Combined Effects Of Drought Research Articles

Impact of Combined Heat and Drought Stress on the Potential Growth Responses of the Desert Grass Artemisia sieberi alba: Relation to Biochemical and Molecular Adaptation.

Artemisia sieberi alba is one of the important plants frequently encountered by the combined effect of drought and heat stress. In the present study, we investigated the individual and combined effect of drought and heat stress on growth, photosynthesis, oxidative damage, and gene expression in A. sieberi alba. Drought and heat stress triggered oxidative damage by increasing the accumulation of hydrogen peroxide, and therefore electrolyte leakage. The accumulation of secondary metabolites, such as phenol and flavonoids, and proline, mannitol, inositol, and sorbitol, was increased due to drought and heat stress exposure. Photosynthetic attributes including chlorophyll synthesis, stomatal conductance, transpiration rate, photosynthetic efficiency, and chlorophyll fluorescence parameters were drastically reduced due to drought and heat stress exposure. Relative water content declined significantly in stressed plants, which was evident by the reduced leaf water potential and the water use efficiency, therefore, affecting the overall growth performance. Relative expression of aquaporin (AQP), dehydrin (DHN1), late embryogenesis abundant (LEA), osmotin (OSM-34), and heat shock proteins (HSP70) were significantly higher in stressed plants. Drought triggered the expression of AQP, DHN1, LEA, and OSM-34 more than heat, which improved the HSP70 transcript levels. A. sieberi alba responded to drought and heat stress by initiating key physio-biochemical and molecular responses, which were distinct in plants exposed to a combination of drought and heat stress.

Repetitive desiccation events weaken a salt marsh mutualism

AbstractSalt marshes suffered large‐scale degradation in recent decades. Extreme events such as hot and dry spells contributed significantly to this, and are predicted to increase not only in intensity, but also in frequency under future climate scenarios. Such repetitive extreme events may generate cumulative effects on ecosystem resilience. It is therefore important to elucidate how marsh vegetation responds to repetitive stress, and whether changes in key species interactions can modulate vegetation resilience.In this study, we investigated how moderate but repetitive desiccation events, caused by the combined effects of drought and high temperatures, affect cordgrass (Spartina alterniflora), the dominant habitat‐forming grass in southeasternUSsalt marshes. In a 4‐month field experiment, we simulated four consecutive desiccation events by periodically excluding tidal flooding and rainfall, while raising temperature. We crossed this desiccation treatment with the presence/absence of ribbed mussels (Geukensia demissa) – a mutualist of cordgrass known to enhance its desiccation resilience – and with grazing pressure by the marsh periwinkle (Littoraria irrorata) that is known to suppress cordgrass’ desiccation resilience.We found that each subsequent desiccation event deteriorated sediment porewater conditions, resulting in high salinity (53 ppt), low pH‐levels (3.7) and increased porewater Al and Fe concentrations (≈800 μmol/L and ≈1,500 μmol/L) upon rewetting. No effects on porewater chemistry were found as a result of snail grazing, while ribbed mussels strongly mitigated desiccation effects almost to control levels and increased cordgrass biomass by approximately 128%. Importantly, although cordgrass generally appeared healthy above‐ground at the end of the experiment, we found clear negative responses of the repetitive desiccation treatment on cordgrass below‐ground biomass, on proline (osmolyte) levels in shoots and on the number of tillers (−40%), regardless of mussel and/or snail presence.Synthesis. Even though the mutualism with mussels strongly mitigated chemical effects in the sediment porewater throughout the experiment, mussels could not buffer the adverse ecophysiological effects observed in cordgrass tissue. Our results therefore suggest that although mussels may alleviate desiccation stress, the predicted increased frequency and intensity of hot dry spells may eventually affect saltmarsh resilience by stressing the mutualism beyond its buffering capacity.

