How does sulphur availability modify N acquisition of white clover (Trifolium repens L.)?

The role of S in legume growth, N uptake, and N2 fixation was investigated using white clover (Trifolium repens L.) as a model species. We examined whether the effect of sulphate addition on N fixation resulted from a stimulation of host plant growth, a specific effect of S on nodulation, or a specific effect of S on nodule metabolism. Clones of white clover, inoculated with Rhizobium leguminosarum, were grown for 140 d in a hydroponic system with three levels of sulphate concentration (0 mM, 0.095 mM, and 0.380 mM). Nodule morphological and biochemical traits, such as root length, nodule biomass and volume, nodule protein contents (nitrogenase and leghaemoglobin obtained by an immunological approach), and root amino acid concentrations, were used to analyse the effect of sulphate availability on N2 fixation. The application of sulphate increased whole plant dry mass, root length, and nodule biomass, expressed on a root-length basis. N uptake proved less sensitive than N2 fixation to the effects of S-deficiency, and decreased as a consequence of the lower root length observed in S-deficient plants. N2 fixation was drastically reduced in S-deficient plants as a consequence of a low nodule development, but also due to low nitrogenase and leghaemoglobin production. This effect is likely to be due to down-regulation by a N-feedback mechanism, as, under severe S-deficiency, the high concentration of whole plant N and the accumulation of N-rich amino acids (such as asparagine) indicated that the assimilation of N exceeded the amount required for plant growth

Grassland species are more efficient in acquisition of S from the atmosphere when pedospheric S availability decreases

International audienceAims Plants can absorb Sulfur (S) either through roots as sulfate or via leaves in a gas form such as SO2 or H2S. This study aims to examine whether the most efficient competitors for root uptake of sulfate among grassland species are also those with the greatest ability for foliar uptake and to test whether all species can increase their ability to use atmospheric S when available sulfate decreases. Methods Six grassland species were grown together in a non-S-enriched-atmosphere for 60 days with two levels of sulfate concentrations. Sulfate was 34S-enriched to distinguish root uptake of sulfate and foliar uptake of gaseous S. Results Grasses were more competitive for sulfate uptake and more efficient at producing biomass for the same amount of S in comparison to the non-fixing forb and the legumes. All species studied were able to increase their ability to use atmospheric sources of S when sulfate availability decreased. The percentage of S derived from the atmosphere was strongly related to sulfate concentration in leaves. Conclusion Grasses were more efficient for root sulfate uptake but forbs seemed more efficient for foliar uptake. Sulfate in plant tissues could play a key role in regulation between the foliar and root S uptake

Conserving "old meadows" as an effective way to extend the service bundle

International audienceThe dichotomy between temporary and permanent grasslands tends to exacerbate the opposition between an agronomic approach that favors management practices that promote biomass production at the expense of biodiversity and a more naturalist vision that favors the maintenance of biodiversity at the expense of forage performance. In fact, the functioning of grasslands results from the interaction between environmental factors (soil and climate, management) and the biological diversity present. It is necessary to consider these different factors (abiotic, biotic and anthropogenic) to identify the performance of agroecosystems and to deduce the services that humans can benefit from. The identification of interactions between management practices, biodiversity and ecosystem age provides a framework for deducing the levels of services that can be expected. Management and agricultural practices are fundamental in the management of the biodiversity-functioning-service relationship, because they reveal the role of the farmer as the pilot of the dynamics of these agro-ecosystems. Our proposal will be illustrated by analyzing the four main categories of service: support, supply, regulation, and cultural that can be expected from grasslands depending on their maturity (young vs. old). Even if biomass production and in some cases nutritional value decreases with age, allowing grasslands to age appears to be an effective lever for preserving the support, regulation and cultural services from which farmers and society benefit

Biodiversité et valeur agronomique dans les prairies humides des marais du Cotentin et du Bessin

International audiencedans le cadre du programme INTERREG WOW (Working Value of Wetlands), le Parc naturel régional des marais du Cotentin et du Bessin et l'Université de Caen se sont associés pour étudier les relations entre pratiques agricoles, valeur agronomique et biodiversité des prairies de marais. Les paramètres de biodiversité étudiés sont la végétation, les coléoptères carabiques, les oiseaux nicheurs et le Courlis cendré. Des liens ont été établis entre pratiques agricoles, végétation et zone de nidification du Courlis cendré. 21 communautés végétales ont été identifiées au sein de 5 marais test. L'étude de la valeur fourragère montre que les apports énergétiques des communautés végétales sont élevés et équivalents à ceux d'un foin ou d'un pâturage mésophile considérés comme référence régionale. Au printemps, les pâtures fournissent l'énergie et les protéines suffisantes pour assurer la production de 35 kg de lait sans complémentation. En conclusion, les prairies de marais ont un fort intérêt pour la biodiversité et constituent un atout pour l'agriculture

Ethylene modifies architecture of root system in response to stomatal opening and water allocation changes between root and shoot

