Upland ecosystems in the UK, including grasslands and heather moorlands, make up approximately one-third of the UK's land area. In addition, the UK uplands are of substantial national and international importance due to their biodiversity, with unique plant assemblages adapted to the specific climate and soil conditions. They also serve important ecosystem services, such as carbon sequestration, clean water provision and fodder production. At present, plants in upland ecosystems, including grasslands and heather moorlands, are experiencing several significant environmental challenges, including increased levels of atmospheric carbon dioxide (CO2), nitrogen (N) pollution, and mismanagement caused by human activity. These could potentially hinder the ability of upland ecosystems to adapt to upcoming environmental changes or maintain ecosystem services. In particular, the effects of elevated CO2 (eCO2) and N pollution on phosphorus-limited grasslands are poorly understood. It is also not clear how Calluna vulgaris (the species that dominates heather moorland) varies ecologically, physiologically, and biochemically across its different life phases.
This thesis uses an empirical methodology to investigate the consequences of eCO2 and N pollution, and their combination for P-limited grassland. It accomplishes this using a CO2 fumigation experiment (miniFACE) on P-limited grassland taken from a long-term nutrient manipulation experiment. It investigates the impacts of eCO2 and nutrient loading (singly and in combination) on plant physiology, leaf biochemistry, and species biodiversity. In addition, this thesis uses field methodology to investigate the ecological, physiological, and biochemical variation through Calluna vulgaris (C. vulgaris) life stages in heather moorland. Also, it explores the ability of remote sensing applications to detect the changes in P-limited grassland plants and C. vulgaris life stages.
It was found that in P-limited grassland, eCO2 affected leaf gas exchange and stimulated photosynthesis; there was also evidence of acclimation, and N addition alleviated the magnitude of acclimation. eCO2 also changed leaf biochemistry, and increased biodiversity and species richness, allowing more species to coexist, but N addition reduced biodiversity. eCO2 and N created different plant communities. Leaf-level hyperspectral reflectance differed with eCO2 combined with N. In addition, C. vulgaris varied considerably ecologically, physiologically, and biochemically across its life phases, with variations in leaf and canopy levels of hyperspectral reflectance. In conclusion, this thesis contributes to the need to comprehend the responses of P-limited ecosystems to a future of increased CO2 and N availability, and the understanding of C. vulgaris variations across life stages.
