Low Drought Resistance Research Articles

Annual yields of multispecies grassland mesocosms outperformed monocultures across a drought gradient due to complementarity effects and rapid recovery

AbstractBackgroundMore frequent and severe drought events due to climate change pose a major challenge for sustainable forage production in managed grasslands. This study investigated whether multispecies grassland communities can provide greater resistance to and/or recovery from drought compared to monoculture communities.MethodsMesocosms of Lolium perenne L., Cichorium intybus L., Trifolium repens L. and Trifolium pratense L. were established as monocultures, and a four‐species mixture. A drought gradient with five levels of water supply ranging from a mild to a severe treatment was applied for 10 weeks, in each of 2 years. Shoot biomass was harvested to assess drought resistance, drought recovery and annual yields. Root mass density and specific root length were measured in Year 2.ResultsAcross the drought gradient, four‐species communities had significantly larger annual yields than each of the four monocultures, indicating transgressive overyielding. This was despite relatively low drought resistance for four‐species communities compared with L. perenne and C. intybus monocultures. Recovery of yields following drought was high for all communities.ConclusionsMultispecies swards with complementary traits can provide a viable adaptation option across a wide range of drought severities. Application of a stress gradient methodology allowed a more detailed understanding of stress responses.

Resistance of Grassland under Different Drought Types in the Inner Mongolia Autonomous Region of China

The increasing frequency of global drought events poses a significant threat to the stability of grassland ecosystems’ functionality. The Inner Mongolian grasslands stand out as one of the world’s most drought-prone regions, facing elevated drought risks compared to other biomes. An in-depth comprehension of the impact of drought on grassland ecosystems is paramount for their long-term sustainability. Using the Standardized Precipitation Evapotranspiration Index (SPEI) from 1982 to 2018, this study identified various drought events within the Inner Mongolian grasslands, encompassing moderate drought, severe drought, and extreme drought. The resistance of the vegetation to the different drought conditions, assessed through net primary productivity (NPP) as a metric (reflecting its capacity to maintain its original level during drought periods), was examined. The research findings indicated that the period from 2001 to 2018 witnessed a substantial increase in both the frequency and the extent of drought events compared to the period from 1982 to 2000, particularly concerning severe and extreme droughts. The areas most severely impacted by extreme drought were the Xilingol League and the Alxa League. From 1982–2000 to 2001–2018, under moderate drought conditions, vegetation resistance exhibited a minor decrease in the central and eastern regions but experienced a slight increase in the western region. In contrast, under severe drought conditions, the western region saw a significant decrease in vegetation resistance. Remarkably, under extreme drought conditions, the western region showed a substantial increase in vegetation resistance, while the central and eastern regions experienced a slight decrease. Across all three drought conditions, as precipitation levels declined, the resistance of the meadow–steppe–desert ecosystems demonstrated a high–low–high distribution pattern. The temperate desert steppe exhibited a minimal vulnerability to drought, boasting resistance levels exceeding 0.9. Notably, extreme drought had the most pronounced impact on the temperate meadow steppe, temperate steppe, and temperate desert steppe, particularly within the temperate meadow steppe category. Given these findings, the authorities responsible for grassland management should prioritize regions characterized by frequent drought occurrences and low drought resistance, such as Ulanqab City, the Xilingol League, and the western part of Hulun Buir City. Safeguarding steppe ecosystems is of paramount importance for stabilizing vegetation productivity and land carbon sinks, especially under the anticipated exacerbation of climate conditions in the future.

