Soil Respiration Across Three Climatically-distinct Chronosequences in Oregon

1. Initiation Young Mature Old Coast Range West Cascades East Cascades Coast West East Range Cascades Cascades Initiation Young Mature Old Coast West East Range Cascades Cascades 1) 2) 3) Base rate Temperature response curve Daily soil temperature Soil Respiration Across Three Climatically-distinct Chronosequences in Oregon R-82830901-0 John Campbell, Osbert Sun, and Beverly Law Dept. of Forest Science, Oregon State University methods To assess soil respiration over the full range of western Oregon’s forest conditions, annual soil respiration, along with soil temperature and moisture was measured at 36 study plots arranged as three independent replicates of four age classes in each of three climatically-distinct cover types. Forest ages range from 10 to 300 years. The three cover types spanned a 200 km transect and included 1) wet coastal Soil respiration varies by site and age hemlock-Sitka spruce 2) montane Douglas fir, and 3) rain shadow ponderosa pine. Annual soil respiration for the year 2001 was computed by combining periodic chamber measurements with continuous soil temperature measurements, which were used along with site-specific Soil respiration insensitive to temp. response curve temperature response curves to interpolate daily soil C-efflux between dates of direct measurement. Between-site variation driven by base rate Annual soil respiration is computed from site-specific estimates of: linear response Soil respiration linked to BNPP but not ANPP Base rates are the only parameter to which annual soil respiration is sensitive and that vary substantially between sites This graph shows which of these parameters annual rates are most sensitive to Soil respiration linked to fine root mass R2 = 0.43 p < 0.001 no significant relationship Fine root mass decoupled from total mass Soil respiration linked to foliage mass Moisture not strongly coupled to soil respiration Coast West East Cascades Cascades Range high understory outliers low understory outliers Our results demonstrate that both the disturbance regimes that result in a diversity of forest age and the edaphoclimatic forces that conclusions result in a diversity of forest type are acting to shape soil respiration on across Oregon. Moreover, our results suggest that temperature and moisture are of minimal importance in defining between-site differences in annual soil respiration. Correlations between annual soil respiration and leaf mass, root mass, and root production are consistent with a growing appreciation that soil respiration is controlled largely by the short-term supply of carbohydrates to the rhizosphere, and that regional assessment of soil respiration may be better improved by understanding belowground carbon allocation than by further regression of respiration with parameters of the soil environment, which at regional scales are often confounded with plant production. [Each point is a plot-wide average efflux measured on a unique day]