International audienceA broad and diversified group of compounds, secondary metabolites, are known to govern species interactions in ecosystems. Recent studies have shown that secondary metabolites can also play a major role in ecosystem processes, such as plant succession or in the process of litter decomposition, by governing the interplay between plant matter and soil organisms. We reviewed the ecological role of the three main classes of secondary metabolites and the methodological challenges and novel avenues for their study. We highlight emerging general patterns of the impacts of secondary metabolites on decomposer communities and litter decomposition and argue for the consideration of secondary compounds as key drivers of soil functioning and ecosystem functioning.Synthesis. Gaining a greater understanding of plant-soil organisms relationships and underlying mechanisms, including the role of secondary metabolites, could improve our ability to understand ecosystem processes. We outline some promising directions for future research that would stimulate studies aiming to understand the interactions of secondary metabolites across a range of spatio-temporal scales. Detailed mechanistic knowledge could help us to develop models for the process of litter decomposition and nutrient cycling in ecosystems and help us to predict future impacts of global changes on ecosystem functioning

International audienceTree species influence the litter decomposition process by influencing litter quality and soil microclimate. Furthermore, over the long term, trees could promote soil communities that are particularly capable of degrading the litter they encounter most often. Thus, plant litter could decompose faster when placed in the habitat from which it was derived than in a foreign habitat, which has been termed home field advantage (HFA) of litter decomposition. In mixed-plant species environments however, it is not known whether a specific decomposer community under one tree species is affected by the presence of another tree species in the vicinity. To address this question, we tested if spruce and poplar litters showed HFA in mono-specific and in mixed species plantations under each tree species by reciprocally transplanting litter in the two plantation types. Decomposition rates, as well as the composition and ability of decomposer communities to degrade the different types of litter, were monitored during two years. Only spruce litter exhibited a faster decomposition rate at home. This HFA could be explained by higher abundance of decomposers. Furthermore, cellulose and poplar litter decomposed less or similarly in spruce plantations, suggesting that soil communities of that environment were capable of specifically degrading spruce litter. In mixed plantations, HFA was in the same direction as in mono-specific plantations, but was not as strong, indicating that HFA is sensitive to the surrounding plant community. Furthermore, this “mixed environment” had synergistic effects on decomposition rates under poplar trees. These `tree environment-specific' results highlighted the possible importance of spatial distribution of each litter on decomposition rates in mixed stands. Thus, the influence of litter dispersal should be taken into account in future studies

International audienceAbandoned lands are increasingly used to establish fast-growing tree plantations, and are often rapidly colonized by a high density of herbaceous undergrowth. These weeds are generally removed since they compete with trees for resources, in particular soil nutrients. However, mixing herbaceous litter with the litter of planted trees could also stimulate the activity of decomposers and associated nutrient release due to an increase of litter quality (lower C:N ratio), plant diversity (more diverse litter traits) and water holding capacity. The objective was to determine the impact of herbaceous litter on the litter decomposition process of white spruce and hybrid poplar litters alone or in mixtures. Litter mass loss rate, nutrient release and decomposer communities were monitored on single and mixed-species litters using litterbags during two years in three plantations types (hybrid poplar, white spruce and mixed plantations). Litters within mixtures were separated by species to identify species-specific responses of leaf mass loss. N release of all litter types increased with the presence of herbaceous litter. This finding could be linked to the greater abundance of decomposers and fungal biomass brought about by the herbaceous litter. Addition of herbaceous litter had no effect on spruce litter mass loss but had positive effects on poplar and mixed spruce/poplar litter mass loss. Abundance of fungi and mites was more affected by litter quality, whereas the abundance of collembola was more affected by the diversity of resources than by litter quality. In these 10-year plantations with poplar, increased litter mass loss for poplar and mixed litters and N release associated to the presence of herbaceous litter showed that weeds may change soil C sequestration and N cycling

Tree water uptake relies on well-developed root systems. However, mine wastes can restrict root growth, in particular metalliferous mill tailings, which consist of the finely crushed ore that remains after valuable metals are removed. Thus, water stress could limit plantation success in reclaimed mine lands. This study evaluates the effect of substrates varying in quality (topsoil, overburden, compost and tailings mixture, and tailings alone) and quantity (50-or 20-cm-thick topsoil layer vs. 1-m 2 plantation holes) on root development and water stress exposure of trees planted in low-sulfide mine tailings under boreal conditions. A field experiment was conducted over 2 yr with two tree species: basket willow (Salix viminalis L.) and hybrid poplar (Populus canadensis Moench × Populus maximowiczii A. Henry). Trees developed roots in the tailings underlying the soil treatments despite tailings' low macroporosity. However, almost no root development occurred in tailings underlying a compost and tailings mixture. Because root development and associated water uptake was not limited to the soil, soil volume influenced neither short-term (water potential and instantaneous transpiration) nor long-term (d 13 C) water stress exposure in trees. However, trees were larger and had greater total leaf area when grown in thicker topsoil. Despite a volumetric water content that always remained above permanent wilting point in the tailings colonized by tree roots, measured foliar water potentials at midday were lower than drought thresholds reported for both tested tree species.

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