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Weed control is generally considered to be essential for crop production and herbicides have become the main method used for weed control in developed countries. However, concerns about harmful environmental consequences have led to strong pressure on farmers to reduce the use of herbicides. As food demand is forecast to increase by 50% over the next century, an in-depth quantitative analysis of crop yields, weeds and herbicides is required to balance economic and environmental issues. This study analysed the relationship between weeds, herbicides and winter wheat yields using data from 150 winter wheat fields in western France. A Bayesian hierarchical model was built to take account of farmers’ behaviour, including implicitly their perception of weeds and weed control practices, on the effectiveness of treatment. No relationship was detected between crop yields and herbicide use. Herbicides were found to be more effective at controlling rare plant species than abundant weed species. These results suggest that reducing the use of herbicides by up to 50% could maintain crop production, a result confirmed by previous studies, while encouraging weed biodiversity. Food security and biodiversity conservation may, therefore, be achieved simultaneously in intensive agriculture simply by reducing the use of herbicides.

Host–parasite stalemate The Red Queen in Lewis Carroll's Through The Looking Glass said that one had to run as fast as possible to stay in the same place. Leigh Van Valen applied the concept to host–parasite and predator–prey interactions, in which each participant evolves as fast as is necessary to outpace the other. But how can these so-called Red-Queen dynamics be tracked through time? By stirring around in the slime at the bottom of a pond, it turns out. The water flea Daphnia and one of its microbial parasites are both able to survive many years dormant in lake mud. In a study that compared revived dormant stages of host and parasite from the sediment beneath a pond in Heverlee, Belgium, with present-day descendants, there was steady increase in parasite virulence through time. But to little overall effect: infection rates between the hosts and their parasite contemporaries remained much the same: as in many an 'arms race', the result is a stalemate. Dormant stages of both the water flea Daphnia and its microparasites are conserved in lake sediments, providing an archive of past gene pools. This is used to reconstruct rapid coevolutionary dynamics in a natural setting and show that the parasite rapidly adapts to its host over a period of only a few years. Antagonistic interactions between hosts and parasites are a key structuring force in natural populations, driving coevolution 1 , 2 . However, direct empirical evidence of long-term host–parasite coevolution, in particular ‘Red Queen’ dynamics—in which antagonistic biotic interactions such as host–parasite interactions can lead to reciprocal evolutionary dynamics—is rare 3 , 4 , 5 , and current data, although consistent with theories of antagonistic coevolution, do not reveal the temporal dynamics of the process 6 . Dormant stages of both the water flea Daphnia and its microparasites are conserved in lake sediments, providing an archive of past gene pools. Here we use this fact to reconstruct rapid coevolutionary dynamics in a natural setting and show that the parasite rapidly adapts to its host over a period of only a few years. A coevolutionary model based on negative frequency-dependent selection, and designed to mimic essential aspects of our host–parasite system, corroborated these experimental results. In line with the idea of continuing host–parasite coevolution, temporal variation in parasite infectivity changed little over time. In contrast, from the moment the parasite was first found in the sediments, we observed a steady increase in virulence over time, associated with higher fitness of the parasite.

Predicting the population dynamics of annual plants is a challenge due to their hidden seed banks in the field. However, such predictions are highly valuable for determining management strategies, specifically in agricultural landscapes. In agroecosystems, most weed seeds survive during unfavourable seasons and persist for several years in the seed bank. This causes difficulties in making accurate predictions of weed population dynamics and life history traits (LHT). Consequently, it is very difficult to identify management strategies that limit both weed populations and species diversity. In this article, we present a method of assessing weed population dynamics from both standing plant time series data and an unknown seed bank. We use a Hidden Markov Model (HMM) to obtain estimates of over 3,080 botanical records for three major LHT: seed survival in the soil, plant establishment (including post-emergence mortality), and seed production of 18 common weed species. Maximum likelihood and Bayesian approaches were complementarily used to estimate LHT values. The results showed that the LHT provided by the HMM enabled fairly accurate estimates of weed populations in different crops. There was a positive correlation between estimated germination rates and an index of the specialisation to the crop type (IndVal). The relationships between estimated LHTs and that between the estimated LHTs and the ecological characteristics of weeds provided insights into weed strategies. For example, a common strategy to cope with agricultural practices in several weeds was to produce less seeds and increase germination rates. This knowledge, especially of LHT for each type of crop, should provide valuable information for developing sustainable weed management strategies.