Drought and heat waves associated with climate change affect performance of the potato aphid Macrosiphum euphorbiae

The combined effect of drought and heat waves on insect-plant interactions is complex and not fully understood. Insects may indirectly benefit from water-deficit stress through increased plant nitrogen levels. Heat stress may have a direct negative effect, yet insect performance may be improved when day-time heat is followed by cooler night temperatures. We show that moderate water-deficit stress (25–30% pot capacity) and high day-night temperatures (30/20 °C) affected Macrosiphum euphorbiae on potato (Solanum tuberosum) differently than their interactions. Water stress lowered stomatal conductance, and both water and heat stress reduced leaf area. The effect of water stress on nymphal and adult survival depended on temperature. Water stress added to reduced nymphal survival at high but not current (25/15 °C) day-night temperatures. Adult survival at high temperatures was reduced only when combined with water stress. Water stress and high temperatures independently but not interactively reduced the number of daily offspring. Moderate water stress when combined with high temperatures had a negative bottom-up effect on aphid survival even though lower night temperatures aided in the recovery from direct heat stress. Our study illustrates the importance of combining multiple stressors to better understand their impact on insect-plant interactions in the context of climate change.

Combined effects of drought and CO2 enrichment on foliar metabolites of potato (Solanum tuberosum L.) cultivars

ABSTRACT Drought invokes a variety of metabolic alterations in plant leaves to cope with stress situations. To understand the effects of CO2 and drought stress for leaf metabolic changes in potato [Solanum tuberosum (L)], two contrasting potato cultivars Harley Blackwell (HB, an early maturing, newer cultivar) and Snowden (SD, an established, full-season cultivar) were tested under water-limited conditions and CO2 enrichment. The results revealed that most of the drought-triggered metabolites were lower in HB compared to SD. However, HB showed quicker adjustments in the metabolic processes such as conversion of starch into soluble sugars and biosynthesis of phenylalanine and other compatible solutes at the early stages of the drought progression. Moreover, the existence of genotypic differences for leaf water potential (LWP) in response to CO2 enrichment was evident. Our study provides insights into the possible metabolic strategies of drought tolerance in potato cultivars under ambient and elevated CO2.

Individual and combined effects of drought and heat on antioxidant parameters and growth performance in Buffel grass (Cenchrus ciliaris L.) genotypes

Drought and heat stress are two critical threats to crop growth and sustainable agriculture worldwide. In the last decade, many studies focused on the response of crops to a single stress, nevertheless studying the response of plants to a combination stress may be critical to our understanding of stress tolerance in plants and the development of tolerant genotypes. Buffel grass (Cenchrus ciliaris L.) is a warm-season grass known in arid and semiarid regions for its tolerance to heat and drought stress, productivity, and forage quality. However, in our previous works, several accessions have exhibited different responses to abiotic stresses. Therefore, the objective of this work was to evaluate the effects of combination of drought and heat stresses on biochemical parameters and plant growth and to compare the impacts of the stresses separately and when combined. We found that sensitive genotype exhibited higher lipid peroxidation content, lower total reducing power values and reduced catalase and superoxide dismutase activities than tolerant under drought or heat stress or combination stress. In this study, heat stress had a predominant effect on buffel grass genotypes over drought stress, which explained why simultaneous application of heat and drought revealed similar biochemical and growth responses to the heat stress. Antioxidant metabolism seems to be critical for tolerate abiotic stress. This study may provide useful information to perform a rapid and low-cost characterization in new buffel grass germplasm and to identify genotypes with better growth performance under drought and heat conditions.

Combined effects of drought and moderately high temperature on the photosynthesis, PS II photochemistry and yield traits in rice (Oryza sativa L.)

