Soil Drought Research Articles

Features Of Photosynthesis And Water Regime Of Quercus Pubescens Willd. Under The Conditions Of Autumn Drought Of The Southern Coast Of The Crimea

The objective of the research is to determine the optimal zones and thresholds of soil moisture, temperature, illumination, limiting photosynthesis and transpiration of Quércus pubéscens Willd. and allowing the introduction of the species to other regions. The dependences of the net photosynthesis rate (Pn) and the transpiration rate (E) on stomatal conductivity (gs), leaf temperature (Tl), and soil moisture (Ws) are shown. The ratio of the processes of photosynthesis and respiration, under the influence of soil drought, allowed us to define their optimal values: Ws = 26 – 28%, Pn = 16 –18 μmol/m2c, Rt = 2 – 4 μmol/m2c. The relationship between the net photosynthesis rate, total respiration, and leaf temperature allowed us to determine the temperature maximum of net photosynthesis (the thermal compensation point): Pn = Rt = 2.0 μmol/m2c at Tl = 37ºC. It was found that in the absence of soil drought, the proportion of respiratory costs (Rt/Pg) from true photosynthesis is 20 – 23%, and with soil moisture of 8 – 10% increases to 55 – 58%.

The effect of soil drought on the content of photosynthetic pigments in barley plants of the Brovar variety

A significant effect of soil drought on the morphometric parameters of the leaves of barley plants of the Brovar variety, as well as the content of photosynthetic pigments (chlorophyll, carotenoids) in them was established. However, a significant decrease in plant growth indicators under drought conditions, a decrease in the amount of chlorophyll and, to a greater extent, carotenoids occurred against the background of the absence of a change in the content of pheophytin. We assume that the decrease in the number of pigments is mainly associated not with destruction due to stress, but with a decrease in their synthesis, which can be an adaptive reaction of plants, which minimizes the likelihood of formation of reactive oxygen species in photosynthetic membranes under conditions of drought, and also optimizes the use of light energy for photosynthetic processes under such conditions, as indicated by the predominant decrease in carotenoids such as neoxanthin, violaxanthin and β-carotene, which are actively involved in light harvesting and energy transfer to reaction centers.

Violation of the structure of the forest biocenosis under the action of stem pests and methods of controlling their numbers

The study of the forest ecosystem as an integral part of the erosion system is associated with a number of issues. The forest is the most powerful and effective tool in the fight against soil erosion, droughts and hot winds, as well as an environmental stabilising factor in general. Human forestry activities in the fight against the drying of coniferous plantations from an outbreak of mass reproduction and spread to large areas of stem pests under the influence of a complex of ecological and climatic factors, is one of the serious factors disrupting the structure of the forest biocenosis. The search for alternative solutions to the localisation of this problem requires a detailed study of the behaviour of the most common bark beetles of coniferous trees in climatic and environmental conditions that developed during 2011-2020. During the period of active temperatures in 2019, namely from the second decade of April to the third decade of October, work on stationary supervision and laboratory field work was carried out to solve the problem of localisation of stem pests of Polissya and Forest-Steppe pine plantations. Methods of laying out hunting trees and pheromone traps were used. In practice, the pest did not inhabit hunting trees and only a few representatives and very small entomophagous traps fell into the traps. Instead, it inhabited healthy stands of trees, where the catchers were located. It is established that from the scientific and practical standpoint, the studied regularity of pine drying centres is clearly confined to highways and timber roads, as well as the area of distribution of relevant species of trunk pests and weakening zones of pine stands in some areas for other reasons. It is proved that to preserve the ecological potential of coniferous plantations and reduce the negative impact of xylophagous insects, it is necessary to design preventive and biological methods of control of the main trunk pests of coniferous trees

Arbuscular mycorrhizal fungi improve the antioxidant capacity of tea (Camellia sinensis) seedlings under drought stress

