Impact Of Water Stress Research Articles

Photosynthetic responses to soil water stress in summer in two Japanese urban landscape tree species (Ginkgo biloba and Prunus yedoensis): effects of pruning mulch and irrigation management

Stomatal regulation involves beneficial effects of pruning mulch and irrigation on leaf photosynthesis in Prunus yedoensis and Ginkgo biloba under moderate drought. G. biloba showed conservative water use under drought. Leaf photosynthesis is highly sensitive to soil water stress via stomatal and/or biochemical responses, which markedly suppress the growth of landscape trees. Effective irrigation management to maintain leaf photosynthesis and information on species-specific photosynthetic responses to soil water stress are essential for the sustainable management of landscape trees in Japan, in which summer drought often occurs. In order to investigate effective irrigation management, we used plants with moderate soil water stress as controls, and examined the effects of daily irrigation and pruning mulch on leaf photosynthesis in container-grown Ginkgo biloba and Prunus yedoensis, which are the first and second main tall roadside trees in Japan. Stomatal conductance was significantly increased by pruning mulch and daily irrigation, with similar increases in leaf photosynthesis being observed in P. yedoensis and G. biloba. In order to obtain information on species-specific photosynthetic responses to soil water stress, we compared the responses of leaf photosynthesis and leaf water status to reductions in soil water content (SWC) between the two species. G. biloba maintained a constant leaf water potential, leaf water content, maximum carboxylation rate, and electron transport rate with reductions in SWC, whereas reductions were observed in P. yedoensis. We concluded that pruning mulch and irrigation effectively offset the negative impact of moderate water stress on leaf photosynthesis in summer in P. yedoensis and G. biloba via stomatal regulation, and also that G. biloba maintained its photosynthetic biochemistry and leaf water status better than P. yedoensis under severe water stress.

Comparison of Spring Maize Root Water Uptake Models Under Water and Salinity Stress Validated with Field Experiment Data

AbstractCrop root water uptake has strong correlations with transpiration and yield. An accurate prediction of crop root water uptake can benefit understanding of the law of transpiration and soil water movement. Under water and salinity stress, maize root water uptake will decrease because of soil water pressure and osmotic head. Usually such reduction of water uptake can be expressed by models such as the additive model and the multiplicative model. Based on a field irrigation experiment, we calculated spring maize root water uptake in this study by setting different combinations of water amount and saline concentration based on the water balance method. One additive model and four multiplicative models of root water uptake were calibrated and verified in order to simulate the impact of water and salt stress on root water uptake. The result shows that multiplicative models are better than the additive model in simulating the experimental data from different treatments. Therefore, the multiplicative model is recommended as the optimal model of root water uptake of spring maize under water and salinity stress in the arid region of north‐west China. Copyright © 2015 John Wiley & Sons, Ltd.

Differential Activity and Expression Profile of Antioxidant Enzymes and Physiological Changes in Wheat (Triticum aestivum L.) Under Drought.

Wheat crop may experience water deficit at crucial stages during its life cycle, which induces oxidative stress in the plants. The antioxidant status of the plant plays an important role in providing tolerance against the water stress. The objective of this study was to investigate the impact of water stress on physiological traits, antioxidant activity and transcript profile of antioxidant enzyme related genes in four wheat genotypes (C306, AKAW3717, HD2687, PBW343) at three crucial stages of plants under medium (75% of field capacity) and severe stress (45% of field capacity) in pots. Drought was applied by withholding water for 10 days at a particular growth stage viz. tillering, anthesis and 15 days after anthesis (15DAA). For physiological traits, a highly significant effect of water stress at a particular stage and genotypic variations for resistance to drought tolerance was observed. Under severe water stress, the malondialdehyde (MDA) content increased while the relative water content (RWC) and chlorophyll index decreased significantly in all the genotypes. The drought susceptibility index (DSI) of the genotypes varied from 0.18 to 1.9. The drought treatment at the tillering and anthesis stages was found more sensitive in terms of reduction in thousand grain weight (TGW) and grain yield. Antioxidant enzyme activities [superoxide dismutase (SOD) and peroxidase (POX)] increased with the decrease in osmotic potential in drought tolerant genotypes C306 and AKAW3717. Moreover, the transcript profile of Mn-SOD upregulated significantly and was consistent with the trend of the variation in SOD activity, which suggests that Mn-SOD might play an important role in drought tolerance.

