Date of Award


Document Type


Degree Name

Doctor of Philosophy in Forest Science (PhD)

College, School or Department Name

School of Forest Resources and Environmental Science


Andrew Burton


The severity of future climate change resulting from anthropogenic alteration of the global C cycle will depend in part on feedbacks between atmospheric greenhouse gases and forest ecosystem carbon balance, but how these two systems will interact is not entirely understood. Forests are both major sinks and sources for atmospheric CO2 through the processes of photosynthesis and ecosystem respiration. The balance between these two processes could be altered if autotrophic respiration were to increase exponentially with temperature as climate warms. Root respiration, and especially fineroot respiration (<1 mm diameter), is a major contributor to total ecosystem C exchange. A study to assess long-term responses of root respiration to warmer soil conditions was conducted at the SMART (sugar maple altered rainfall and temperature) experiment located in Alberta, MI at the Michigan Technological University’s Ford Center and Forest. It was found that acclimation of fine-root respiration in this system was not due to an insufficient supply of carbohydrates from photosynthesis (substrate limitation), but was the result of adenylate control. As a result, fine root respiration was constrained to levels needed to perform work required of the fine roots (e.g. nutrient acquisition). Acclimation also occurred for roots 1-2 mm in diameter at the 0-10 cm soil depth, but not in any roots larger than 2 mm or in roots of any size at deeper soil depths. As a result, at the ecosystem level, total root system respiration was 60% greater in warmed soil than in unwarmed soil. The studies in experimentally warmed sugar maple forests were complemented by an examination of fine-root respiration and root biomass at sixteen sugar maple forests located across a latitudinal gradient across sugar maple’s native range, spanning approximately 10°C of mean annual temperature. Sugar maple in the southern, warmer sites had lower root N, lower specific fine-root respiration at a given temperature, and less fine-root biomass than that from the northern cooler regions. Fine root respiration at ambient soil temperature actually decreased from north to south, despite a nearly 10°C increase in soil temperature. However, within sites respiration measured across three sample dates did increase with temperature. The next big question is whether these adjustments that exist across sugar maple’s range are plastic responses to l local climate or result from genotypic differences among populations in different locations. If the former is true, all sugar maple would be capable of acclimation, reduction in root biomass, and/or reduction in root N as mechanisms for dealing with climatic warming, and sugar maple would have a large capacity to adjust to future climate change. The latter would suggest that predicted rates of climatic warming could have negative impacts on this important species across its entire current range. The lack of changes in fine root biomass and root N concentration at the SMART study location after four plus years of soil warming support the possibility that differences along the latitudinal transect are largely the result of inherent genetic differences among population.