Negative Effects Of Water Stress Research Articles

Combined application of native mycorrhizal and cellulolytic fungi to manage drought effects on maize

Drought become the foremost abiotic stress limiting plant growth and leading to crop-yield loss. This study was aimed to evaluate the effect of native arbuscular mycorrhizal (AM) and cellulolytic fungi (CF) on the growth, yield, mycorrhizal colonization, and the phosphorous (P) and proline contents of maize under drought. This study was conducted using a 3 x 3 factorial arranged in randomized complete block design with three replications The treatments were inoculation of native AM fungi (no AM fungi, Acaulospora tuberculata, and Gigaspora cf. gigantea) and native celluloltic fungi (no CF, Talaromyces pinophilus strain MR107 and Talaromyces pinophilus isolate OK3SP103P) evaluated under 50% field capacity (FC). Our results clearly indicated that increasing plant height, plant diameter, mycorrhizal colonization, and P content and decreasing proline content were affected either by native AM or cellulolytic fungi, but dry weight of 100-grain was only increased by native cellulolytic fungi. Combined inoculation of native AM and cellulolytic fungi improved P content and mycorrhizal colonization. Gi. cf. gigantea and T. pinophilus strain MR107 were more potential native inoculants to eliminate negative effect of water stress on maize.

Variability of leaf photosynthetic characteristics in rice and its relationship with resistance to water stress under different nitrogen nutrition regimes.

The negative effects of water stress on rice can be alleviated by NH4 + nutrition. However, the effects of mixed nitrogen (N) nutrition (NO3 - + NH4 + ) on resistance to water stress are still not well known. To investigate the response of rice growth to water stress and its relationship with photosynthetic characteristics, a hydroponic experiment supplying different N forms was conducted. Compared with NO3 - nutrition, mixed-N and NH4 + nutrition greatly alleviated the reduction of leaf area, chlorophyll content, and photosynthesis under water stress, whilst subsequently maintaining higher biomass. In contrast, water stress inhibited the root-shoot ratios in NH4 + - and mixed-N-supplied plants, indicating reduced root growth and higher photosynthate availability to shoots. The following key observations were made: (1) a similar stomatal limitation and low proportion of activated Rubisco were observed among the three different N nutrition regimes; (2) increased mesophyll conductance in NH4 + - and mixed-N-supplied plants simultaneously stimulated leaf photosynthesis and improved the water use efficiency and (3), the maximum carboxylation rate and actual photochemical efficiency of photosystem II in NH4 + - and mixed-N-supplied plants were significantly higher than that in NO3 - -supplied plants, thus resulting in higher photochemical efficiency under water stress. In conclusion, mixed-N and NH4 + nutrition may be used to develop strategies for improved water stress resistance and stimulated biomass production under conditions of osmotic stress and possibly drought.

Compost and mulching modulates morphological, physiological responses and water use efficiency in sorghum (bicolor L. Moench) under low moisture regime

Supplying organic compost and mulching could be a practical solution to alleviate the negative effects of water stress on sorghum (bicolor L. Moench) in newly reclaimed soils. For this purpose, two field experiments were conducted during 2016 and 2017 seasons. This investigation was conducted as split-split experiments based on randomized complete blocks design with organic compost (OC) as a soil amendment at three levels (0, 15 and 30 t ha−1), rice straw as a soil mulching (M) at two levels (0, and 10 t ha−1) and soil moisture at three levels (100, 85 and 70% of ETc) using three replications. Sorghum yields (forage and seed), and forage and seed water use efficiencies (F-WUE and S-WUE) were significantly (P < 0.05) affected by irrigation quantity and by both compost and mulching application. Plant growth (e.i. plant height, shoot dry, and leaf area), leaf photosynthetic pigments, plant water status (canopy temperature, relative water content (RWC%), and harvest index (HI) were also significantly (P < 0.05) affected in two seasons. The highest yields (41.41 and 7.8 t ha−1 for forage and seed yields) as the average for both seasons were recorded under full irrigation, 10 t ha−1 of M and 30 10 t ha−1 of OC. It can be concluded that organic compost and soil mulching improved significantly seed and forage yield production under deficit irrigation conditions. The results indicate that under scarcity water, application of (I85 ×OC30×M10) treatment was found to be favorable to save 15% of the applied irrigation water, to produce not only the same yields, approximately, but also to save more of water as compared to I100%.

