Combined Effects Of Drought Stress Research Articles

Drought Stress and High Temperature Affect the Antioxidant Metabolism of Cotton (Gossypium hirsutum L.) Anthers and Reduce Pollen Fertility

Both drought and high temperature can influence the antioxidant metabolism of crop reproductive organs in different ways, affecting the fertility of reproductive organs and yield formation. However, the combined effects of drought stress and high temperature on the crop reproductive physiology have not yet been widely considered. In order to broaden our understanding of this mechanism of influence, a pond experiment was conducted using a cotton variety Yuzaomian 9110 divided into four treatment groups: control (CK), drought stress (DS), high temperature (HT), and drought stress coupled with high temperature (DS+HT). Results showed a significant negative correlation between pollen viability and superoxide anion (O2−) content, as well as hydrogen peroxide (H2O2). Compared with CK, DS did not alter O2− content in anthers, but HT treatment resulted in higher anther O2−. Compared with single-stress groups, DS+HT further promoted the formation of O2− in anthers, leading to more malondialdehyde in anthers. Moreover, a higher H2O2 content in anthers was found in DS and HT than in CK. DS+HT did not show altered H2O2 content relative to HT treatment, although its H2O2 was higher than in DS. Further analyses of the antioxidant enzyme system showed that DS had no significant effect on superoxide dismutase gene (GhCu/ZnSOD) expression, but HT and DS+HT significantly downregulated its expression. The expression of GhCu/ZnSOD was lower under DS+HT than HT, which might be why O2− content was not altered under DS treatment compared with CK and was higher in DS+HT than HT. DS and HT significantly downregulated the expression of the peroxidase gene (GhPOD) and catalase gene (GhCAT), which should be the main reason for the larger accumulation of H2O2 under drought stress and high-temperature conditions. Compared with single-stress groups, DS+HT had lower expression of GhCAT, resulting in a larger H2O2 content. Regarding the ascorbic acid–glutathione (AsA–GSH) cycle, DS and HT significantly downregulated the expression of monodehydroascorbate reductase gene (GhMDHAR) to hinder the production of AsA and upregulated the expression of ascorbate oxidase gene (GhAAO) to promote the oxidation of AsA, which was theoretically detrimental to AsA accumulation. However, HT downregulated the expression of the ascorbate peroxidase gene (GhAPX), hindering the reduction of H2O2 by AsA, which was the reason for AsA and H2O2 accumulation. Moreover, DS also significantly upregulated the expression of the dehydroascorbate reductase gene (GhDHAR2) to enhance the reduction of dehydroascorbate to form AsA, leading to a higher content of AsA under DS than HT. The combined stress significantly downregulated the expression of GhAAO to inhibit the oxidation of AsA but significantly upregulated the expression of GhMDHAR and GhDHAR2, promoting the AsA production, and downregulated the expression of GhAPX, hindering the reduction of H2O2 by AsA. All these resulted in increased AsA content under combined stresses. In addition, HT significantly downregulated the glutathione reductase gene (GhGR) expression, hindering the reduction of oxidized glutathione (GSSG), which led to the reduction of GSH. However, DS and DS+HT significantly downregulated the glutathione peroxidase gene (GhGPX) expression, resulting in the accumulation of GSH. Overall, compared with single-stress treatments, the effects of DS+HT on cotton pollen fertility and peroxide accumulation were more significant. The effects of DS+HT on the antioxidant enzyme system were mainly caused by high temperature, while the mechanism of abnormal accumulation of AsA and GSH caused by DS+HT was different from those of single-stress groups.

Combined effects of drought stress and different forms of nitrogen deposition as response mechanism to environmental change

Combined effects of drought stress and different forms of nitrogen deposition as response mechanism to environmental change

Combined effects of drought stress and psyllid herbivory on the invasive weed Scotch broom, Cytisus scoparius

AbstractIncreases in the frequency and duration of droughts under global climate change could have implications for plant–insect interactions, and could either increase or decrease the effects of weed biological control agents. In this study, we used greenhouse and field experiments to examine the impacts of drought stress on the abundance and impacts of the adventive psyllid Arytainilla spartiophila Forster (Hemiptera: Psyllidae, Arytaininae) on its target weed Scotch broom, Cytisus scoparius (L.) Link (Fabaceae), in California, USA. The psyllid impacted plant growth in both field and greenhouse experiments, whereas drought stress affected plant growth in the greenhouse only, suggesting that other factors besides water availability may be more limiting for plants in the field. Effects on psyllid survival were consistent with the plant vigor hypothesis, which predicts that herbivores will perform better on vigorously growing plants; psyllid numbers were lower on drought‐stressed plants in the greenhouse and were correlated with plant growth in both the greenhouse and the field. In the greenhouse, the combined effects of the psyllid and drought stress were additive, indicating that the effects of the psyllid were consistent across unstressed and drought‐stressed plants. Although the psyllid is unlikely to control Scotch broom on its own, results suggest that it may work in conjunction with drought stress to suppress Scotch broom.

