Over the past decades, climate change has induced transformations in the weed flora of arable ecosystems in Europe. For instance, thermophile weeds, late-emerging weeds, and some opportunistic weeds have become more abundant in some cropping systems. The composition of arable weed species is indeed ruled by environmental conditions such as temperature and precipitation. Climate change also influences weeds indirectly by enforcing adaptations of agronomic practice. We therefore need more accurate estimations of the damage potential of arable weeds to develop effective weed control strategies while maintaining crop yield. Here we review the mechanisms of responses of arable weeds to the direct and indirect effects of climate change. Climate change effects are categorized into three distinct types of shifts occurring at different scales: (1) range shifts at the landscape scale, (2) niche shifts at the community scale, and (3) trait shifts of individual species at the population scale. Our main conclusions are changes in the species composition and new species introductions are favored, which facilitate major ecological and agronomical implications. Current research mainly considers processes at the landscape scale. Processes at the population and community scales have prevalent importance to devise sustainable management strategies. Trait-climate and niche-climate relationships warrant closer consideration when modeling the possible future distribution and damage potential of weeds with climate change.

Grassland-based ruminant production systems are integral to sustainable food production in Europe, converting plant materials indigestible to humans into nutritious food, while providing a range of environmental and cultural benefits. Climate change poses significant challenges for such systems, their productivity and the wider benefits they supply. In this context, grassland models have an important role in predicting and understanding the impacts of climate change on grassland systems, and assessing the efficacy of potential adaptation and mitigation strategies. In order to identify the key challenges for European grassland modelling under climate change, modellers and researchers from across Europe were consulted via workshop and questionnaire. Participants identified fifteen challenges and considered the current state of modelling and priorities for future research in relation to each. A review of literature was undertaken to corroborate and enrich the information provided during the horizon scanning activities. Challenges were in four categories relating to: 1) the direct and indirect effects of climate change on the sward 2) climate change effects on grassland systems outputs 3) mediation of climate change impacts by site, system and management and 4) cross-cutting methodological issues. While research priorities differed between challenges, an underlying theme was the need for accessible, shared inventories of models, approaches and data, as a resource for stakeholders and to stimulate new research. Developing grassland models to effectively support efforts to tackle climate change impacts, while increasing productivity and enhancing ecosystem services, will require engagement with stakeholders and policy-makers, as well as modellers and experimental researchers across many disciplines. The challenges and priorities identified are intended to be a resource 1) for grassland modellers and experimental researchers, to stimulate the development of new research directions and collaborative opportunities, and 2) for policy-makers involved in shaping the research agenda for European grassland modelling under climate change.

Yield development of agricultural crops over time is not merely the result of genetic and agronomic factors, but also the outcome of a complex interaction between climatic and site-specific soil conditions. However, the influence of past climatic changes on yield trends remains unclear, particularly under consideration of different soil conditions. In this study, we determine the effects of single agrometeorological factors on the evolution of German winter wheat yields between 1958 and 2015 from 298 published nitrogen (N)-fertilization experiments. For this purpose, we separate climatic from genetic and agronomic yield effects using linear mixed effect models and estimate the climatic influence based on a coefficient of determination for these models. We found earlier occurrence of wheat growth stages, and shortened development phases except for the phase of stem elongation. Agrometeorological factors are defined as climate covariates related to the growth of winter wheat. Our results indicate a general and strong effect of agroclimatic changes on yield development, in particular due to increasing mean temperatures and heat stress events during the grain-filling period. Except for heat stress days with more than 31°C, yields at sites with higher yield potential were less prone to adverse weather effects than at sites with lower yield potential. Our data furthermore reveal that a potential yield levelling, as found for many West-European countries, predominantly occurred at sites with relatively low yield potential and about one decade earlier (mid-1980s) compared to averaged yield data for the whole of Germany. Interestingly, effects related to high precipitation events were less relevant than temperature-related effects and became relevant particularly during the vegetative growth phase. Overall, this study emphasizes the sensitivity of yield productivity to past climatic conditions, under consideration of regional differences, and underlines the necessity of finding adaptation strategies for food production under ongoing and expected climate change. K E Y W O R D Sclimate change impact, climate trend, long-term yield development, phenology trend, R 2 for mixed effect models, soil yield potential, weather extremes, Winter wheat