Question: Which weed traits respond to the community assembly filters imposed by cropping regimes and how do they respond? Which crop characteristics (traits or aspects of field management) represent the strongest filters on weed traits? Location: France. Methods: In 561 arable fields, we measured associations between crop characteristics and (i) mean values of quantitative weed traits at each site and (ii) composition of optimally defined weed functional types, based on both qualitative and quantitative weed traits and typologies. The crop characteristics included crop height, propagule size, family and sowing date; we also used basic types (winter wheat, maize, etc.) for comparison. Results: Crop sowing date was strongly related to many weed traits, whereas crop type was not the strongest predictor of any trait. With later sowing of crops, weeds started flowering later, germinated later and had shorter flowering periods. Sowing date was also associated with the distribution of Raunkiaer life forms, while crop architecture was associated with the distribution of weed heights and a C-S-R classification. Conclusions: Cropping regimes can usefully be summarized by the crop sowing date. Phenological traits of weeds as well as classifications based on life form and C-S-R are important descriptors of weed community composition. Such findings may help predict the effects of particular crop rotations, novel crop varieties and invasive weed species.

Reducing agricultural inputs is necessary for sustainable farming, but raises concerns over yields and farmers’ income. Here, we used large-scale experimental trials on cereal fields in western France for the period 2022–2023 to assess the effects of input reductions on yields and gross margins under real farming conditions. The trials, co-designed with farmers, involved substantial nitrogen and pesticide reductions in conventional fields, and reductions in soil work or mechanical weeding in organic fields. The results showed that input reductions led to average yield gaps of about 5% in both conventional and organic systems. Cost savings compensated for economic losses and even surpassed these in many conventional field experiments. Simulated price scenarios confirmed the economic viability of input reductions, with heightened advantages during price crises driven by energy or inflation shocks. These findings demonstrate that input-reduction strategies can align environmental and economic goals in real farming conditions, challenging concerns about profitability while supporting the ambitious sustainability targets of policies. In western France, nitrogen and pesticide input reductions led to cereal crop yield gaps in conventional and organic farm systems and economic losses were compensated by cost savings, according to an analysis that combines co-designed farm experiments and a statistical approach.

AimsIn agro-ecosystems, crop types, i.e., the crop species and its associated agricultural practices, have been shown to influence the taxonomic as well as functional composition of weed communities. However, the processes underlying weed community assembly within a crop type are poorly understood, especially regarding the contributions of local factors and stochastic processes. In this study, we investigate the effects of the crop type in shaping local weed communities.LocationLTER Zone Atelier Plaine et Val de Sèvre, an intensive cereal system in western France.MethodsWe selected 105 fields of five crop types and investigated the functional structure of weed communities for those traits that define the Leaf–Height–Seed (L-H-S) strategy as well as phenological traits. We compared the observed trait distribution to trait distributions expected under random assembly. The trait distributions were described by the range, the community-weighted mean and the dispersion of each trait, and simulated communities were generated with a null model approach that randomizes the ‘species × traits’ matrix to maintain equiprobable the occurrence of each trait combination. The relationship between trait values and species abundance within each community was investigated using Kendall rank correlation tests.ResultsOur results showed that, in ca. 90% of the fields, the functional diversity of weed communities did not differ from what would be expected under random assembly. Departures from random expectations essentially resulted from shifts in weighted mean values for phenological traits. Weed communities of sunflower, maize and spring pea had later onsets of emergence and flowering than randomly expected. Communities of winter wheat had smaller species and earlier onset of flowering, and communities from oilseed rape had a larger duration of the emergence period and earlier onset of flowering. In addition, we found a positive significant relationship between species abundance and trait values for phenology for spring pea, sunflower and maize, suggesting that species with a later onset of emergence and flowering period have higher performance in these weed communities.ConclusionsAt landscape scale, weed communities generally showed patterns of functional diversity in accordance with those expected under random community assembly, except for phenological traits in spring and summer crops, where patterns were rather consistent with environmental filtering.

Most organisms in ephemeral habitat patches have resting stages which form a local species pool in response to temporal variations in the patch's availability and suitability. Temporal dispersal from the local species pool may, therefore, be an important process shaping the community assembly, particularly soon after patch creation, and possibly interacting with environmental filtering. As the temporal variation of the environmental conditions has a major effect on the composition of the local species pool, we investigated how well contemporary conditions (both patch availability and patch suitability) and temporal dispersal (approximated by environmental temporal variation and temporal distance) explain the changes in community composition in a given locality through successive ephemeral habitat cycles. We used arable weeds in annual crops as models. We calculated temporal weed community dissimilarity indices between weed communities surveyed in cropping seasons at intervals of two to eight years within a given field. The weeds were surveyed twice each cropping season to account for any changes in the relative contributions of temporal dispersal and contemporary conditions during the season. Patch availability explained most of the temporal weed dissimilarity, suggesting that patch dynamics have the greatest effect on weed community assembly. Temporal distance and temporal variation of the environmental conditions had more effect at the start of the cropping season than later, while patch suitability had more effect in the middle of the season. These results suggest that temporal dispersal drives the weed community assembly when ephemeral habitat patches are created. These assemblies are further shaped by environmental filtering. This is consistent with a temporal source sink dynamic mechanism where the seed bank acts as the main weed source. However, a large part of temporal weed dissimilarity remains unexplained, suggesting that other ecological processes such as spatial dispersal and founder effect may also shape the weed community.