Irrigation Regimes and Bio-stimulant Application Effects on Yield and Morpho-Physiological Responses of Strawberry

In the Mediterranean region of Turkey, strawberry production is a vital part of the agricultural sector, providing high rates of employment and farm income. Optimizing water application and effective cultivation practices are of considerable importance in improving strawberry yield. In this study the response of strawberry a cultivar (Fragaria ananassa Duch. cv. Rubygem) to irrigation regimes and bio-stimulant (seaweed extract) use were investigated, by evaluating the yield and morpho-physiological parameters under high tunnel conditions in the Mediterranean environment. The amounts of irrigation water applied were 0.50, 0.75, 1.00 and 1.25 times the water surface evaporation, measured by a standard Class A pan, and the corresponding regimes were denoted as Ir50, Ir75, Ir100, and Ir125, respectively. There was a significant decrease in total berry yield and number of berries in the Ir50 irrigation regime. The maximum total berry yield was attained at Ir75 in both applications (585.7 g/plant and 521.9 g/plant under bio-stimulant and control applications, respectively). However, the results of Ir75, Ir100 and Ir125 did not reveal any significant yield benefit. The bio-stimulant application provided a significant, 17% increase, in berry yield. The stomatal conductance and leaf water potential were reduced as irrigation application rates decreased. Conversely, stomatal conductance and leaf water potential were statistically higher, 41 µmol·m-2·s-1 and 0.5 bar, respectively, after the use of the bio-stimulant, as it alleviated the negative effects of water stress. Bio-stimulant application also significantly increased fruit nitrogen content by approximately 14%. In conclusion, considering the irrigation regimes of strawberries grown under high tunnels in the Mediterranean environment, water use is recommended at around 274 mm (Ir75), along with bio-stimulant application for optimal yield.

Tolerance of tomato plants to water stress is improved by the root endophyte Fusarium solani FsK

The endophyte Fusarium solani strain FsK may colonize the roots of tomato plants and protect them against fungal pathogens. Here we show that the fungus can alleviate the strong negative effects of water stress on the development and growth of tomato seedlings that were co-cultivated with FsK under in vitro conditions. In a succeeding pot experiment, the presence of FsK ameliorated physiological stress in plants grown in peat under water deficit irrigation conditions: plants practically restored levels of net photosynthesis rate (PN), maximal potential yield of PSII (Fv/Fm) and relative water content (% RWC) and displayed a 4-fold increase in stomatal conductivity (gs) and a 7-fold decrease in proline levels compared to mock-inoculated plants. These changes indicate a shift towards an anisohydric type response to water stress, aided by mechanisms maintaining efficient water absorption by roots and high-water conductance in planta. Effects on the accumulation of reactive oxygen species and relevant antioxidant enzymes were less dramatic. Our data indicate that the endophyte may reduce stomatal closure response to water stress, and potentially improve water acquisition by roots and/or water conductance in planta, thus preventing reduction in photosynthesis rates and minimizing water loss; this, results in increased tolerance of tomato plants to water deprivation, conferred by the endophyte.

Higher absorbed solar radiation partly offset the negative effects of water stress on the photosynthesis of Amazon forests during the 2015 drought

