PARENT SESSION
Oral Session #52: Carbon and Nitrogen Cycling: Soil processes and patterns. Presiding: F. Gilliam.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas E.

Detrital controls on SOM and nutrient dynamics in an old-growth forest soil.

Lajtha, Kate¹, Spears, Julie¹, Holub, Scot¹, Yano, Yuriko¹, Caldwell, Bruce¹, ¹

ABSTRACT- Despite growing knowledge of short-term litter dynamics, we know relatively little about the role of plant litter in determining SOM content and nutrient cycling over time scales ranging from decades to centuries. To address this gap, we established long term manipulations at the H.J. Andrews Experimental Forest, OR, to assess how rates and sources of plant litter inputs control the accumulation and dynamics of organic matter and nutrients in forest soils. Manipulations include litter additions, litter removal, and root trenching. Initial data from lysimeters show increases in DIN leaching in trenched plots, indicating the importance of roots and/or root exudates in controlling N losses even in this very high C:N, unpolluted forest. Data also show increases in DOC leaching at depth in double wood and double needle plots, with decreases in nitrate leaching. This pattern may be an initial disturbance effect, or may indicate DOC control over N immobilization and retention. Gross N transformation data suggest strong differences in gross rates of N immobilization among plots. Although we hypothesized that DON:DIN would increase in double wood treatments due to control by secondary chemicals on leachate DON:DIN, this pattern has not emerged to date. We are following three groups of soil enzymes that are directly involved in processing the major SOM-C classes and expect increasing detrital quantity to increase overall enzyme activities, with higher quality inputs disproportionately increasing processing of o-alkyl-C.

KEY WORDS: soil organic matter, soil solution chemistry, dissolved organic carbon, gross N transformations