Spatiotemporal characteristics and obstacle factors identification of agricultural drought disaster risk: A case study across Anhui Province, China

Identifying the spatiotemporal characteristics and obstacle factors of the agricultural drought disaster risk is essential to reduce grain losses and ensure food security. However, due to the high uncertainty in drought disaster risk system, there are few effective risk evaluation and diagnosis methods. In this study, the uncertain information contained in sample data was mined and utilized, and a calculation method of the dynamic difference degree coefficients for the five-element connection number was proposed. Then, a quantitative risk evaluation and diagnosis model was established. Furthermore, the spatiotemporal characteristics and key obstacle factors of the agricultural drought disaster risk across Anhui Province, China from 2008 to 2017 were identified. The results indicated that the risk grades of the connection number values of North Anhui, Central Anhui, and South Anhui in 2008 were 0.359 (high risk), 0.072 (medium risk), and 0.097 (medium risk), respectively, and those in 2017 were 0.103 (medium risk), 0.196 (medium risk), and 0.368 (low risk), respectively. Thus, there were salient spatiotemporal characteristics in which the risk decreased from north to south and tended to decrease over time. In addition, the long-term high risk in North Anhui was due to the severe drought hazard, low forest cover, high exposure to drought, and low drought resistance capacity. The worse risk status in Central Anhui was caused by the small precipitation and water resources amount, low relative humidity, and large agricultural population. The factors inhibiting risk reduction in South Anhui were the large paddy field areas, low reservoir regulation and storage, and fewer water-saving irrigation areas. In summary, this method is effective and exhibits high sensitivity to risk change, and it can be applied to other grain production areas. The results can provide a scientific basis for formulating the targeted measures of agricultural drought disaster risk control in Anhui Province.

Effects of thinning on tradeoffs between drought resistance, drought resilience, and wood production in mature Douglas-fir in western Oregon, USA

Climate projections predict more frequent and severe drought in coastal Pseudotsuga menziesii forests of western North America, raising concerns over how to promote drought adaptation. Thinning often increases drought resistance (the ability to maintain growth during a drought) and resilience (the ability to recover growth after a drought), but these effects vary with thinning intensity, shift over time, and may have tradeoffs with fiber production. We collected tree cores from a long-term thinning study with four residual density levels replicated across both uniform thinning and thinning with gaps, and used annual growth data to investigate responses to droughts occurring 8 and 21 years after thinning. For the first drought, resistance and resilience were higher in treatments with lower residual densities. For the second drought, there were no differences in drought response between the lowest and highest residual density treatments, and all treatments had lower drought resistance and resilience than for the first drought. Spatial arrangement had little impact on drought resistance or resilience and residual density level had a significant effect on the periodic annual volume increment—drought resistance tradeoff. Our results suggest that thinning can promote drought adaptation in Pseudotsuga menziesii forests, but these effects dissipate over time.

ПОСУХОСТІЙКІ ВИДИ ДЕРЕВ ТА КУЩІВ – ВАЖЛИВА ЛАНКА ДЛЯ ЗМЕНШЕННЯ НЕГАТИВНИХ ЕФЕКТІВ «МІСЬКИХ ОСТРОВІВ ТЕПЛА»

The water parameters of the leaves of 9 species of medium-sized trees (Aesculus pavia L., Aralia elata (Miq,) Seem., Broussonetia papyrifera (L.) L’Hér. ex Vent., Cercis canadensis L., Platycarya strobilacea Siebold & Zucc., Prunus dulcis (Mill.) D.A.Webb., Tetradium daniellii (Benn.) T.G. Hartley, Zizyphus jujuba Mill., Robinia viscosa Vent.) and 4 species of bushes (Cotinus coggygrya Scop., Cotinus coggygrya Scop. ‘Royal Purple’, Berberis vulgaris L. ‘Atropurpurea’, Corylus maxima Mill. ‘Atropurpurea’) were investigated in order to identify the most promising drought-tolerant ornamental species of woody plants from the temperate and continental climate zones, which are still not widely cultivated in the Polissia and Forest-Steppe zones of Ukraine. It will be a further recommendation to include them in the ecosystems of the urban environment to overcome the negative impact of the "urban heat island". In order to determine the relative drought resistance of plants, the following parameters of the water regime were measured: tissue hydration and water loss per unit of time.
 The test for drought resistance was carried out twice, when high temperatures are maintained: in early June (the leaves on trees and bushes are young), and also in early September (the leaves have already acquired all the features characteristic of their species). According to the results of the study, such medium-sized trees as: Aesculus pavia, Aralia elata, Cercis canadensis, Tetradium daniellii and Zizyphus jujube, as well as Cotinus coggygrya, Berberis vulgaris 'Atropurpurea' and Cotinus coggygrya 'Royal Purple' bushes can be recommended for urban landscaping as drought-resistant plants. Whereas, the tree species Broussonetia papurifera, Robinia viscosa, Prunus dulcis and Platycarya strobilacea, as well as the bushes Corylus maxima 'Atropurpurea' showed relatively lower drought resistance, which must be taken into account when landscaping, since, on the one hand, there is a need for additional watering, on the other hand in in one landscape exposure, it is appropriate to plant species with a similar level of drought resistance, which will facilitate further plant care. The slightly lower tolerance to drought of Corylus maxima 'Atropurpurea' may be due to the fact that only this species of the studied shrubs is shade-tolerant, while the other three species are light-loving plants, which must also be taken into account when creating plant compositions.