Adaptation strategies for water supply management in a drought prone Mediterranean river basin: Application of outranking method

The regional water allocation planning is one of those complex decision problems where holistic approach to water supply management considering different criteria would be valuable. However, multi-criteria decision making with diverse indicators measured on different scales and uncertainty levels is difficult to solve. Objective of this paper is to develop scenarios for the future imbalances in water supply and demand for a water stressed Mediterranean area of Northern Spain (Tarragona) and to test the applicability and suitability of an outranking method ELECTRE-III-H for evaluating sectoral water allocation policies. This study is focused on the use of alternative water supply scenarios to fulfil the demand of water from three major sectors: domestic, industrial and agricultural. A detail scenario planning for regional water demand and supply has been discussed. For each future scenario of climate change, the goal is to obtain a ranking of a set of possible actions with regards to different types of indicators (costs, water stress and environmental impact). The analytical method used is based on outranking models for decision aid with hierarchical structures of criteria and ranking alternatives using partial preorders based on pairwise preference relations. We compare several adaptation measures including alternative water sources (reclaimed water and desalination); inter basin water transfer and sectoral demand management coming from industry, agriculture and domestic sectors and tested the sustainability of management actions for different climate change scenarios. Results have shown use of alternative water resources as the most reliable alternative with medium reclaimed water reuse in industry and agriculture and low to medium use of desalination water in domestic and industrial sectors as the best alternative. The proposed method has several advantages such as the management of heterogeneous scales of measurement without requiring any artificial transformation and the management of uncertainty by means of comparisons at a qualitative level in terms of the decision maker preferences.

Comparison of canopy temperature-based water stress indices for maize

Infrared thermal radiometers (IRTs) are an affordable tool for researchers to monitor canopy temperature. In this maize experiment, six treatments of regulated deficit irrigation levels were evaluated. The main objective was to evaluate these six treatments in terms of six indices (three previously proposed and three introduced in this study) used to quantify water stress. Three are point-in-time indices where one daily reading is assumed representative of the day (Crop Water Stress Index – CWSI, Degrees Above Non-Stressed – DANS, Degrees Above Canopy Threshold – DACT) and three integrate the cumulative impact of water stress over time (Time Temperature Threshold – TTT, Integrated Degrees Above Non-Stressed – IDANS, Integrated Degrees Above Canopy Threshold – IDACT). Canopy temperature was highly correlated with leaf water potential (R2=0.895). To avoid potential bias, the lowest observation from the non-stressed treatment was chosen as the baseline for DANS and IDANS indices. Early afternoon temperatures showed the most divergence and thus this is the ideal time to obtain spot index values. Canopy temperatures and stress indices were responsive to evapotranspiration-based irrigation treatments. DANS and DACT were highly correlated with CWSI above the corn threshold 28°C used in the TTT method, and all indices showed linear relationship with soil water deficit at high temperatures. Recommendations are given to consider soils with high water-holding capacity when choosing a site for non-stressed reference crops used in the DANS method. The DACT may be the most convenient index, as all it requires is a single canopy temperature measurement yet has strong relationships with other indices and crop water measurements.

Identifying the Impact of Temperature and Water Stress on Growth and Yield Parameters of Chilli (Capsicum annuum L.)