Leaf photosynthesis, which determines the yield in rice, is greatly affected by heat and drought stresses during reproductive phenophase. The effect of short term natural high temperatures above 35 °C and drought in the range of − 50 to − 70 kPa was assessed on leaf photosynthesis (PN), stomatal conductance (gs), transpiration rate (Tr), chlorophyll fluorescence (Fv/Fm) and yield characteristics in three rice cultivars (ADT 43, TKM 9 and N 22). Drought stress coupled with natural high temperature was imposed at two critical phenophases i.e., at panicle initiation (PI) and anthesis stages under rain out shelter facility. N 22 was found to be the tolerant genotype followed by TKM 9. ADT 43 was observed to be susceptible genotype. Irrespective of genotypes, stress at anthesis stage caused more severe yield reduction compared to stress at PI stage. ADT 43 recorded photosynthetic rate of (20.5 µmol CO2 m−2s−1), stomatal conductance of (0.23 mol H2O m−2s−1) transpiration rate of (3.8 mmol H2O m−2s−1) and Fv/Fm value of (0.34) with 62.70% of yield reduction under stress, while N 22 recorded higher photosynthetic rate with less reduction per cent over control (28.47%) and Fv/Fm value (0.41) with 31.22% of yield reduction during stress at anthesis stage. The tolerance of N 22 over other varieties showed that lesser reduction of photosynthetic gas exchange and minimal damage to PS II photochemistry was the major physiological mechanism underlying stress tolerance in rice.

Combined effects of drought and high temperature on photosynthetic characteristics in four winter wheat genotypes

Terrestrial ecosystems are expected to experience more intense and longer drought and heat-waves in the future. How these environmental factors and their interaction influence photosynthetic activity and water use efficiency remains, however, an open question. Since the photosynthetic activity determines yield response, we investigated gas-exchange and chlorophyll fluorescence traits of flag leaves in four winter wheat cultivars, including two genotypes widely grown in Central Europe and two genotypes considered as drought tolerant. Pot-grown plants were cultivated under natural field conditions until anthesis (DC 61). Subsequently, the plants were exposed to a set of temperature regimes with daily maxima of 26–41 °C (temperature treatment) and maximum soil water holding capacity above 70% and below 30% (drought treatment) using laboratory growth chambers. Primary photochemical reactions after 7 and 14 days of acclimation, measured as maximum quantum yield of photosystem II photochemistry and total chlorophyll content, showed typical interactions of temperature and water availability resulting in an amplified response under combined influence of drought and temperatures above 35 °C. In contrast, drought and temperature treatment had only minor effects on content of epidermal flavonols. A dominant effect of drought over temperature on stomatal conductance (GSmax) was observed. Although substantial genotype-specific responses were found, reduced stomatal conductance resulted in significant decrease in light-saturated rates of CO2 assimilation (Amax) in all genotypes studied. The GSmax–Amax relationship, however, revealed limitation of CO2 uptake by other, non-stomatal processes at temperatures above 32 °C, particularly in the sensitive genotypes. Strong interaction of combined drought and temperature treatments was found on water use efficiency (WUE). Decline in WUE with increasing temperature was steeper in water-deficit than well-watered plants of all genotypes studied. Our results thus document a strong interactive effect of elevated temperature and drought on photosynthetic carbon uptake. Detected thresholds of sensitivity to combined drought and heat stress will contribute to improved modelling of wheat growth and production under expected future climate conditions.

Dehydration Stress Contributes to the Enhancement of Plant Defense Response and Mite Performance on Barley.

Under natural conditions, plants suffer different stresses simultaneously or in a sequential way. At present, the combined effect of biotic and abiotic stressors is one of the most important threats to crop production. Understanding how plants deal with the panoply of potential stresses affecting them is crucial to develop biotechnological tools to protect plants. As well as for drought stress, the economic importance of the spider mite on agriculture is expected to increase due to climate change. Barley is a host of the polyphagous spider mite Tetranychus urticae and drought produces important yield losses. To obtain insights on the combined effect of drought and mite stresses on the defensive response of this cereal, we have analyzed the transcriptomic responses of barley plants subjected to dehydration (water-deficit) treatment, spider mite attack, or to the combined dehydration-spider mite stress. The expression patterns of mite-induced responsive genes included many jasmonic acid responsive genes and were quickly induced. In contrast, genes related to dehydration tolerance were later up-regulated. Besides, a higher up-regulation of mite-induced defenses was showed by the combined dehydration and mite treatment than by the individual mite stress. On the other hand, the performance of the mite in dehydration stressed and well-watered plants was tested. Despite the stronger defensive response in plants that suffer dehydration and mite stresses, the spider mite demonstrates a better performance under dehydration condition than in well-watered plants. These results highlight the complexity of the regulatory events leading to the response to a combination of stresses and emphasize the difficulties to predict their consequences on crop production.

