High Water Deficit Research Articles

Excized leaf water status as a measure of drought resistance of Ukrainian spring wheat

Drought tolerance of 24 Ukrainian spring wheat ( Triticum aestivum L ., T. durum Desf., T. turgidum subsp. dicoccum) genotypes was estimated by determining water deficit (WD), relative water content (RWC), excised leaves water loss weight (EL WLW), excised leaves water loss per area (EL WLA) in flag leaves of plants grown in a field conditions during Y2018 vegetative season, that was characterized by low precipitation and high temperatures. Field experimental plots were located near Dmytriv village, Lviv region (50°13 ′ 26.6 ′ ′ N 24°36 ′ 50.5 ′ ′ E) on the Chernozem on eluvium of carbonate rock soil. Wheat was sown in a randomized complete block design in four replications of 30 m 2 plot area. The purpose of this study was to verify more reliably a physiological traits used for screening of the performance under the restricted water supply and to correlate the varietal tolerance with the final grain yield. Water status parameters were determined on the Zadoks 4.3 growth stage. Water deficit caused a reduction in the leaf RWC for all studied varieties. Differences in the drought response between T . aestivum and T . durum varieties were confirmed. The WD of flag leaves ranged from 18.0 to 37.8 % for bread and from 19.4 to 33.3 % for durum wheat varieties. The lowest WD (less or equal 20 %) has been recorded for bread varieties Kolektyvna 3, Elehiia myronivs’ka and durum varieties – Diana, Chado. High WD noted for the Simkoda myronivs’ka and MIP Raiduzhna. The low EL WLW and therefore higher drought tolerance was noticed for durum wheat varieties, namely for Spadschyna, Diana. Bread wheat varieties Simkoda myronivs’ka, Panianka, and durum wheat Zhizel’, Tera, MIP Raiduzhna and emmer Holikovs’ka varieties lost less water per leaf area (EL WLA). Past 3 biplot correlation analysis confirmed MIP Raiduzhna drought tolerance, and allowed to choose Zhizel’ (durum), Holikovs’ka (emmer) and Simkoda myronivs’ka (bread) as varieties with a high yield performance and drought tolerance. Bread varieties Bozhena and Dubravka, durum Spadschyna, Diana varieties were susceptible to drought in spite of relatively high leaf RWC. Thus, excised leaves water loss – EL WLW and EL WLA indices characte­rizing water-retaining ability of leaf tissues could be recommended as additional indicators of water stress tolerance. RWC as drought tolerance parameter is more applicable for durum varieties, whereas EL WLA 2–6 h for the bread varieties. Keywords : drought, Ukrainian spring wheat, relative water content, water deficit, excised leaves water loss, EL WLW, EL WLA

Fine-scale stand structure mediates drought-induced tree mortality in pinyon-juniper woodlands.

Severe drought has resulted in widespread tree die-off events in forests and woodlands globally and is forecast to become more frequent in coming decades. Tree mortality is a complex process influenced by climate, soils, characteristics of individual trees, interactions between trees, and the dynamics of pests and pathogens. The role of stand structure and stand density in mediating the resistance of trees to drought remains poorly understood, especially in semiarid woodlands, which are expected to be highly susceptible to future severe drought. We sampled permanent plots in central Nevada woodlands dominated by single-leaf pinyon pine and Utah juniper before and after a severe multi-year drought (2013-2015) to investigate the importance of climate, tree attributes, and local-neighborhood stand structure on tree mortality and canopy dieback at the level of individual trees and 0.1-ha plots. We observed widespread tree mortality of pinyon at approximately eight times the reported background mortality rate, and substantial canopy dieback in both pinyon and juniper. Both species were more prone to mortality and dieback in hotter, drier sites. Canopy dieback was associated with both long-term average climate and the severity of recent drought, with elevated mortality on sites with higher water deficits, average summer temperatures, and vapor pressure deficits. Soils also played a role in tree dieback, with greater mortality on deeper soils. While mortality was driven largely by climate at coarse scales, fine-scale stand structure interacted with climate to mediate mortality and dieback. Neighborhood statistics showed that trees were susceptible to competitive influence, and pinyon trees were especially sensitive to neighborhood density on drier sites. Mortality and dieback were associated with diverse, co-occurring insect and parasitic plant mortality agents. Canopy dieback prior to the drought was strongly associated with tree mortality during the drought, implying that current widespread defoliation caused by these agents may foreshadow future elevated woodland decline. Fine-scale influences such as stand structure and soil characteristics play a key role in the long-term dynamics of semiarid woodlands, and these factors should be considered in predictive models of forest and woodland susceptibility to drought.