Amazon forests play an important role in the global carbon cycle and Earth’s climate. The vulnerability of Amazon forests to drought remains highly controversial. Here we examine the impacts of the 2015 drought on the photosynthesis of Amazon forests to understand how solar radiation and precipitation jointly control forest photosynthesis during the severe drought. We use a variety of gridded vegetation and climate datasets, including solar-induced chlorophyll fluorescence (SIF), photosynthetic active radiation (PAR), the fraction of absorbed PAR (APAR), leaf area index (LAI), precipitation, soil moisture, cloud cover, and vapor pressure deficit (VPD) in our analysis. Satellite-derived SIF observations provide a direct diagnosis of plant photosynthesis from space. The decomposition of SIF to SIF yield (SIFyield) and APAR (the product of PAR and fPAR) reveals the relative effects of precipitation and solar radiation on photosynthesis. We found that the drought significantly reduced SIFyield, the emitted SIF per photon absorbed. The higher APAR resulting from lower cloud cover and higher LAI partly offset the negative effects of water stress on the photosynthesis of Amazon forests, leading to a smaller reduction in SIF than in SIFyield and precipitation. We further found that SIFyield anomalies were more sensitive to precipitation and VPD anomalies in the southern regions of the Amazon than in the central and northern regions. Our findings shed light on the relative and combined effects of precipitation and solar radiation on photosynthesis, and can improve our understanding of the responses of Amazon forests to drought.

Water stress index on sugarcane in different developmental phases

ABSTRACT Brazil is the world leader in the production of sugar and ethanol due to its intensive cultivation of the sugarcane crop, mainly in the Southeast region of the country. However, its expansion into other areas has gained strength in recent years and has caused significant variations in the harvest due to problems related to the climate of the region. The use of water stress indexes in the developmental phases of the crop can be an essential tool for irrigation control, preventing the negative effects of water stress on the plants. The aim of this study was to determine the ideal time to irrigate a sugarcane crop, using a water stress index found using infrared thermometry. The research was developed in an area called the “Experimental Hydrographic Basin” and employed surfaces with different slopes (0% to 40%) and solar exposures (North, South, East and West), under an induced water deficit. The analyses were performed in the field and in the laboratory. The results of this study indicate that the ideal time for irrigation differs for each phase of sugarcane development, in a range between 2.0 °C and 5.0 °C, and is more critical in the tillering phase. A surface maintained at field capacity had a lower water stress index and a higher productivity (124 Mg ha-1).

Simulating the impact of climate change (elevated CO2 and temperature, and water deficit) on the growth of red and white Tempranillo grapevine in three consecutive growing seasons (2013–2015)

In recent decades, agricultural production is being affected by a sharp increase in atmospheric CO2 concentration. Due to the greenhouse effect gases, crops are impacted by enhanced temperatures and concomitantly by increased scarce water availability. All arid and semiarid areas, including Mediterranean viticulture, must face these three climate change-related factors: atmospheric CO2 concentration and temperature increases, and scarce water for irrigation. Scarce water is a problem even in irrigated viticulture, as irrigation is becoming more and more restricted. Within this context, the aim of this work was to investigate grapevine (Vitis vinifera L. cv. red and white Tempranillo) vegetative and reproductive growth. Fruit-bearing cuttings were grown under elevated CO2 (around 700 μmol mol−1 or ppm, versus 400), high temperature (ambient temperature + 4 °C, versus ambient) and water deficit (cyclic drought, versus full irrigated) in temperature gradient greenhouses for three consecutive growing seasons (years 2013, 2014 and 2015). Climate change impacted markedly vegetative growth. Within the abovementioned factors, vegetative growth (total vegetative mass) was significantly reduced by drought (consistent the three years) and was associated to a low substrate water status and low leaf stomatal conductance. Elevated CO2 stimulated total vegetative mass, whereas leaf area was not affected. When plants were grown under elevated CO2, the largest increases were observed in leaf (white) and root (red) growth. In these experiments, elevated CO2 did not compensate the negative effects of water stress. An increase of the mean temperature 4 °C had no consequences on vegetative growth. Yield and yield-related traits were unaffected by the climate change scenario.

Sewage sludge fertilization alleviates drought stress and improves physiological adaptation and yield performances in Durum Wheat (Triticum durum): A double-edged sword