Antagonistic effects of drought and sand burial enable the survival of the biocrust moss <i>Bryum argenteum</i> in an arid sandy desert

Abstract. Biocrust moss is an essential soil surface bio-cover. It can represent the latest succession stage among the diverse range of surface-dwelling cryptogams (e.g., cyanobacteria, green algae, and lichen, which are also referred to as biocrusts), and it can make a major contribution to soil stability and fertility in many arid sandy desert ecosystems. The soil surface represents a very large ecological niche that is poikilohydric in nature. Biocrust moss is therefore highly susceptible to drought and sand burial, which are two ubiquitous stressors in arid sandy deserts. However, little information is available regarding the mechanism by which biocrust moss can survive and flourish in these habitats when stressed simultaneously by the two stressors. The combined effects of drought and sand burial were evaluated in a field experiment using the predominant biocrust moss, Bryum argenteum Hedw., in the Tengger Desert, China. Drought was simulated by applying distilled water in three artificial rainfall regimes at 8-day intervals in spring and autumn: 4 and 6 mm (average rainfall, control), 2 and 3 mm (double drought), and 1 and 1.5 mm (4-fold drought), respectively. The effect of sand burial was determined by applying six treatments, i.e., sand depths of 0 (control), 0.5, 1, 2, 4, and 10 mm. The four parameters of chlorophyll a content, PSII photochemical efficiency, regeneration potential, and shoot upgrowth were evaluated in the moss. It was found that the combined effects of drought and sand burial did not exacerbate the single negative effects of the four parameters tested. Drought significantly ameliorated the negative effects of deep-sand burial on the retention of chlorophyll a content, PSII photochemical efficiency, and the regeneration potential of B. argenteum. Sand burial diminished and even reversed the negative effects of drought on the maintenance of chlorophyll a content, PSII photochemical efficiency, and regeneration potential. Although drought and sand burial imposed an additive negative effect on shoot upgrowth, which suggested a trade-off between growth ability and stress tolerance, their mutually antagonistic effect on the physiological vigor of B. argenteum provided an opportunity for the biocrust moss to overcome the two co-occurring stressors. In addition to providing a strong stress tolerance, drought and sand burial may provide an important mechanism for the biodiversity maintenance of biocrust mosses in arid sandy ecosystems.

Combined effects of drought and cold acclimation on phospholipid fatty acid composition and cold-shock tolerance in the springtail Protaphorura fimata

Terrestrial arthropods' ability to survive sub-zero winter temperatures is an important factor influencing their abundance and geographic distribution. It is, therefore, important to understand their physiological mechanisms of low-temperature survival. Acclimation to moderate-low temperature can improve cold tolerance, and pre-acclimation to mild desiccation can also improve survival of a subsequent cold exposure. However, very few studies have assessed the combined actions of cold and drought acclimations. In the present study, we combined cold acclimation with drought acclimation making it possible to assess the interactions between effects of these two stressors using the springtail Protaphorura fimata as a model organism. We investigated the interacting effects of drought and cold acclimation on body fluid osmolality, membrane phospholipid fatty acid (PLFA) composition, and cold-shock tolerance. Acclimation to mild drought (- 2.46MPa) increased body fluid osmolality from 0.33 to 1.25Osm at all acclimation temperatures (5, 10, 15, or 20°C) likely due to accumulation of the compatible osmolytes, trehalose, and alanine. Interestingly, the expected positive effect of drought acclimation on cold-shock tolerance was only evident at high acclimation temperature (20°C), whereas at intermediate temperatures (10 and 15°C), there was an interaction between acclimation temperature and drought. At 5°C, no effect of drought acclimation on cold-shock tolerance was observed despite high osmolality. The positive effect of drought acclimation at 20°C on subsequent cold-shock survival coincided with a drought-induced effect on PLFA composition only detectable at high temperature. We discuss the possible roles of drought-induced compatible osmolytes and an altered PLFA composition in the cold-shock tolerance of arthropods.