The effect of climate change on global food security has assumed a frightening dimension in developing nations. The need for efficient management to cope with the effect of climate change became imperative. The main aim of this research is to compare the growth and yield parameters of Chilli when it subjected to temperature and water stress. Experiments were conducted on the growing seasons of 2010 and 2011 at the Open University Sri Lanka Agricultural field located at Nawala, Nugegoda using Chilli Varity MI-2 in temperature regulated polytunnels. Split plot experiment based on Completely Randomized Design with 10 replicates was applied as an experimental design. Main plot included two different wetting applications (No water stress-at field capacity level and water stress at 50 % depletion from the field capacity level) and sub plots contained 3 different temperature regimes (34 °C, 32 °C temperature and ambient temperature). According to the results the temperature stress has especially affected the plant height, branches, canopy diameter and number of fruit weight at 0.01 probability levels. Further temperature stress showed significant effect at 0.05 probability level on transplant success, fruit diameter and number of fruits per plant. According to the yield parameters it was observed that interaction effect of the stresses of temperature and water had higher significant impact on growth and yield of Chilli. Yield reduction of Chilli due to temperature stress can be overcome by providing water at field capacity level of the soil moisture during growing period. DOI: http://dx.doi.org/10.4038/ouslj.v7i0.7306 OUSL Journal Vol.7 2014: 25-42

Growing Algae for Biodiesel on Direct Sunlight or Sugars: A Comparative Life Cycle Assessment

Growing heterotrophic algae in reactors with sugar as the energy and carbon source rather than sunlight and carbon dioxide is an approach being commercialized today. However, the full environmental impacts of this fuel pathway have not been explored. The objective of this analysis was to compare the life cycle impacts of algal biodiesel produced heterotrophically to a phototrophic pathway featuring algae grown in ponds. A third, hybrid approach utilizing algae capable of both phototrophy and heterotrophy was also explored. Sugar beet and sugarcane were examined as feedstocks for the heterotrophic process. The results indicate that a reduction in the global warming potential (GWP) and an improvement in the net energy ratio (NER) for algal biodiesel could be possible for the heterotrophic and hybrid pathways relative to the phototrophic, but only if reactor cultivation can be performed efficiently and with sugarcane as the feedstock. For example, the NER varies from 0.6 to 1.6 for the heterotrophic pathway, depending on reactor performance, compared to 1.3 for the phototrophic pathway. Sugar crops used as feedstocks for heterotrophic cultivation present concerns about land constraints that are less of an issue for the phototrophic pathway. No pathway presented a clear advantage for the water stress impact metric.

膜統合型システム（IMS）による中国の排水再利用の実際

Water stress, regulation and environmental impact have been driving the need for waste water reuse systems in China in recent years. Especially for industrial activity in water stressed regions, the Chinese government is imposing stringent restrictions to encourage industries to treat and reuse their waste waters. Integrated Membrane Systems (IMS) system is generally used for industrial waste water reuse in China. Some case studies for industrial waste water reuse in China are shown in this paper. These case studies demonstrate the reliable and long term operation of integrated UF+RO operation in commercial cases with challenging water quality requirements, which support the continued development of IMS operations for industrial wastewater reuse applications.

Changes in henna (Lawsonia inermis L.) morphological traits under different deficit irrigations in the southern Tunisia

Henna plant belongs to continental oases where water shortage constitutes the essential limiting factors of its agricultural production. Lawsonia inermis L. (Lytraceae) is often exposed to severe drought stress in Gabes; a Tunisian arid region. The present study was carried out to evaluate the impact of water stress on the morphology of Tunisian henna plants. Thus, an experiment of four months was carried out under greenhouse at the Institute of Arid Region in Medenine, Tunisia. Henna was exposed to three different irrigation regimes, whereby the plants where irrigated to field capacity (control, T0), 50% of the control (moderate stress, T1) and 25% of the control (severe deficit irrigation, T2). Results showed that, leaf area (LA), leaf number and stem length of henna, decreased in response to the studied stress. The effect of water stress was clearly observed on those parameters. Moderate drought (T1) did not damage henna morphology, and the plants grew better than without water limitation (T0). Furthermore, the water stress-typical responses were shown as time and severity dependent in all the measured parameters. Indeed, lowest water availability treatment (T2) induced significant decrease in total number of leaves, as well as reductions in LA. Under this severe water stress (T2); LA was reduced by 65.79%, compared to control, at 60 days after the initiation of the bioassay. Stem length decreased significantly in the most severe water stress, this reduction was about 44%. Globally, we conclude that henna plant growth decreased progressively to long-term water limitation.

