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 forests. To determine what controls the quantity and quality of the DOC produced, we examined the effects of microclimate on DOC production in Oa-horizon material from a red spruce forest. Samples incubated under different temperature and moisture conditions were leached with a mechanical-vacuum extractor every 7 days for 8 to 10 weeks, or once after 1 to 14 days. The concentration and, in some cases, the composition of the 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 samples, production declined to 40% of initial values, whereas production in unsieved, moist samples declined by less than 30%. In wetter samples (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 moisture content. The production of DOC increased exponentially with temperature, with Q10 values of 1.7 for soil with a moisture content of 2.5 g g-1, and 2 for wetter material. The composition of the DOC extracted from the chest samples suggested disruption of microbial biomass. Wetter incubation conditions increased the proportion of hydrophobic acids, whereas warmer incubation conditions increased the proportion of hydrophilic acids. The production of DOC was relatively fast in the first 2 days of incubation, and then slowed to approximately 90 micrograms g-1 week-1. Production rates in the first 2 days of incubation were higher under warmer conditions. Replicated experiments were useful in constructing precise curves relating the response of DOC production and composition to temperature and moisture.