Effects of individual and combined heat and drought stress during seed filling on the oxidative metabolism and yield of chickpea (Cicer arietinum) genotypes differing in heat and drought tolerance

Drought and heat stress are two major constraints that limit chickpea (Cicer arietinum L.) yield, particularly during seed filling. The present study aimed (i) to assess the individual and combined effects of drought and heat stress on oxidative metabolism during seed filling, and (ii) to determine any genetic variation in oxidative metabolism among genotypes differing in drought and heat tolerance and sensitivity. The plants were raised in outdoor conditions with two different times of sowing, one in November (normal-sown, temperatures <32°C−20°C (day–night) during seed filling), and the other in February (late-sown, temperatures >32°C−20°C (day–night) during seed filling). Plants were regularly irrigated to prevent any water shortage until the water treatments were applied. At both sowing times, the drought treatment was applied during seed filling (at ~75% podding) by withholding water from half of the pots until the relative leaf water content (RLWC) of leaves on the top three branches reached 42–45%, whereas leaves in the fully irrigated control plants were maintained at RLWC 85–90%. Drought-stressed plants were then rewatered and maintained under fully irrigated conditions until maturity. Several biochemical parameters were measured on the leaves and seeds at the end of the stress treatments, and seed yield and aboveground biomass were measured at maturity. Individual and combined stresses damaged membranes, and decreased PSII function and leaf chlorophyll content, more so under the combined stress treatment. The levels of oxidative molecules (malondialdehyde (MDA) and H2O2) markedly increased compared with the control plants in all stress treatments, especially across genotypes in the combined heat + drought stress treatment (increases in leaves: MDA 5.4–8.4-fold and H2O2 5.1–7.1-fold; in seeds: MDA 1.9–3.3-fold and H2O2 3.8–7.9-fold). The enzymatic and non-enzymatic antioxidants related to oxidative metabolism increased under individual stress treatments but decreased in the combined heat + drought stress treatment. Leaves had higher oxidative damage than seeds, and this likely inhibited their photosynthetic efficiency. Yields were reduced more by drought stress than by heat stress, with the lowest yields in the combined heat + drought stress treatment. Heat- and drought-tolerant genotypes suffered less damage and had higher yields than the heat- and drought-sensitive genotypes under the individual and combined stress treatments, suggesting partial cross-tolerance in these genotypes. A drought-tolerant genotype ICC8950 produced more seed yield under the combined heat + drought stress than other genotypes, and this was associated with low oxidative damage in leaves and seeds.

Mitigating the Stress of Drought on Soil Respiration by Selective Thinning: Contrasting Effects of Drought on Soil Respiration of Two Oak Species in a Mediterranean Forest

Drought has been shown to reduce soil respiration (SR) in previous studies. Meanwhile, studies of the effect of forest management on SR yielded contrasting results. However, little is known about the combined effect of drought and forest management on SR. To investigate if the drought stress on SR can be mitigated by thinning, we implemented plots of selective thinning and 15% reduced rainfall in a mixed forest consisting of the evergreen Quercus ilex and deciduous Quercus cerrioides; we measured SR seasonally from 2004 to 2007. Our results showed a clear soil moisture threshold of 9%; above this value, SR was strongly dependent on soil temperature, with Q10 of 3.0–3.8. Below this threshold, the relationship between SR and soil temperature weakened. We observed contrasting responses of SR of target oak species to drought and thinning. Reduced rainfall had a strong negative impact on SR of Q. cerrioides, whereas the effect on SR for Q. ilex was marginal or even positive. Meanwhile, selective thinning increased SR of Q. cerrioides, but reduced that of Q. ilex. Overall, our results showed that the negative effect of drought on SR can be offset through selective thinning, but the effect is attenuated with time.