A pot experiment was carried out to evaluate the response of leaf antioxidant enzyme systems to inoculation with arbuscular mycorrhizal fungus (AMF) Clariodeoglomus etunicatum in tea (Camellia sinensis cv. ‘Fuding Dabaicha’) seedlings under drought stress (DS). Root AMF colonization was significantly decreased after an eight-week soil drought treatment. Plant growth performance (plant height, stem diameter, leaf number and root biomass), leaf relative water content, and leaf water potential were notably decreased under DS conditions, whereas these variables exhibited significantly higher responses in mycorrhizal seedlings than in non-mycorrhizal seedlings. The DS treatment markedly increased leaf superoxide anion concentration but did not affect malondialdehyde content, whereas both were reasonably decreased by AMF colonization regardless of water status. The seedlings colonized by AMF showed substantially higher antioxidant enzyme activities including superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase, and ascorbate peroxidase than the non-AMF colonized seedlings under both well-watered and DS conditions. DS markedly upregulated the relative expression of CsSOD in both AMF and non-AMF seedlings and the relative expression of CsCAT in AMF seedlings. Meanwhile, AMF-colonized seedlings represent markedly higher relative expressions of CsSOD and CsCAT than non-AMF seedlings, irrespective of water status. It concludes that mycorrhizal tea plants had higher antioxidant enzyme activity and corresponding gene expression under DS, indicating a stronger ability to alleviate the oxidative damage of drought.

Study of drought manifestation and its effect on the thermal regime of vegetation surface of crops under irrigation

Relevance of the topic. In recent years, irrigation management practices have faced new challenges related to climate change and the increase in the frequency and intensity of droughts in the southern regions. In addition, the latest technical and technological capabilities have emerged in irrigated agriculture to more effectively manage technological processes. All these processes occurring in real production and in the market of scientific and technical products, have determined the possibility and necessity of studying the influence of natural and agricultural conditions on the processes of energymass transfer in the "soil-plant-atmosphere" environment to improve management methods in modern irrigation conditions. Purpose of research is to investigate the features of formation of crop thermal regime in the conditions of air and soil drought manifestation under irrigation during 2018-2019. Research object. The research was carried out at the production fields of the farm “Freedom Farm International” in the Kakhovsky district of Kherson region during 2018-2019. Two experimental sites were equipped to carry out experimental studies on the crop rotation of "Gornostayevske -2". Methodology and Research methods. The methodology for the conduct of thermal water balance and phenological observations on the growth and development of crops at the experimental sites was applied. Standard field research techniques were used. Analytical, field, simulation modeling, mathematical statistics, geoinformation technologies (GIS), remote sensing of the Earth (RS) methods were used. Research results. As a result of the research in 2018-2019 a database of farm fields (crops, sowing dates, soil conditions, initial moisture reserves, irrigation machines and their characteristics) was created; phenological observations of plant growth and development were performed, heat and water balance calculations were made. It was established that to ensure optimal conditions for the use of thermal energy in different drought conditions, it is necessary to improve models and algorithms for operational planning of crop irrigation. Thus, to mitigate the influence of atmospheric drought, it is recommended to conduct refreshing irrigation, the timing of which can be determined on the basis of monitoring the temperature of the vegetation surface, using the data from the space images or ground-based observations. In addition, under drought conditions, in the case of applying water-balance methods used in irrigation management, it is necessary to adjust the biological coefficients of water consumption by crops, based on modeling the production process using the WOFOST model and identifying its parameters with the help of space images. The obtained new knowledge is aimed at improving irrigation management methods in modern conditions.

