PhD Abstract

The impact of climate and land use change on soil respiratory fluxes

Erica Cacciotti, University College Dublin, 2015

The impact of climate and land use change on soil respiration was investigated in both a coniferous (Sitka spruce) and deciduous (Ash) forest in the Irish Midlands.

A chronosequence approach was utilized to examine age-dependent effects at sites that represented the typical Irish land use change of grassland conversion to forestry. Reductions in soil respiration were associated with declining productivity as forest age in both chronosequences, suggesting that the availability of labile carbon may be an important driver and that the associated grasslands always showed the higher rates of soil respiration.

Generally, soil respiration was positively correlated with soil temperature and negatively correlated with soil water content at all the sites. Simulated reductions in summer precipitation using rain-out shelters at grassland and forest sites resulted in a strong impact on soil respiration, although the results varied with differences in the initial amounts of water present in the soil.

Variations in soil water content were probably due the different water-holding capacities of the soil and to differences in the height of the water table (mineral water gley = high water table in Dooary; brown earth = low water table in Mt. Lucas). Consequently, reductions in soil moisture increased respiration at the Dooary site and decreased those at the Mt Lucas site.

The re-wetting of soils to simulate extreme rainfall events generally resulted in significant and often prolonged increases in soil respiration that depended on the initial soil moisture content and were independent of the site or ecosystem examined.

These results indicate that short and long-term variations in rainfall can have both positive and negative impacts on soil respiratory losses and that projected increases in extreme rainfall events could compromise the carbon balance of grassland and forest ecosystems.