Dr. Pierre Mariotte
Toward sustainable agroecosystems

Dr. Pierre Mariotte

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Projects

Sustainable agricultural production systems (SPAD, 2020-2022, Interreg France-Switzerland project n°6125)

Grasslands are the core of forage production worldwide and are severely threatened by climate changes, which can strongly reduce grassland productivity. Climate change is happening at a worldwide scale but not all parts of the world are affected similarly. Thus, understanding local and regional effects of climate change on grassland ecosystems is crucial to adapt management practices accordingly and ensure sufficient forage production. The goal of the SPAD project is to increase sustainability and adapt food production systems to climate change in the French departments of Doubs, Territoire de Belfort, Haute-Saône and Jura, as well as in the Swiss cantons of Jura and Jura Bernois. The novelty of the project consists in including quantitative criteria of sustainability based on local farming conditions (grassland type, common management practices, production system). Based on local climatic scenarios, future sustainability and environmental impacts of farms will be determined and adapted management practices will be developed to mitigate such impacts and increase the sustainability of grassland systems at the regional scale.

Targeted grazing of robust livestock for the restoration of green alder-encroached pastures (ROBUSTALPS, 2019-2023, SNSF project n°184925)

Throughout the last decades, the reduction of agro-pastoral activities in Swiss mountain areas has determined profound landscape modifications, with extensive reforestation processes over former pastures, particularly by green alder (Alnus viridis), which is the most expanding shrub species across all Central Europe. The project aims to investigate specific ecological dynamics, such as botanical composition evolution and N translocation fluxes, in A. viridis-encroached pastures under the challenge of targeted grazing. We propose to strategically place attractive points (AP), i.e. molasses-based salt blocks, within encroached areas to increase their exploitation by robust livestock species (here Highland cattle). With AP placement, we expect to increase the time spent by livestock herds within A. viridis-encroached areas, their consumption of green alder foliage, N content in their excreta, and consequently N translocation towards livestock resting areas. Moreover, thanks to the actions exerted by animals around AP locations, such as increased A. viridis defoliation, mechanical damages to green alder branches by trampling, as well as seed transportation, significant variations in vegetation communities are also expected, with beneficial effects on the restoration of typical pasture botanical composition. Therefore, this research could help filling knowledge gaps on the (i) forage potential of A. viridis foliage for robust animals, (ii) short-term vegetation dynamics after intense livestock pressure in green alder-dominated areas, (iii) and N redistribution fluxes within encroached pastures. As a consequence, it could provide useful insights to design innovative and sustainable grazing management systems for the restoration of A. viridis-encroached pastures.

Integrated tools for optimised grassland and forage utilisation (INTOGRASS, 2018-2021, Agroscope project 18.01.17.06.03)

Swiss grasslands supply multiple benefits and services as a function of their management, the plant species of which they are composed, and pedo-climatic conditions. Thanks to the development of cross-disciplinary decision-support tools, the farmer or any other decision-maker should be able to grasp these services in their multiplicity and optimise them for contrasting conditions and production systems. Managing grasslands also means managing species communities. To make the best use of these communities, we must also know about grass growth and quality, and master grassland conservation. The ‘IntoGrass’ project aims to develop tools to facilitate grassland management, grass utilization and grass quality assessment, focusing particular attention on the effect of pedo-climatic factors. Launched in 2017, this transdisciplinary project involves four Agroscope teams, and is based on a network of 32 grasslands distributed across Switzerland, which will help us better understand the impact of climatic conditions (temperature, precipitation) on grass growth and quality.

Interactive effects of altitude and management on resistance and resilience of permanent grasslands to drought: combining agronomic, functional and ecophysiological approaches (GRASSALT, 2016-2019, SNSF project n°156282)

Grasslands are at the core of Swiss agriculture and justify financial support of the government, whose agricultural policy supports forage autonomy of herbivore herds. Identifying potential interactive effects of different factors, such as altitude and management, with different climate change scenarios is therefore a major challenge to anticipate the performance of grasslands and the reliability of production in the future. The project focused on the response of grasslands to simulated early and late-season droughts along an altitudinal gradient and according to two management schemes. The objective of the project were twofold: i) provide agronomical references and management clues for forage production under altered precipitation regimes, ii) identify ecological mechanisms that drive grassland response to drought events. To achieve both goals, agronomical monitoring were combined with ecological approaches. A plant functional approach was implemented to address changes in community functional traits in response to altered environmental conditions. Moreover, relevant and innovative ecophysiological measurements were developed to assess drought resistance mechanisms at the plant species level. The project significantly added in our understanding of the response of grassland communities to future climate variability, and contributed to ecological theories. Further, the project included an effective integration of fundamental ecological principles into an agronomic issue, and led to the development of references directly relevant to agriculture.

Climate change impacts on soil N:P stoichiometry and consequent feedback on plant-microbe interactions in Australian grasslands (2014-2016, Advanced postdoctoral fellowship, SNSF project n°144648)

In South-Australia, a trend of prolonged periods without rain, alternated with increasing rainfall intensity, has already emerged during the last 50 years and is likely to continue during this century. Drought impact on the relative supply of nitrogen (N) and phosphorus (P) to plants and microbes but because plants and microbes have limited flexibility to take up N and P under conditions of unbalanced supply, drought affecting N:P stoichiometry can have large impacts on primary productivity and carbon sequestration. By using field and glasshouse experiments, this project aimed at assessing limitation of soil N and P for plant growth and microbes under climate change (drought) in Australian grasslands. Isotopes tracers (15N, 32P) were used to determine N and P uptake by plants and microbes under drought. Moreover, several ecosystem functions were measured in order to related changes in soil N:P stoichiometry, plant and microbes uptakes and grassland functioning and sustainability. This project identified important drought resistance mechanisms and provided tools to improve predictions about drought impacts on productivity and nutrient availability, that have important implications for grassland management.

Exploring threshold dynamics in noxious plant invasion of Californian rangelands (2013-2014, Early postdoctoral fellowship, SNSF project n°146538)

Alternative states represent major shifts in ecosystem function due to changes in abundance and composition of dominant species, and associated biological and physical processes. The objectives of this project were to determine how feedbacks between plants and soil and threshold dynamics influence the establishment of noxious weed invasion. In this project, we used the noxious weed Medusahead (Elymus caput-medusae) that is target for management intervention in Californian rangelands. Indeed, weed infestations by Medusahead on annual rangeland can reduce forage production by 75-80%. In this study, we used seed addition experiments, in the Sierra Foothills Research Extension Center, to establish populations of different densities. Then, we followed population dynamics and changes in soil properties and soil microbial communities. We also studied the role of litter accumulation on the growth of the invasive and introduced species. Overall, we tested the generalities and predictability of patch formation and spatial contagion, widely thought to be critical components of abrupt and sudden threshold effects, in weed invasion. 

Effects of subordinate plant species on plant and soil community structure and ecosystem functioning (SUBFUNC, 2008-2012, SNSF project n°114139)

Despite their low relative abundance, subordinate plant species may have larger impacts on ecosystem functioning than expected, but their role in plant communities remained poorly understood. While dominant species are supposed to be the most important species-group in plant communities, I demonstrated, during my PhD research, that subordinate species may also play a role in ecosystem functioning. Using removal experiments in two field sites of semi-natural mountain grasslands (Swiss Jura), I demonstrated that the loss of subordinate species can have significant consequences for soil microbial communities (especially fungi) and ecosystem functions (biomass production, soil respiration, litter decomposition), suggesting that subordinate species are important drivers of ecosystem properties.