Effects of drought and rainfall events on soil autotrophic respiration and heterotrophic respiration

The changes of surface vegetation cover, caused by the return of farmland to forest and grassland, can not only effectively control soil erosion, but also significantly increase soil organic carbon reserves. However, few studies are currently available on the control mechanism of soil CO2 emission after artificial vegetation restoration, particularly on sloping land. This lack of knowledge increases the uncertainty of quantitative estimations of the effect of soil carbon cycle in conversions of cultivated land to forest. This study selected three different plantation types from re-forested hillslopes and monitored both soil respiration and its component changes. The goal was to describe the responses of soil heterotrophic respiration (Rh), soil autotrophic respiration (Ra), and total soil respiration (Rt) to drought and precipitation. Furthermore, the effects of climate warming and drought on soil respiration were evaluated in these reforested areas. A two-year experiment was conducted in the Haihe River Basin of China to study the effects of drought and precipitation on Rt and Rh. The results showed that: (1) soil drought significantly decreased soil respiration carbon emissions. In 2014, rainfall was 20.25 % lower than in 2013, and soil respiration carbon emissions were 5% lower (95 % confidence interval from 1% to 8.1 %). (2) Rainfall significantly increased carbon emissions from soil respiration by 33 % after rainfall (95 % confidence interval from 29.9%–36.5%). (3) Ra and Rh showed different responses to climate warming and drought, where Rh is more sensitive to drought than Ra, and the percentage of Rh in Rt (PRh) was positively correlated with soil moisture. These results show that the increase in soil respiration after vegetation restoration may not be as strong as predicted for semi-humid regions. Climate warming also results in lower soil moisture and less precipitation, which neutralizes part of the positive feedback from the soil-carbon climate.

Impact of Water Deficit on Seasonal and Diurnal Dynamics of European Beech Transpiration and Time-Lag Effect between Stand Transpiration and Environmental Drivers

In-situ measurements of tree sap flow enable the analysis of derived forest transpiration and also the water state of the entire ecosystem. The process of water transport (by sap flow) and transpiration through vegetation organisms are strongly influenced by the synergistic effect of numerous external factors, some of which are predicted to alter due to climate change. The study was carried out by in-situ monitoring sap flow and related environmental factors in the years 2014 and 2015 on a research plot in Bienska dolina (Slovakia). We evaluated the relationship between derived transpiration of the adult beech (Fagus sylvatica L.) forest stand, environmental conditions, and soil water deficit. Seasonal beech transpiration (from May to September) achieved 59% of potential evapotranspiration (PET) in 2014 and 46% in 2015. Our study confirmed that soil water deficit leads to a radical limitation of transpiration and fundamentally affects the relationship between transpiration and environmental drivers. The ratio of transpiration (E) against PET was significantly affected by a deficit of soil water and in dry September 2015 decreased to the value of 0.2. The maximum monthly value (0.8) of E/PET was recorded in August and September 2014. It was demonstrated that a time lag exists between the course of transpiration and environmental factors on a diurnal basis. An application of the time lags within the analysis increased the strength of the association between transpiration and the variables. However, the length of these time lags changed in conditions of soil drought (on average by 25 min). Transpiration is driven by energy income and connected evaporative demand, provided a sufficient amount of extractable soil water. A multiple regression model constructed from measured global radiation (RS), air temperature (AT), and air humidity (RH) explained 69% of the variability in beech stand transpiration (entire season), whereas (RS) was the primary driving force. The same factors that were shifted in time explained 73% of the transpiration variability. Cross-correlation analysis of data measured in time without water deficit demonstrated a tighter dependency of transpiration (E) on environmental drivers shifted in time (−60 min RS, +40 min RH and +20 min vapour pressure deficit against E). Due to an occurrence and duration of soil water stress, the dependence of transpiration on the environmental variables became weaker, and at the same time, the time lags were prolonged. Hence, the course of transpiration lagged behind the course of global radiation by 60 (R2 = 0.76) and 80 (R2 = 0.69) minutes in conditions without and with water deficit, respectively.

