TEMPERATURE AND MOISTURE EFFECTS ON THE PRODUCTION OF DISSOLVED ORGANIC-CARBON IN A SPODOSOL

Leaching of dissolved organic carbon (DOC) from the forest floor is an important C flux and influences other biogeochemical fluxes in forest s. To determine what controls the quantity and quality of the DOC prod uced, we examined the effects of microclimate on DOC production in Oa- horizon material from a red spruce forest. Samples incubated under dif ferent temperature and moisture conditions were leached with a mechani cal-vacuum extractor every 7 days for 8 to 10 weeks, or once after 1 t o 14 days. The concentration and, in some cases, the composition of th e DOC in the extracts were measured. Production of DOC in dry samples (moisture content from 0.5 to 1.7 g g(-1)) was approximately 1.2 mg g( -1) in the first week, but declined by 77% over 8 weeks. In sieved sam ples, production declined to 40% of initial values, whereas production in unsieved, moist samples declined by less than 30%. In wetter sampl es (moisture content from 1.8 to 5 mg g(-1)) DOC production increased by approximately 0.1 mg g(-1) week(-1) for every g g(-1) increase in m oisture content. The production of DOC increased exponentially with te mperature, with Q(10) values of 1.7 for soil with a moisture content o f 2.5 g g(-1), and 2 for wetter material. The composition of the DOC e xtracted from the driest samples suggested disruption of microbial bio mass. Wetter incubation conditions increased the proportion of hydroph obic acids, whereas warmer incubation conditions increased the proport ion of hydrophilic acids. The production of DOC was relatively fast in the first 2 days of incubation, and then slowed to approximately 90 m u g g(-1) week(-1). Production rates in the first 2 days of incubation were higher under warmer conditions. Replicated experiments were usef ul in constructing precise curves relating the response of DOC product ion and composition to temperature and moisture. Copyright (C) 1996 El sevier Science Ltd