Ethylene plays a key role in the elongation of exploratory and root hair systems in plants, as demonstrated by pharmacological modulation of the activity of ethylene biosynthesis enzymes: ACC synthase (ACS) and ACC oxidase (ACO). Thus, treatments with high concentrations (10 µM) of aminoethoxyvinylglycine (AVG, inhibitor of ACS) and 1-aminocyclopropane carboxylic acid (ACC, ethylene precursor, ACO activator) severely decrease the elongation of the exploratory root system but induce opposite effects on the root hair system: root hair length and numbers were increased in seedlings treated with ACC, whereas they were reduced in seedlings treated with AVG. Until now, such elongation changes of root architecture had not been questioned in terms of nitrate uptake. In the march issue of Plant Physiology we report that N uptake and nitrate transporter BnNrt2.1 transcript level were markedly reduced in ACC treated seedlings, but were increased in AVG treated seedlings compared to the control.1 Because recent studies have revealed that ethylene can also modulate stomatal opening as well as root hair cell elongation, we have examined whether pharmacological modulation of ethylene biosynthesis could affect, in an integrated manner, and at a whole-plant level, the exploratory and root hair systems, through changes of stomatal conductance and water allocation between the root and shoot

Comparaison de l’impact de deux méthodes de rénovation d’une prairie du domaine expérimental INRAE du Pin-au-Haras sur la productivité et l’évolution des stocks de Carbone du sol : le resemis et le sursemis

International audienceThe aim of this study was to evaluate the short-term effects of two grassland restoration methods on biomass yield and carbon storage in the upper soil layer. We used a grassland located on the INRAE Pin-au-Haras experimental farm (Normandy), which had been seeded 12 years ago. It was divided up into three subplots: (i) a control subplot; (ii) a subplot restored via reseeding; and (iii) a subplot restored via overseeding. Biomass yield, carbon levels in the top 10 cm of the soil, and the properties of the soil organic matter were examined 8 months and 20 months after the treatments were applied. The reseeding and overseeding methods increased annual biomass yield by 50%; the levels of organic carbon in the soil were maintained, and the amount of soil organic matter increased. Neither restoration method changed the C/N ratio or the proportion of soluble carbon in the soil. Our findings indicate that the overseeding method and the reseeding method similarly increased grassland productivity. However, the former does not require the use of glyphosate, allowing levels of carbon storage in the soil to remain stable.L’objectif de cette étude est de déterminer l’effet à court terme de deux techniques de rénovation des prairies sur la productivité et le stock de C du sol superficiel. Une prairie semée 12 ans auparavant située sur le Domaine Expérimental INRAE du Pin-au-Haras (Normandie) a été divisée en trois sous-parcelles : (i) non rénové, (ii) rénové par resemis et (iii) rénové par sursemis. Le rendement, les stocks de C de l’horizon 0-10 cm du sol et les propriétés de la matière organique du sol ont été comparés 8 et 20 mois plus tard. Les rénovations par resemis ou sursemis ont augmenté la production annuelle de 50 %. Dans les deux sous-parcelles rénovées, le stock de C organique de l’horizon 0-10 cm a été maintenu et la quantité de matière organique a augmenté. Le ratio C/N ainsi que la proportion de C soluble dans le sol n’ont pas été modifiés. Dans cet essai, la rénovation par sursemis a abouti à un gain de productivité comparable à celui du resemis sans nécessiter d’application de glyphosate permettant de maintenir le stock de C dans le sol

Tradeoff between the Conservation of Soil C Stocks and Vegetation Productivity in Temperate Grasslands

International audienceGrassland management affects ecosystem services such as the conservation of C stocks. The aim of this study was to analyze the relation between vegetation production and soil C stocks for a set of seven temperate grasslands of various productivity levels. We estimated vegetation production directly through measurements of aboveground biomass (>5 cm), stubble and root biomass, and indirectly via plant community functioning. Soil C stocks were measured for bulk soil (organic C, SOC) and hot-water-extractable C (HWC) of topsoil. Plant community functioning was characterized by community-weighted mean (CWM) traits and functional diversity index. Results show a negative relation between biomass production and SOC stock. The tradeoff between productivity and SOC stock could be linked to plant community functioning and particularly Leaf Dry Matter content (LDMC CWM) which appeared to be the most relevant descriptor of plant community functioning. High SOC stock could be associated to low productivity, conservative strategy (high LDMC CWM), low soil labile C content and grassland age. Our results show a strong direct effect of management and grassland age on plant community, which in turn affects plant tissue quality and subsequent organic matter mineralization. Old permanent grasslands appeared less productive but represent an occasion for C storage and thus global change mitigation

The role of grasslands in biogeochemical cycles and biodiversity conservation

Grasslands have a multifunctional role in producing forage for animal production systems while providing a wide array of ecosystem services, including the regulation of biogeochemical cycles and the maintenance of biodiversity which are of utmost importance for agriculture and society as a whole. This chapter provides an overview of current knowledge on the roles of grasslands in regulating the carbon (C) and nitrogen (N) cycles and conserving biodiversity. The chapter describes the ways in which environmental roles of grasslands are driven by nutrient management, frequency and timing of utilization, type of utilization (mowing or grazing), the lifespan of the grasslands and their position and diversity in the landscape. It then explains how different grassland types are necessary to target multiple services because the services of food production, carbon storage in soils, regulation of the N cycle and biodiversity conservation are maximized at different levels of grassland intensification