Sewage sludge-based fertilization could be the most effective way to mitigate the negative effects of water stress on wheat yield in arid and semi-arid regions. The study examines morpho-physiological and yield performances of the waha variety of durum wheat (an introduced variety in North Africa) at different levels of sewage sludge-based fertilizer combined with drought stress gradient. The experiment was conducted under greenhouse in plastic pots divided into four water stress levels (100%, 80%, 50%, 30% of field capacity). Each level contained five fertilization treatments of the soil (each one replicated four times): (i) control soil (without fertilization), (ii) urea, (iii) 56.67 g DM of sewage sludge (SS)/pot, (iv) 141.67 g DM of SS/pot, (v) 283.33 g DM of SS/pot. Two-way ANOVA and Tukey tests were applied to estimate variations of morphophysiological and grain yield parameters (number of tillers, height, membrane integrity, nitrogen content, soluble sugars, grain weight, number of grain per spike). Drought stress adversely affected plant growth in height and number of tillers and therefore yield components. The application of SS mitigated the effect of water stress by improving all study growth and yield parameters. This improvement mainly resulted from the effect of SS that allowed a good root growth of plants to explore deep the soil and absorb more water, thus avoiding the effects of water deficit. Sewage sludge-based amendment is revealed as a promising solution that increases crop yields under severe environmental conditions. This biosolid alleviates stress effect, allowing the plant to survive and cope with drought conditions.

Paclobutrazol e restrição hídrica no crescimento e desenvolvimento de plantas de café

O paclobutrazol pode atenuar os efeitos negativos do estresse hídrico em diversas espécies vegetais, todavia, para cafeeiros é necessário ampliar a base de conhecimentos sobre este tema. Neste estudo, objetivou-se avaliar a morfofisiologia de plantas jovens de Coffea arabica var. ‘Catuaí Vermelho IAC 144’ em resposta a diferentes regimes hídricos e concentrações de paclobutrazol aplicado via solo. O experimento foi conduzido em casa de vegetação em Vitória da Conquista, BA. O delineamento experimental foi em blocos casualizados, com esquema fatorial representado por cinco concentrações de paclobutrazol (0, 50, 100, 150 e 200 mg L-1) aplicado via solo e dois regimes hídricos (com e sem restrição hídrica), em cinco repetições. Aos 120 dias após a aplicação do regulador vegetal avaliou-se o status hídrico, o índice SPAD e as características morfológicas das plantas. A aplicação de paclobutrazol reduziu o índice SPAD e a área foliar individual, e favoreceu o status hídrico dos cafeeiros sob restrição hídrica. As plantas jovens de café, sem restrição hídrica e tratadas com o regulador vegetal, tiveram maior retenção foliar e índice SPAD, e menor área foliar individual. A aplicação de paclobutrazol em concentrações elevadas resultou em plantas mais compactas. A restrição hídrica proporcionou menor área foliar total, número de ramos e massa seca dos cafeeiros.

Nutrition and biochemical responses of chickpea (Cicer Arietinum L.) to vermicompost fertilizer and water deficit stress

ABSTRACTVermicompost can have an effective role in plant growth and nutrition. It can also reduce the harmful effects of stress caused by environmental factors. This study was a factorial experiment with a completely randomized plot design and three replications. The results showed that the calcium concentration (+40% +39%) of root and calcium (+71% +67%) and potassium contents (+49% +59%) of leaf under conditions of moderate and severe water stress increased under vermicompost treatments at the ratio of 30%. Sodium absorption (−37% −21%) in moderate and severe conditions was significantly reduced by vermicompost treatment. In moderate and severe water stress, the growth medium of 30% vermicompost significantly enhanced proline (+39%) and soluble protein content (+28%) compared to the control. In conclusion, our results proved vermicompost fertilizer due to its structural properties and components, served to reduce the negative effects of water stress by increasing the absorption of calcium (Ca) and potassium (K), and decreasing sodium (Na) absorption that resulted in increased evaluations for proline and protein content.

Inoculation with Azospirillum sp. and Herbaspirillum sp. Bacteria Increases the Tolerance of Maize to Drought Stress.

