INTERSPECIFIC LEAF INTERACTIONS DURING DECOMPOSITION IN AQUATIC AND FLOODPLAIN ECOSYSTEMS

An experiment was designed to test the importance of the potential int eraction (inhibition or enhancement) between slow and fast decaying le af species on processing rates in a stream and its floodplain. The dec omposition of water oak (Quercus nigra) and sweetgum (Liquidambar styr aciflua) in single-species packs was compared with water oak plus swee tgum in mixed-species packs within three habitats (stream snags, flood plain pools, and elevated floodplain surfaces) at three sites in coast al plain streams. Fast-decaying sweetgum leaves did not enhance the ra te of oak decomposition. Sweetgum leaves in mixed packs decomposed mor e slowly than single species packs in seven out of nine comparisons. I ncreases in bacterial density on leaves were depressed in mixed-specie s packs relative to single-species sweetgum packs. Fungal hyphae could not be observed in mixed or single-species packs. The effect of oak l eaves on sweetgum leaves was affected by frequency and period of inund ation. Macroinvertebrate shredders were rare or absent from most leaf packs collected from stream snags and floodplain pools. Over 40% of le af packs placed in the stream contained no shredders, while another 28 % contained <0.001 g shredders/g leaf dry weight. Therefore, shredders were to rare to influence overall leaf processing rates. These studie s suggest that microbial processing accounts for most leaf decompositi on and oak leaf leachate is shown to be inhibitory to microbial proces sing of sweetgum leaves.