Wednesday, August 8, 2007

PS 40-10: Elevation affects soil respiration in a northern Idaho mixed-conifer forest

Erin M. Berryman, John D. Marshall, Katy L. Kavanagh, and Alisa Schotzko. University of Idaho

In temperate forest ecosystems, soil surface CO2 efflux (Rsoil) is estimated to represent from 50% to 80% of total annual ecosystem respiration. Forest stands at higher elevations generally show lower annual productivity, and this may result in lower soil respiration rates due to reduction of carbon substrate quantity for both root and soil heterotrophic respiration. At a mixed-conifer forest in northern Idaho, summertime soil respiration was measured monthly at nine plots contained in three elevation classes, varying from 854 m to 1521 m (above sea level). Mean plot-level Rsoil varied from 1.1 µmol C m-2s-1 to 5.9 µmol C m-2s-1. At the subplot level, "CO2 chimneys" (measurement locations showing 2 to 3 times higher Rsoil than the plot-level mean Rsoil) persisted throughout the growing season, causing high variation at the plot level. One-way ANOVA revealed some significant differences in mean Rsoil by elevation class. High elevation plots had significantly lower Rsoil than low elevation plots in July and September, and lower Rsoil than middle elevation plots in August and September. No differences occurred among elevation classes in June or October. Temperature at 5 cm below the forest floor at each measurement location significantly described Rsoil at each plot using least-squares regression, but there was no trend in slopes by elevation class. We conclude that factors other than soil temperature and moisture control soil surface CO2 efflux in northern Idaho mixed-conifer forests, and some of those factors provide preferred diffusion pathways. We propose further work to explore the relationship between substrate availability, surface conditions, and Rsoil.