Stress drought is an important abiotic factor that leads to immense losses in crop yields around the world. Strategies are urgently needed to help plants adapt to drought in order to mitigate crop losses. Here we investigated the bioprotective effects of inoculating corn grown under drought conditions with two types of plant growth-promoting rhizobacteria (PGPR), A. brasilense, strain SP-7, and H. seropedicae, strain Z-152. Plants inoculated with the bacteria were grown in a greenhouse with perlite as a substrate. Two hydric conditions were tested: normal well-watered conditions and drought conditions. Compared to control non-inoculated plants, those that were inoculated with PGPR bacteria showed a higher tolerance to the negative effects of water stress in drought conditions, with higher biomass production; higher carbon, nitrogen, and chlorophyll levels; and lower levels of abscisic acid and ethylene, which are plant hormones that affect the stress response. The oxidative stress levels of these plants were similar to those of non-inoculated plants grown in well-watered conditions, showing fewer injuries to the cell membrane. We also noted higher relative water content in the vegetal tissue and better osmoregulation in drought conditions in inoculated plants, as reflected by significantly lower proline content. Finally, we observed lower gene expression of ZmVP14 in the inoculated plants; notably, ZmVP14 is involved in the biosynthesis of abscisic acid. Taken together, these results demonstrate that these bacteria could be used to help plants cope with the negative effects of drought stress conditions.

Salicylic acid mediated growth, physiological and proteomic responses in two wheat varieties under drought stress

Salicylic acid (SA) induced drought tolerance can be a key trait for increasing and stabilizing wheat production. These SA induced traits were studied in two Triticum aestivum L. varieties; drought tolerant, Kundan and drought sensitive, Lok1 under two different water deficit regimes: and rehydration at vegetative and flowering stages. SA alleviated the negative effects of water stress on photosynthesis more in Kundan. SA induced defense responses against drought by increasing antioxidative enzymes and osmolytes (proline and total soluble sugars). Differential proteomics revealed major role of carbon metabolism and signal transduction in enhancing drought tolerance in Kundan which was shifted towards defense, energy production and protection in Lok1. Thioredoxins played important role between SA and redox signaling in activating defense responses. SA showed substantial impact on physiology and carbon assimilation in tolerant variety for better growth under drought. Lok1 exhibited SA induced drought tolerance through enhanced defense system and energy metabolism. Plants after rehydration showed complete recovery of physiological functions under SA treatment. SA mediated constitutive defense against water stress did not compromise yield. These results suggest that exogenously applied SA under drought stress confer growth promoting and stress priming effects on wheat plants thus alleviating yield limitation. Biological significanceStudies have shown morphological, physiological and biochemical aspects associated with the SA mediated drought tolerance in wheat while understanding of molecular mechanism is limited. Herein, proteomics approach has identified significantly changed proteins and their potential relevance to SA mediated drought stress responses in drought tolerant and sensitive wheat varieties. SA regulates wide range of processes such as photosynthesis, carbon assimilation, protein metabolism, amino acid and energy metabolism, redox homeostasis and signal transduction under drought. Proteome response to SA during vegetative and reproductive growth gave an insight on mechanism related water stress acclimation for growth and development to attain potential yield under drought. The knowledge gained can be potentially applied to provide fundamental basis for new strategies aiming towards improved crop drought tolerance and productivity.

Effect of Foliar Spraying with Nano and Natural Materials under Water Stress Conditions on Cotton Leaves Chemical Composition