Hurricanes increase tropical forest vulnerability to drought.

Rapid changes in climate and disturbance regimes, including droughts and hurricanes, are likely to influence tropical forests, but our understanding of the compound effects of disturbances on forest ecosystems is extremely limited. Filling this knowledge gap is necessary to elucidate the future of these ecosystems under a changing climate. We examined the relationship between hurricane response (damage, mortality, and resilience) and four hydraulic traits of 13 dominant woody species in a wet tropical forest subject to periodic hurricanes. Species with high resistance to embolisms (low P50 values) and higher safety margins ( ) were more resistant to immediate hurricane mortality and breakage, whereas species with higher hurricane resilience (rapid post-hurricane growth) had high capacitance and P50 values and low . During 26 yr of post-hurricane recovery, we found a decrease in community-weighted mean values for traits associated with greater drought resistance (leaf turgor loss point, P50 , ) and an increase in capacitance, which has been linked with lower drought resistance. Hurricane damage favors slow-growing, drought-tolerant species, whereas post-hurricane high resource conditions favor acquisitive, fast-growing but drought-vulnerable species, increasing forest productivity at the expense of drought tolerance and leading to higher overall forest vulnerability to drought.

Потенциальное влияние изменения климата на распространение ели обыкновенной (Picea abies Karst.) в Боснии и Герцеговине

As forests in Bosnia and Herzegovina cover 2,904,600 ha or 56.7 % of its total area, and since the meteorological data analysis for the period 1961–2014 shows that the mean annual temperature maintains a continuous rise, сlose attention should be paid to these fragile ecosystems. It is important to note that one of the most economically valuable species for forestry in Bosnia and Herzegovina, Norway spruce, is particularly endangered due to its very low drought resistance and spread of various diseases. Comparing the last climate sequence (1991–2019) with the previous one (1961–1990) we found that the spruce-inhabited areas showed an average increase in the values of the Forest Aridity Index of 0.929. As for the Ellenberg’s climate quotient, it is noticeable that climate change is not as strong as in the case of the Forest Aridity Index. Based on projections for the mid- (2041–2070) and late-century (2071–2100) under the RCP 4.5, there will be no change that is likely to significantly affect the distribution of spruce. The predicted rates of decline and altitudinal shifts of favorable habitats are negligible. On the contrary, projections under the RCP 8.5 predict a significant reduction of suitable habitats, both for the existing range of Norway spruce and the entire territory of Bosnia and Herzegovina. Particularly, late-century projection under the RCP 8.5 predicts an almost complete reduction of suitable habitats, while small areas of suitable habitats at higher elevations will remain intact.

Satellite data reveal differential responses of Swiss forests to unprecedented 2018 drought.