Past and future changes in regional crop water requirements in Northwest China

Northwest China is characterized by a high water deficit and regular water resource shortages. These issues have become limiting factors for agricultural and socioeconomic development. Based on a trend-preserving method of bias correction, we calibrated the maximum temperature and minimum temperature in four CMIP5 GCMs (CNRM, IPSL, BCC, and CMCC). Then, we investigated variations in the regional crop water requirement (CWR) in the total growth stages for five main crops (cotton, spring corn, summer corn, spring wheat, and winter wheat) in the past (1961–2005) and future (2006–2100). The results suggest that the MK test yielded insignificant decreasing CWR trends in the total growth stages of cotton (0.10 mm/year), spring corn (0.13 mm/year), and spring wheat (0.05 mm/year) and insignificant increasing trends for summer corn (0.02 mm/year) and winter wheat (0.32 mm/year) historically. In the future period, for the same type of crops (cotton), the CWRs in all scenarios (RCP 2.6, 4.5, and 8.5 scenarios) for all GCMs exhibited significant positive trends; for the same GCM (BCC), the CWRs projected for five major crops in the RCP 4.5 and 8.5 scenarios all exhibited extremely significant MK trends (99%); in addition, the CWRs’ rate increases of the five crops projected in RCP8.5 scenario by BCC exhibited the following order: winter wheat (1.25 mm/year), summer corn (1.15 mm/year), spring corn (1.02 mm/year), cotton (0.97 mm/year), and spring wheat (0.87 mm/year). The maximum CWRs of winter wheat were mainly observed in southeastern Northwest China, while those of the other four crops occurred in southern Xinjiang.

Diversidad de cianobacterias en costras biológicas de suelo de la ecorregión del Monte Central (Mendoza, Argentina)

The ecoregion of Monte Central has a high water deficit. Scarcity and variability of the water resource determine the spatial distribution of vascular plants. Areas devoid of vegetation are commonly colonized by microbial communities (mosses, cyanobacteria, lichens) called biological soil crusts (BSCs), which modify numerous biogeochemical properties of the substrate. Cyanobacteria are fundamental constituents of BSCs, they synthesize chlorophyll a, phycobilins and fix atmospheric nitrogen (N), representing one of the main sources of N for some arid ecosystems. The objective of this work is to contribute to the knowledge of the cyanobacteria present in BSCs of the Monte Central desert, in different landscape units of eastern Mendoza (natural reserves and grazing lands). Biotic and abiotic material was collected during the years 2015 and 2016 in each environmental unit. For the identification of cyanobacteria, morphological characteristics observed under light microscope, along with taxonomic keys were used. Thus, 12 new records of cyanobacteria are repor ted in BSCs, improving our knowledge of these biocrusts, their geographical distribution and ecology in the province of Mendoza, Argentina.

Nutrient and water dynamics of Amazonian canga vegetation differ among physiognomies and from those of other neotropical ecosystems

Ferriferous savannas, also known as cangas in Brazil, are nutrient-impoverished ecosystems adapted to seasonal droughts. These ecosystems support distinctive vegetation physiognomies and high plant diversity, although little is known about how nutrient and water availability shape these ecosystems. Our study was carried out in the cangas from Carajas, eastern Amazonia, Brazil. To investigate the N cycling and drought adaptations of different canga physiognomies and compare the findings with those from other ecosystems, we analyzed nutrient concentrations and isotope ratios (δ13C and δ15N) of plants, litter, and soils from 36 plots distributed in three physiognomies: typical scrubland (SB), Vellozia scrubland (VL), and woodland (WD). Foliar δ15N values in cangas were higher than those in savannas but lower than those in tropical forests, indicating more conservative N cycles in Amazonian cangas than in forests. The lower δ15N in savanna formations may be due to a higher importance of mycorrhizal species in savanna vegetation than in canga vegetation. Elevated δ13C values indicate higher water shortage in canga ecosystems than in forests. Foliar and litter nutrient concentrations vary among canga physiognomies, indicating differences in nutrient dynamics. Lower nutrient availability, higher C:N ratios, and lower δ15N values characterize VL, whereas WD is delineated by lower δ13C values and higher soil P. These results suggest lower water restriction and lower P limitation in WD, whereas VL shows more conserved N cycles due to lower nutrient availability. Differences in nutrient and water dynamics among physiognomies indicate different ecological processes; thus, the conservation of all physiognomies is required to ensure the maintenance of functional diversity in this unique ecosystem.