Two field experiments were conducted on a clay soil at El-Gemmeiza Agricultural Research Station, , Egypt during growing 2015 and 2016 seasons, to find out the proper irrigation interval and the effect of Nano and natural materials in reducing the negative effect of water stress on cotton leaves chemical composition of the Egyptian cotton cultivar Giza 86 through study the effect of three Nano-materials treatments (without, 7.5g/L lithovit and 1 cm3/L amino mineral) and three natural materials treatments (without, 200 ppm salicylic acid and 5cm3/L humic acid) under three irrigation intervals (every14, 21 and 28 days) as well as their interactions. Each experiment contained three separate experiments represented the three irrigation intervals; i.e. every 14, 21 and 28 days. Also, the combined analysis between the three experiments was done. The two other factors distributed in each experiment in a strip plot design with four replicates, where the horizontal plots were assigned to the foliar of Nano-materials and the vertical plots contained natural materials treatments. Results showed that: The highest percentages of N, P and K in leaves were obtained from irrigation interval of 21 days followed by irrigation interval of 28 days. Also, irrigation intervals exhibited significant differences in leaves concentrations of photosynthetic pigments i.e. chlorophyll a and total chlorophyll, total carbohydrates and total sugars in both seasons and chlorophyll b and carotenoids in the 2nd season only, under irrigation interval of 21 days. The minimum values of leaves proline concentration, peroxidase and phenoloxidase activity in cotton leaves were obtained from irrigated every 21 days which induced favorable conditions and reduces water stress effect. Foliar CO2 as a Nano fertilizer (in the form of lithovit) three times at a rate of 7.5g/L significantly increased percentage of N, P and K in leaves and leaves concentrations of photosynthetic pigments such as chlorophyll a, chlorophyll b, total chlorophyll and carotenoids, leaves total carbohydrates and total sugars contents in both seasons. Also, it significantly decreased leaves proline content, peroxidase and phenoloxidase activity which indicates favorable conditions and reduces water stress effect; however untreated plants recorded the highest values. Foliar feeding with 5 cm3/L humic acid three times significantly increased percentage of N, P and K in leaves, values of leaves concentrations of photosynthetic pigments i.e. chlorophyll a, chlorophyll b, total chlorophyll and carotenoids, total carbohydrates and total sugars followed by using salicylic acid as foliar spraying at a rate of 200 ppm and the least values were obtained from untreated plants (without natural materials application) in both seasons. In contrary, applying 5 cm3/L humic acid results recorded the lowest values of proline content, peroxidase and phenoloxidase activity in leaves in both seasons followed by applying salicylic acid at a rate of 200 ppm. Plants irrigated every 21 days which received CO2 as a Nano fertilizer at a rate of 7.5 g/L in combination with 5 cm3/L humic acid led to a significant increase in P, K, total sugars and total carbohydrates concentrations in leaves compared to the other interaction treatments; however, cotton plants irrigated every 14 days without application with Nano or natural treatments produced the lowest concentrations. Also, plants irrigated every 21 days which received CO2 as a Nano fertilizer at a rate of 7.5 g/L in combination with 5 cm3/L humic acid gave the lowest values of proline content, peroxidase and phenoloxidase activity in cotton leaves in the first season, which induced proper conditions for plant growth and reflect on reduce water stress effect. It could be concluding the irrigation cotton plants every 21 days in combination with foliar CO2 as a Nano fertilizer (in the form of lithovit) at a rate of 7.5g/L and foliar feeding spraying with 5 cm3/L humic acid three times (at the squaring stage, flowering initiation and at the top of flowering) to overcome the water shortage at the end of water sources (canals) as well as when water scarcity becomes wide spread, where this combination is the best treatment for good leaves chemical composition under the conditions of El-Gemmeiza location.

Exogenous nitric oxide improves sugarcane growth and photosynthesis under water deficit.

Nitric oxide (NO)-mediated redox signaling plays a role in alleviating the negative impact of water stress in sugarcane plants by improving root growth and photosynthesis. Drought is an environmental limitation affecting sugarcane growth and yield. The redox-active molecule nitric oxide (NO) is known to modulate plant responses to stressful conditions. NO may react with glutathione (GSH) to form S-nitrosoglutathione (GSNO), which is considered the main reservoir of NO in cells. Here, we investigate the role of NO in alleviating the effects of water deficit on growth and photosynthesis of sugarcane plants. Well-hydrated plants were compared to plants under drought and sprayed with mock (water) or GSNO at concentrations ranging from 10 to 1000μM. Leaf GSNO sprayed plants showed significant improvement of relative water content and leaf and root dry matter under drought compared to mock-sprayed plants. Additionally, plants sprayed with GSNO (≥100μM) showed higher leaf gas exchange and photochemical activity as compared to mock-sprayed plants under water deficit and after rehydration. Surprisingly, a raise in the total S-nitrosothiols content was observed in leaves sprayed with GSH or GSNO, suggesting a long-term role of NO-mediated responses to water deficit. Experiments with leaf discs fumigated with NO gas also suggested a role of NO in drought tolerance of sugarcane plants. Overall, our data indicate that the NO-mediated redox signaling plays a role in alleviating the negative effects of water stress in sugarcane plants by protecting the photosynthetic apparatus and improving shoot and root growth.

