PARENT SESSION
Poster Session #26: Soil Ecology I.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Nitrogen availability and non-symbiotic nitrogen fixation in early and late successional forests in southern Chile.

PEREZ, CECILIA^*,1,2, CARMONA, MARTIN^1,2, ARAVENA, JUAN^1,2, ARMESTO, JUAN^1,2, ¹ UNIVERSIDAD DE CHILE, SANTIAGO, CHILE² FUNDACION SENDA DARWIN, CHILOE, CHILE

ABSTRACT- Large areas of southern Chile are covered by secondary forests generated by anthropogenic fire disturbance. In this paper we assess changes in N availability, non-symbiotic N-fixation and other chemical properties of soils in early (2-62 years old, N=5) and late (130 years, N=2) successional forest. Soil available nitrogen and phosphorous, total carbon and nitrogen, net N mineralization rates, pH and water contents were determined seasonally from July 1999 to April 2001. N-fixation rates in soil were determined seasonally over one year by the acetylene-reduction technique. Soils of early-successional stands had higher C/N ratios and lower N availability (ANOVA, p<0.05). Other variables did not differ between the two groups of stands. A subgroup of younger stands without remnant trees differed from all other stands because of their higher N-fixation rates and soil water contents (ANOVA, p<0.05). Disturbance altered the water table with consequent accumulation of recalcitrant carbon in early-successional soils. Non-symbiotic N-fixation may be a mechanism to recover from gaseous losses in recently disturbed stands. Functionally, 60 year-old stands with remnant trees did not differ from late-successional stands.

KEY WORDS: fire disturbance, net N mineralization rates, C/N ratios, forest succession