Soil:plant relationships of species-rich Molinia caerulea dominated communities of the Culm Measures, North Devon, with special reference given to phosphorus cycling
A semi-natural community known locally as Culm grassland in Devon and N. E. Cornwall is under threat from agricultural improvement, abandonment and inappropriate management In the last fifty years 87% of the original area has been lost. Further loss may be prevented by an examination of the factors that influence the plant community and how they may be manipulated by management. Thus the research described in this thesis addressed the soil conditions and the plant communities, with particular reference to phosphorus cycling. In 1992 a preliminary characterisation of soil nutrient and water conditions, and species composition was conducted on a pristine Culm grassland, an improved grassland and a formerly abandoned Culm grassland. A significant elevation in soil extractable phosphorus was found in mid-April in response to fertiliser applications on the improved grassland. Similarities with previous research and an absence of a similar pattern in mineral nitrogen prompted a detailed investigation of phosphorus dynamics in 1993. A better indication of plant 'available' P was found by removing soil solution directly using novel methods of centrifuging and suction cups. Environmental conditions were highly influential. Low concentrations of P in suction cup solutions on Culm grassland indicated that Culm species may remove P at very low concentrations. An investigation of the above-ground biomass found that the uptake of P was highest in M. caerulea. M. Caerulea also influenced the return of P to the soil via organic matter through the production and subsequent breakdown of large quantities of litter. Additions of P to turfs caused a perturbation by enhancing the uptake of P by M. caerulea and increasing P fixation. The data was employed to produce a schematic model of the Culm grassland which identified input and outputs, storage compartments and transfers within the P cycle. This contributed towards making management recommendations for a range of Culm grassland communities which may be maintained, improved or recreated.