Microtopography on Mountains : Complex terrain augments heterogeneity of belowground carbon and nitrogen in the Swiss Central Alps

Appleton, David and Ostle, Nick and Mills, Robert (2020) Microtopography on Mountains : Complex terrain augments heterogeneity of belowground carbon and nitrogen in the Swiss Central Alps. Masters thesis, Lancaster University.

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Abstract

Mountain ecosystems are experiencing accelerated climate change and more frequent climatic extremes. Mountain soils play a critical role in local and regional biogeochemistry, while underpinning ecological stability and ecosystem multifunctionality. In the European Alps, mountain soils represent a critical carbon pool with the potential to modulate climate change through the sequestration of atmospheric carbon dioxide (CO2). However, climate warming may exacerbate soil carbon (C) and nitrous oxide (N2O) fluxes to the atmosphere. Consequently, European mountain ecosystems may become strong sources of atmospheric greenhouse gases, however, the environmental factors controlling the distribution of belowground C and N in mountain ecosystems and their relative importance across different spatial scales are largely unexplored. I aim to demonstrate that heterogeneity in the distribution of total soil C and N, and total organic C and N in microbial biomass, would occur with elevation and be augmented by microtopography. I explore elevation gradients stratified by life zone, underlying geology, parent material, vegetation composition and land-use type, differing only in proxy variables for microtopography. Heterogeneity in belowground C and N occurred with elevation and between sites of the same altitude for all transects. Slope angle was the most important topographic variable at lower elevations, likely due to the relationship with aboveground vegetation. Heterogeneity was constrained across the treeline ecotone, likely due to the overarching effect of declining temperature with increasing elevation on aboveground vegetation and second-order soil physicochemical drivers. The effect of slope was closely linked to response values at higher altitudes but was augmented by the effects of microtopography which became more pronounced with elevation. Overall, it emerged that the macro-scale effects of elevation-dependent factors may control belowground C and N in a general way, and site-specific conditions as a consequence of microtopographic and microclimatic dynamics may augment their heterogeneity at smaller scales.