Drought and Carbon Cycling of Grassland Ecosystems under Global Change: A Review

In recent years, the increased intensity and duration of droughts have dramatically altered the structure and function of grassland ecosystems, which have been forced to adapt to this change in climate. Combinations of global change drivers such as elevated atmospheric CO2 concentration, warming, nitrogen (N) deposition, grazing, and land-use change have influenced the impact that droughts have on grassland C cycling. This influence, to some extent, can modify the relationship between droughts and grassland carbon (C) cycling in the multi-factor world. Unfortunately, prior reviews have been primarily anecdotal from the 1930s to the 2010s. We investigated the current state of the study on the interactive impacts of multiple factors under drought scenarios in grassland C cycling and provided scientific advice for dealing with droughts and managing grassland C cycling in a multi-factor world. Currently, adequate information is not available on the interaction between droughts and global change drivers, which would advance our understanding of grassland C cycling responses. It was determined that future experiments and models should specifically test how droughts regulate grassland C cycling under global changes. Previous multi-factor experiments of current and future global change conditions have studied various drought scenarios poorly, including changes in precipitation frequency and amplitude, timing, and interactions with other global change drivers. Multi-factor experiments have contributed to quantifying these potential changes and have provided important information on how water affects ecosystem processes under global change. There is an urgent need to establish a systematic framework that can assess ecosystem dynamic responses to droughts under current and future global change and human activity, with a focus on the combined effects of droughts, global change drivers, and the corresponding hierarchical responses of an ecosystem.

Effects of duration and combination of drought and flood conditions on leaf photosynthesis, growth and sugar content in sugarcane

Global climate change will result in extreme environments, such as droughts and floods. We investigated the individual and combined effects of droughts and floods of varying duration on sugarcane (Saccharum spp.) growth using a pot experiment under glasshouse conditions with the following six treatments: drought for 15 d, prolonged drought for 30 d, flood for 15 d, prolonged flood for 30 d, short flood followed by prolonged drought, and prolonged flood followed by prolonged drought. Plants that were subjected to drought conditions, including drought after a flood, had reduced CO2 assimilation (through stomatal closure) and leaf areas, whereas flood conditions showed no effect. During flooding, some roots died, and adventitious roots with well-developed aerenchyma appeared from the submerged nodes. At the time of harvest, there were no significant differences in stem fresh weight, sucrose content, or sugar yield between the treatments. However, ion content analysis revealed that flood conditions caused an accumulation of sodium in the bottom of stems and adventitious roots. Therefore, under flood conditions, plants may develop adventitious roots, which may offset the negative effects of root death, helping them to maintain their growth and yield.

Pressions Anthropiques Et Dynamique D’occupation Des Terres Dans Le Terroir De Ziguéna, Zone Cotonnière Du Mali

In Ziguéna terroir, the combined effects of drought and anthropogenic actions led to the widespread degradation of vegetation cover and of land. This work aimed at characterizing the dynamics of land use and land cover in relation to anthropogenic pressures in Ziguéna terroir. The methodology consisted in identifying and characterizing land use and land cover classes. Landsat images for the years 1986 and 2013 and population data for the years 1987, 1998 and 2009 were used. Visual interpretation of the images and post-classification comparison of the results were used to generate land use and land cover classes and calculate their rate of change. The results reveal that the natural vegetation has lost 55% of its original coverage (1514.3 ha) between 1987 and 2013. During the same period, the agricultural area increased by 47% (1608 ha). The projection of land use and land cover classes predicted an increase of agricultural land of about 34.60% by year 2030 compared to its coverage of year 2013 (+1191.03 ha) at the expense of natural vegetation which will lose about 40.63% of its coverage (-1121.70 ha). The dynamics of agricultural land is strongly linked to population growth rates with a correlation coefficient r equal to 0.99. This confirms a strong anthropogenic influence on land use and land cover dynamics. The results show the usefulness of remote sensing for mapping land use and land cover. Nevertheless it would be interesting to take into account the socioeconomic aspects for proper understanding of the dynamics.