Current Problems and Tasks of Forest Protection in Poland

Abstract Current problems of forest protection concern the declining health of forest stands due to climate change and the resulting extreme weather events such as heat waves, droughts, hurricane winds, heavy rainfalls and floods. Repeated impacts of these factors increase susceptibility of forest stands to pest insects and fungal pathogens. Norway spruce (Picea abies [L.] H. Karst) is sensitive to high air temperatures and water shortage. Long lasting droughts during the last two decades, have been one of the reasons behind Norway spruce dieback due to severe outbreak of European spruce bark beetle Ips typographus (L.) in the mountainous regions of southern Poland. In the Scots pine (Pinus sylvestris L.) stands, water balance disorders have enhanced the colonization of weekend trees by steelblue jewel beetle Phaenops cyanea (F.) and engraver beetle Ips acuminatus (Gyll.), as well as contributed to the spread of fungal diseases caused by Gremmeniella abietina (Lagerb.) Cenangium ferruginosum Fr. and Sphaeropsis sapinea Fr. fungi. Water related stress leads to weakening of oak stands, which are attacked by Agrilus spp. beetles and pathogens from the genus Phytophthora. It is possible that long lasting droughts initiated the spread of infectious ash disease caused by Hymenoscyphus fraxineus (= Chalara fraxinea), which resulted in the epidemic of ash dieback throughout Europe. Until recently, the use of plant protection products was the most common method of forest protection against pest insects and pathogens. Poland’s accession to the European Union has affected the marketing and use of plant protection products in the country. The implementation of the EU legislation (Directive 91/414/EEC, Directive 2009/128/ EC and Regulation No 1107/2009) has resulted in decreased assortment of pesticides registered for the protection of forests. High costs and long registration process considerably limited the interest of producers in placing the plant protection products on the market. Systematic decrease in the number of plant protection products possible to register for use in forestry, as well as the principles of integrated plant protection established in the EU in 2014 call for seeking plant protection methods based on the natural enemies of pests, such as pathogenic microorganisms, parasites and predators. Therefore, contemporary forest protection requires the advancement of integrated methods for pest insect and disease control through developing methods of forecasting forest dangers, the use of natural enemies and agro-technical methods for regulation of pests, as well as the development of decision support systems as a tool facilitating introduction of integrated forest protection principles. Such support systems help to establish optimal terms for the implementation of protection measures, so as to increase their efficiency while limiting the use of chemical pesticides to an absolute minimum.

Inferring diversity patterns along an elevation gradient from stacked SDMs: A case study on Mesoamerican ferns

An enduring challenge in ecology is to characterise and understand species richness patterns in tropical regions. Species richness maps produced by stacking species distribution model (SDM) range maps could prove useful in this regard, but little attention has been given to this approach. Here we generate a species richness map by stacking the ranges of 86 Mesoamerican fern species modelled by MaxEnt from field data collected by the Sampled Red List Index for Plants project. Predicted species richness showed a hump-backed relationship with elevation, peaking at mid-elevation (1800–2000 m). A remarkably similar pattern was observed in a field survey conducted to validate the approach. Predicted species richness was also low in sites with high water deficits, as previously shown in the fern literature. Beta-diversity in the lowlands was greatest between sites with strongly contrasting water deficits, further emphasising the importance of this environmental variable. The stacked SDM approach was thus able to reproduce broad biogeographical patterns of species richness, despite many of the fern species being represented by fewer than 20 samples.

A multifaceted rhizobacterium Bacillus licheniformis functions as a fungal antagonist and a promoter of plant growth and abiotic stress tolerance

