Linkages between plant functional diversity soil biological communities and ecosystem services in agricultural grassland

An increasing human population and the associated need to produce food in a changing world is one of the greatest challenge facing our generation. It is clear that we need to manage our agricultural systems more judiciously to yield benefits from ecosystem services, including biodiversity conservation, carbon and nutrient cycling and greenhouse gas regulation, along with food production. Grasslands are thought to be a key system for provision of these ecosystem services due to their large global coverage, but also because of their potential as reservoirs of biodiversity and nutrients. For instance, in the UK grasslands cover 36% of the land surface and already hold 32% of the UK soil carbon stock, and if managed correctly they could store even more. The Intergovernmental Panel on Climate Change have identified grassland management as having the greatest potential to sequester additional C if managed correctly, and so grasslands are a key system for climate change mitigation. Here we propose that multiple ecosystem services, such as carbon storage, nutrient retention and reduced greenhouse gas emissions in grassland can be enhanced with management of the diversity and composition of the plant community. The reason for this is that plant species differ greatly in their functional characteristics, or traits, and these differences strongly influence the amount and quality of organic inputs to the soil, which in turn stimulates components of the soil microbial community responsible for soil carbon and nitrogen cycling. Moreover, these differences in traits could change the magnitude and direction of ecosystem services such as from net emission of greenhouse gases, towards mitigation via vegetation management. In this study we will characterise the differing traits of key grassland plant species associated with grassland biodiversity restoration, and test their impact on grassland ecosystem services including emissions of the greenhouse gases carbon dioxide, methane and nitrous oxide, soil microbial activity and nutrient cycling and retention. This will provide the first information on the potential for plant diversity to be utilised to manipulate soil nutrient cycling towards greater carbon and nitrogen storage, and lower greenhouse gas emission.

A key challenge facing agriculture is the need to manage farmland to provide non-market ecosystem services, such as C sequestration and efficient nutrient cycling, along with the maintenance of economically viable production. There is now widespread recognition that in many farming systems the delivery of ecosystem services depends on the maintenance of both above- and below-ground biodiversity, although the mechanisms involved, and the interactions between the two, are poorly understood. This project tests, in agricultural grassland, how variations in plant functional diversity - namely the type, range and relative abundance - influence soil microbial communities, and ultimately rates of soil carbon (C) and nitrogen (N) cycling processes that underpin the delivery of the ecosystem services of C and N retention and greenhouse gas (GHG) mitigation. Specifically, we test the overarching hypothesis that soil biogeochemical cycling underpinning ecosystem service delivery can be predicted from plant species' traits, when weighted according to the relative abundance of species, and hence that easily measured plant traits could provide a means to scale-up from the properties of individual species to ecosystem processes in diverse grassland systems. Based on findings from our previous research, we also test the hypothesis that the delivery of these ecosystem services will be maximised in high diversity grassland with plant trait assemblages that promote fungal-dominated decomposer communities, characterised by 'slow' cycling of C and N. In contrast, these services will be minimised and there will be greater emissions of GHGs in low diversity grassland with trait assemblages that promote bacterial-dominated communities associated with 'fast' C and N cycling. This research will provide major advances in our understanding of the importance and nature of interactions between above- and below-ground diversity for multi-functional objectives of grassland agriculture.

The development of sward management practices to enhance C storage and lower greenhouse gas emission will have a major impact on a range of stakeholder groups and policy makers. There will be enormous benefits to society through the contribution to climate change mitigation, in a way that utilises, or even enhances, biodiversity, informed from better understanding of links between aboveground diversity and belowground functioning. Our proposed stakeholder meetings specific to facilitating communication, will provide a platform for knowledge exchange, and the real opportunity for translating our results into future development of sward management options to address real practical solutions. The main vehicles we will adopt to maximise the impact of our work and raise public awareness include academic publications, presentation at conferences, stakeholder workshops, initiatives with local schools and public scientific forums and lectures. We propose to hold two workshops, for which scientists, policy makers and stakeholders will be invited to participate in dissemination and development of our research activities. These workshops will scope existing policy and stakeholder contexts and perspectives, projected future grassland and agricultural management and policy scenarios, linking plant functional diversity and carbon storage in grassland, will evaluate ecosystem services in grasslands, as well as offering more detailed consideration of stable isotope techniques in terrestrial environments, and modelling of plant-soil interactions in C cycle models. From the greenhouse gas mitigation perspective, we will engage with stakeholders through the UK Nitrous Oxide Focus Group which serves to raise awareness, and propose mitigation solutions. We will also raise public awareness of our science through local and national media interviews, and by presenting at local forums such as Café Scientifique, or delivering public lectures, and organising outreach activities for local schools.