Combined effects of drought and the fungicide tebuconazole on aquatic leaf litter decomposition

Loss of biodiversity and altered ecosystem functioning are driven by the cumulative effects of multiple natural and anthropogenic stressors affecting both quantity and quality of water resources. Here we performed a 40-day laboratory microcosm experiment to assess the individual and combined effects of drought and the model fungicide tebuconazole (TBZ) on leaf litter decomposition (LLD), a fundamental biogeochemical process in freshwater ecosystems. Starting out from a worst-case scenario perspective, leaf-associated microbial communities were exposed to severe drought conditions (four 5-day drought periods alternated with 4-day immersion periods) and/or a chronic exposure to TBZ (nominal concentration of 20μgL−1). We assessed the direct effects of drought and fungicide on the structure (biomass, diversity) and activity (extracellular enzymatic potential) of fungal and bacterial assemblages colonizing leaves. We also investigated indirect effects on the feeding rates of the amphipod Gammarus fossarum on leaves previously exposed to drought and/or TBZ contamination. Results indicate a stronger effect of drought stress than fungicide contamination under the experimental conditions applied. Indeed, the drought stress strongly impacted microbial community structure and activities, inhibiting the LLD process and leading to cascading effects on macroinvertebrate feeding. However, despite the lack of significant effect of TBZ applied alone, the effects of drought on microbial functions (i.e., decrease in LLD and in enzymatic activities) and on Gammarus feeding rates were more pronounced when drought and TBZ stresses were applied together. In a perspective of ecological risk assessment and ecosystem management for sustainability, these findings stress the need for deeper insight into how multiple stressors can affect the functioning of aquatic ecosystems and associated services.

Drought and saltwater incursion synergistically reduce dissolved organic carbon export from coastal freshwater wetlands

The hydrologic transport of dissolved organic carbon (DOC) represents both a primary energetic loss from and a critical energetic link between ecosystems. Coastal freshwater wetlands serve as a primary source of DOC to estuaries; historically the magnitude and timing of DOC transfers has been driven by water movement. Extensive agricultural development throughout the coastal plain of the southeastern US has hydrologically connected much of the landscape via canals to facilitate drainage. The resulting large-scale loss of topographic relief and reduced mean elevation is interacting with increasingly frequent and severe droughts to facilitate the landward movement of seawater through the highly connected artificial drainage networks. The resulting changes in hydrologic regime and salinity are each expected to reduce DOC export from coastal freshwater wetlands, yet their individual and combined impacts are not well understood. Here we show that repeated saltwater incursion during late summer droughts substantially decreased DOC concentrations in surface water (from ~40 to ~18 mg/L) from a mature and a restored forested wetland in the coastal plain of North Carolina, USA. These declines in DOC concentration reduced annual export of DOC to the estuary by 70 % and dampened storm fluxes by 76 %. We used a long-term experiment with intact soil columns to measure the independent and combined effects of drought, salinity, and sulfate loading as potential drivers of the large changes in DOC concentration. We found that soil drying and salinization each reduced DOC similarly (20 % reduction by drought alone, 29 % by salinization) and their combined effect was additive (49 % reduction in salinization + drought treatments). Our results demonstrate that, well in advance of significant sea-level rise, drought and relatively low levels of saltwater incursion (<6 ppt) are already significantly altering the timing and magnitude of dissolved organic carbon flux between coastal forested wetlands and downstream estuaries.