Dairy livestock production systems rely on high‐quality forage legumes, which are widely present in grassland swards all over Europe. A future climatic scenario with higher average annual temperatures and lower precipitation is expected to affect grassland productivity in general and the productivity of the most important forage legume species Trifolium repens in particular. One way to cope with such constraints is the adoption of currently underutilized minor legume species with a higher tolerance towards drought stress. Therefore, the present study investigated legume species with lower moisture requirements than T. repens, these are Lotus corniculatus, Medicago falcata, Medicago lupulina and Onobrychis viciifolia in comparison with T. repens. Legumes were grown in containers as monocultures in a roofed open‐sided greenhouse under conditions of optimal water supply or periodic drought stress. Generally, drought stress decreased the biomass production, but species differed in their reaction. Particularly, M. lupulina and L. corniculatus had lower relative biomass losses (−26%) compared to T. repens (−43%, as averaged over drought stress periods). However, in overall biomass production T. repens still was at one level with M. lupulina and L. corniculatus under drought stress. This was related to high stomata control as indicated by the intrinsic water‐use efficiency. We conclude that there are promising future options of forage legumes as alternatives to T. repens.

The return of slurry is the most important means of fertilization in grassland dairy farming. Broadcast application of slurry induces air pollution by ammonia. Alternatives to broadcast application like sliding shoe or injection have therefore been introduced. These alternatives might, however, cause higher N losses by nitrate leaching because N prevented from volatilization may not completely be utilized for dry matter production. Information on the interactive effects of amount of N input and slurry application technique on nitrate leaching from productive organic-sandy soils are still scarce. Therefore, we tested the hypothesis that slurry application by sliding shoe or injection leads to larger NO 3-N losses via leaching than broadcast application. In a 4-year experiment on cut grassland, we applied N at 0, 160, 240, and 320 kg ha −1 year −1 using four application techniques: in the form of a chemical-synthetic N fertilizer or as cattle slurry applied broadcast, by sliding shoe or shallow injection. We assessed nitrate leaching during winter using suction cups. Additionally, we determined herbage dry matter yields, N offtake, and soil mineral N content to compile N balances for the individual treatments based on these data. Our results show that nitrate leaching during winter did not differ significantly among treatments of N application technique. Nitrate leaching increased significantly with increasing amount of N input, but was on average lower than 16.5 kg N ha −1 for application rates of up to 320 kg N ha −1. Soil mineral N content in autumn was a reasonably good predictor for nitrate leaching, with R 2 of 0.65. The proportion of nitrate leaching of positive N surpluses increased in the order broadcast, sliding shoe, injection, and chemicalsynthetic N application. Our findings demonstrate that the amount of N input but not the technique of application results in a significant effect on nitrate leaching.