The response of Pinus species to ozone uptake in different climate regions of Europe

Abstract This study is focused on the research of selected Pinus species exposed to high ozone concentrations in the mountain environment. We noticed different values of modelled ozone doses (MOD) up-taken by Mountain pine (Pinus mugo Turra) in the High Tatra Mts (SK–HTMts) and Swiss stone pine (Pinus cembra L.) in the Alpes-Mercantour (FR–AlpMar) during the growing season 2019. The MOD values were obtained by multiplicative DO3SE model, while we also tested a new approach based on modification of input ozone data. The MOD values were obtained by multiplicative DO3SE model, while we also tested a new approach based on modification of input ozone data. Testing has shown that ozone input based on passive sampling may be used in MOD modelling for sites situated in the subalpine zone where the operation of active monitors is limited.. Presented results confirmed the assumption regarding stomatal ozone flux reduction due to the occurrence of soil drought in hot and dry summer weather typical for the Mediterranean climate region. Despite the limitation of stomatal flux, foliar ozone specific injury on two years needles of P. cembra was substantially higher in comparison to the incidence of ozone injury symptoms observed on two years needles of P. mugo in SK–HTMts. It may suggest low phytotoxicity of given MOD or efficient resistance of P. mugo against oxidative stress. In addition, the visible injury index (VINX) covering the broad effect of biotic and abiotic harmful agents was appraised on P. mugo. Percentage of affected surface indicated moderate deterioration of needle injury at the end of the growing season, particularly due to traces of mechanical damage.

Abscisic Acid Mediates Drought and Salt Stress Responses in Vitis vinifera-A Review.

The foreseen increase in evaporative demand and reduction in rainfall occurrence are expected to stress the abiotic constrains of drought and salt concentration in soil. The intensification of abiotic stresses coupled with the progressive depletion in water pools is a major concern especially in viticulture, as most vineyards rely on water provided by rainfall. Because its economical relevance and its use as a model species for the study of abiotic stress effect on perennial plants, a significant amount of literature has focused on Vitis vinifera, assessing the physiological mechanisms occurring under stress. Despite the complexity of the stress-resistance strategy of grapevine, the ensemble of phenomena involved seems to be regulated by the key hormone abscisic acid (ABA). This review aims at summarizing our knowledge on the role of ABA in mediating mechanisms whereby grapevine copes with abiotic stresses and to highlight aspects that deserve more attention in future research.

Metabolite profiling of semi-leafless pea (Pisum sativum L.) under progressive soil drought and subsequent re-watering

Four semi-leafless pea (Pisum sativum L.) cultivars at the vegetative stage of growth were exposed to progressive soil drought, which lasted for 18 days until the plants began to wilt, after which a 7-day period of the recovery from stress followed, when plant watering was resumed. The soil drought negatively affected plant growth, slowing down the rate of shoot elongation, decreasing the accumulation of fresh and dry weight, inhibiting the development of new leaves, and delaying the flowering of plants. Changes in the levels of 41 polar metabolites (identified by GC–MS) were established by the GC-FID method in the shoot tip, stem, stipules and tendrils, separately. Drought caused re-arrangement in the metabolism in all parts of the pea shoot, leading to a significant increase in the content of total polar metabolites. Although changes in most metabolites in the same parts of shoot were not identical among the pea cultivars studied, some metabolites were uniformly accumulated until 18th day of drought and decreased after recovery. They were i) proline and malate in all, while myo-inositol in most parts of shoot (of all the pea cultivars), ii) sucrose and glycine in the shoot tip, iii) homoserine in the stem and iv) GABA in stipules. These findings signify that the pea adjustment to progressive soil drought includes both accumulation of osmolytes and osmoprotectants and translocation of some of them (proline, sucrose, myo-inositol) to the shoot tip, thereby protecting the youngest tissues from damage caused by water deficit.

The Enhanced Management of Water Resources Improves Ecosystem Services in a Typical Arid Basin

