| Popis: |
Agricultural grasslands constitute over 50% of the total land area in the UK and are principally managed for the delivery of an important ecosystem service: increased biomass yields. Unfortunately, increasing the production of animal and plant biomass from these grasslands is rarely measured against the effects that agricultural management practices may have on other important ecosystem services i.e. soil carbon (C) sequestration or nutrient cycling. The main aim of this thesis was to address how the common agricultural management practices of nutrient fertilisation, liming and livestock farming, with a particular focus on traditional grassland re-seeding, could potentially affect key ecosystem properties and functions across 45 improved agricultural grasslands in Northern Ireland. Re-seeding was found to significantly reduce plant species diversity and total C and nitrogen (N) root pools in these grasslands. Re-seeding also influenced plant tissue stoichiometry, soil microbial activity and induced soil C losses through increased soil CO2 respiration. Surprisingly, only the simple soil property of bulk density, not re-seeding, was associated with changes in total soil C stocks. Livestock farming was found to have a strong influence on grassland C balance by significantly increasing their global warming potential (GWP). Calculations of net radiative forcing potential for each individual farm site suggest that high rates of soil C sequestration would be required to mitigate the GWP of current management practices. Artificial nutrient fertilisation was found to contribute to increased potential net soil N mineralisation rates and ' inherent' soil properties such as C:N ratios and pH were significantly related to changes in extracellular enzyme activity (i.e. P-l,4-glucosidase, P-Nacetylglucosaminidase and leucine aminopeptidase). Overall results demonstrate that amongst multiple agricultural practices, re-seeding is a particularly important influence on multiple ecosystem properties and functions. This research highlights the existence of complex interactions between multiple management practices and ecosystem variables, meaning it is difficult to predict long-term changes in the functioning of these grasslands. Future studies could address how anthropogenic management activities in these agro-ecosystems affect key above ground-below ground biogeochemical interactions in order to improve their long-term sustainability. |