Conservatives and Gamblers: Interpreting plant functional response to water stress in terms of a single indicator

Water availability has a decisive impact on plant growth, survival and distribution. Climate change is expected to alter both the amount and variability of precipitation. To predict and understand plant responses to water stress, efficient and robust mechanisms for describing their functional responses to water availability are needed. However, most ecohydrological processes and models which take into account these responses are inherently complex, difficult to understand and require large amounts of data. We develop a novel straightforward approach and hypothesize that: (1) Plants exhibit two archetypical response patterns under water stress, one typical to slow-growing plants and one typical to fast-growing ones, with most plants being situated between these two. (2) Differences within and between these functional types can be adequately described by a single parameter - the threshold of relative soil water content - at which plants reduce their transpiration in response to water stress. This indicator is straightforward and relies on data which is relatively easy to measure. Its effect has been previously described and it is already used in several models to simulate the effect of water stress on plants. In our approach, we combine this indicator with a description of reactions patterns. This combination provides a general and efficient way of classifying plant responses and allows the assessment of the impact of water stress on a wide variety of plants. Due to its simplicity, our approach offers the opportunity to include water relations of plants in a larger set of models and descriptions than it is possible with more complex ecohydrological descriptions. It also can be used to explain biodiversity in fluctuating environments.

Impact of cyclic water stress on growth, physiological responses and yield of rice (Oryza sativa L.) grown in tropical environment

A series of water stress cycles [5, 10, 15, 20, 25 and 30 days of irrigation intervel including control flooded (CF), control saturated (CS)] were exposed to investigate the impact of cyclic water stress on growth, physiological responses and yield of a famous Malaysian rice variety, MR220. The study also aimed to determine optimum irrigation schedule for better production of rice. It was observed that grain yield, total biomass, filled spikelet, 1000 grain weight, total panicle, tillers mortality, plant height and number of tillers per plant reduces with increased duration of water stress cycles. Grain yield was higher both in CF and CS condition and those are statistically identical to 5 days of stress cycle or irrigation intervel. The present experiment shows that growth performance and physiological activities of rice differ marginally for 5 days of irrigation difference, exceding that time would reduce yield significantly. The study also showed that proline accumulation and malondialdehyde (MDA) contents in levels increased with increasing duration of water stress cycle. Depending on the findings of the present, it can be stated that rice variety MR220 do not require flooding irrigation and irrigation cycle of 5 days interval is more apprapriate to increase water use and higher yield of rice

Isoprene emissions from downy oak under water limitation during an entire growing season: what cost for growth?

Increases in the production of terpene- and phenolic-like compounds in plant species under abiotic stress conditions have been interpreted in physiological studies as a supplementary defense system due to their capacity to limit cell oxidation. From an ecological perspective however, these increases are only expected to confer competitive advantages if they do not imply a significant cost for the plant, that is, growth reduction. We investigated shifts of isoprene emissions, and to a lesser extent phenolic compound concentration, of Quercus pubescens Willd. from early leaf development to leaf senescence under optimal watering (control: C), mild and severe water stress (MS, SS). The impact of water stress was concomitantly assessed on plant physiological (chlorophyll fluorescence, stomatal conductance, net photosynthesis, water potential) functional (relative leaf water content, leaf mass per area ratio) and growth (aerial and root biomass) traits. Growth changes allowed to estimate the eventual costs related to the production of isoprene and phenolics. The total phenolic content was not modified under water stress whereas isoprene emissions were promoted under MS over the entire growing cycle despite the decline of Pn by 35%. Under SS, isoprene emissions remained similar to C all over the study despite the decline of Pn by 47% and were thereby clearly uncoupled to Pn leading to an overestimation of the isoprene emission factor by 44%. Under SS, maintenance of isoprene emissions and phenolic compound concentration resulted in very significant costs for the plants as growth rates were very significantly reduced. Under MS, increases of isoprene emission and maintenance of phenolic compound concentration resulted in moderate growth reduction. Hence, it is likely that investment in isoprene emissions confers Q. pubescens an important competitive advantage during moderate but not severe periods of water scarcity. Consequences of this response for air quality in North Mediterranean areas are also discussed.