Plant-growth-promoting rhizobacteria play a beneficial role in plant growth through various mechanisms. In this study, an isolated rhizobacterial strain, Bacillus licheniformis CH102 (hereafter CH102), exhibited antifungal activity and harbored genes required for lantibiotic and 2,3-butanediol production. In Arabidopsis, increased root hair number and fresh weight were obtained in the CH102-inoculated seedlings. Moreover, increases in chlorophyll content, H2O2 concentration and activities of antioxidant enzymes including catalase and POD were observed in the treated seedlings. Exposure to CH102 increased the tolerance toward high temperatures and water deficits in Arabidopsis seedlings. CH102 induced gene expression involved in induced disease resistance, nitrogen assimilation, antioxidants, photosystem II, ion transport and synthesis of secondary metabolites. Arabidopsis transcriptomic analysis revealed the CH102-upregulated genes were associated with several cellular pathways including the PEP-PEPR system, cell wall modification, and biosynthesis of osmoprotectants including choline, proline, and galactinol. The presence of CH102 elicited increased response of Arabidopsis genes associated with the jasmonic acid (JA) and abscisic acid (ABA) signaling pathways. Moreover, the upregulated expression of SLAC1 HOMOLOGUE 3 (SLAH3) function in the regulation of stomatal closure was detected. Furthermore, CH102 inoculation increased expression of transcription factors implicated in the regulation of abiotic stress responses, including DDF2, CBF1, DREB2A, HSFA2, WRKY30 and WRKY33. In summary, CH102 exerts effects on multiple cellular pathways involved in defense response, metabolism, antioxidant system and hormone signaling such as JA and ABA to regulate plant growth and tolerance to heat and drought stress.

Performance of potato (Solanum tuberosum) advanced hybrid MS/6-1947 under high temperature stress and water deficit conditions

In present investigation, potato (Solanum tuberosum L.) advanced stage hybrid MS/6-1947 was evaluated along with controls under high temperature and water stress regimes for three successive winter crop seasons. Under high temperature at Modipuram, MS/6-1947 (13.3 t/ha) showed yield enhancement of 20, 9 and 11% over the controls Kufri Bahar, Kufri Pukhraj and Kufri Surya. It also exhibited at par tolerance to hopper with Kufri Surya and damages due to mite burn were lower than Kufri Bahar and Kufri Pukhraj. The hybrid possessed 18% tuber dry matter. Results ondrought toleranceat Modipuram revealed superior performance of MS/6-1947 under normal irrigation, mild water and severe water stress conditions as compared to best control Kufri Pukhraj as yield reduction was comparatively lower under mild and severe water stress treatments. Drought tolerance index (DTI) values were maximum in MS/6-1947 (1.02 and 0.79) followed by Kufri Pukhraj (0.86 and 0.51) and Kufri Bahar (0.72 and 0.58) under mild and severe water deficit treatments, respectively. Drought tolerance studies at Jodhpur revealed better performance of MS/6-1947 under normal and mild water stress conditions as compared to the controls Kufri Pukhraj and Kufri Surya as yield reduction was comparatively lower under mild water stress conditions. DTI values were maximum in MS/6-1947 (1.08) followed by Kufri Puhkraj (1.01) and Kufri Surya (0.41) under mild water deficit treatment. Tuber dry matter content increased under water stress over normal irrigation at both the locations. MS/6-1947 is suitable for table potatoes. MS/6-1947 may be a better option for integrating in cereal based crop sequences, for exploiting its yield potential in early season and for attaining sustainable productivity in areas where high temperature and lower water availability are constraint for raising the successful potato crop.

Stable isotope ecology of black rhinos (Diceros bicornis) in Kenya.

Stable isotope and elemental ratios in hair are influenced by the environment, including both climate and geology. Stable carbon isotopes can be used to give estimates of the C4/CAM fraction of diets of herbivorous mammals; stable nitrogen isotopes are related to the local water deficit; strontium isotopes are determined by the local geology. We studied hair from rhinos in Kenya to determine spatial patterns in δ13C, δ15N, and 87Sr/86Sr ratios. The samples of rhino hair were collected during Kenya Wildlife Service translocation or veterinary activities. δ13C values showed diets dominated by C3 foods, but in some regions the diet, at least seasonally, contained significant quantities (i.e., >ca. 20%) of C4/CAM foods. δ15N values were related to water deficit, with higher δ15N values in regions with high water deficit. 87Sr/86Sr isotope ratios were found to be related to the local geological substrate suggesting that 87Sr/86Sr isotope ratios are provisionally useful for determining the origins of illegal wildlife materials in Kenya and elsewhere in Africa.

