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Aim: Climate change regulates autumn leaf senescence date (LSD), exhibiting a strong phenological control of plant carbon uptake. Unlike the delaying effect of daily mean temperature (Tmean) on LSD, the impact of warming asymmetry in daytime and nighttime, as evidenced by variations of the diurnal temperature range (DTR), remains elusive. The objectives of this study were to investigate physiological and ecological impacts of DTR on LSD using long‐term in situ observations and to predict the future trends of LSD under warming. Location: Europe. Time period: 1950–2015. Major taxa studied: Plant phenology. Methods: We used partial correlation analysis, multiple linear regression and ridge regression to explore the impacts of DTR on LSD. To quantify the importance of potential drivers of LSD, we trained random forest models and applied the SHapley Additive exPlanations method to isolate the marginal contributions of each predictor on LSD. For LSD modelling and projection, we first evaluated two temperature‐driven LSD models [i.e., cooling‐degree‐day (CDD, without DTR effect) and day–night‐temperature CDD (DNCDD, with DTR effect)], then applied them to predict future LSDs. Results: We found that observational increases in Tmean and DTR had contrasting effects on LSD. Increased Tmean delayed the LSD, whereas larger DTR overall had an advancing effect. Considering the DTR effect, the Tmean sensitivity of LSD was 14% lower than presently estimated (2.4 vs. 2.8 days °C−1). Warming asymmetry‐related drought stress and plant functional traits (i.e., plant isohydricity and water‐use efficiency) potentially explained the advancing effect of DTR on LSD. We found that current projections of future LSD are overestimated because the DTR effect is discounted, suggesting the need for an adequate understanding of how plant phenology responds to warming asymmetry. Main conclusions: Our findings highlight the importance of DTR in controlling LSD variations with an advancing‐dominant effect and call for the improvement of phenology modelling incorporating the DTR effect. Given that DTR showed a globally narrowing trend over the last several decades, more efforts are needed to understand the potential ecological impacts of warming asymmetry and vegetation response to climate change. [ABSTRACT FROM AUTHOR]

In Europe, most of vineyards are managed under rainfed conditions, where water deficit has become increasingly an issue. The flowering-veraison phenophase represents an important period for vine response to water stress, which is known to depend on variety characteristics, soil and climate conditions. In this paper, we have carried out a retrospective analysis for important European wine regions over 1986–2015, with objectives to assess the mean Crop Water Stress Indicator (CWSI) during flowering-veraison phase, and potential Yield Lose Rate (YLR) due to seasonal cumulative water stress. Moreover, we also investigate if advanced flowering-veraison phase can lead to alleviated CWSI under recent-past conditions, thus contributing to reduced YLR. A process-based grapevine model is employed, which has been extensively calibrated for simulating both flowering and veraison stages using location-specific observations representing 10 different varieties. Subsequently, grid-based modelling is implemented with gridded climate and soil datasets and calibrated phenology parameters. The findings suggest wine regions with higher mean CWSI of flowering-veraison phase tend to have higher potential YLR. However, contrasting patterns are found between wine regions in France-Germany-Luxembourg and Italy-Portugal-Spain. The former tends to have slight-to-moderate drought conditions (CWSI<0.5) along with a negligible-to-moderate YLR (<30%), whereas the latter is found to have severe-to-extreme drought (CWSI>0.5) and substantial YLR (>40%). Wine regions prone to a high drought risk (CWSI>0.75) are also identified, which are concentrated in southern Mediterranean Europe. Advanced flowering-veraison phase over 1986–2015, could have benefited from more spring precipitation and cooler temperatures for wine regions of Italy-Portugal-Spain, leading to reduced mean CWSI and YLR. For those of France-Germany-Luxembourg, this can have reduced flowering-veraison precipitation, but prevalent reductions of YLR are also found, possibly due to shifted phase towards a cooler growing-season with reduced evaporative demands. Our study demonstrates flowering-verasion water deficit is critical for potential yield, which can have different impacts between Central and Southern European wine regions. This phase can be advanced under a warmer climate, thus having important implications for European rainfed vineyards. The overall outcome may provide new insights for appropriate viticultural management of seasonal water deficits under climate change. • Water stress of a drought-sensitive period is assessed for European rainfed vineyards. • Wine regions prone to a high flowering-veraison drought risk are identified. • Flowering-veraison water stress strongly affects water-limited potential yields. • Advanced flowering-veraison phase differently impacts European wine regions. • The outcomes improve understandings of seasonal water deficits of rainfed viticulture. [ABSTRACT FROM AUTHOR]