Extreme events such as the summer drought of 2018 in Central Europe are projected to occur more frequently in the future and may cause major damages including increased tree mortality and negative impacts on forest ecosystem services. Here, we quantify the response of >1 million forest pixels of 10 × 10 m across Switzerland to the 2018 drought in terms of resistance, recovery, and resilience. We used the Normalized Difference Water Index (NDWI) derived from Sentinel‐2 satellite data as a proxy for canopy water content and analyzed its relative change. We calculated NDWI change between the 2017 pre‐drought and 2018 drought years (indicating resistance), 2018 and the 2019 post‐drought (indicating recovery), and between 2017–2019 (indicating resilience). Analyzing the data from this large natural experiment, we found that for 4.3% of the Swiss forest the NDWI declined between 2017 and 2018, indicating areas with low resistance of the forest canopy to drought effects. While roughly 50% of this area recovered, in 2.7% of the forested area NDWI continued to decline from 2018 to 2019, suggesting prolonged negative effects or delayed damage. We found differential forest responses to drought associated with site topographic characteristics and forest stand characteristics, and to a lesser extent with climatic conditions and interactions between these drivers. Low drought resistance and high recovery were most prominent at forest edges, but also on south‐facing slopes and lower elevations. Tree functional type was the most important driver of drought resilience, with most of the damage in stands with high conifer abundance. Our results demonstrate the suitability of satellite‐based quantification of drought‐induced forest damage at high spatial resolution across large areas. Such information is important to predict how local site characteristics may impact forest vulnerability to future extreme events and help in the search for appropriate adaptation strategies.

INTRODUCTION OF WOODY LIANAS AND PROSPECTS OF THEIR USE IN KRYVYI RIH GARDENING

Problem. Due to the rapid trend of growth and spread of vertical landscaping in landscaping of settlements in Ukraine, studying woody lianas is quite active. There is almost no information on the bioecological features of woody lianas in conditions of our region and their use in landscaping of urban areas. Therefore, the aim of the work was to summarize the introduction of woody lianas in the Kryvyi Rih Botanical Garden of the National Academy of Sciences of Ukraine, to analyze the current state of vertical landscaping in Kryvyi Rih, to find out the range of plants used and to prove the possibilities of its expansion. Methods. The distribution of introduced woody lianas by origin was carried out according to A.L. Takhtadzhyan . Assessment of viability was performed by the scale of viability of shrubs modified on the basis of the classification by Z.I. Luchnyk. Estimation of drought resistance of lianas was made by the scale of S.S. Piatnytskyi , winter hardiness was estimated on the scale adopted for botanical gardens of the USSR. Results and conclusions For Kryvyi Rih, one of the promising areas in the creation of modern landscape and architectural landscaping of the city is vertical landscaping based on twisted plants. The source for enrichment of the range of plants for urban area landscaping is the collections of the botanical garden. The introduction of woody lianas in the Kryvyi Rih Botanical Garden began in 1983. Today, the collection fund includes 31 species and 42 cultivars, representing 15 genera and 13 families. We determined that the phenorhythmics of the introduced species is consistent with the climatic conditions of the Right-Bank Steppe Dnieper Area, most of the species bloom annually, bear fruit, have high living conditions and decorativeness. Most woody lianas introduced in the KRBG are quite drought-resistant (they scored point I by Piatnytskyi scale), they tolerate short periods of drought without significant morphological changes (species of the genera Wisteria, Campsis, Celastrus, Parthenocissus, Vitis, Ampelopsis). Lower drought resistance (drought resistance scores point II) in species of the genera Lonicera, Actinidia was manifested by the loss of turgor in the leaves, which was restored during the night, and partial yellowing of the leaves. Groups of introduced woody lianas were selected according to the method of attachment to the support and the degree of decorativeness. A survey of the urban areas of Kryvyi Rih revealed that the range of woody lianas used is represented by 10 species and 7 cultivars from 10 genera and 10 families. According to the results of studying morpho-biological, ecological properties and decorative qualities, it is recommended to introduce Aristolochia manshuriensis, Akebia quinata, Celastrus flagellaris, Celastrus orbiculatus, Lonicera caprifolium, Wisteria sinensis more widely in landscaping of urban areas.

