Effects of Inorganic Nutrients on Microbial Leaf Decomposition and Mitigation of Chemical Perturbation

Abstract

ABSTRACT A laboratory study was conducted to determine (1) the effects of inorganic nitrogen and phosphorus enrichment on microbial leaf processing, and (2) whether inorganic nutrient enrichment would mitigate the effects of chemical perturbation of microbial leaf processing. Pre-leached disks from leaves of Acer saccharum were incubated in flasks of unfiltered stream water at 20°C for 56 days. Treatments consisted of a control, killed control (100.0 mg/1 HgCl2), nitrogen (3.0 mg/1 NO3-N), phosphorus (0.1 mg/1 PO4-P), nitrogen + phosphorus (3.0 mg/1 NO3-N + 0.1 mg/1 PO4-P), pentachlorophenol (10.0 mg/1 Na-salt of pentachlorophenol), and pentachlorophenol + nitrogen + phosphorus (10.0 mg/1 Na-salt of pentachlorophenol t 3.0 mg/1 NO3-N + 0.1 mg/1 PO4-P). Leaf disks in the control treatment lost 31% of ash-free dry weight in 56 days. Leaf decomposition, microbial biomass, and microbial activity increased in all treatments enriched with nitrogen. However, there were no increases in the treatment receiving only phosphorus. This implied that microbial leaf processing in certain aquatic systems may be nitrogen limited. Chemical perturbation by pentachlorophenol significantly reduced biomass and activity of microbes associated with leaves. However, nitrogen + phosphorus enrichment mitigated the effects of chemical perturbation.