PARENT SESSION
Contributed Oral Session 26: Soil Fungi
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal
Tree species and mycorrhizal associations influence the magnitude of rhizosphere effects.
Phillips, Richard*,1, Fahey, Timothy1, 1 Cornell University, Ithaca, NY, USA
ABSTRACT- Previous research on the effects of tree species on soil processes has focused primarily on the role of leaf litter inputs. In this study, we sought to quantify the extent to which arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) tree species influence soil microbial activity and nutrient availability through rhizosphere effects. Rhizosphere soil, bulk soil and fine roots were collected from twelve monospecifc plots (6 AM and 6 EM tree species) at the Turkey Hill Plantations in Dryden, NY. Rhizosphere effects were estimated by the percent difference between rhizosphere and bulk soil samples for several assays. Rhizosphere effects on soil microbes and their activities were significant for EM species but in only a few cases for AM species. In AM tree species, microbial biomass, net N mineralization, and phosphatase enzyme activity in the rhizosphere were 10-12% greater than in bulk soil. In EM tree species, rhizosphere effects for microbial biomass, C mineralization rates, net N mineralization and phosphatase activity were 25-30% greater than bulk soil, and significantly greater than AM rhizosphere effects. The magnitude of rhizosphere effects was negatively correlated with the degree of mycorrhizal colonization in AM tree species (r = -0.83) and fine root biomass (r = -0.88) in EM tree species, suggesting that different factors influence rhizosphere effects in tree species from different mycorrhizal associations. Rhizosphere effects on net N mineralization and phosphatase activity were also much greater in soils with pH < 4.3 for both AM and EM tree species suggesting that soil fertility may also influence the magnitude of rhizosphere effects. Our results support the idea that tree roots stimulate nutrient availability in the rhizosphere, and that systematic differences between AM and EM roots may result in distinctive rhizosphere effects for C, N and P cycling between AM and EM tree species.
Key words: rhizosphere C flux, arbuscular mycorrhizae, ectomycorrhizae, nitrogen availability