Effect of water depth on eight varieties of rice in Obukiyo, Oju lga of Benue state, Nigeria

Water depth has been described as one of the most important environmental factors determining the growth and yield of rice. Different rice varieties respond differently to various water levels. Three (3) naturally existing water levels (5cm, 10cm and 15cm) at Obukyo Oju Local Government Area of Benue State were studied to evaluate their impact on eight varieties of rice (FARO 15, 37, 44, 52, 57, 60, 61 and 62). The data collected showed significant different (P< 0. 05) in plant height, blade area, panicle length and dry seed weight, while the number of leaves and tillers were not significantly affected by the various water levels. Generally, the rice performed better in high water levels (15cm) than the medium (10cm) and low water depth (5cm). FARO 57 (9.86t/ha), FARO 61(9.86t/ha), FARO15 (8.78t/ha) and FARO 52 (8.28t/ha) were significantly higher while FARO 44 (5.24t/ha) the dwarf variety and FARO 37 (5 54t/ha) the lodging and low drought resistance variety yielded very poor in high and medium water levels but encouragingly high in low water depth. FARO 57 (5.75t/ha) and FARO 60 (5.65t/ha) were the lowest in low water levels. FARO 15, 52, 57, 60, 61 and 62 were recommended for high water levels while FARO 15, 52, 57, 60, 61 and 62 were recommended for medium water levels. FARO15, 37, 44, 52, 61 and 62 are recommended for low water level. FARO 15, 52, 61 and 62 had encouraging yield in all water levels and are recommended as such.

Seedling root characteristics and drought resistance of wheat in Shanxi province

<p indent=0mm>Wheat root morphology at the seedling stage is the basis of root distribution at the adult stage. It is closely related to stress resistance and yield. A comprehensive understanding of the root system characteristics at seedling stage and drought resistance is of great significance for the excellent germplasm utilization and early screening of drought resistance. Using 239 wheat varieties (lines) from Shanxi province, the root traits at seedling stage and their response to water stress were evaluated. The results showed that under normal growth, Shanxi wheat had a great variation in root traits at seedling stage, with the greatest variation in landraces. The maximum root length (MRL) tended to decrease slightly with the years, while other root traits were first increased and then decreased. There were differences among the root traits in response to water stress. The total root length (TRL) is the most sensitive to water, followed by root surface area (RSA), root volume (RV) and root biomass. The maximum root length (MRL) and the average number of roots (RN) were insensitive. The drought resistance of seedling roots showed a trend of decreasing first and then increasing with the years. Landraces and varieties released from 1970 to 1979 had moderately resistance to water stress, varieties released from 1980 to 1999 had lower drought resistance, and varieties released after 2000 had the better resistance, of which the dryland varieties were the best resistance. Correlation analysis of the seedling root characteristics and yield related traits suggested that the maximum root length, total root length, root volume and root biomass were significantly positively correlated with 1000-kernel weight and yield under rain-fed conditions, and the maximum root length and root biomass were also significantly positively correlated with adult plant drought resistance. The present study suggests that the maximum root length and root biomass at the seedling stage can be used as early generation selection parameters for drought resistance and yield in dryland breeding in semi-arid areas.

Make it simpler: Alien species decrease functional diversity of coastal plant communities

AbstractQuestions(a) Are there differences in abundance‐weighted functional trait values between native and alien species in coastal plant communities? (b) Which functional traits are associated with a higher level of invasion in these communities? (c) Do functional diversity patterns differ between native and alien species? (d) Is alien species occurrence linked to small‐scale functional homogenization effects on the resident native species?LocationN‐Adriatic coastal ecosystems (Marano and Grado lagoon, Friuli Venezia Giulia region, Italy).MethodsWe sampled coastal vegetation within two habitats (foredunes and saltmarshes) along nine belt transects in two sampling sites. Plant species richness and abundance were assessed in 128 plots along with a suite of plant functional traits. We tested for differences in community‐weighted means between native and alien species within the two habitats, and Linear Mixed Models provided insights into traits fostering the invasion success among alien species. To check for potential functional homogenization driven by alien species invasion, we explored functional diversity patterns of native and alien species (β and γ functional diversity) and the relationship between α functional diversity and alien cover.ResultsAlien species had lower functional diversity than natives and were characterized by lower leaf construction costs coupled with lower drought resistance and higher water transport efficiency. The most abundant aliens were the ones minimizing carbon investment for leaf construction. In addition, we also found evidence for small‐scale functional homogenization driven by alien invasion.ConclusionsOur results suggested that native species adopt a resource conservative strategy whereas alien species are characterized by a higher resource acquisition capacity (i.e., acquisitive strategy). Our data also confirmed that alien species are less functionally diverse than natives, potentially driving the community towards small‐scale functional homogenization, resulting in a loss of species and a reduction in the functional space.

