Linking Carbon, Nitrogen, And Calcium Cycling In Northeastern U.S. Forests
Carbon (C), nitrogen (N), and calcium (Ca) cycling in forest ecosystems is controlled largely by the recycling of organic matter by biota and by the balance of new inputs and losses. In the northeastern U.S., the availability of these elements has been dramatically altered by human activities. Acid deposition has increased N inputs and caused declines in soil Ca concentrations. Concurrently, atmospheric carbon dioxide concentrations are rising. My dissertation research focused on understanding how individual tree species influence ecosystem C, N, and Ca cycling, and how increasing soil Ca by liming affects C and N pools, fluxes, and dissolved organic matter retention. In chapter 1, I show how Norway spruce, red oak, and sugar maple planted in a common garden influence soil C, N, and Ca pools. Norway spruce had the largest C and N stocks in the forest floor and upper mineral soils. No differences among species were observed in soil exchangeable Ca availability. Red oak plots displayed the highest foliar litter lignin concentrations, the shortest residence time for C and N in the forest floor, and the highest earthworm densities. This suggests that leaf litter recalcitrance is not the dominant driver of decomposition in this forest and that other factors, such as the presence of earthworms, can influence organic matter turnover in ways that are unexpected when only considering litter chemistry. In chapters 2 and 3, I discuss the long-term effects of liming on ecosystem C and N dynamics. Twenty years after lime addition, there was no evidence of a tree response. Within the forest floor, C and N stocks in limed soils were double that found in controls. I observed reductions in both soil basal respiration and net N mineralization, indicating that liming has altered C and N cycling within this ecosystem. I also investigated how soil exchangeable Ca concentrations influence dissolved organic C and N retention. Soils higher in exchangeable Ca tended to release less C and N, suggesting that liming may facilitate Ca-organic matter bridging, thereby reducing C and N losses from the upper mineral soils.
forest; soils; carbon; nitrogen; calcium; nitrogen; dissolved organic carbon; tree species
Goodale, Christine L
Fahey, Timothy James
Ph.D. of Ecology
Doctor of Philosophy
dissertation or thesis