Aim: The stress‐gradient hypothesis (SGH) postulates that species interactions shift from negative to positive with increasing abiotic stress. Interactions between species are increasingly being recognized as important drivers of species distributions, but it is still unclear whether stress‐induced changes in interactions affect continental‐to‐global scale species distributions. Here, we tested whether associations of vascular plant species in dry grasslands in Europe follow the SGH along a climatic water deficit (CWD) gradient across the continent. Location: Dry grasslands in Europe. Time period: Present. Major taxa studied: Vascular plants. Methods: We built a context‐dependent joint species distribution model (JSDM) to estimate the residual associations (i.e., associations that are not explained by the abiotic environment) of 161 plant species as a function of the CWD based on community data from 8,660 vegetation plots. We evaluated changes in residual associations between species for pairs and on the community level, and we compared responses for groups of species with different drought tolerances. Results: We found contrasting shifts in associations for drought‐sensitive and drought‐tolerant species. For drought‐sensitive species, 21% of the pairwise associations became more positive with increasing CWD, whereas 17% became more negative. In contrast, only 17% of the pairwise associations involving drought‐tolerant species became more positive, whereas 27% became more negative in areas with a high CWD. Additionally, the incidence of positive associations increased with drought for drought‐sensitive species and decreased for drought‐tolerant species. Main conclusions: We found that associations of drought‐sensitive plant species became more positive with drought, in line with the SGH. In contrast, associations of drought‐tolerant species became more negative. Additionally, changes in associations of single species pairs were highly variable. Our results indicate that stress‐modulated species associations might influence the distribution of species over large geographical extents, thus leading to unexpected responses under climate change through shifts in species associations. [ABSTRACT FROM AUTHOR]

Since the 1980s, Ramularia leaf spot (RLS) is an emerging barley disease worldwide. The control of RLS is increasingly aggravated by a recent decline in fungicide efficacy and a lack of RLS-resistant cultivars. Furthermore, climate change increases drought periods in Europe, enhances variable weather conditions, and thus will have an impact on severity of plant diseases. Hence, identification of RLS-resistant cultivars and understanding of disease progression under abiotic stress are important aims in integrated disease management under climate change. In the present study, we evaluated quantitative RLS resistance of 15 spring barley genotypes under drought, controlled irrigation and field conditions between 2016 and 2019 and monitored microclimatic conditions within the canopy. We identified genotypes that show robust quantitative resistance to RLS in different field environments. Our findings suggest that long-lasting drought periods create unfavourable conditions for the disease and supports that the extent and duration of leaf wetness is a key factor for RLS epidemics. [ABSTRACT FROM AUTHOR]

Aim: The aim was to decipher Europe‐wide spatio‐temporal patterns of forest growth dynamics and their associations with carbon isotope fractionation processes inferred from tree rings as modulated by climate warming. Location: Europe and North Africa (30‒70° N, 10° W‒35° E). Time period: 1901‒2003. Major taxa studied: Temperate and Euro‐Siberian trees. Methods: We characterize changes in the relationship between tree growth and carbon isotope fractionation over the 20th century using a European network consisting of 20 site chronologies. Using indexed tree‐ring widths (TRWi), we assess shifts in the temporal coherence of radial growth across sites (synchrony) for five forest ecosystems (Atlantic, boreal, cold continental, Mediterranean and temperate). We also examine whether TRWi shows variable coupling with leaf‐level gas exchange, inferred from indexed carbon isotope discrimination of tree‐ring cellulose (Δ13Ci). Results: We find spatial autocorrelation for TRWi and Δ13Ci extending over a maximum of 1,000 km among forest stands. However, growth synchrony is not uniform across Europe, but increases along a latitudinal gradient concurrent with decreasing temperature and evapotranspiration. Latitudinal relationships between TRWi and Δ13Ci (changing from negative to positive southwards) point to drought impairing carbon uptake via stomatal regulation for water saving occurring at forests below 60° N in continental Europe. An increase in forest growth synchrony over the 20th century together with increasingly positive relationships between TRWi and Δ13Ci indicate intensifying impacts of drought on tree performance. These effects are noticeable in drought‐prone biomes (Mediterranean, temperate and cold continental). Main conclusions: At the turn of this century, convergence in growth synchrony across European forest ecosystems is coupled with coordinated warming‐induced effects of drought on leaf physiology and tree growth spreading northwards. Such a tendency towards exacerbated moisture‐sensitive growth and physiology could override positive effects of enhanced leaf intercellular CO2 concentrations, possibly resulting in Europe‐wide declines of forest carbon gain in the coming decades. [ABSTRACT FROM AUTHOR]

