PARENT SESSION
Oral Session #25: Soil Ecology: Microbial and Invertebrate. Presiding: W. Parsons.
Tuesday, August 7, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.

The effects of chronic N deposition on extracellular enzyme activity in an Acer saccharum forest.

Saiya-Cork, Kellyanne¹, Sinsabaugh, Robert¹, ¹

ABSTRACT- Rates of anthropogenic N deposition on forest soils continue to rise. Increased N availability affects litter decomposition and soil organic matter (SOM) storage through multiple mechanisms that have received scant study. We sampled litter and soil collected from three chronically fertilized experimental plots (30 kg N/ha/yr) and three control plots within a sugar maple forest in northern Michigan during the growing seasons 1998-2000. The activities of ten enzymes were assayed. Fungal mass in litter, soil and fine roots was quantified by ergosterol extraction. ANOVA and meta-analysis techniques were used to compare treatment responses. EEA responses in litter were greater than those of soil (litter mean effect size (d) = 0.534 std. dev., = 0.0003; soil d = 0.308; = 0.0015). Cellulase and urease activities were higher in treatment plots for both soil and litter; phenol oxidase activity was lower in soil but higher in litter. The ergosterol content of mycorrhizal roots declined significantly (p = 0.000007, = 0.05). The data indicate that N deposition has increased litter decomposition rate and depressed SOM decomposition. The loss of phenol oxidase activity in bacterially-dominated soil suggests that N inhibition of recalcitrant organic matter decomposition may involve more than suppression of lignin-degrading basidiomycetes.

KEY WORDS: extracellular enzyme activity , nitrogen deposition, soil ecology, decomposition