Disentangling plant-microbe interactions under environmental change

The application of nitrogen fertiliser to maintain agricultural productivity is one of the key aspects of modern farming. These activities help provide for a growing population under climate change pressures with higher intensity droughts occurring more frequently. However, such manipulations alter soil health, lowering carbon: nitrogen (C:N) ratios and shifting plant-microbial interactions, on which plants are largely dependent. This thesis addresses the potential impacts on plant-microbial interactions under different C:N fertiliser regimes and water-availability by analysing the overall and N-cycling rhizosphere microbial communities and plant performance of a modern wheat variety, Triticum aestivumcv Mulika. In this thesis we have analysed the effects of concurrent drought and C:N fertiliser application on T. aestivumcv Mulika and its associated rhizosphere communities. We observed significant differences (P < 0.05) in plant Asat, size, and grain weight between well-watered and droughted conditions. Lower C:N performed better than higher C:N treated plants, but N-only treatments were significantly higher (P < 0.05) in plant size, grain weight, and Asat. Despite analysing root exudates, we did not find many significant differences as previously noted in the literature. This is likely due to the limited scope and analysis of root exudates in this thesis, with previous research performing broader analyses of compounds being exported from roots. However, due to an inability to analyse poor quality MiSeq reads we find that drought application alongside C:N fertilisation has little effect on plant-microbial interactions for T. aestivum. In conclusion, high C:N treatments move mineralised N away from plant use and toward plant-host specific microbial communities, with low C:N and N-only treatments preferentially favouring plant growth. Whilst significant differences were seen between droughted and well-watered plants, little effect was observed for the microbial communities.