A trait‐mediated, neighbourhood approach to quantify climate impacts on successional dynamics of tropical rainforests

Summary Second‐growth forests account for 40% of the terrestrial forest carbon sink and represent the dominant forest cover in tropical regions. Uncertainties in predicting responses of these ecosystems to climate change arise from high tree species diversity, complex links between eco‐physiology and demography, and the role of ontogeny and competition in mediating individual tree responses to climate. The dynamic nature of second‐growth forests adds further uncertainty to our ability to quantify the relative importance of climate in mediating successional trajectories. To address these uncertainties, we develop a hierarchical Bayesian neighbourhood modelling approach that quantifies how the joint response of two key functional axes, wood density and specific leaf area (SLA), modulate impacts of inter‐annual variation in seasonal water stress (number of days during dry season &gt; 1 kPa vapour pressure deficit) and night‐time temperature on growth and survival of small (5–10 cm dbh) and large (≥ 10 cm dbh) trees for 171 rainforest species in 6 s‐growth and 2 old‐growth 1‐ha mapped stands. We use model results to examine potential climate impacts on the successional trajectories of these stands. High water stress reduced large tree growth but favoured growth of small trees. Drought also reduced tree survival for both large and small trees. Tree species with high wood density suffered lower growth reductions and had higher survival under water stress. High SLA magnified the negative effects of water stress on tree growth and survival. Across all tree sizes, high night‐time temperatures did not influence growth or survival. Simulated successional trajectories under different climate scenarios using these results suggest that multi‐annual droughts will have substantial impacts of the successional trajectories of tropical forests, leading to lower stem numbers, basal area and biomass. Sustained drought will also shift functional composition of second‐growth forest by favouring species with low SLA which tend to dominate in late stages of succession. By incorporating trait‐mediated effects on key drivers of tree demography and successional dynamics, our approach provides an integrated perspective on interspecific variation in vulnerability to drought and consequences for successional trajectories in tropical rainforests. Our results suggest that multi‐annual drought stress will significantly alter structure, composition and dynamics of second‐growth forests and, from a functional perspective, accelerate succession. However, this effect may be hampered by dispersal limitation of old‐growth species into second‐growth forests.

Growth, yield, chemical composition, and antioxidant activity of essential oils from two thyme species under foliar application of jasmonic acid and water deficit conditions

Jasmonic acid (JA) exerts biological activity in plant responses to environmental stress as well as development. The effect of foliar application of JA and combination with deficit irrigation on some characteristics of two thyme species, including Thymus vulgaris and T. daenensis were investigated. Treatments comprised 0, 200, and 400 µL JA applied to plants under normal, slight drought, and mild drought stress conditions. Irrigation levels had a significant effect on growth traits in terms of herbage dry weight, plant height, number of branches, and leaf area index. Foliar application of JA influenced the essential oil yield and the main components of the oils. Percentages of carvacrol, γ-terpinene, and p-cymene in the oil extracted from the plants under stressed conditions were higher than non-stressed plants, whereas percentage of thymol was significantly reduced under drought stress. In both thyme species, the JA significantly improved carvacrol and thymol contents in the oils, antioxidant activity, plant height, and root length, but reduced the essential oil yield and amount of γ-terpinene in the oils. In conclusion, the foliar application of JA reduced the negative effects of water stress on thymol amount in T. daenensis, and γ-terpinene content in T. vuglaris.

Irrigation Water Quality and Trinexapac-ethyl Effects on Bermudagrass Response to Deficit Irrigation