Quantification of transpiration and evaporation of okra under subsurface drip irrigation using SIMDualKc model during vegetative development

ABSTRACTKnowledge of productive and nonproductive water loss of okra [Abelmoschus esculentus (L.) Moench] is essential during water scarcity, and for assessing links between yield and water use. The study was conducted using subsurface drip irrigation to evaluate okra transpiration and evaporation using the SIMDualKc Model. The model computed soil evaporation was 132.89 and 157.84 mm, respectively, whereas transpiration was 381.22 and 340.36 mm in 2016 and 2017, respectively. Pod yield of okra was 12.1 and 12.5 t∙ha−1; dry biomass above ground was 5.7 and 4.9 t∙ha−1 in 2016 and 2017. Biomass above ground and fresh pod yield of okra indicates that high water deficit before harvesting pods causes a depression in fresh fruit yield and decreases total pod yield. Several water deficit occurrences during the growing period lowers total transpiration and adversely impacts okra dry biomass above ground. The SIMDualKc Model is capable of quantifying evaporation, transpiration and other water balance components. It is an effective tool for assessing and predicting the impact of water deficit on plant development and yield and can be used to identify the correct irrigation strategy for maximizing crop production.

When is the best time to flower and disperse? A comparative analysis of plant reproductive phenology in the Mediterranean

Abstract The phenology of organisms corresponds to the temporal match between the components of their life cycle and the seasonal distribution of resources and hazards. Flowering has been extensively studied to describe the reproductive phenology of plants, but in comparison, other key events for reproductive success such as the seed maturation period and the time of seed dispersal have been considerably less investigated. This study describes the temporal sequence of onset of flowering and seed dispersal, and the time necessary to mature seeds in 138 species growing in the strongly seasonal climate of Mediterranean southern France. Data for the three traits were compiled from several original surveys to characterize the reproductive phenology of 47 annual, 67 perennial herbaceous and 24 low stature woody species. The timing of these three phases was assessed in relation to local climatic conditions, and the degree to which they were coordinated was tested. All three phenological traits spanned a wide range of values from early spring to late summer. Annuals flowered slightly earlier than perennials but the largest difference between these groups was found for the seed maturation period, which was much shorter in annuals. This resulted in earlier dispersal dates in these species, which occurred before periods of high water deficit. Significant positive correlations were found between onset of flowering, onset of seed dispersal and seed maturation period. This suggests a consistent pattern of coordination between the different phases of reproductive phenology across species. Our results show that while the time slot for flowering appears restricted to periods with adequate temperature and water availability for most species, the seed maturation period and dispersal phase can occur during periods of substantial water deficit, at least for perennials. They also suggest that the different species can be arrayed along a fast‐slow continuum based on reproductive events, from early flowering species with short seed maturation and early dispersal to late flowering species with long seed maturation and late dispersal. Whether this relates to the postulated fast‐slow continuum identified for the functioning of vegetative organs is a promising avenue for future research. A plain language summary is available for this article.

EVALUATION OF THE GENETIC VARIATION FOR SOME GENOTYPES IN COTTON (GOSSYPIUM BARBADENSE L.) TO WATER STRESS

Sixteen cotton genotypes representing a wide range of cotton characteristics, were used in two concurrent trials (laboratory and field) at Sakha Agric. Res. Station under well-watered and water-limited regimes during 2016 and 2017 seasons. The objectives were to determine genotypic variability among cotton varieties in their response to deficit water stress and to detect the most suitable genotypes, traits and selection procedure for water stress condition. The genotypes were evaluated for water deficit stress in laboratory by the simulation of water potentials with polyethylene glycol-6000 (0.0 and -0.4 MPa), at 25oC using aerated hydroponic culture box. After 18 days the following seedling traits were measured, root length (cm) (RL), root fresh weight (g) (RFW), root dry weight (g) (RDW), shoot length (cm) (SHL), shoot fresh weight (g) (SHFW) and shoot dry weight (g) (SHDW). Field trail conducted to measure vegetative traits, yield and yield components and fiber traits. Analysis of variance for the growing seasons 2016 and 2017 revealed significant differences with respect to water regimes, genotypes and water regimes x genotypes for most of the studied traits, confirming the presence of genotypic variability among the studied cotton genotypes. Mean values exhibited decreasing in traits from normal to water deficit conditions in all traits except for maturity (M). The relative reduction (RD%) varied from 1.25% for pressley index(PI) to 51.6% for lint yield/plant (LY/P). Fiber traits were the lowest affected traits by water stress. G. 88, G. 93 and Suvin were less affected by water stress for seedling traits. For vegetative traits, G.77, G.94, G.89xG.86, Ashmouni, Menoufi and Suvin showed higher values under water deficit. Regarding to yield and yield components traits G.89xG.86, Menoufi, Suvin and G.86 showed the highest water deficit tolerance with acceptable production under limited water regime. On the other hand, most of extra-long staple cotton varieties G.87, G.88 and G.93 were most susceptible to water deficit stress in production term. Drought susceptibility index (DSI) showed significant negative correlation with yield under water deficit regime suggesting DSI as a useful predictor of drought tolerance in cotton and confirming the need of performing genotype evaluation under water stress in case of breeding for water deficit tolerance. Generally, the extra-long genotypes were more susceptible to water deficit stress than long staple genotypes for fiber traits. Correlation coefficients between all the studied traits under well watered and limited water regimes over two years revealed that, yield was positively correlated with yield components traits and plant height (PH); and negatively correlated with most fiber traits. The path coefficient analysis revealed positive and negative direct effect of traits on seed cotton yield (SCY/P). The highest direct effect on SCY/P was exhibited by bolls/plant (B/P) (1.36) followed by boll weight (BW) (0.91) and lint percentage (L%) (0.53). The highest indirect effect of most of yield and vegetative traits were through B/P and BW. These results confirming that, selection to improve productivity under water deficit stress could be more effective throughout direct selection for B/P and BW. Factor analysis revealed that first three components accounted for about 88.51% % of the total variation among the studied traits. Results exhibited the importance of LI, SI, L%, BW, LY/P, SCY/P and PH traits in factor 1 and B/P, SCY/P and LY/P in factor 2 confirming the importance of these traits in the total variance to improve productivity under deficit water stress.

