摘要：Abstract We tested whether leaf breakdown of American beech (Fagus grandifolia) and sugar maple (Acer saccharum) was sensitive to slight differences in episodic acidification. We measured leaf breakdown in four headwater streams within the Adirondack Mountains, New York, USA, in summer and autumn 2005. We also investigated whether episodic acidification influenced the breakdown of beech and maple in leaf litter mixtures in autumn. Breakdown of maple was faster than that of beech for both summer and autumn, and species mixtures did not affect the breakdown rates of maple or beech. Breakdown rates of maple but not beech were highest in the circumneutral stream, but only in summer. Although microbial respiration rate for maple was greatest in the circumneutral stream in autumn, both maple and beech breakdown in autumn were greatest in one of the episodically acidified streams. Higher discharge and a greater proportion of riffle areas in this stream probably led to greater physical fragmentation rates in autumn when discharge was higher but not during summer. Due to this discrepancy between summer and autumn, we suggest that leaf breakdown should be used in combination with other functional metrics (e.g., microbial respiration) to assess the response of stream ecosystems to anthropogenic disturbances.