As the need for landscape and golf course water conservation increases, use of low-quality irrigation water combined with deficit irrigation practices is becoming more common. Information is lacking concerning the effects of water quality on bermudagrass response to deficit irrigation, as well as the extent to which plant growth regulators may ameliorate or delay the negative effects of water stress on warm-season turfgrass. The objectives of this 10-week greenhouse study were to 1) characterize growth, quality, and evapotranspiration (ET) of ‘Tifway’ bermudagrass (Cynodon dactylon × C. traansvalensis Burt Davy) when irrigated at full (1.0 × ETa) or deficit (0.3 × ETa) levels of actual turfgrass evapotranspiration (ETa) using three irrigation water sources [reverse osmosis (RO), sodic potable, and saline] and 2) determine whether application of trinexapac-ethyl (TE) could mitigate turfgrass quality decline under deficit irrigation. Results indicated that turf irrigated with sodic irrigation water exhibited significantly elevated ETa and shoot growth compared with turf receiving RO or saline irrigation water in both studies. Irrigation water source affected turfgrass quality differently at each irrigation level. TE application improved turfgrass quality and/or delayed firing under soil moisture stress in both studies, with the greatest benefit noted under the less intense conditions of the spring experiment. Elevated canopy temperatures were observed within all deficit irrigation treatments, regardless of water chemistry. Results demonstrate that irrigation water quality may influence turfgrass ET rates. In addition, they suggest that trinexapac-ethyl may offer short-term mitigation of drought stress under deficit irrigation.

Organo mineral fertilizer can mitigate water stress for cucumber production (Cucumis sativus L.)

Supplying organo mineral fertilizer [a 2:10:1 (w/w/w) mixture of sulfur, compost and potassium humate] under deficit irrigation conditions could be a practical solution to compensate the negative effect of water stress on cucumber crop. For this purpose, two consecutive field experiments (summer and fall seasons) were conducted during 2014. Three organo mineral fertilizer (OMF) levels (0, 5 and 10tha−1) were supplied as a soil amendment combined with three irrigation levels (100, 80 and 60% of crop evapotranspiration). Under full irrigation, seasonal water use by cucumber was 397mm over 76 days in summer season and 292mm over 86 days in fall season, respectively. Cucumber fruit quality, yield, and water use efficiency (WUE) were significantly (p<0.05) affected by season and both irrigation quantity and organo mineral fertilizer application. Leaf area, dry matter, relative water content (RWC %), membrane stability index (MSI %), and harvest index (HI) were also significantly (p<0.05) affected by irrigation quantity and organo menial fertilizer and were not significantly affected by season except for dry matter. Interaction between growing season and both irrigation and organo mineral fertilizer were not significantly affected. The highest fruit yields (19.76tha−1 and 15.94tha−1 in fall and summer season) were recorded under full irrigation and 10tha−1 of OMF. Organo mineral fertilizer of 10tha−1 and 5tha−1 significantly (p≤0.05) increased fruit yield by 53.49 and 15.93% compared to control. The results suggest that the detrimental effects of drought stress can be reduced by using organo mineral fertilizer as a soil amendment for vegetable crops. Combining deficit irrigation and organo mineral fertilizer maximized crop water productivity.

Water availability and formation of propagules of arbuscular mycorrhizal fungi associated with sorghum

Arbuscular mycorrhizal fungi (AMF) promote greater tolerance to the negative effects of water stress in their host plants, yet may also be influenced by the availability of water in the production of their infective propagules. The objective of this study was to assess the effect of water availability in the soil on the sporulation of Claroideoglomus etunicatum, Gigaspora albida and Scutellospora heterogama, and the influence of this condition on the infective potential and number of nuclei in glomerospores of these species. The reduction of water availability from 75 to 25% did not decrease significantly the sporulation of C. etunicatum, but resulted in decrease of sporulation of G. albida (600 to 7 glomerospores per 30g−1 soil) and S. heterogama (274 to 2 glomerospores per 30g−1 soil). The water availability at 75 and 71% promoted maximum sporulation of G. albida and S. heterogama, respectively. While G. albida and S. heterogama had greater sporulation than C. etunicatum, the infective potential of these species was lower, which may be related to the life-strategy and type of infective propagules of each species. The number of nuclei per glomerospore varied only among the species (p<0.05), with C. etunicatum and G. albida presenting the higher number of nuclei when compared to S. heterogama, but no differences were found among the treatments of water availability (p>0.05). These results suggest that AMF have distinct sporulation strategies and the amount of glomerospores is not directly related to the infectivity of the inoculum. Possibly, the differences in the life-strategies among the species were greater than the effects of water availability.