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In most ecosystems, plant roots from different species decompose in mixtures and in the presence of living roots; however much root decomposition research has focused on how roots of individual species or artificial mixtures decompose in the absence of living plants. We thus examined two poorly studied components of root litter decomposition: 1) whether decomposition of root mixtures can be predicted from the sum of the decomposition rates of each component species and 2) how living plants influence rates of root decomposition. Decomposition rates of roots from three perennial herbaceous Mediterranean species grown in monocultures and in two- and three-species mixtures were determined after a one-year incubation period under their living community and in non-vegetated soil (bare soil). Soil respiration in the presence of glucose (substrate induced respiration, SIR) was measured in each plant community and in bare soil. Decomposition rates of root mixtures cannot be predicted from decomposition rates of the component species, both additive and non-additive effects were observed; the presence of low quality roots of Carex humilis in mixtures strongly negatively influenced root decomposition. The presence of living plants stimulated root decomposition in monocultures and two-species communities, likely through an enhanced microbial activity (SIR) under plant communities. This study highlights that root decomposition cannot be predicted from decomposition rates of the component species and is more influenced by endogenous factors or root litter functional composition than by plant community composition.

Made available in DSpace on 2018-12-11T17:30:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-05-01 Agence Nationale de la Recherche Centre de Coopération Internationale en Recherche Agronomique pour le Développement Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Universidade de São Paulo Background and aims: Comparing root functioning under contrasting rainfall regimes can help assessing the capacity of plant species to cope with more intense and frequent drought predicted under climate change context. While the awareness of the need to study the whole root system is growing, most of the studies of root functioning through rhizosphere analyses have been restricted to the topsoil. Our study aimed to assess whether the depth in the soil and the rainfall amount affect root functioning, and notably the fate of nutrients within the rhizosphere. Methods: We compared pH and nutrient availability within the rhizosphere and bulk soil along a 4-m deep soil profile in a 5-year-old eucalypt (Eucalyptus grandis) plantation under undisturbed and reduced rainfall treatments. Results: The exchangeable K concentration and the pH of the bulk soil were not influenced by the reduced rainfall treatment. By contrast, the H3O+ concentration in the rhizosphere was significantly greater than that of the bulk soil, only in the reduced rainfall plot. The concentrations of exchangeable K in the rhizosphere were significantly larger than those of the bulk soil in both treatments but this difference was higher in the reduced rainfall plot, notably below the depth of 2 m. Both exchangeable K and H3O+ concentration significantly increased within the rhizosphere in the reduced rainfall treatment at soil depth down to 4 m. Conclusions: The amount of K brought to the roots by mass flow was estimated and could not explain the observed increase in exchangeable K concentration within the rhizosphere. A more likely explanation was root-induced weathering of K-bearing minerals, partly related to enhanced rhizosphere acidification. Our results demonstrate that root functioning can be considerably altered as a response to drought down to large depths. CIRAD UMR Eco&Sols, 2 Place Viala INRA UMR Eco&Sols, 2 Place Viala FCA UNESP LCF ESALQ CENA ESALQ FCA UNESP Agence Nationale de la Recherche: ANR-13-AGRO-0005 FAPESP: 2013/25998-4

Background and Aims Root anchorage function is crucial for tree survival as most trees are exposed to recurrent wind throughout their lifespan. Trees exhibit a large variability of root system architecture (RSA) due genetic and environmental factors. This study aims to understand the links between RSA and tree stability. Methods A 3D biomechanical model was used to simulate tree overturning. To capture the variability of sinker RSA, fourteen virtual root patterns were created from an ensemble average of measured Pinus pinaster root systems. Root virtual patterns and tree-pulling simulations were verified against experimental data. Results The model predicts realistic tree anchorage strength, root stress, and failure patterns. Only a few root components contribute significantly to anchorage strength. The taproot contributes the most to anchorage rigidity, representing 61 % of the anchorage strength. The windward roots failure drives ultimate anchorage failure, representing 25 % of the anchorage strength. Simulations show that root secondary thickening induces higher anchorage rigidity and increases anchorage strength by 58 %. Conclusions This innovative approach appears promising for describing tree stability and its acclimation to external constraints.