Ecosystem services (ES) are essential for human well-being. However, few studies have investigated the optimization of the management of water resources based on trade-offs of ES in arid areas. In order to solve this problem, four important ES that affect the carbon cycle and water cycle were selected from the regulating ecosystem services (carbon storage (CAS), evapotranspiration (ET)), the supporting ecosystem services (soil drought index (TVDI)) and the provisioning ecosystem services (groundwater depth (GWD)) in arid areas. The spatiotemporal distribution of these four ES were quantitatively analyzed—using related models—in the Tarim River, situated in a typical arid inland basin, in 2000, 2010, and 2018, in order to determine the fundamental driving factors of change in ES. The results showed that CAS was mainly affected by changes in land use, while ET, TVDI, and GWD were mainly affected by changes in water volume. The unified management of water resources improved the regulating ecosystem services (an initial increase in CAS, followed by a decrease; ET continued to grow from 2000 to 2018), the supporting ecosystem services (TVDI was maintained at 0.69–0.74), and the provisioning ecosystem services (GWD rose 5.77% in 2000–2010, and stabilized at 3.05 m in 2018). The trade-off/synergy relationships of the four ES were further analyzed at different geographical scales through correlation analysis and the trade-off index (RMSD). In different river sections, the ES that affect carbon and water cycles were highly dependent on each other. In areas with high CAS, the groundwater depth was low, and the soil moisture and ET were high. With different land use types, there was a synergistic relationship between CAS and GWD in woodland and grassland areas, and between ET and GWD in farmland areas. This showed that there was still strong competition between natural vegetation and groundwater, represented by woodland and grassland, and the ineffective loss of water resources such as ET through expansion of farmland. Finally, this study innovatively incorporated the results of trade-offs of ES into water resource management. In order to reduce the trade-offs between ES, and to improve ES, to achieve the ecological protection and restoration of desert riparian forests, and to optimize the water resource management in arid areas, different ecological water regulation and control measures were proposed in the high-flow years and the low-flow years of arid areas. This study can provide important scientific references for the improvement of ES and the optimization of the management of water resources in other similar river basins in arid areas.

Soil drought and circulation types in a longitudinal transect over central Europe

AbstractAmong the variables that can be employed to characterize agricultural drought, soil drought is of particular importance. This contribution uses gridded soil‐drought values calculated from the SoilClim model for the 1961–2019 period to analyse soil drought episodes (based on the 10th percentile) in four lowlands, relatively homogeneous regions in central Europe that provide a longitudinal transect over central Europe. These areas are predominantly located at altitudes of below 400 m asl and include central Bohemia, southern Moravia and an adjacent part of Slovakia, southern Slovakia and eastern Slovakia. The results indicate that, after 1990, such episodes occurred largely in the summer half‐year (April–September), accompanied by an increasing linear trend in the 1961–2019 period, while the situation was reversed in the winter half‐year (October–March). Selected drought episodes are further divided into three phases (Phase I – origin, Phase II – course, Phase III – end) and investigated separately in terms of precipitation and objective classification of circulation types based on flow strength, direction and vorticity. Decreases in the frequency of precipitation‐rich cyclonic and the directional types associated with higher daily precipitation totals, together with increases in precipitation‐poor anticyclonic types, were responsible for soil‐drought Phases I and II, with the opposite pertaining to Phase III. Differences in the effects of circulation types on precipitation and soil‐drought occurrence were considerable, particularly for central Bohemia compared with the other three regions. The results obtained are also discussed with respect to data uncertainty and their broader spatiotemporal context.

Selenium and silica nanostructure-based recovery of strawberry plants subjected to drought stress

Drought is an important environmental stress that has negative effects on plant growth leading to a reduction in yield. In this study, the positive role of nanoparticles of SiO2, Se, and Se/SiO2 (SiO2-NPs, Se-NPs and Se/SiO2-NPs) has been investigated in modulating negative effects of drought on the growth and yield of strawberry plants. Spraying of solutions containing nanoparticles of SiO2, Se, and Se/SiO2 (50 and 100 mg L−1) improved the growth and yield parameters of strawberry plants grown under normal and drought stress conditions (30, 60, and 100%FC). Plants treated with Se/SiO2 (100 mg L−1) preserved more of their photosynthetic pigments compared with other treated plants and presented higher levels of key osmolytes such as carbohydrate and proline. This treatment also increased relative water content (RWC), membrane stability index (MSI) and water use efficiency (WUE). In addition, exogenous spraying of Se/SiO2 increased drought tolerance through increasing the activity of antioxidant enzymes including catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and superoxide dismutase (SOD) as well as decreasing lipid peroxidation and hydrogen peroxide (H2O2) content. Increase in biochemical parameters of fruits such as anthocyanin, total phenolic compounds (TPC), vitamin C and antioxidant activity (DPPH) in strawberry plants treated with Se/SiO2 under drought stress revealed the positive effects of these nanoparticles in improving fruit quality and nutritional value. In general, our results supported the positive effect of the application of selenium and silicon nanoparticles, especially the absolute role of Se/SiO2 (100 mg L−1), on the management of harmful effects of soil drought stress not only in strawberry plants, but also in other agricultural crops.