Multi-Objective Optimization of the Reservoir System Operation by Using the Hedging Policy

In the present study the WEAP-NSGA-II coupling model was developed in order to apply the hedging policy in a two-reservoir system, including Gavoshan and Shohada dams, located in the west of Iran. For this purpose after adjusting the input files of WEAP model, it was calibrated and verified for a statistical period of 4 and 2 years respectively (2008 till 2013). Then periods of water shortage were simulated for the next 20 years by defining a reference scenario and applying the operation policy based on the current situation. Finally, the water released from reservoirs was optimized based on the hedging policy and was compared with the reference scenario in coupled models. To ensure the superiority of the proposed method, its results was compared with the results of two well-known multi-objective algorithms called PESA-II and SPEA-II. Results show that NSGA-II algorithm is able to generate a better Pareto front in terms of minimizing the objective functions in compare with PESA-II and SPEA-II algorithms. An improvement of about 20% in the demand site coverage reliability of the optimum scenario was obtained in comparison with the reference scenario for the months with a higher water shortage. In addition, considering the hedging policy, the demand site coverage in the critical months increased about 35% in compared with the reference scenario.

Olive oil quality response to irrigation cut-off strategies in a super-high density orchard

An increase in olive oil consumption has occurred worldwide in the last decades and has resulted in more land area being dedicated to olive orchards in several southern hemisphere countries. In order to achieve sustainable productivity under the increasing water scarcity, optimal water use is essential. Thus, a field experiment was conducted during four consecutive growing seasons (2010–2011 to 2013–2014) to evaluate olive oil quality in response to irrigation cut-off strategies applied after fruit set using midday stem water potential (Ψstem) thresholds in a super-high density olive orchard (cv. Arbequina) located in the Pencahue Valley, Maule Region, Chile. The experimental design was completely randomized with four treatments and four replicates. In treatment T1 (control), Ψstem was between −1.4 and −2.2 MPa (100% of actual evapotranspiration) throughout the season, while the T2, T3 and T4 treatments did not receive irrigation from fruit set until they reached a Ψstem threshold of approximately −3.5, −5.0, and −6.0 MPa, respectively. Once these thresholds were reached, irrigation was reestablished and maintained as T1 in all treatments until olives were harvested. Fruit oil and water content (%) at harvest were not affected by the different treatments. Free acidity was also not affected, while peroxide and extinction coefficients only showed minor differences between treatments that were within the limits established for commercial extra virgin oil quality. Total polyphenols at harvest were much higher in the water deficit treatments and showed a significant linear relationship each year with the water stress integral. The percentages of the main fatty acids were not affected by the treatments. However, they were significantly different between seasons. Sensory tests indicated that the higher total polyphenol content positively contributed to more pronounced bitter and pungent attributes of olive oil from trees with higher water deficit. Thus, the irrigation cut-off strategies evaluated at our four-year study can be an excellent management tool to both improve the oil quality of cv. Arbequina and reduce water use in super-high density orchard.

