Nutrient addition accelerates leaf breakdown in an alpine springbrook

This study assessed the effect of nutrient enrichment on organic matter bre akdown in an alpine springbrook, using alder leaf packs to which phosphorus and nitrogen were added in the form of slow-release fertilizer briquettes. The breakdown of leaf packs with nutrients added (k=0.0284 day(-1)) was si gnificantly faster than that of unfertilized packs (k=0.0137 day(-1)), resu lting in a 30% higher mass loss after 42 days. Unfertilized leaves enclosed in fine-mesh bags broke down at an even slower rate (k=0.0062 day(-1)). Ph osphorus and nitrogen concentrations were initially higher in leaf packs wi th nutrients added, but this difference disappeared within 3 weeks. Fungal biomass developing in decomposing leaves was substantial (c. 55 mg dry mass per 1 g leaf dry mass) although similar between fertilized and unfertilize d packs, as was the sporulation activity of aquatic hyphomycetes. There was a significantly greater number and higher biomass of macroinvertebrates (s hredding nemourid stoneflies in particular) on the fertilized packs, sugges ting that the increased leaf mass loss was brought about by shredder feedin g.