Environmental sensitivity to desertification in northern Mesopotamia; application of modified MEDALUS by using analytical hierarchy process

Poor management, low vegetation cover, and severe erosion are undermining the stability and sustainability of lands. In this study, modified Mediterranean Desertification and Land Use (MEDALUS) method was used to identify environmentally sensitive areas (ESA) to desertification in Tigris Basin, Turkey. Soil samplings (0–20 cm) and field observations were conducted within 3.752 km2 land. Biophysical and anthropogenic parameters of sampling locations have been integrated and processed by geographic information systems obtaining soil, climate, vegetation, and management quality indexes. Additional six parameters for soil quality and one for management quality were used to adopt MEDALUS to the context of Tigris Basin. The weights for parameters and indicators were calculated using analytical hierarchy process (AHP). Tigris Basin was classified into one fragile and two critical areas using original method, whereas one fragile and three critical classes were defined with the modified method. In the original method, fragile areas represented 5.65% and low-degree critical areas 24.49% and moderate critical areas 69.86% of the study area, which are needed to be monitored for severe land degradation. Modifying MEDALUS allowed to define highly critical areas (51.41%) which have not been detected in the original method. The critical areas are primarily used for field crops with extensive tillage, medium degree of plant cover, low drought resistance, and erosion along with low management quality due to the lack of required environmental protection. The results revealed that adaptation of new parameters and weighting in MEDALUS improved the ability of classifying ESAs for a regional scale to desertification.

Shifting species and functional diversity due to abrupt changes in water availability in tropical dry forests

Abstract Recent insights show that tropical forests are shifting in species composition, possibly due to changing environmental conditions. However, we still poorly understand the forest response to different environmental change drivers, which limits our ability to predict the future of tropical forests. Although some studies have evaluated drought effects on tree communities, we know little about the influence of increased water availability. Here, we evaluated how an increase in water availability caused by an artificial reservoir affected temporal changes in forest structure, species and functional diversity, and community‐weighted mean traits. Furthermore, we evaluated how demographical groups (recruits, survivors and trees that died) contributed to these temporal changes in tropical dry forests. We present data for the dynamics of forest change over a 10‐year period for 120 permanent plots that were far from the water’s edge before reservoir construction and are now close to the water’s edge (0–60 m). Plots close to the water’s edge had an abrupt increase in water availability, while distant plots did not. Plots close to the water’s edge showed an increase in species and functional diversity, and in the abundance of species with traits associated with low drought resistance (i.e., evergreen species with simple leaves and low wood density), whereas plots far from the water’s edge did not change. Changes in overall community metrics were mainly due to recruits rather than to survivors or dead trees. Overall stand basal area did not change because growth and recruitment were balanced by mortality. Synthesis. Our results showed that tropical dry forests can respond quickly to abrupt changes in environmental conditions. Temporal changes in vegetation metrics due to increased water availability were mainly attributed to recruits, suggesting that these effects are lasting and may become stronger over time. The lack of increase in basal area towards the water’s edge, and the shift towards higher abundance of soft‐wooded species, could reduce the carbon stored and increase the forest’s vulnerability to extreme weather events. Further “accidental” large‐scale field experiments like ours could provide more insights into forest responses and resilience to global change.

