Impacts of climate change and land management on carbon dynamics of British upland grassland soils

This thesis sought to improve understanding of the effects of typical management regimes (conventional pasture and traditional hay meadow under agri-environment schemes) in the British upland grasslands and climate change on soil carbon (C) dynamics. Two upland grassland locations in northern England, UK were investigated. Results showed that the upland grasslands were a net atmospheric C sink (1822 – 2758 g CO2-eq m-2 year-1), with a significant SOC stock (59 – 101 Mg ha-1) which was predominantly (60%) protected in the soil mineral mass. The conventional pasture site receiving inorganic nitrogen (N) addition had a significantly higher SOC stock (101 Mg ha-1) and the greatest ecosystem C uptake (2758 g CO2-eq m-2 year-1) compared to all other sites. Experimental summer climate of late 21st Century (+3°C increase in temperature and -23% decrease in precipitation) resulted in a significant decline in the net ecosystem C sink (-13 to -29%) and plant biomass productivity (-29 to -77%) of the grasslands, regardless of management regimes. Overall, the results indicate that both conventional pasture and hay meadow management regimes maintain C sequestration in the upland grasslands, with the hay meadow management being less efficient. Also, warmer climate and drought by the end of the 21st Century will most likely lead to a significant decline in both C sink and forage production in the upland grasslands regardless of management. Moderate levels of inorganic N fertilizers plus organic manures is recommended to enhance biomass production and C sequestration in the traditional hay meadows. In addition, hay mulching is recommended as a viable management option to mitigate against the potential negative effects of climate change on both biomass productivity and C sequestration. Finally, pilot studies on a greater number of managed grasslands are needed to test the effectiveness of the recommended management changes for providing targeted outcomes.