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Title: Investigation of rhizosphere priming effects for N mineralisation in contrasting soils
Author: Murphy, Conor
ISNI:       0000 0004 5918 0384
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2015
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In the context of nutrient cycling in soil, plant-mediated mineralisation of carbon (C) and nitrogen (N) is poorly understood. The broad focus of this thesis was to investigate the potential importance of plant-mediated mineralisation (i.e.priming) on C and N mineralisation in soils with contrasting crop productivities. The studies focus on two soils, which had similar chemical and physical properties but contrasting plant productivities relating to their N supply capacity. These soils were used to investigate the potential importance of priming processes in contributing to the contrasting capacities of these soils to supply N for plant growth. 13C and 15N stable isotopes were used to measure specific gross C and N fluxes. Sole C or N and combined C with N treatments were established to disentangle the effect of carbon and nitrogen availability on plant-mediated mineralisation. The addition of labile C increased gross carbon and nitrogen fluxes from native soil organic matter (SOM) but the effect was soil specific. The addition of nitrogen did not affect SOM mineralisation in either soil. The much lower C-to-N ratio of the 'primed' flux compared to the 'basal' flux indicated that the primed flux utilises different OM pools highlighting that primed and basal mineralisation may be distinct processes. The priming response (i.e. positive or negative and associated mechanisms) was different depending on carbon and nitrogen supply to the microbial community. Overall, the studies in this thesis places the microbial community as the focal point of soil N supply. This data strongly supports the concept that the release of labile carbon from plant roots functions as a nutrient acquisition response, increasing mineralisation of SOM. From the data a conceptual model of priming mechanisms, based on nutrient availability to the microbial community, was established. This could be used as the foundation to develop key concepts for sustainable agricultural practice.
Supervisor: Not available Sponsor: Walsh Fellowship
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nutrient cycles ; Soils ; Growth (Plants)