Drought stress during reproductive development could drastically reduce wheat grain number and yield, but quantitative evaluation of such an effect is unknown under climate change. The objectives of this study were to evaluate potential yield benefits of drought tolerance during reproductive development for wheat ideotypes under climate change in Europe, and to identify potential cultivar parameters for improvement. We used the Sirius wheat model to optimize drought-tolerant (DT) and drought-sensitive (DS) wheat ideotypes under a future 2050 climate scenario at 13 contrasting sites, representing major wheat growing regions in Europe. Averaged over the sites, DT ideotypes achieved 13.4% greater yield compared with DS, with higher yield stability. However, the performances of the ideotypes were site dependent. Mean yield of DT was 28–37% greater compared with DS in southern Europe. In contrast, no yield difference (≤1%) between ideotypes was found in north-western Europe. An intermediate yield benefit of 10–23% was found due to drought tolerance in central and eastern Europe. We conclude that tolerance to drought stress during reproductive development is important for high yield potentials and greater yield stability of wheat under climate change in Europe. [ABSTRACT FROM AUTHOR]

Vicia cracca diploids and autotetraploids are highly parapatric in Europe; tetraploids reside in western and northern part, whereas diploids occupy much drier south-eastern part. They meet together in a Central European contact zone. This distribution pattern raised questions about a transformative effect of polyploidization on plant performance and environmental tolerances. We investigated plant survival, growth, and seed production in two water regimes in a common garden experiment using seeds collected from five localities in the Central European contact zone where diploids and tetraploids occur in sympatry. Obtained data imply that tetraploids of V. cracca are not generally superior in performance to diploids. Significantly larger seeds from tetraploid mother plants collected in the field were not correlated with greater stature of the seedlings. Nonetheless, tetraploids might have a potential to out-compete diploids in the long run due to the tetraploids' ability of greater growth which manifested in the second year of cultivation. Considering the response of diploids and tetraploids to water supply, drought stressed tetraploids but not diploids produced a higher proportion of aborted seeds than watered ones, which implies that tetraploids are more drought susceptible than diploids. On the other hand, decreased plant height in drought stresses tetraploids, which simultaneously increased total seed production, may suggest that tetraploids have a greater ability to avoid local extinction under unfavourable conditions by enhancing biomass allocation into production of seeds at the cost of lower growth. The significant interaction between ploidy level and locality in several traits suggests possible polyfyletic origin of tetraploids and the necessity to clarify the history of the tetraploids in Europe. [ABSTRACT FROM AUTHOR]

Research Highlights: Data of advanced-age provenance tests were reanalyzed applying a new approach, to directly estimate the growth of populations at their original sites under individually generated future climates. The results revealed the high resilience potential of fir species. Background and Objectives: The growth and survival of silver fir under future climatic scenarios are insufficiently investigated at the xeric limits. The selective signature of past climate determining the current and projected growth was investigated to analyze the prospects of adaptive silviculture and assisted transfer of silver fir populations, and the introduction of non-autochthonous species. Materials and Methods: Hargreaves' climatic moisture deficit was selected to model height responses of adult populations. Climatic transfer distance was used to assess the relative drought stress of populations at the test site, relating these to the past conditions to which the populations had adapted. ClimateEU and ClimateWNA pathway RCP8.5 data served to determine individually past, current, and future moisture deficit conditions. Besides silver fir, other fir species from South Europe and the American Northwest were also tested. Results: Drought tolerance profiles explained the responses of transferred provenances and predicted their future performance and survival. Silver fir displayed significant within-species differentiation regarding drought stress response. Applying the assumed drought tolerance limit of 100 mm relative moisture deficit, most of the tested silver fir populations seem to survive their projected climate at their origin until the end of the century. Survival is likely also for transferred Balkan fir species and for grand fir populations, but not for the Mediterranean species. Conclusions: The projections are less dramatic than provided by usual inventory assessments, considering also the resilience of populations. The method fills the existing gap between experimentally determined adaptive response and the predictions needed for management decisions. It also underscores the unique potential of provenance tests. [ABSTRACT FROM AUTHOR]

Arbutus unedo L. is a small Ericaceae tree with a circum-Mediterranean distribution. It has a huge ecological impact on southern Europe forests and a great economic importance as a source of phytochemicals with bioactive properties and for fruit production. On the foreseen climate change context, breeding toward drought tolerance is necessary in order to ameliorate plant performance. Therefore, the aim of this work was to study the reproduction mechanisms of the strawberry tree, obtain new genetic combinations by hybridization, and select genotypes more tolerant to drought stress. A morphological analysis of flowers and pollen was carried out, and controlled pollinations were performed both in vitro and ex vitro. The very first approach on strawberry tree breeding by means of hybridization is also presented. Several physiological parameters were evaluated on 26 genotypes submitted to a water-deficit regime. Plant behavior under drought greatly varied among genotypes, which showed high phenotype plasticity. Three genotypes that were able to cope with water restriction without compromising net CO2 assimilation were identified as highly tolerant to drought stress. The results obtained elucidate the reproduction mechanisms of the strawberry tree and open the way for a long-term breeding program based on the selection of drought-tolerant plants. [ABSTRACT FROM AUTHOR]