Quantifying drylands' drought resistance and recovery: the importance of drought intensity, dominant life history and grazing regime.

Projected global change will increase the level of land-use and environmental stressors such as drought and grazing, particularly in drylands. Still, combined effects of drought and grazing on plant production are poorly understood, thus hampering adequate projections and development of mitigation strategies. We used a large, cross-continental database consisting of 174 long-term datasets from >30 dryland regions to quantify ecosystem responses to drought and grazing with the ultimate goal to increase functional understanding in these responses. Two key aspects of ecosystem stability, resistance to and recovery after a drought, were evaluated based on standardized and normalized aboveground net primary production (ANPP) data. Drought intensity was quantified using the standardized precipitation index. We tested effects of drought intensity, grazing regime (grazed, ungrazed), biome (grassland, shrubland, savanna) or dominant life history (annual, perennial) of the herbaceous layer to assess the relative importance of these factors for ecosystem stability, and to identify predictable relationships between drought intensity and ecosystem resistance and recovery. We found that both components of ecosystem stability were better explained by dominant herbaceous life history than by biome. Increasing drought intensity (quasi-) linearly reduced ecosystem resistance. Even though annual and perennial systems showed the same response rate to increasing drought intensity, they differed in their general magnitude of resistance, with annual systems being ca. 27% less resistant. In contrast, systems with an herbaceous layer dominated by annuals had substantially higher postdrought recovery, particularly when grazed. Combined effects of drought and grazing were not merely additive but modulated by dominant life history of the herbaceous layer. To the best of our knowledge, our study established the first predictive, cross-continental model between drought intensity and drought-related relative losses in ANPP, and suggests that systems with an herbaceous layer dominated by annuals are more prone to ecosystem degradation under future global change regimes.

Analysis of land cover change and its driving forces in a desert oasis landscape of Xinjiang, northwest China

Abstract. The combined effects of drought, warming and the changes in land cover have caused severe land degradation for several decades in the extremely arid desert oases of southern Xinjiang, northwest China. Land cover classifications of Landsat images in 1990, 2000 and 2008 were performed based on the multistage supervised classification scheme using the maximum likelihood classifier integrated with conventional vegetation and soil indexes, which improved overall accuracies by 4–5% compared to the standard classification method. Based on the detection of changes in land cover during 1990–2008 using remote sensing (RS) and a geographic information system (GIS), it can be found that the oasis significantly (+35%) increased, while the area of ecotone decreased (−43%). The major trends of the land cover changes were the notable growth of the oasis and the reduction of the desert–oasis ecotone. These changes were mainly a result of the intensified human activities such as land and water exploitation as well as overgrazing. The results of this study indicate that the oasis environment will be deteriorated by increase in potential areas of land degradation if the trend of desert moving further inward and the shrinking of the ecotone continues over the next decades.

Independent and combined effects of heat and drought stress in the Seri M82 × Babax bread wheat population

AbstractHeat and drought are the most important wheat production constraints worldwide. The objectives of this research were to evaluate the independent and combined effects of drought and heat in SeriM82/Babax population. Genotypes showed 11, 38 and 52% losses in grain yield (YLD) in 2010–11 and 18, 25 and 48% in 2011–12 under heat, drought and combined stress, respectively. Seri M82 had higher YLD than Babax under heat and combined stress. Grain per spike and canopy temperature at vegetative stage (CTv) in irrigated, day to heading and CT at grain‐filling stage (CTg) in drought, CTg and thousand‐grain weight (TGW) in heat and in combined trials were the best predictors of YLD. Results indicated that due to genotype by environment interactions not all stress‐adaptive traits could be accumulated in a single genotype. In general, day to heading, CTg and grain weight are suggested as indirect selection criteria for increasing YLD under heat and drought stresses. In particular, CTg could be used as a rapid and effective criterion for screening a high number of genotypes.