Rôle des traits fonctionnels des plantes dans le cycle du phosphore et sa disponibilité au sein des agroécosystèmes : agroécologie des cultures intermédiaires

Le phosphore (P) est l'un des principaux facteurs limitant dans la plupart des sols du monde. Améliorer sa disponibilité dans les agrosystèmes et assurer son utilisation efficace est donc un défi majeur de l'agriculture moderne. Plusieurs pratiques, telles que les couverts intermédiaires, peuvent potentiellement augmenter la disponibilité du P dans les agrosystèmes. Cependant, les effets de ces pratiques sur la disponibilité du P ont rarement été étudiés. Ce projet de doctorat vise à mieux comprendre le rôle des traits fonctionnels des cultures intermédiaires dans les processus influençant la disponibilité du P dans les agrosystèmes. La caractérisation d'un large éventail de traits d'acquisition de P a mis en évidence de multiples compromis racinaires, notamment entre la capacité des plantes à mobiliser le P et explorer un large volume de sol pour capturer le P disponible, tout en soulignant la contribution considérable des interactions plantes-microbes à l'acquisition de P par les plantes. Les multiples stratégies d'acquisition de P identifiées offrent l'opportunité de concevoir des cultures intermédiaires multi-espèces complémentaires dans leur utilisation du P. L'examen du rôle des traits des cultures intermédiaires sur la libération de P depuis leurs résidus et son impact sur la disponibilité du P a offert des indications précieuses sur les dynamiques microbiennes impliquées et le rôle central du ratio C:P. Les nouveaux éléments de compréhensions apportés sur les effets des cultures intermédiaires sur la disponibilité du P pourraient constituer une base solide pour la modélisation des effets des cultures intermédiaires sur la disponibilité du PPhosphorus (P) is a key limiting element in most of the soils worldwide. Overcoming poor P availability and ensuring productive agriculture requires significant P inputs. Improving P use efficiency and availability is thus a major challenge of modern agriculture. Several agroecological practices such as cover cropping can increase P cycling efficiency and availability in agrosystems. However the effects of these practices on P availability have rarely been addressed. This PhD project aims at getting a better understanding of the role of cover crops functional traits in the plant-soil-microbes processes influencing P availability in agrosystems. Characterising a wide range of P acquisition traits highlighted multiple tradeoffs, notably between P mining traits and P foraging traits, while also underlining the considerable contribution of plant-soil-microbes interactions to P acquisition. The spectrum of diverging P acquisition strategies identified could underpin complementary multispecies cover crops designs. The examination of the role of cover crop residue traits on P release from residues and its impact on P availability offered precious insights into the soil microbial dynamics involved and the role of residue C:P ratio. The effects of cover crop residues on P availability via P release were however projected to be highly mediated by soil P availability. The new understanding gained on the effects of cover crops on P availability via their diverse traits and strategies for P acquisition, the impact of their traits on P release from residue, and its mediation by soil properties could constitute a sound basis for modelling cover crops effects on P availabilit

Mixing ratio and Nitrogen fertilization drive synergistic effects between biochar and compost

International audienceCompost and biochar mixtures used to replace mineral N fertilisers in agricultural systems showed contrasting results, especially when applied in combination. We hypothesised that their effect may depend on the mixing ratio between the two components. The aim of our study was to determine if varying ratios of biochar/compost mixtures in presence or absence of chemical nitrogen (N) fertilisation influence ryegrass growth and nutrient uptake. To this end, we set up a pot experiment with an agricultural soil amended with five compost and biochar mixtures differentiated by their mixing ratio. We followed soil fertility parameters and ryegrass growth over three harvests.Results showed that the addition of amendments improved nutrient availability. The highest nutrient availability was observed with pure compost. Despite their high C/N ratios, biochar and compost increased N availability while preventing its microbial immobilisation. Biomass and nutrient uptake by plants were improved by amendments, but were dependent on the biochar/compost ratio. Addition of a mixture containing less biochar than compost (30% biochar/70% compost, on a dry weight basis) showed highest plant growth response and nutrient uptake as compared to the chemical N fertilisation. In addition, the beneficial effects of biochar and compost on plant growth were strengthened by N fertiliser. All in all, we demonstrated the synergistic effects between biochar and compost, which were predominantly driven by the mixing ratio between those two materials, and highlighted their potential use as a sustainable alternative to chemical fertilisers

Direct and indirect interactions between biochar properties, plant belowground traits and plant performance

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Highlighting phosphorus-acquisition strategies in intermediate crops: a functional approach

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Highlighting phosphorus-acquisition strategies in intermediate crops, a functional approach.

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Tradeoffs among phosphorus-acquisition root traits of crop species for agroecological intensification

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Plant functional diversity effects on phosphorus availability in soils, the case of intermediate crops

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Influence des traits des résidus des cultures des couverts sur la disponibilité du phosphore et son acquisition ultérieure par les plantes

International audienceCover crops are typically thought to increase the P nutrition of crops. However, there are mixed reports on this with some studies reporting a negative effect. An improved understanding of cover crop residues and their P release dynamics could offer new insight with the benefit of improved management for optimal P availability in cropping systems. Here, we examined the influence of cover crop residue traits for six different crop types on soil P availability and subsequent plant (ryegrass) P uptake over a four-month period in a soil with moderate P availability. Among the residue traits examined (residue P concentration, N concentration, C:P ratio, C:N ratio, N:P ratio and specific leaf area), only residue P concentration and C:P ratio were related to soil P availability and subsequent crop P uptake. Important short-term effects of residue C:P ratio on P availability were highlighted. Strong to moderate negative correlations between residue C:P ratio and subsequent crop P uptake (R² between 0.4 and 0.8) were observed. Decreases in subsequent crop uptake of up to 43 % compared to unfertilized pots occurred for residues with high C:P ratios for the first cut, strongly suggesting microbial P immobilization. Effects faded with time, with most cover crop residue additions having little to no influence on ryegrass P uptake over a four month period. Residues with the highest C:P ratio nonetheless resulted in a 22 % decrease in cumulative P uptake compared to unfertilized pots. Our study highlighted that cover crop C:P ratio should be managed in order to ensure minimized adverse effects of microbial P immobilization. The observed low effects of cover crop residues on P uptake in a subsequent crop suggest that improving P availability in context with moderate P limitations via cover cropping may require relying on other services provided by cover crops such as mobilization of sparingly available P pools

Phosphorus acquisition strategies of different crop species in Calcosol amended with sewage sludge

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