Soil erosion control and wheat productivity are improved by a developed ridge-furrow and reservoir tillage systems

ABSTRACT Soil erosion and drought are significant environmental hazards for crop production in the northwestern coastal zone of Egypt, leading to increased soil resources degradation. In-situ rainwater harvesting techniques by changing the micro-topography of soil via tillage practices can increase runoff retention and improve soil productivity. In this study, field trials were conducted on a sandy loam soil to determine the effects of four tillage systems [integrated ridge-furrow tillage (RFT), integrated reservoir tillage (RT), conventional tillage (CT), and No tillage (NT)] on soil bulk density, volumetric water content, runoff, soil loss, precipitation use efficiency, and winter wheat yield during two growing seasons under-rainfed conditions. The results indicated that tillage systems significantly affected soil properties, precipitation use efficiency and wheat yield in the order of: RFT > RT > CT > NT. Compared with the CT, the mean runoff with the developed RFT and RT was significantly decreased by 55.4% and 40.3%, respectively. Meanwhile, the precipitation use efficiency increased by 18.1% and 9.5%, respectively. By taking into account the stability of soil productivity along with environmental protection, it is suggested that the RFT and RT are the tillage systems that can efficiently increase the availability of soil water and, consequently, wheat yield.

Unravelling the role of arbuscular mycorrhizal fungi in mitigating the oxidative burst of plants under drought stress.

With continued climate changes, soil drought stress has become the main limiting factor for crop growth in arid and semi-arid regions. A typical characteristic of drought stress is the burst of reactive oxygen species (ROS), causing oxidative damage. Plant-associated microbes, such as arbuscular mycorrhizal fungi (AMF), can regulate physiological and molecular responses to tolerate drought stress, and they have a strong ability to cope with drought-induced oxidative damage via enhanced antioxidant defence systems. AMF produce a limited oxidative burst in the arbuscule-containing root cortical cells. Similar to plants, AMF modulate a fungal network in enzymatic (e.g. GmarCuZnSOD and GintSOD1) and non-enzymatic (e.g. GintMT1, GinPDX1 and GintGRX1) antioxidant defence systems to scavenge ROS. Plants also respond to mycorrhization to enhance stress tolerance via metabolites and the induction of genes. The present review provides an overview of the network of plant - arbuscular mycorrhizal fungus dialogue in mitigating oxidative stress. Future studies should involve identifying genes and transcription factors from both AMF and host plants in response to drought stress, and utilize transcriptomics, proteomics and metabolomics to clarify a clear dialogue mechanism between plants and AMF in mitigating oxidative burst.

Multi-stemming strategies of Quercus glauca in an evergreen broad-leaved forest: when and where

