Increasing the Multifunctionality Agroecosystems by Harnessing Foodwebs – IMAgHO

In a context of ever-increasing demand for food, the future of farming requires to develop sustainable solutions to produce more food without causing major harmful effects on the environment. In particular, broad-range pesticides and chemical fertilisers need to be phased out in favour of naturally-occurring ecosystem services, such as biocontrol. Among the potential solutions for a sustainable agriculture, the concept of ecological intensification is particularly promising. It hinges on the hypothesis that by acting on populations and diversity of service providers, it is possible to increase the multi-functionality of ecosystems. In agroecosystems, regulation services such as animal pollination and biocontrol of pests by predators and parasitoids are particularly important because they have the potential to maintain or increase crop production while reducing chemical inputs. These services are based not only on key species but also on their trophic interactions. The IMAgHo project aims at harnessing these naturally-occurring interactions to maximise regulatory services in agroecosystems and thus maintain or increase yield while reducing chemical inputs. Key regulatory services will be studied in oilseed rape crop through the deciphering of food web dynamics at very fine temporal scale (monthly sampling), and wide spatial scale (from plot to landscape) in a setting that allows the testing of critical environmental and management gradients. Massively parallel DNA sequencing, and field observations will be used to decrypt food webs and quantify regulatory services of carabids on various pests species, parasitoids attacking aphids and wild and domesticated bees foraging on flowers. Traditionally, food webs are often described as stable states while they are inherently dynamic. Although, the temporal variation in species assemblages and their interactions may strongly impact the delivery of ecosystem services, this remains poorly explored. This is particularly important in agricultural landscapes of annual crops where resources vary greatly throughout the season until the almost complete disappearance of the base of the food web (the primary producer), leading to a drastic reduction of invertebrate populations and consequently a collapse of the food webs. Yet these networks are re-built every year. The dynamics of the selected food webs will be described in oilseed rape fields over a period of two years with samples collected every month during the animals' period of activity in real farming conditions. The mechanisms underpinning the relationship between interaction networks and ecosystem services are still largely unknown. For example, if the biological control of aphids is improved by increasing floral resources in simplified landscapes, this is not always the case in more complex ones. Among the key variables that could explain this context-dependency, agricultural practices, distance from source populations and crop intensification are major elements. IMAgHo will take advantage of the Zone Atelier Plaine & Val de Sèvre (ZA-PVS), which offers a quasi-experimental context to decouple multiple environmental and management gradients and test their respective effect of food webs and regulatory services. The structure and connectedness of the food webs will be analysed in relation to historical data on agricultural practices and biodiversity, which have been recorded on the ZA-PVS for more than 25 years.
The ZA-PVS also allows to perform field experiments through existing research partnerships with farmers. Field experiments will be implemented to test how changes in management modify food webs and the related regulation services, and ultimately affect yield. As well as generating fundamental ecological knowledge on ecosystem functioning, this project will produce operational guidelines to limit agrochemical inputs and enhance ecological intensification in agroecosystems.