(BBSRC DTP) Adaptation to land use: the effects of long-term fertiliser use on plant-microbe interactions

Research proposed in this project is truly multidisciplinary by bringing together techniques from the fields of evolutionary ecology, soil science and plant physiology to gain deep understanding of a complex biological phenomenon – association between plants and mycorrhizal fungi – that underpins essential ecosystem services such productivity and efficient nutrient cycling and carbon storage in soil. The student will be trained in analysis of complex datasets and will use latest technologies from different disciplines that are rarely applied in combination, thus meeting the BBSRC’s ENWW goal of integrating different approaches and building the skills base necessary for multidisciplinary research.

Grasslands are a major type of agricultural land use and, through intimate relationships between soil organisms and plants, also provide important ecosystem services such as mitigating greenhouse gas emissions and maintaining efficient nutrient and water cycling. Two thirds of British grasslands have been subject to land use intensification, a key aspect of which is the application of inorganic fertilisers. This boosts agricultural production but inevitably causes a drastic drop in biodiversity and detrimental effects on ecosystem services. In particular, intensive land use causes a decline in the abundance of arbuscular mycorrhizal fungi (AMF), which play an essential role in transfer of mineral nutrients and carbon between plants and soil. Long-term fertilisation drives a decline in AMF by favouring plant species less reliant on mutualistic relationships with fungi. Moreover, it is likely that both plant and AMF populations undergo evolutionary changes in response to long-term fertilisation leading to a shift from mutualistic to antagonistic interactions but such responses are still poorly understood. Moreover, global warming and extreme weather events such as floods and droughts are predicted to increase in frequency with direct effects on plant functioning as well as indirect consequences such as pest and disease outbreaks. Under such conditions, the role of AMF may shift from nutrient provision to stress protection. How climate change and land use intensity will jointly shape associations between plants and AMF is largely unknown but has important implications for agricultural production and sustainable use of soil resources. This studentship will address this knowledge gap by examining and experimentally manipulating plant genotypes and soil microbial communities collected from the classic Park Grass Experiment at Rothamsted where grassland plots were either not fertilised or consistently fertilised for the last 160 years. Coadaptation in plant-AMF associations will be assessed and different temperature and precipitation regimes will be applied to determine the sensitivity of plant-AMF association to different global change scenarios. Plant physiological responses and carbon and nutrient exchange between plants and AMF will be measured using techniques such as chlorophyll fluorescence as a non-invasive probe of photosynthetic performance, gas exchange to assay photosynthesis and stomatal conductance, metabolite analysis and pulse labelling with stable isotopes. The student will be trained in a wide range of techniques used to measure plant and soil functioning in the plant stress biology lab of Giles Johnson and in the Soil and Ecosystem Ecology lab of Marina Semchenko and David Johnson.

http://www.soilecosystemecologylab.manchester.ac.uk
https://www.research.manchester.ac.uk/portal/marina.semchenko.html
https://www.research.manchester.ac.uk/portal/david.johnson-2.html
http://personalpages.manchester.ac.uk/staff/giles.johnson/default.php?page=home
Project Outline
Objectives:

The aim of this project is to improve the mechanistic understanding of interactions between plants and arbuscular mycorrhizal fungi (AMF) focusing on a) the mutual benefit of interaction to plant physiological and nutritional status and allocation of carbon to soil fungi, and b) the change in the function of this interaction in response to long-term land use intensification and stress associated with climate change. Specifically, the following hypotheses will be tested:
1) Long-term use of fertilisers leads to evolutionary changes in plant and AMF populations towards higher prevalence of plant genotypes with lower levels of carbon investment into fungi and of fungal lineages providing lower nutritional benefits to plants;
2) Plant productivity is the highest, and nutrient and carbon exchange most efficient, when plant genotypes are coupled with AMF inoculum and soil nutrient levels characteristic of their home habitat;
3) Under climate change scenarios of increased abiotic stress, the function of AMF shifts from nutritional provision to stress protection.

Potential outcomes:

This project is ideally placed within BBSRC’s remit as it investigates a complex biological phenomenon of interaction between plants and mycorrhizal fungi that is fundamental to the provision of ecosystem services, such carbon storage, nutrient cycling and soil aggregate stability, and enables better plant nutrition and resilience to multiple stresses. Despite the importance of mycorrhiza for both natural and agricultural ecosystems, and its potential for reducing reliance on fertilisers and pesticides and improving resilience to abiotic stress, we still lack understanding of the mechanisms underlying mycorrhizal associations and longterm dynamics of plant and fungal populations that are necessary for harnessing this beneficial association to deliver sustainable and resilient food production, which is one of the strategic priorities for BBSRC. This project aims to fill this important knowledge gap.

Methodology and multidisciplinary training:

The student will use field collected plant genotypes and soil inocula in a series of controlled-environment experiments to gain mechanistic understanding of interactions between plants and AMF under different environmental settings. This will be complemented by a common garden mesocosm experiment to test for coadaptation between plants and fungi under more realistic conditions. The student will be trained in a wide range of techniques spanning plant ecology and physiology, soil microbiology and evolutionary ecology and will gain essential analytical skills to handle large datasets. The project is ideally placed within BBSRC’s remit by addressing the strategic priority of sustainable intensification in agriculture and providing access to and training in state-of-the-art approaches necessary for the investigation of complex biological phenomena. In particular, the student will be trained in the latest techniques to measure plant physiological status and stress responses, and high-resolution measurements of fungal performance and resource exchange between plant and soil subsystems.

Marina Semchenko will provide training in the use of specialist equipment to measure plant functional traits, carbon and nitrogen allocation and nutrient cycling, soil microbial inoculation techniques, plant propagation techniques and advanced statistical analysis.

Giles Johnson will provide training in the measurement of chlorophyll fluorescence, water and carbon fluxes using infrared gas analysers, protein production and associated data processing to assess plant physiological status such as the photosynthetic performance and water and nitrogen use efficiency.

David Johnson will train the student in the use of stable isotopes to trace resource exchange between plants and fungal partners and techniques to assess the diversity and abundance of soil microbiota.