Combined effects of drought stress and Armillaria infection on tree mortality in Norway spruce plantations

For the past two decades in the Czech Republic, Norway spruce (Picea abies) trees have been weakened by drought and subsequent attack by Armillaria root disease and bark beetles (Ips typographus, I. duplicatus, and Pityogenes chalcographus). We determined whether thinning of trees decreased mortality at 40 forest locations in the Czech Republic. The majority of the locations experienced long-term drought stress and very low groundwater levels. We also identified the species of Armillaria associated with the spruce decline and determined the reliability of visual detection of Armillaria infection.The mortality of trees at the 40 locations increased nearly linearly during the 5 years of the study. Sites were established in 2012, thinned or not thinned in October 2012, and were assessed in September and October in each year from 2012 to 2016. Thinning, with an intervention intensity of 30–40%, did not alter tree mortality at the locations. The proportion of dead trees was significantly greater in older than in younger stands in the last 3 years of the study.Among the trees that were suspected of being attacked by Armillaria based on visual inspection by foresters, 53% were confirmed (supported by statistical significance) to be infected by Armillaria spp. after morphological and genetic assessment. Among the trees with confirmed infections, 56% were infected by Armillaria ostoyae, 32% were infected by A. cepistipes, and 1% were infected by A. gallica (the rest could not be identified). Resinosis was positively associated with the occurrence of A. ostoyae. This species was more common on loamy flat locations, whereas A. cepistipes was more common on stony, sloped locations. The occurrence of Armillaria was negatively associated with increasing pH.Although our results indicate that spruce decline is strongly associated with the presence of Armillaria and that visual detection of Armillaria is reliable, management options for reducing Armillaria infection and damage appear to be highly limited. Forest managers should begin preparing to convert stands of Norway spruce to stands of other tree species that are better adapted to the local conditions and that are less susceptible to attack by Armillaria species.

Synergistic and additive effects of drought stress and simulated herbivory on two goldenrods, Solidago altissima and S. gigantea

Understanding the combined effects of stressors on plants is important for understanding how they will tolerate herbivory and other damage under unfavorable conditions. When two stresses have synergistic effects, plants may experience particularly strong impacts. We examined individual and combined effects of drought stress and clipping (simulated herbivory) on two species of goldenrods (Solidago altissima L. and S. gigantea Ait.). Each stress reduced production of most plant structures, with drought stress having stronger impacts than clipping. The effects of the two stresses were additive for S. gigantea but synergistic for S. altissima, at least for aboveground biomass and inflorescence biomass. Both species, when under stress, reallocated resources toward asexual reproduction (rhizomes) and away from sexual reproduction (inflorescences). Our results suggest that even closely related plants may tolerate damage differently when under abiotic stresses, and that predicting the additive vs. synergistic action of combined stresses will be difficult.

Effects of grazing intensity on seed production of Caragana stenophylla along a climatic aridity gradient in the Inner Mongolia Steppe, China

As the increases of climatic aridity and grazing intensity, shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions, and its abundance also generally increases. However, the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grassland remain largely unclear. In order to understand the effects of grazing intensity and climatic drought stress, and their interaction on seed production of shrub species, we examined the seed number, seed weight and seed yield of Caragana stenophylla under three grazing intensities (fenced, mild grazing and severe grazing) across a climatic aridity gradient (semi-arid, arid, very arid and intensively arid zones) in the Inner Mongolia Steppe, northern China during 2012–2013. The seed number, seed weight and seed yield gradually increased from the semi-arid to the very arid zones, but decreased from the very arid to the intensively arid zones in fenced plots. The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots, therefore, grazing enhanced the suppression effect of climatic aridity on seed production of C. stenophylla. The seed number and seed yield gradually decreased as grazing intensity increased. The seed weight was highest in severe grazing plots, followed by the mild grazing plots and then the fenced plots. Precipitation varied interannually during the study period. We observed that the seed number, seed weight and seed yield were lower in the low precipitation year (2013) than in the high precipitation year (2012). As climatic drought stress increased, the negative effects of grazing on seed production of C. stenophylla also gradually increased. Our results indicated that climatic drought stress may contribute to the encroachment of C. stenophylla shrub in arid zones by promoting its seed production. However, grazing had negative effects on sexual reproduction of C. stenophylla, and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C. stenophylla in the intensively arid zone.