Abstract Aims Multi-stemming supports plants’ resilience to disturbances and then contributes to soil stabilization and forest function, especially in mountain habitats. Many questions remain about (i) the ontogenetic phase at which multiple stems can occur, (ii) how habitat drivers affect multi-stemming and (iii) whether ontogenetic phase and habitat drivers interact. We asked these questions for Quercus glauca (ring-cupped oak), the dominant species and sprouter across large warm-temperate areas of Asia; its multi-stemmed trees reflect individual survival, population regeneration and forest ecosystem stability. Methods In a 5-ha permanent plot of subtropical evergreen broad-leaved forest in eastern China, we examined the temporal patterns and spatial distribution of multi-stemmed trees of Q. glauca within 99 quadrats of 20 m × 20 m. Important Findings There were three temporal modes for multi-stemming among the Q. glauca trees and most of them appeared to produce multiple stems from an early stage. Environmental disturbances related to slope convexity appear to be the main drivers of multi-stemming of Q. glauca. Moreover, the closer to the ridge, the earlier the multi-stemming occurs. Thus, also for other woody species in other forests and climate zones, ontogeny and environmental drivers promoting disturbance (not only geomorphology, but also extreme weather events, soil drought, fire), as well as soil fertility, need to be considered in combination to better understand multi-stemming and its consequences for community structure.

Influence of drought on the photosynthetic apparatus activity, senescence rate, and productivity in wheat plants

Effects of soil drought at flowering stage on the functional state of photosynthetic apparatus and chloroplast enzymatic antioxidant defense systems in flag leaf during reproductive period, and the productivity of winter wheat plants of high-protein Natalka variety and drought-tolerant Podolyanka variety were studied in pot experiment. Until flowering and for the control plants during the entire vegetation, the soil moisture content was maintained at a level of 60—70 % of field capacity (FC). Drought treatment (soil moisture 30 % FC) was applied for 7 days covering flowering—early kernel watery ripe period (BBCH 61—71). After that, watering of plants was resumed to a control level which was maintained until the end of the growing season. The estimation of the chlorophyll and Rubisco content, the chloroplast antioxidant enzymes activity, and the net CO2 assimilation and transpiration rates was carried out on flag leaves. The measurements were taken on the third day of watering cessation (the first day the soil moisture reached 30 % FC, BBCH 61), at the end of the drought period (seventh day at 30 % FC, BBCH 71), and after watering resumed at the medium milk (BBCH 75) and late milk (BBCH 77) stages. The components of plant grain productivity were determined by weighing air-dry material at grain full ripeness. It was revealed, that drought stress during flowering inhibited CO2 assimilation and accelerated induction of senescence processes in wheat plants associated with degradation of photosynthetic apparatus and manifested in quicker ontogenetic drop in chlorophyll and Rubisco contents and loss of leaf photosynthetic activity. This exacerbated the drought impact on the plant organism so that after optimal watering return, the physiological and biochemical parameters were not restored to the values of control plants that were all time under optimal moisture supply. Stress-induced premature senescence reduced the supply of plants with assimilates and ultimately led to a decrease in their grain productivity. Impact of drought on flag leaf photosynthetic activity and especially on senescence induction were much more pronounced in the high-protein wheat variety Natalka with a genetically programmed earlier start of the nitrogen-containing compounds remobilization from leaves than in Podolyanka variety. The drought-tolerant variety Podolyanka keep ability to maintain much higher CO2 assimilation activity during drought period and to preserve photosynthetic apparatus from early induction of senescence due to likely more efficient chloroplast antioxidant defense systems, thereby gaining a better assimilates supply for yield formation.

Resistance of genetically modified wheat plants, containing a double-stranded RNA suppressor of the