Sensing Nitrogen Requirements forIrrigated and Rainfed Cotton

Abstract. Crop canopy sensor-based nitrogen (N) recommendations have been established for grain crops including corn and wheat, but less information exists for using these sensors in cotton. Further, little is known about the impact of crop water stress on sensor-based recommendations. To address these problems, a field experiment was conducted in 2010-2012 at the University of Missouri Fisher Delta Research Center to investigate the performance of crop canopy sensors and the timing of sensor data collection for both irrigated and rainfed cotton receiving different N rates and timings of N application. Eleven N treatments were included, with total N ranging from 0 to 134 kg ha-1 and application timings from preplant to 10 days after first flower. A data collection platform including sensors for visible and near-infrared canopy reflectance, crop height, and canopy temperature was driven through the plots once preflower and once postflower each season. While growing degree days indicated that air temperatures were similar all three years, rainfall varied, which is typical for the Mid-South region. Which in-season (e.g., sensor readings) and end-of-season (e.g., yield and quality) factors were statistically significant varied considerably among years. For irrigation: normalized difference vegetation index (NDVI) ‑ calculated from the reflectance measurements, height, temperature, yield, turnout, micronaire, length, uniformity, and strength all exhibited significant differences, but none were consistent over all three years of the study. Similarly, NDVI, height, yield, turnout, and micronaire exhibited significant N-treatment effects but none were consistent over all three years. The lack of N response for some of the sensor data was affected by the fact that not all of the N treatments had been applied when the sensor data were collected, especially for the preflower readings. However, the lack of significant irrigation-by-N treatment interactions suggests that the same N relationship exists in water-stressed and non-stressed cotton, which will greatly improve the utility of the resulting N recommendations. When the data from all three years were combined in a correlation analysis, only correlations between yield and both postflower NDVI and height and between uniformity and both postflower NDVI and temperature had |r| > 0.5. However, as more data are collected and additional variables are investigated the relationship between in-season and end-of-season observations should improve. While these data demonstrate that in-season sensor measurements can detect differences in water and N status for cotton that result in end-of-season differences in yield and fiber properties, further research, including evaluation of additional sensors, is needed before real-time N-application algorithms that account for the effects of drought stress can be established.

Effect of Irrigating with Slightly Acidic Electrolyzed Water on LettucePhotosynthesis under Mild Water Stress

Abstract. To investigate if slightly acidic electrolyzed water (SAEW) can alleviate mild water stress on plants, we compared the influence of irrigating with SAEW and tap water on growth, chlorophyll content, and photosynthetic characteristics in lettuce (Lactuca sativa L. cv. Italy lettuce) under mild water stress. In this study, lettuce was irrigated with SAEW and tap water at different times. The available chlorine concentration, pH, and oxidation-reduction potential (ORP) of SAEW were 27.75 mg/L, 5.0 and 819 mV, respectively. Both SAEW treatments (long time watering before water stress and re-watering after water stress) showed increases in stem diameter, root length, and biomass accumulation in lettuce when compared with tap water treatments, which meant that inhibition in plant growth was greatly alleviated. Besides, lettuce treated with SAEW maintained a relatively high gas exchange and significantly increased water use efficiency (WUE), showing the better adaptation to water stress. The quality of lettuce was also investigated, and the vitamin C (VC) content in lettuce was not evidently different between these two treatments. Therefore, irrigation with SAEW on lettuce may enhance the photosynthetic efficiency and alleviate the impact of water stress on lettuce growth without destroying VC content of lettuce. Taking the disinfection effect of SAEW into consideration, this work provided a feasible way to lower the risks of pesticide residues in lettuce and alleviate the water stress at the same time.