DIEBACK, LEAF AREA INDEX AND YIELD OF YOUNG EUCALYPT CLONES PLANTATION IN THE BRAZILIAN SAVANNAH REGION

ABSTRACT Eucalypt has been widely planted in Brazil, in the savannah region, which is characterized by high soil water deficit and low fertility. Dieback, leaf area index (LAI) and yield of young stands of 16 eucalypt clones were studied in Vazante, MG, Brazil (17º36’09"S and 46º 42’02"W). It was determined for each clone: a) the proportion of the tree height with dieback symptoms in the apical terminal (HWD%) and the proportion of trees with dieback (NWD%), at 13 months (end of the first dry season); b) the LAI at 13 and 21 months, and c) the yield at the age of 13, 19 and 25 months. HWD% reached 5-9%, and NWD%, 50-80%, for the five most susceptible clones, when the soil water deficit reached 508 mm in the year. LAI varied from 0.61 to 1.56, at 13 months, and from 2.31 to 3.48 at 21 months, presenting inverse relationship with dieback. The least susceptible clones to dieback achieved the highest yield up to 25 months of age. There was interaction between dieback and fertilizer levels only for three clones. There was a positive correlation (p < 0.001) between the LAI at the age of 13 months and the periodic monthly increment from 0 to 11 months, and from 11 to 19 months. The difference in dieback susceptibility among clones allows the selection of genotypes for regions where the soil water deficit is a major limiting factor.

Interannual Variation in Temperature and Rainfall can Modulate the Physiological and Photoprotective Mechanisms of a Native Semiarid Plant Species

Climate change may affect ecosystems worldwide, but can be aggravated in arid environments, leading to decreased rainfall and a consequent increase in air temperature. Objective: The present investigation aimed to study the behavior of a native plant, adapted to seasonal dry conditions, when faced with different conditions in two years: one extremely dry and the other with rains within the expected range. Methods/Analysis: To study the effects of the seasonal water deficiency, we collected all data in two consecutive years: 2012 and 2013. Results: In both years, we obtained data in May (rainy season) and August (dry season). The predawn water potential ( Ψw) ranged from -5.6 to -4.2 MPa in 2012 and from-2.16 to -2.98 MPa in 2013. These patterns show that even in the rainy season of the dry year, the plants were subjected to a very high water deficit when compared to the wet year; this was due to the sparse rains of 2012, the driest year of the preceding decade in the study area. All gas exchange and carbon uptake tended to zero in 2012; however, all the parameters recovered when the rains returned in 2013. Considering the entire data set, the water use efficiency (WUE) data presented a positive and significant correlation with all the photosynthetic parameters. However, when we excluded the 2012 data, the WUE was negatively correlated with transpiration (E ), stomatal conductance ( gs ) and leaf temperature ( Tleaf ). One average, the potential photosynthesis (PN-pot), maximum carboxylation velocity of Rubisco ( Vc-max ) and the maximum electron transport rate ( Jmax ) values were on average 62%, 50% and 63% lower in the dry season than in rainy season in 2013. Discussion/Conclusions: We argue that the increase of intercellular carbon caused the increase in photosynthesis to its limitation point of photosynthesis by Jmax . Below the collimation point, the photosynthetic rates were limited by Vc-max . Thus, the prolongation of the dry season could have potential impacts on the electron transport rate and on Rubisco carboxylation efficiency, taking into account the current concentrations of atmospheric carbon dioxide. During a prolonged drought, the reduced Ψw , osmotic adjustment and efficient antioxidative system appear to be the main strategies that C. pyramidale uses to avoid fatal plant dehydration, maintaining basal rates of net photosynthesis. However, with the intensification of climate changes expected for the study area, the species may no longer be a symbol of the ecosystem but rather a symbol of environmental degradation. Keywords: World Climatic Change, Electron Transport Rate, Carbon Uptake, Gas Exchange, Reactive Oxygen Species, Water Scarcity

Modelling climate change impacts on early and late harvest grassland systems in Portugal