Evaluation of drought resistance in Iris germanica L. based on subordination function and principal component analysis

Drought is one of the major environment stresses that have a wide range of impact on plants. In this study, seven physiological indexes including the content of soluble protein (SP), chlorophyll (Chl) and malondialdehyde (MDA), superoxide dismutase (SOD) and peroxidase (POD) activities, leaf relative water content (RWC), rate of water loss (RWL) from excised leaves were measured in leaves of Iris germanica before and after the drought treatment. It was found that the content of MDA and SP, POD and SOD activity increased, while RWL and RWC decreased in response to drought stress. Based on the subordinate function values of seven physiological indexes, seven single indexes were transformed into three principal components namely damage degree, active oxygen removal ability and moisture condition and the composite score (F value) of each iris variety was calculated by principal component analysis (PCA). Based on the F values, 10 iris cultivars could be divided into three groups by cluster analysis (CA): drought-resistance (2 varieties), medium drought-resistance (5 varieties), and low drought-resistance (3 varieties). Meanwhile, optimum regression equation was constructed. Therefore, this work provides a comprehensive and reliable method for evaluating drought resistance in the varieties of Iris germanica.

Woody Vegetation Die off and Regeneration in Response to Rainfall Variability in the West African Sahel

The greening in the Senegalese Sahel has been linked to an increase in net primary productivity, with significant long-term trends being closely related to the woody strata. This study investigates woody plant growth and mortality within greening areas in the pastoral areas of Senegal, and how these dynamics are linked to species diversity, climate, soil and human management. We analyse woody cover dynamics by means of multi-temporal and multi-scale Earth Observation, satellite based rainfall and in situ data sets covering the period 1994 to 2015. We find that favourable conditions (forest reserves, low human population density, sufficient rainfall) led to a rapid growth of Combretaceae and Balanites aegyptiaca between 2000 and 2013 with an average increase of 4% woody cover. However, the increasing dominance and low drought resistance of drought prone species bears the risk of substantial woody cover losses following drought years. This was observed in 2014–2015, with a die off of Guiera senegalensis in most places of the study area. We show that woody cover and woody cover trends are closely related to mean annual rainfall, but no clear relationship with rainfall trends was found over the entire study period. The observed spatial and temporal variation contrasts with the simplified labels of “greening” or “degradation”. While in principal a low woody plant diversity negatively impacts regional resilience, the Sahelian system is showing signs of resilience at decadal time scales through widespread increases in woody cover and high regeneration rates after periodic droughts. We have reaffirmed that the woody cover in Sahel responds to its inherent climatic variability and does not follow a linear trend.

Drought resistance across California ecosystems: evaluating changes in carbon dynamics using satellite imagery

AbstractDrought is a global issue that is exacerbated by climate change and increasing anthropogenic water demands. The recent occurrence of drought in California provides an important opportunity to examine drought response across ecosystem classes (forests, shrublands, grasslands, and wetlands), which is essential to understand how climate influences ecosystem structure and function. We quantified ecosystem resistance to drought by comparing changes in satellite‐derived estimates of water‐use efficiency (WUE = net primary productivity [NPP]/evapotranspiration [ET]) under normal (i.e., baseline) and drought conditions (ΔWUE = WUE2014 − baseline WUE). With this method, areas with increasing WUE under drought conditions are considered more resilient than systems with declining WUE. Baseline WUE varied across California (0.08 to 3.85 g C/mm H2O) and WUE generally increased under severe drought conditions in 2014. Strong correlations between ΔWUE, precipitation, and leaf area index (LAI) indicate that ecosystems with a lower average LAI (i.e., grasslands) also had greater C‐uptake rates when water was limiting and higher rates of carbon‐uptake efficiency (CUE = NPP/LAI) under drought conditions. We also found that systems with a baseline WUE ≤ 0.4 exhibited a decline in WUE under drought conditions, suggesting that a baseline WUE ≤ 0.4 might be indicative of low drought resistance. Drought severity, precipitation, and WUE were identified as important drivers of shifts in ecosystem classes over the study period. These findings have important implications for understanding climate change effects on primary productivity and C sequestration across ecosystems and how this may influence ecosystem resistance in the future.

