review on the impact of combined thermal and water stresses on grapevine physiology, we will examine (1) how this combination of stresses might influence the lifestyle of GTD pathogens, (2) learnings from grapevine field experiments and modelling aiming at studying biotic and abiotic stresses, and (3) what mechanistic concepts can be used to explain how these stresses might affect the grapevine plant status.

Moderate plant water stress improves larval development, and impacts immunity and gut microbiota of a specialist herbivore.

While host plant drought is generally viewed as a negative phenomenon, its impact on insect herbivores can vary largely depending on the species involved and on the intensity of the drought. Extreme drought killing host plants can clearly reduce herbivore fitness, but the impact of moderate host plant water stress on insect herbivores can vary, and may even be beneficial. The populations of the Finnish Glanville fritillary butterfly (Melitaea cinxia) have faced reduced precipitation in recent years, with impacts even on population dynamics. Whether the negative effects of low precipitation are solely due to extreme desiccation killing the host plant or whether moderate drought reduces plant quality for the larvae remains unknown. We assessed the performance of larvae fed on moderately water-stressed Plantago lanceolata in terms of growth, survival, and immune response, and additionally were interested to assess whether the gut microbial composition of the larvae changed due to modification of the host plant. We found that larvae fed on water-stressed plants had increased growth, with no impact on survival, up-regulated the expression of one candidate immune gene (pelle), and had a more heterogeneous bacterial community and a shifted fungal community in the gut. Most of the measured traits showed considerable variation due to family structure. Our data suggest that in temperate regions moderate host plant water stress can positively shape resource acquisition of this specialized insect herbivore, potentially by increasing nutrient accessibility or concentration. Potentially, the better larval performance may be mediated by a shift of the microbiota on water-stressed plants, calling for further research especially on the understudied gut fungal community.

Yield Performance of Barley Hybrids (Hordeum vulgare L.) under Drought stress and non-stressed Conditions

This study was carried out at the experiment field, Kalar Technical Institute, Garmian Region in two growing seasons of 2016-2017 and 2017-2018 in order to evaluate the growth and yield potentials of barley under water stressed using hybrids as a source of wide range of genotypic variations. Therefore, five F2 barley hybrids (Hordeum vulgare L.) were screened for grain yield, biomass dry matter, plant height and harvest index under irrigated and drought conditions. Results showed that there was no effect of drought on grain yield (P&gt;0.05) in 2017, while significantly reduced yield in 2018 and across-year mean (P-2 (3//14) under irrigated condition, and 267.8 (3//5) to 302.3 g m-2 (3//4) under unirrigated condition (P=0.001), biomass dry matter was ranged from 1099.1 (3//1) to 1370.5 g m-2 (3//14) under irrigated condition, and 892.6 (3//1) to 1153.9 g m-2 (3//14) under unirrigated condition (P=0.05), and harvest index were from 25.1 (3//14) to 28.0 (3//1) under irrigated conditions, and 25.9 (3//14) to 31.2 (3//1) under unirrigated conditions (P=0.04). Regression analysis, averaging over years, showed a positive relationship between grain yield and biomass under irrigated (R2=0.76; P=0.05), despite that, any positive relation was not found under unirrigated conditions (R2=0.43; P=0.23) due to post-anthesis drought stress. A strong relationship was also found between plant height and biomass dry matter under both irrigated (R2=0.89; P=0.02) and unirrigated (R2=0.97; P=0.003) conditions due to the high contribution of plant height in increasing plant biomass. It is concluded that genotypes had different response to drought due to their genetic diversity, and relatively low impact of water stress was appeared on growth and grain yield of barley in this semi-arid region compared to worldwide expected range of yield reduction.

Effects of elevated CO2 and water stress on population growth of the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), on sweet pepper under environmentally controlled conditions

Weather events such as drought and elevated atmospheric CO2 are likely to interact with plants in numerous ways with diverse mechanisms. As a consequence of changes in quality of plants, the performance parameters and population dynamics of herbivores are expected to be influenced. In this study, a split-plot design was used to evaluate the interaction of elevated CO2 and irrigation regime on population growth of the two-spotted spider mite, Tetranychus urticae Koch (Tetranychidae: Tetranychini), feeding on sweet pepper, Capsicum annum L. (Solanaceae), in environmentally controlled chambers. Results showed that exposure to elevated CO2 significantly increased the C/N ratio in sweet pepper plants. Except in case of the adult stage, elevated CO2 did not significantly increase the population density of other developmental stages or the overall population of T. urticae. However, water stress by itself and in combination with elevated CO2 had significant effects on per capita population growth rate (r) and population density of mites. Maximum growth rate and population density of mites were observed at a combination of elevated CO2 and intermediate water stress. Further studies, especially in field conditions, investigating the impact of elevated CO2 and water stress on population size and growth of herbivores in other plant species may contribute to a greater understanding of the implications of global climate change on future crop productivity.

Assessment of algal biofuel resource potential in the United States with consideration of regional water stress

Algae is a promising feedstock for biofuels. Because scaling up the production of algae-based biofuels consumes a significant amount of water, it is important to consider the impact it has on water stress. This study evaluates the potential for algae-derived biofuel production in the United States (US) and considers regional water stress. We used the Biomass Assessment Tool (BAT) to identify potential sites in the US that meet land, biomass productivity, and CO2 co-locating criteria. We quantify the water stress impacts of algal biofuel production in terms of water scarcity footprint using water consumption from BAT, and the water stress indicator from Available Water Remaining for the US (AWARE-US) system. We assess long-term (20 billion gal per year [BGY]) and near-term (5 BGY by 2030) renewable diesel (RD) production targets. To select suitable algae sites, we consider biomass yield and water use with and without water stress constraints. We found that ranking sites based on biomass yield results in a high water stress impact (24.5 × 103 US equivalent BGY [BGYe]) for the long-term RD target. If we instead rank sites on water use efficiency, water consumption decreases on average by 62%, with an average reduction in biomass yield of 25%. To reconcile tradeoffs between biomass yield and water stress impacts, water stress indicator (AWARE-US) that represents relative water availability by region can be applied while considering biomass yield. This strategy removes sites located in water-stressed areas and keeps high-productivity sites. For the long-term RD target, this reduces water stress impacts by 55% (13.8 BGYe) without lowering yield or 97% (24.2 BGYe) with moderately lower (4%) yield, compared to the sites ranked by biomass yield alone. The results demonstrate that incorporating water stress into energy-scale algae biofuel production planning is key to achieving synergies between biofuel yield and fresh water stress impacts.

Automation for Water and Nitrogen Deficit Stress Detection in Soilless Tomato Crops Based on Spectral Indices

Water and nitrogen deficit stress are some of the most important growth limiting factors in crop production. Several methods have been used to quantify the impact of water and nitrogen deficit stress on plant physiology. However, by performing machine learning with hyperspectral sensor data, crop physiology management systems are integrated into real artificial intelligence systems, providing richer recommendations and insights into implementing appropriate irrigation and environment control management strategies. In this study, the Classification Tree model was used to group complex hyperspectral datasets in order to provide remote visual results about plant water and nitrogen deficit stress. Soilless tomato crops are grown under varying water and nitrogen regimes. The model that we developed was trained using 75% of the total sample dataset, while the rest (25%) of the data were used to validate the model. The results showed that the combination of MSAVI, mrNDVI, and PRI had the potential to determine water and nitrogen deficit stress with 89.6% and 91.4% classification accuracy values for the training and testing samples, respectively. The results of the current study are promising for developing control strategies for sustainable greenhouse production.