Models that quantify the effects of cropping systems on weed dynamics are useful tools for testing innovative cropping systems. In these models, seed mortality in the soil is a key parameter to account for the cumulated effect of cropping systems over time via the soil seed-bank. Since seed mortality is difficult to measure, our objective was to develop a method to estimate it from easily accessible information. Seeds of 13 weed species were buried 30cm deep in fields and were recovered regularly for 2 years to measure their viability. Seed mass, dimensions, shape, and protein and lipid contents as well as coat thickness were measured. To estimate seed mortality of species not included in the study, we searched for relationships between mortality rates and seed traits. Seed viability mainly decreased during the second year of burial, with mortality rates ranging from 0.01 to 0.63 seeds.seeds(-1).year 21, depending on the species. Seed mortality decreased with increasing seed coat thickness. No correlation was found with other measured traits or with seed persistence data in the literature. These results were confirmed when the effects of phylogenetic relatedness with phylogenetically independent contrasts were included. The thickness of the seed coat, which varied between 17 and 231 mm over the range of species studied, can protect the seed from external attacks in the soil and slow down seed decay. This trait can be easily measured via X-ray images and could be used to estimate the seed mortality rate for a wider range of species

International audienc

Integrating principles of ecological intensification into weed management strategies requires an understanding of the many relationships among weeds, crops and other organisms of agro-ecosystems in a changing context. Extensively used during the last two decades in weed science, trait-based approaches have provided general insights into weed community response to agricultural practices, and recently to understanding the effect of weeds on agro-ecosystem functioning. In this review, we provide a holistic synthesis of the current knowledge on weed response and effect functional traits. Based on the literature and recent advances in weed science, we review current knowledge on (i) weed functional groups and ecological strategies, (ii) weed functional response traits to cropping systems and (iii) weed functional effect traits affecting agro-ecosystem functioning. For each functional trait, we explicitly present the assumptions and evidence on the linkage between trait values and ecological functions, in response to either management practices, for example tillage, sowing and herbicides, or biotic interactions, for example crop-weed competition and pollination. Finally, we address and discuss major research avenues that may significantly improve the use of traits and the knowledge of functional diversity in weed science for the future, especially to design and implement more environmentally sustainable weed management strategies.

International audience1. Dry matter digestibility is a critical component of herbage nutritive value, a major service delivered by grasslands. The aim of this study was to test whether the dominance hypothesis applies to assess the impacts of environmental gradients and management regimes on thiscomponent of herbage nutritive value in permanent grasslands. 2. At the plant level, digestibility has been related to a number of functional traits, but whether this can be scaled up to the community level in species-rich grasslands and how such relationships are modulated by environmental conditions and management regimes remainunknown. Our primary objective was to test whether community-weighted means – species trait values weighted by the species abundance – of morphological, phenological and chemical traits could be used to explain variations in digestibility over a large range of climatic contexts,soil resource levels and management regimes. Our second objective was to explain variations in community digestibility within and among nine contrasting sites along large natural and man-induced environmental gradients.3. Over the whole data set, digestibility and most community-weighted means of traits responded to climatic factors and management regimes, but relations were not always significant when each site was considered separately. Community digestibility was significantly related to one or more plant traits within each site and to all of the measured traits when considering all the sites. Leaf dry matter content (LDMC) had the most consistent effects on digestibility, with a strikingly similar negative effect within each site. Potential evapotranspiration was negatively related to digestibility and contributed to explain a large part of the among-site variance. In addition, a low return interval of disturbance and a high disturbance intensity (biomass removal) were both associated with a high digestibility.4. Synthesis and applications. Disturbance regime, plant traits and local climate impacted dry matter digestibility roughly equally in grasslands. The effects of community composition on digestibility and its response to abiotic factors could be successfully captured by community weightedmeans of leaf dry matter content. This functional marker can be used to develop indicators and grassland management rules to support farmers in the refinement of their practices towards specific needs, such as target production outputs

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The role of biodiversity in the delivery of ecosystem services is increasingly being studied by traitbased functional approaches. Here, we review and discuss the contribution of a trait-based approach to understanding plant-arthropod interactions and improving conservation biological control. The stable biological control of multispecies herbivore communities requires functional diversity and a redundancy of natural enemies, including specialists and generalists, with minimal antagonistic interactions. The management of arthropod communities through plant community requires the plant community to perform several functions, including the provision of diversified trophic resources and appropriate physical habitats. Many studies have investigated the ability of plants to provide these functions, but many of the results obtained were limited to single species. The description of communities in terms of traits underlying trophic and non-trophic interactions between plants and animals would make it possible to extrapolate findings to other species. Studies on plant-herbivore and plant-pollinator interactions have identified several traits as important for trophic resource provision, in terms of resource quantity, accessibility, quality and temporal availability. By contrast, traits relating to physical habitat provision and microclimate modification have been little explored. Several metrics describing the functional composition and diversity of communities have been proposed, to extend the trait-based approach to plant community level, but the extent to which multitrophic communities are affected by plant traits remains largely unexplored. The next step will be to identify the combinations of these plant community metrics best explaining their impact on arthropod communities and disentangling the roles of plant functional composition and diversity.

Gardarin A, Dürr C & Colbach N (2010). Effects of seed depth and soil aggregates on the emergence of weeds with contrasting seed traits. Weed Research50, 91–101. Summary Tillage has a strong impact on weed emergence by burying seeds in the soil and modifying soil structure. Its influence can vary according to seed and seedling characteristics. This article focuses on shoot and radicle elongation in the soil and on seedling mortality caused by soil obstacles. Germinated seeds of nine contrasting weeds were planted in pots and grown in the dark to measure shoot and radicle elongation. Second, the proportion of seedlings blocked under aggregates (20–50 mm) was measured. Shoot growth rate, maximal shoot and radicle lengths were positively correlated with seed mass. Large‐seeded species (e.g. Avena fatua) were more likely to emerge from greater depths (exceeding 20 cm deep). Seedling mortality increased with increasing obstacle size for all species; it was greater for monocotyledonous than for dicotyledonous species and decreased with the shoot diameter. Weed seed depth and soil structure influence emergence of weed species differently, depending on seed mass, shoot diameter and taxa. Including the results of this study in a cropping system‐weed dynamics model would help to predict responses of weeds species to tillage.