Soybean is less impacted by water stress using Bradyrhizobium japonicum and thuricin-17 from Bacillus thuringiensis

Climate change is forecasted to induce more drought stress events. Water scarcity is already the most limiting abiotic stress for crop production. With higher food demand, there is a need for sustainable solutions to cope with the loss of productivity due to water stress. It is known that plant growth-promoting rhizobacteria (PGPR) can colonize plant roots and increase plant growth. However, there is actually no sustainable method to decrease the impact of water stress. Therefore, we hypothesized that an application of thuricin-17, a molecule produced by the PGPR Bacillus thuringiensis, could enhance soybean tolerance to water stress. We grew soybean plants for 1 month in growth chambers in order to evaluate their response to thuricin-17 root application under drought, in association with the inoculation of N2-fixing Bradyrhizobium japonicum. We measured traits reflecting root architecture: number of tips, root diameter, root length, number of nodules; water fluxes: water potential, stomatal conductance; carbon nutrition: leaf area, photosynthetic rate, biomass and carbon partitioning; nitrogen nutrition: nitrogen partitioning and hormone signalling: abscisic acid concentration during the vegetative growth period. Our results show that thuricin-17 application under water stress increased plant biomass by 17 %, thus masking drought impact. This effect is due to modifications of below-ground structures, with 37 % increase of root and 55 % increase of nodule biomass, and to slight increases of leaf area and photosynthetic rate. We also observed that application of thuricin-17 induced a 30 % increase of root abscisic acid, an increase of root length and of leaf water potential. Finally, thuricin-17 induced an activation of nodule formation by 40 %, a partial restoration of nodule-specific activity, nodule growth and consequently, an increase by 17 % of the total nitrogen amount in the plant. Overall, our findings reveal a new method to decrease the negative impact of water stress. Results also demonstrate that the plant restored an adequate water and N balance by changing its root structure.

Influence of Water Stress on Root Development of Opuntia ficus-indica and O. robusta

The study aimed at determining the root dynamics of cactus pear following a soil-water gradient and to characterize some root types of the species O. ficus-indica (L.) Miller (cultivar Morado–green cladode) and O. robusta Wendl. (cultivar Monterey–blue cladode). One-year-old plants, planted in pots (210 mm diameter and 550 mm deep soil) and grown in the greenhouse at day/night temperatures of 25–30/15–18°C, were investigated. The water treatments applied were 0–25%, 25–50%, 50–75%, and 75–100% depletion of plant available soil water. The impact of water stress was quandtified in terms of root and cladode mass, root length, water-use efficiency (WUE: dry weight gain for roots and/or cladodes per unit water used–evapotranspiration), and water needed to fill up a cladode. Root mass decreased and root length increased significantly for both species with water stress. The root mass and length of O. ficus-indica were for all water treatments higher (p <0.05) than that of O. robusta. By contrast, the root length/root mass ratio was higher4 for O. robusta than O. ficus-indica. Roots of O. ficus-indica and O. robusta, on average for all water treatments, comprised only 8.6% and 8.9% of the total plant biomass (dry weight), respectively. Root WUE decreased significantly (p <0.05) with water stress for both species. A water application of only 12 to 14 mm is needed to fill up the cladodes of the two Opuntia species with water stress. Given water shortages on arid lands and climate change, more development attention needs to be given to Opuntia species.

Combined effects of defoliation and water stress on pine growth and non-structural carbohydrates.

Climate change is expected to increase both pest insect damage and the occurrence of severe drought. There is therefore a need to better understand the combined effects of biotic and abiotic damage on tree growth in order to predict the multi-factorial effect of climate change on forest ecosystem productivity. Indeed, the effect of stress interactions on tree growth is an increasingly important topic that greatly lacks experiments and data, and it is unlikely that the impact of combined stresses can be extrapolated from the outcomes of studies that focused on a single stress. We developed an original manipulative study under real field conditions where we applied artificial defoliation and induced water stress on 10-year-old (∼10 m high) maritime pine trees (Pinus pinaster Ait.). Tree response to combined stresses was quantitatively assessed following tree secondary growth and carbohydrate pools. Such a design allowed us to address the crucial question of combined stresses on trees under stand conditions, sharing soil supplies with neighboring trees. Our initial hypotheses were that (i) moderate defoliation can limit the impact of water stress on tree growth through reduced transpiration demand by a tree canopy partly defoliated and that (ii) defoliation results in reduced non-structural carbohydrate (NSC) pools, affecting tree tolerance to drought. Our results showed additive effects of defoliation and water stress on tree growth and contradict our initial hypothesis. Indeed, under stand conditions, we found that partial defoliation does not limit the impact of water stress through reduced transpiration. Our study also highlighted that, even if NSC in all organs were affected by defoliation, tree response to water stress was not triggered. We found that stem NSC were maintained or increased during the entire growing season, supporting literature-based hypotheses such as an active maintenance of the hydraulic system or another limiting resource for tree growth under defoliation. We also observed a significant decrease in root carbohydrates, which suggests a shift in the root carbon balance under defoliation. The decrease in carbohydrate supply under defoliation may not counterbalance the carbon use for mineral and water uptakes or a translocation to other tissues.