Aim. Analysis of physiological and biochemical characteristics and grain productivity traits of transgenic common wheat plants (Triticum aestivum L.) with a double-stranded RNA suppressor of the proline dehydrogenase gene (pdh) compared to non-transgenic genotypes under conditions of soil drought. Methods. Biochemical assays: spectrophotometric measurements of antioxidant enzymes (SOD, APX) activity, proline dehydrogenase activity and free L-proline content; biotechnological assays: Agrobacterium-mediated transformation in planta; physiological: morphometric traits and elements of grain productivity; mathematical statistics. Results. The presence of a double-stranded RNA suppressor of the gene pdh in transgenic plants leads not only to a decrease in enzyme activity (on average 2 times compared to the nontransgenic plants), but also to an increase in the content of free L-proline both under optimal conditions and under soil drought (2.6–4.1 times). Under soil moisture defi ciency, transgenic plants with reduced pdh gene activity in terms of yield structure signifi cantly exceeded the corresponding values of grain productivity elements for the non-transformed ones. In terms of the grain weight from the main stem, the biotechnological plants under soil moisture defi ciency exceeded the control plants 1.5–1.6 times, while the number of grains did not differ signifi cantly. The grain productivity of the whole plant in the transformed lines under conditions of soil moisture defi ciency was somewhat inferior to those in the nontransformed plants grown under optimal conditions. Soil drought caused a signifi cant increase in SOD and APX activity (by 40 and 11 %, respectively) in plants of the original variety. On the contrary, the activity of both antioxidant enzymes under drought conditions in transgenic plants decreased: SOD – down to 73–76 %, APX – down to 82–86 %, compared with the variant of 70 % of fi eld capacity. Conclusions. The analysis of physiological and biochemical characteristics, as well as economic and grain productivity elements of transgenic common wheat plants with a double-stranded RNA suppressor of the proline dehydrogenase gene showed their increased tolerance to soil drought, compared with non-transgenic genotypes, which may be associated with higher proline accumulation and an increase in the antioxidant enzymes activity. Under soil moisture defi ciency, transgenic wheat plants with reduced pdh gene activity signifi cantly exceeded the corresponding values of grain productivity elements for non-transformed plants. The analysis of the antioxidant enzymes activity in the chloroplasts of transgenic plants showed that under physiological conditions, the antioxidant system works more actively in comparison with non-transgenic genotypes, which may be a prerequisite for increasing the tolerance of these plants to the infl uence of stressors of various origin. It is likely that the positive relationship between the level of free L-proline and the resistance of transgenic wheat plants to osmotic stress is associated either with the effect of L-proline on the expression of other genes of the stress-strain response of plants, or with the positive effect of the increased content of this amino acid on resistance at the early stages of stress development. It has been suggested that an increase in the antioxidant enzymes activity in biotechnological plants can be caused by the expression of heterologous genes.

Drought response strategies of deciduous and evergreen woody species in a seasonally dry neotropical forest.

Deciduous and evergreen trees are usually considered the main coexisting functional groups in seasonally dry tropical forests (SDTF). We compared leaf and stem traits of 22 woody species in the Brazilian Caatinga to investigate whether deciduous (DC) and evergreen (EV) species have divergent water-use strategies. Our hypothesis was that DC trees compensate for their short leaf longevity by being less conservative in water use and showing higher variation in the seasonal water potential after leaf shedding. Evergreen species should exhibit a highly conservative water use strategy, which reduces variations in seasonal water potential and the negative effects of desiccation. Our leaf dynamics results indicate that the crown area of DC trees is more sensitive to air and soil drought, whereas EV trees are only sensitive to soil drought. Deciduous species exhibit differences in a set of leaf traits confirming their acquisitive strategy, which contrasts with evergreen species. However, when stomatal traits are considered, we found that DC and EV have similar stomatal regulation strategies (partially isohydric). We also found divergent physiological strategies within DC. For high wood density DC, the xylem water potential (Ψxylem) continued to drop during the dry season. We also found a negative linear relationship between leaf life span (LL) and the transpiration rate per unit of hydraulic conductivity (Λ), indicating that species with high LL are less vulnerable to hydraulic conductivity loss than early-deciduous species. Collectively, our results indicate divergence in the physiology of deciduous species, which suggests that categorizing species based solely on their leaf phenology may be an oversimplification.

Picea abies–Armillaria–Ips: A Strategy or Coincidence?

Norway spruce trees weakened by soil drought and progressive die-off of mycorrhizas in root systems become susceptible to infection by rhizomorphs of Armillaria spp. The developing mycelium of this necrotroph induces resin channels in wood, and the induced resin releases some volatile compounds which falsely signal bark beetles that it is safe to invade the host. As a result of the developing beetle outbreak, host trees die, becoming a long-term stock of substrate for the fungus in its saprotrophic stage. This hypothesis is discussed as a fungal survival strategy.