Drought resistance of wheat alien chromosome addition lines evaluated by membership function value based on multiple traits and drought resistance index of grain yield

Drought is the single greatest abiotic stress leading to yield loss of wheat worldwide. The long-term domestication and selective breeding in artificial environments may have reduced the drought resistance of wheat. Wheat alien chromosome addition lines, with chromosomes derived from wild species, may possess drought resistant genetic potential and could serve as a bridge for transferring those traits to wheat. The drought resistance of 82 wheat alien chromosome addition lines along with their common parent Chinese Spring were evaluated for 10 agronomic traits under both well-watered and water-stressed conditions. Spike length was the most stable trait while biomass plant−1 was the most sensitive trait when subjected to drought stress. Evaluation of heritability and correlations with yield plant−1 suggested that plant height, peduncle length, distance between spike and flag leaf, grain number spike−1 and thousand-grain weight could be used as indicators of drought resistance. The membership function value of drought resistance (MFVD) based on those traits and grain yield plant−1, indicated 26 of the 82 wheat addition lines expressed high drought resistance. Higher MFVD was observed in the Agropyron elongatum 3E addition line in two years, and it was considered as the most drought resistant material. Analysis of the yield plant−1 suggested that the drought resistant addition lines identified by MFVD were drought resistant but not very high-yielding, thus they could be used to improve germplasm with high-yield potential but low drought resistance. The drought resistance index (DI) based on yield plant−1 indicated that 10 addition lines included both drought resistance and greater grain yield, which could be used in moderate stressed areas for improving drought resistance. Among them, addition lines with Aegilops peregrina 4SV and Ae. peregrina 3UV chromosome showed excellent performance and could be further investigated in drought resistance studies or breeding programs.

Effects of Exogenous Spermidine on Reactive Oxygen Levels and Antioxidative System of Tomato Seedling under Polyethlene Glycol Stress*

Two different drought-tolerant tomato cultivars were investigated under drought stress induced by 7.5% polyethylene glycol (PEG6000) in a nutrient solution culture system. The results showed that exogenous spermidine (Spd) (0.1 mmol L-1 ) treatment decreased O2-· production rate, and MDA and H2O2 contents, raised SOD, POD, CAT, APX and GR activities in the seedlings, and had no effect on MDHAR and DHAR activities. Spd treatment of ‘Huangguan’ seedlings with lower drought-resistance was more effective than that of ‘Maofen No. 802’ seedlings with stronger drought-resistance. It indicated that exogenous Spd treatment could to enhance the activities of some antioxidant enzymes and the contents of antioxidant substances, restrain embrane lipid peroxidation, reduce ROS levels and finally enhance the tolerance of tomato seedlings to drought environments. Fig 4, Ref 32

Zum Einfluß der Feuchte auf die Schlupfrate und Entwicklungsdauer der Eier mitteleuropäischer Feldheuschrecken (Orthoptera, Acrididae)

Eggs of 12 Central European grasshopper species were incubated under different moisture conditions. These ranged from flooded eggs down to 30% RH. Three series of experiments were carried out: 1. To test the moisture requirement and resistance to drought before and after the winter period, 2. to test only the drought resistance after overwintering, and 3. to test drought resistance before overwintering. During the winter period all eggs were kept uniformly in contact with water. For each species the number of hoppers hatching under the different moisture conditions are presented as well as the number of days required for the eggs to hatch at 24 °C, counting only the time after the winter period. The occurence of Acrididae in specific habitats rests partly on the effect of moisture on egg development. The species differ with regard to the drought resistance of their eggs, expressed as the number of larvae hatching at different humidities. This is correlated with the place of oviposition (above or below ground) and with the typical microclimate of the species habitats. The time needed to hatch varies considerably between species and also within species when the eggs are kept at different humidities. The hatching sequence of the species under suitable conditions in the laboratory is comparable with that in nature. When contact water is lacking hatching occurs later. This retardation in development is more expressed in species with low drought resistance in the egg stage. Leaving the eggs inside the pods does not reduce the number of hatchlings except when there is no contact water or when the pods are flooded. However, hatching occurs later in species with hard egg pods.