The responsive C and N biogeochemistry of the temperate forest floor.

Soil organic matter is often viewed as comprising large pools of carbon and nitrogen with long residence times. However, the organic horizon that lies on the soil surface in temperate forests is a dynamic component of ecosystem carbon and nitrogen cycling. Responses to elevated inputs of nitrogen in this organic layer are emerging as key facets of ecosystem retention or loss of dissolved nitrogen. Research along nitrogen deposition gradients in the USA and Europe reveals a link between the ratio of organic carbon:nitrogen in the forest floor and nitrogen turnover rates, nitrification and leaching losses. Characteristics and processes in the forest floor are now recognized as key indicators or determinants of ecosystem 'nitrogen status'.