Drought and grazing combined: Contrasting shifts in plant interactions at species pair and community level

The combined effects of drought stress and grazing pressure on shaping plant–plant interactions are still poorly understood, while this combination is common in arid ecosystems. In this study we assessed the relative effect of grazing pressure and slope aspect (drought stress) on vegetation cover and soil functioning in semi-arid Mediterranean grassland–shrublands in southeastern Spain. Moreover, we linked these two stress factors to plant co-occurrence patterns at species-pair and community levels, by performing C-score analyses. Vegetation cover and soil functioning decreased with higher grazing pressure and more south-facing (drier) slopes. At the community level, plants at south-facing slopes were negatively associated at no grazing but positively associated at low grazing pressure and randomly associated at high grazing pressure. At north-facing slopes, grazing did not result in a shift in the direction of the association. In contrast, analysis of pairwise species co-occurrence patterns showed that the dominant species Stipa tenacissima and Anthyllis cytisoides shifted from excluding each other to co-occurring with increasing grazing pressure at north-facing slopes. Our findings highlight that for improved understanding of plant interactions along stress gradients, interactions between species pairs and interactions at the community level should be assessed, as these may reveal contrasting results.

How do extreme drought and plant community composition affect host plant metabolites and herbivore performance?

Water availability and plant community composition alter plant nutrient availability and the accumulation of plant defence compounds therefore having an impact on herbivore performance. Combined effects of drought stress and plant community composition on leaf chemicals and herbivore performance are largely unexplored. The objective of our study was, therefore, to find out the impact of extreme drought and of plant community composition on plant–herbivore interactions. Larvae of the generalist butterfly Spodoptera littoralis were reared on leaves of the grass Holcus lanatus which was grown in experimental communities, differing in species- and functional group richness. These communities were either subjected to extreme drought or remained under ambient climatic conditions. Drought decreased relative water content, soluble protein content, nitrogen and total phenol content and increased the content of carbohydrates in the grass. As a consequence, the larvae feeding on drought-exposed plants revealed a longer larval stage, increased pupal weight and higher adult eclosion rates. Plant community composition mainly caused changes to the defensive compounds of the grass, but also marginally affected protein and carbohydrate content. Larvae feeding on species-richest communities without legumes showed the highest mortality. Our findings imply that climate change that is projected to increase the frequency of severe droughts, as well as alter plant community compositions, is likely to affect arthropod–plant interactions through an alteration of leaf chemicals.

Effects of copper on enchytraeids in the field under differing soil moisture regimes

The aims of this study were to investigate the combined effects of drought stress and copper pollution on enchytraeids under natural conditions in the field and to compare the results of laboratory toxicity tests with results of the field study. Such studies were conducted to increase the understanding of interactions between chemicals and natural stressors and assess the predictive value of standardized laboratory tests with enchytraeids. The combined effect of copper and summer drought on enchytraeids was investigated in an old copper-contaminated field site at Hygum, Denmark, in three areas with different copper burdens. Each area consisted of five plots, which were divided into two subplots: one control and one drought subplot in which precipitation was excluded for a 45-d period during summer. Enchytraeids were sampled in spring (before the enforced drought began) and in autumn (after recovery from drought). Clear effects of copper were evident in both the field and the laboratory experiment. The field population density and species composition was highly affected by copper at concentrations in the range 300 to 500 mg Cu/kg dry soil and higher. In particular, a greatly impoverished species diversity was found in the copper-polluted areas. The effects of copper in the field compared reasonably well with the results of the laboratory tests. Surprisingly, possible effects of summer drought in the field were not detected in the autumn sampling, perhaps because of rapid recovery of the enchytraeid populations in both unpolluted and copper-polluted areas.

The Synergistic Effect of Drought and Light Stresses in Sorghum and Pearl Millet

The effects of drought stress and high irradiance and their combination were studied under laboratory conditions using young plants of a very drought-resistant variety, ICMH 451, of pearl millet (Pennisetum glaucum) and three varieties of sorghum (Sorghum bicolor)-one drought-resistant from India, one drought-tolerant from Texas, and one drought-sensitive variety from France. CO(2) assimilation rates and photosystem II fluorescence in leaves were analyzed in parallel with photosynthetic electron transport, photosystem II fluorescence, and chlorophyll-protein composition in chloroplasts isolated from these leaves. High irradiance slightly increased CO(2) assimilation rates and electron transport activities of irrigated plants but not fluorescence. Drought stress (less than -1 megapascal) decreased CO(2) assimilation rates, fluorescence, and electron transport. Under the combined effects of drought stress and high irradiance, CO(2) assimilation rates and fluorescence were severely inhibited in leaves, as were the photosynthetic electron transport activities and fluorescence in chloroplasts (but not photosystem I activity). The synergistic or distinctive effect of drought and high irradiance is discussed. The experiments with pearl millet and three varieties of sorghum showed that different responses of plants to drought and light stresses can be monitored by plant physiological and biochemical techniques. Some of these techniques may have a potential for selection of stress-resistant varieties using seedlings.