Bare soil areas, which commonly arise as an unwanted consequence of overstraining of the vegetation cover at highly frequented sites, cause various environmental problems (Morgan 2005). In grassland sites which are subject to continuous mechanical disturbance, e.g. resulting from freerange chicken or horse husbandry or intensive leisure sports use, the maintenance of an intact vegetation cover remains a challenge to be tackled. The choice of plant species with strong tolerance to mechanical damage for the establishment of durable swards may be an answer to this issue.Physical disturbance generally impacts on plants by tear-off or wounding of leaf, shoot or root tissue or by combinations of these. In agricultural contexts, studies on tolerance to disturbance in plants mainly focus on recovery from loss of biomass related to harvesting, e.g. mowing or grazing in grasslands (Ferraro and Oesterheld 2002), and on root or shoot herbivory by pest organisms (Maron 1998). In horse or chicken pasture or on sports grounds, however, different types of damaging impacts simultaneously and in an undirected way act upon the plant by wounding or tearing off leaves, parts of the shoot, and root tissue. So far, studies elucidating the tolerance of herbaceous plants to these combined damage regimes are rare.Within the present study, we aim at filling this gap of knowledge. We investigated the response of ten grassland plant species to comprehensive mechanical strain by simulating disturbance arising e.g. from the action of scratching chicken or of soccer boots. Within a greenhouse experiment, we subjected potted plants to three standardized levels of mechanical damage (moderate, medium and strong) impacting on shoot and root simultaneously; non-treated plants served as a control. We used the ratio of post-treatment shoot biomass in relation to shoot biomass of the non-treated control as a measure of damage tolerance. We based species selection on high performance within intensive cutting and grazing systems. Despite their relative homogeneity in terms of tolerance towards the latter types of disturbance, we firstly hypothesized the species to differ markedly in tolerance to comprehensive mechanical disturbance ABSTRACTThe establishment of plants with high damage tolerance may provide a means for soil protection on sites exposed to strong disturbance. In a pot experiment, we investigated the tolerance to mechanical strain of ten grassland plant species representing three growth form groups (cespitose: Festuca arundinacea, Lolium perenne, Taraxacum officinale; rhizomatous: Achillea millefolium, Elymus repens, Poa pratensis; stoloniferous: Agrostis stolonifera, Festuca rubra rubra, Poa supina, Trifolium repens). We hypothesised that growth form and pre-disturbance biomass allocation to the root serve as predictors of damage tolerance. With a tool imitating the action of cleated football boots or scratching chicken, we applied three standardized levels (moderate, medium, strong) of a torsional force which exceeded the shear strength o...

Maintaining intact vegetation in the outdoor run of chickens (Gallus gallus domesticus) can be difficult due to intense stresses such as defoliation and concentrated manure. The aim of this study was to determine the extent to which damage‐tolerant plant species can improve canopy cover. In a 2‐yr field experiment, we subjected 14 disturbance‐tolerant grassland plant species (nine grasses and five forbs) to stocking with laying hens for short (1‐d), medium (2‐d), and long (3‐d) periods in a rotational stocking system. The species differed strongly in resistance (canopy cover and density of tillers and vegetation growing points) and resilience (herbage accumulation) to stocking. Repeated stocking but not duration of stocking had a significant effect on herbage accumulation and canopy cover in most of the species. Canopy cover decreased with repeated stocking in the majority of the tested species. In most forbs, increasing stocking duration significantly decreased the density of vegetation growing points; in most grass species, this factor had no significant effect on tiller density. Our results indicated that grasses are generally more suitable for an outdoor chicken run than forbs. The best performance was recorded for Schedonorus phoenix (Scop.) Holub and Poa supina (Schrad.), with >80% canopy cover, constant tiller density, and herbage accumulation of >4.8 g dry matter m−2 d−1 after repeated 3‐d stocking. We conclude that the use of disturbance‐tolerant grassland species will improve swards in outdoor chicken runs.

We investigated the effects of simulated prospective increased temperatures and reduced soil moisture during the vegetation period on the early growth of three weed species that co-occur in spring crops and are currently spreading in Europe. Potted four-species crop-weed-communities of Abutilon theophrasti, Datura stramonium, Iva xanthiifolia, and maize were exposed to warming (ambient temperature + 2.5°C, treatment "warm") and drought (soil water potential of -0.1 to -1.5 MPa, "dry") versus ambient temperature (treatment "ambient") and a soil water potential of -0.0036 MPa ("moist"), in four soil types (clay, loess, peat, sand based mixtures) in greenhouse settings. We determined the performance of the weeds in terms of total biomass accumulation as well as their morphological acclimation regarding root length, leaf size and root-to-shoot ratio at various combinations of the experimental factors. Warm-dry conditions had a significant negative effect on total weed biomass and also resulted in a higher proportion of maize in total aboveground biomass. In D. stramonium, aboveground vs. belowground allocation and leaf size responded more strongly to the experimental factors than in the other two species. Total biomass values of individual plants in warm-dry conditions on average were > 50%, 40 to 55%, and < 40% of those in ambient-moist conditions for A. theophrasti, I. xanthiifolia, and D. stramonium, respectively. Soil and its interaction with moisture and temperature additionally had a significant effect on various traits of the weed species which highlights the importance of considering this factor when investigating plant responses to altered climate conditions.