Climate change projections for Portugal showed warming and drying trends, representing a substantial threat for the sustainability of forage production in perennial grassland. The objective of the present study was to assess climate change impacts on seasonal dry matter yield (DMY) in three locations (North-west-, Central-inner and South-Portugal) with different climatic conditions, for two grassland production systems deviating in growing season length, either early cuts in spring (ES) or late cuts in summer (LS). Impacts were estimated using the STICS (Simulateur mulTIdisciplinaire pour les Cultures Standard) crop model, by comparing a historical baseline period (1985–2006) with simulated projections over future periods (2021–2080). For this purpose, the STICS crop model was driven by high-resolution climate data from a coupled Global Climate Model/Regional Climate Model chain. As a result, we obtained that, during the baseline period, DMY of LS was consistently much higher than that of ES in all three locations. For LS, significant reductions in mean DMY were forecasted during 2061–2080, ranging from mild (–13%) in the north to severe (–31%) in the south of Portugal. In contrast, seasonal DMY was largely maintained for ES among sites until 2080, benefiting from low water deficits, the expected atmospheric CO2 rise and the forecasted temperature increase during cool season. Thus, the yield gap was projected to gradually decrease between the two regimes, in which mean DMY for ES was foreseen to exceed that of LS over 2061–2080 in the southern site. Moreover, ES was projected to have very low exposure to extreme heat and severe water stresses. Conversely, LS, subjected to high summer water deficit and irrigation needs, was projected to experience increased summertime water stress (9–11%) and drastically increased heat stress (33–57%) in 2061–2080, with more pronounced heat stress occurring in the south. Frequency of occurrence of extreme heat stress was projected to gradually increase in summer over successive study periods, with a concomitant increased intensity of DMY response to inter-annual variability of heat stress during 2061–2080. Heat stress tended to be more important than water stress under the prescribed irrigation strategy for LS, potentially being the main limiting factor for summertime DMY production under climate change scenario.

Physiological characterization of rhizobial strains nodulating alfalfa (Medicago sativa) isolated from soils of Southeastern Morocco

The legume-rhizobia symbiosis provides the necessary nitrogen for plants growth and contributes to the improvement of soil nitrogen level. However, environmental constraints prevailing in many Moroccan regions constitute the limiting factors for this symbiotic interaction. For this reason, the present work aims to select some rhizobial strains nodulating alfalfa ( Medicago sativa L.) for their performance under environmental stresses. Rhizobial strains nodulating alfalfa were isolated from soils of Tafilalet region ( Arfoud 1 , Arfoud 4 , Aoufous and Rich ) and purified in yeast extract mannitol (YMA) medium. After nodulation test, 20 strains were able to induce root nodulation in alfalfa and they were tested for their tolerance to high salinity, water deficit, acidity and temperature. These strains were also assessed for their abilities to solubilize inorganic phosphorus using Pikovskaya (PVK) medium. The results indicated that the studied strains developed different behaviors in response to all considered abiotic stresses. The positive correlations between strains behaviors and origin were noted. In general, strains from Arfoud1 and Arfoud 4 were qualified as the most tolerant to salt stress and can grow under extreme pH levels (4 to 10). Whereas, strains from Rich were the most tolerant to water deficit. Results recorded on PVK medium mentioned that some strains ( Arf1RL1 , RYRL9 and Arf4RL16 ) showed a high potential of inorganic phosphorus solubilization. Some strains such as Arf1RL1 and Arf4RL13 both high tolerance level to considered environmental constraints and high potential of inorganic phosphorus solubilization.

The microtubule-associated RING finger protein 1 (OsMAR1) acts as a negative regulator for salt-stress response through the regulation of OCPI2 (O. sativa chymotrypsin protease inhibitor 2).

Our results suggest that a rice E3 ligase, OsMAR1, physically interacts with a cytosolic protein OCPI2 and may play an important role under salinity stress. Salt is an important abiotic stressor that negatively affects plant growth phases and alters development. Herein, we found that a rice gene, OsMAR1 (Oryza sativa microtubule-associated RING finger protein 1), encoding the RING E3 ligase was highly expressed in response to high salinity, water deficit, and ABA treatment. Fluorescence signals of its recombinant proteins were clearly associated with the microtubules in rice protoplasts. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) showed that OsMAR1 interacted with a cytosolic protein OCPI2 (O. sativa chymotrypsin protease inhibitor 2) and led to its degradation via the 26S proteasome. Heterogeneous overexpression of OsMAR1 in Arabidopsis showed retarded root growth compared with that of control plants, and then led to hypersensitivity phenotypes under high salinity stress. Taken together, OsMAR1 negatively regulates the salt-stress response via the regulation of the OCPI2 protein in rice.