ICOM1 Abstract

BAXTER, JAMES W.1, STEWARD T. A. PICKETT2, MARGARET M. CARREIRO3 & JOHN DIGHTON1. 1Rutgers University, Piscataway, NJ 08855-1059 USA, 2Institute of Ecosystem Studies, Millbrook, NY 12545-0129 USA, 3Fordham University, Louis Calder Center, Armonk, NY 10504 USA. - Ectomycorrhizae and oak seedling performance in human altered forest ecosystems. We examine ectomycorrhizal (EM) status, oak seedling performance, and soil nutrient availability in similar mature oak-dominated forests in urban Bronx Co., NY, and rural Litchfield Co., CT, U.S.A. Consistent with their increased exposure to pollution, the urban forest soils contain elevated levels of heavy metals and inorganic N (primarily as nitrate). Red oak (Quercus rubra) seedlings were grown for 16 weeks in the greenhouse in soil cores collected from 5 urban and 5 rural forest stands. EM infection and morphotype composition was quantified on half the seedlings (n = 50), while plant height, leaf area, leaf number, root and shoot biomass, and total N and P status were measured on the other half (n = 50). Soil cores were also collected from the field sites to quantify EM status. Soil N and P availability was assessed by measuring NH4 and PO4 uptake rates into mature red oak roots collected from the field. Total EM infection was higher in urban seedlings. However, EM richness was higher in rural seedlings and EM composition differed between the treatments. Similar differences in EM status were observed on oak roots collected from the field. Seedlings grown in the rural forest soils had higher leaf area and total N content with trends toward increased foliar biomass and P content. Uptake rates of NH4 and PO4 in urban roots were 75% higher for NH4 and 3 times higher for PO4, suggesting that both of these nutrients are relatively limiting in the urban forest soils. Whether it is altered EM composition and abundance or changes in N and P availability that are responsible for decreased oak seedling performance in the urban soils is a question that is currently being investigated.