Giardina, Christian (USDA FS Houghton, MIUSDA Forest Service, North Central Research Station, Houghton, MI, 49931; Phone: 906-482-6303 Ex 20; Fax: 906-482-6355; Email: cgiardina@fs.fed.us)

Belowground Carbon Allocation in Forests in Response to Global Change

C.P. Giardina *

Belowground carbon allocation (BCA) in forests regulates soil organic matter formation and influences biotic and abiotic properties of soil such as bulk density, cation exchange capacity, and water holding capacity. On a global scale, the total quantity of carbon allocated belowground by terrestrial plants is enormous, exceeding by an order of magnitude the quantity of carbon emitted to the atmosphere through combustion of fossil fuels. Despite the importance of BCA to the functioning of plant and soil communities, as well as the global carbon budget, controls on BCA are relatively poorly understood. Consequently, our ability to predict how BCA will respond to changes in atmospheric greenhouse gases, climate, nutrient deposition, and plant community composition remains rudimentary. In this synthesis, BCA will be examined from three perspectives: coarse-root standing stock, belowground net primary production (BNPP), and total belowground carbon allocation (TBCA). For each, methodologies and methodological constraints are described. Available data are then used to understand variation in BCA that relates to changes in species composition, mean annual temperature, or elevated CO2 in existing Free Air CO2 Exposure (FACE) experiments.