In species across taxa, offspring have means to influence parental investment (PI). PI thus evolves as an interacting phenotype and indirect genetic effects may strongly affect the co-evolutionary dynamics of offspring and parental behaviors. Evolutionary theory focused on explaining how exaggerated offspring solicitation can be understood as resolution of parent-offspring conflict, but the evolutionary origin and diversification of different forms of family interactions remains unclear. In contrast to previous theory that largely uses a static approach to predict how \"offspring individuals\" and \"parental individuals\" should interact given conflict over PI, we present a dynamic theoretical framework of antagonistic selection on the PI individuals obtain/take as offspring and the PI they provide as parents to maximize individual lifetime reproductive success; we analyze a deterministic and a stochastic version of this dynamic framework. We show that a zone for equivalent co-adaptation outcomes exists in which stable levels of PI can evolve and be maintained despite fast strategy transitions and ongoing co-evolutionary dynamics. Under antagonistic co-adaptation, cost-free solicitation can evolve as an adaptation to emerging preferences in parents. We show that antagonistic selection across the offspring and parental life-stage of individuals favors co-adapted offspring and parental behavior within a zone of equivalent outcomes. This antagonistic parent-offspring co-adaptation does not require solicitation to be costly, allows for rapid divergence and evolutionary novelty and potentially explains the origin and diversification of the observed provisioning forms in family life.

A paradigm shift is needed to make agriculture sustainable, and various substitutes for intensive agriculture have been proposed. However, moving from theory to practice, in the context of climate change, natural resource depletion and worldwide economic and social disorder requires a novel approach that goes beyond the confines of ‘normal’ scientific practice, to (a) consider ecological and socioeconomic processes within the agricultural socio‐ecosystem and (b) involving stakeholders in the research process. We propose an innovative experimental approach for identifying management practices that optimize multiple objectives, deliver a portfolio of ecosystem services and satisfy the social demands of key stakeholders while improving the socio‐economic welfare of farmers. Social–ecological experiments are undertaken in real‐field conditions, involving stakeholders explicitly, all along the experimental pathway, to help untangle the drivers of social–ecological dynamics under various practices of land management and farming. As an example, we describe a social–ecological experiment to reduce the intensity of weed control. These ‘social–ecological experiments’ go further, to participatory action research by not only involving stakeholders in the research process but also by manipulating simultaneously socioeconomic and ecological processes under real‐field conditions to foster agroecological transition. Such experiments are distinct from adaptive management, participatory agricultural research and scenario‐planning approaches as they highlight the interactions between ecological and social processes, manipulate the processes shaping the system and show causal links between patterns and processes. Social–ecological experiments offer great opportunities for increasing stakeholders' acceptance of environmental policies or sustainable agriculture programmes implemented through adaptive management. These experiments may help to identify management practices that deliver a portfolio of ecosystem services and satisfy key stakeholders. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

The definition of “arable weeds” remains contentious. Although much attention has been devoted to specialized, segetal weeds, many taxa found in arable fields also commonly occur in other habitats. The extent to which adjacent habitats are favorable to the weed flora and act as potential sources of colonizers in arable fields remains unclear. In addition, weeds form assemblages with large spatiotemporal variability, so that many taxa in weed flora are rarely observed in plot-based surveys. We thus addressed the following questions: How often do weeds occur in other habitats than arable fields? How does including field edges extend the taxonomic and ecological diversity of weeds? How does the weed flora vary across surveys at different spatial and temporal scales? We built a comprehensive dataset of weed taxa in France by compiling weed flora, lists of specialized segetal weeds, and plot-based surveys in agricultural fields, with different spatial and temporal coverages. We informed life forms, biogeographical origins and conservation status of these weeds. We also defined a broader dataset of plants occupying open habitats in France and assessed habitat specialization of weeds and of other plant species absent from arable fields. Our results show that many arable weeds are frequently recorded in both arable fields and non-cultivated open habitats and are, on average, more generalist than species absent from arable fields. Surveys encompassing field edges included species also occurring in mesic grasslands and nitrophilous fringes, suggesting spill-over from surrounding habitats. A total of 71.5% of the French weed flora was not captured in plot-based surveys at regional and national scales, and many rare and declining taxa were of Mediterranean origin. This result underlines the importance of implementing conservation measures for specialist plant species that are particularly reliant on arable fields as a habitat, while also pointing out biotic homogenization of agricultural landscapes as a factor in the declining plant diversity of farmed landscapes. Our dataset provides a reference species pool for France, with associated ecological and biogeographical information.