Dissolved organic element dynamics in terrestrial ecosystem

In this thesis, I report a series of laboratory experiments focusing on the factors that control the ratios of C:N:P in DOM and the fluxes of DOC, DON and DOP from organic soils. For these experiments, I used soils from natural and artificial fertility gradients in the Hawaiian islands and from differing vegetation types in Alaska to evaluate C, N, P relationships in DOM. These experiments showed that DON fluxes and DOC:DON ratios are weakly linked to N availability. Fertilization with N caused a 43% narrowing of DOC:DON ratios in the most N-poor Hawaiian soil but had no effect on DON for more N rich sites in Hawaii. For both Hawaiian and Alaskan soils, DOC:DON ratios were more related to soil organic matter C:N ratios than microbial C:N ratios or microbial demand for N. In contrast, net production of dissolved organic phosphorus (DOP) and DOC:DOP ratios in the Hawaiian soils responded to long-term fertilization and natural fertility gradients. These results indicate that DOP losses and DOM C:P stoichiometry are likely controlled by the availability of inorganic P. Overall losses of DOC and DON were correlated with the size of soil organic matter pools of C and N in the Hawaiian, but not the Alaskan soils. Release of DOC from the Hawaiian soils appeared to be controlled by the sorption capacity of the soils. In contrast, there were correlative links between overall DOC leaching and CO2 evolution in the low mineral content Alaskan soils. There were not however, indications of instantaneous correlations between CO2 release and DOC release suggesting that microbial turnover and DOC production may be controlled by similar factors but are not necessarily mechanistically linked. DOC release also varied across vegetation types with higher release from spruce and shrub soils relative to tussock and wet sedge soils. Finally, I used these results in combination with literature data to produce a model of terrestrial DOC fluxes through soils. This model successfully reproduced the fluxes of DOC through the soils of a temperate deciduous forest and illustrates which mechanisms regulating DOC dynamics in terrestrial ecosystems are likely to reward future study.