Response of plants to water stress

Water stress adversely impacts many aspects of the physiology of plants, especially photosynthetic capacity. If the stress is prolonged, plant growth, and productivity are severely diminished. Plants have evolved complex physiological and biochemical adaptations to adjust and adapt to a variety of environmental stresses. The molecular and physiological mechanisms associated with water-stress tolerance and water-use efficiency have been extensively studied. The systems that regulate plant adaptation to water stress through a sophisticated regulatory network are the subject of the current review. Molecular mechanisms that plants use to increase stress tolerance, maintain appropriate hormone homeostasis and responses and prevent excess light damage, are also discussed. An understanding of how these systems are regulated and ameliorate the impact of water stress on plant productivity will provide the information needed to improve plant stress tolerance using biotechnology, while maintaining the yield and quality of crops.

Effects of Water Stress and Potassium on Quantity Traits of Two Varieties of Mung Bean (Vigna Radiata L.)

ABSTRACT Water stress is known as the major threat to reduced growth and yield of plants in arid and semi-arid regions. Potassium is one of the indicators of plant responses to water stress. To evaluate the impact of water stress and levels of potassium on yield and yield components of two varieties of mung bean (Vigna radiata) (promising lines VC6172 and Indian), an experiment in the form of split factorial, based on randomized complete block design with three replicates was conducted in 2011, at the research farm of Safi-Abad Dezfool, Iran (latitude 32°16’ N, longitude 48°26’ E and altitude 82.9 m above sea level) .Water stress in three levels: irrigation at 120 (no stress), 180 (moderate stress) and 240 (severe stress) mm evaporation from pan, were allocated to the main plots and potassium fertilizer at three levels (0, 90, 180 kg /ha) and two varieties of mung bean (promising line VC6172 and Indian) were allotted to the sub-plots. Results showed that water stress and potassium fertilizer significantly affect all traits. The highest grain yield (2093 kg /ha) was obtained from no stress treatment in the case of 180 kg /ha potassium. Total dry matter, number of pods and grain yield, were significantly different between the two varieties. The interaction between fertilizer and variety, on dry matter and grain yield and the interaction between irrigation and variety, on dry matter were significant. We conclude that use of potassium fertilizer can reduce the adverse effects of water stress.

Development and reproduction of spider mites Tetranychus turkestani (Acari: Tetranychidae) under water deficit condition in soybeans

One of the major pests of soybeans in Bulgaria is the spider mite Tetranychus turkestani Ug et Nik (Acari: Tetranychidae) and different results have been reported about the impact of water stress on its development and reproduction. Soybean plants exposed to natural infestation by spider mites, water deficit and treatment with imidacloprid were examined under greenhouse conditions at the Institute of Forage Crops, Pleven, Bulgaria, over the period 2011-2012. The development of mites and their eggs was faster when plants were exposed to water deficit, which created favorable conditions for high density and reproduction of T. turkestani. There was a vertical distribution of protonymphs, deutonymphs and adults as their numbers and egg counts were significantly higher under conditions of water deficit on the upper and middle plant parts, compared with their bottom parts, and imidacloprid treatment had a stronger and more prolonged activity against mites, compared to its influence on well-watered plants. Spider mites on water-stressed plants caused a 24.8% reduction in the contents of plastid pigments, and carotenoids, and 21.5% decrease on well-watered plants.