Leaf-litter-associated fungi and bacteria along temporal and environmental gradients in boreal streams

Aquatic fungi and bacteria have long been recognized as key drivers in ecosystem processes such as leaf litter decomposition. We examined fungal and bacterial communities on decaying alder Alnus glutinosa (L.) Gaertner leaves along a gradient of increasing agricultural land use and associated nutrient enrichment in 9 boreal streams during 4 separate seasons (fall 2003, spring 2005, fall 2005, and spring 2006). Denaturing gradient gel electrophoresis (DGGE) and quantitative polymerase chain reactions (qPCR) showed that agricultural land use had significant effects on both bacterial and fungal communities, and on the ratios of fungi to total microbes associated with decomposing leaf litter. Furthermore, landscape factors and fluvial geomorphology appeared to influence the community composition of fungi and bacteria. Seasonal effects were found for fungal community structure only, indicating a higher temperature sensitivity of fungi compared to bacteria.