Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2000
Publication Date: N/A
Interpretive Summary: Biologically active pools of soil organic matter are important in understanding decomposition potential of organic materials, nutrient cycling dynamics, and biophysical manipulation of soil structure. Macroclimatic influences on biologically active pools of organic matter are not well understood, but would improve regional- or national-level predictions of potential soil carbon storage and nutrient cycling as a function of management. We evaluated the quantitative relationships among potential carbon and net nitrogen mineralization, soil microbial biomass carbon, and soil organic carbon under four contrasting climatic conditions in Alberta/British Columbia (frigid-dry), Maine (frigid-wet), Texas (thermic-dry), and Georgia (thermic-wet). We observed that biologically active pools of organic matter were similar among regions on a soil mass basis, but 2 to 3 times greater in thermic than frigid regions relative to soil organic carbon. Frigid regions store more soil organic carbon in the long-term than thermic regions and a greater portion of this organic carbon is biologically unavailable.
Technical Abstract: We evaluated the quantitative relationships among potential C and net N mineralization, soil microbial biomass C (SMBC), and soil organic C (SOC) under four contrasting climatic conditions. Mean SOC values were 28 +/- 11 mg/g (n=24) in a frigid-dry region (Alberta/British Columbia), 25 +/- 5 mg/g (n=12) in a frigid-wet region (Maine), 11 +/- 4 mg/g (n=117) in a thermic-dry region (Texas), and 12 +/- 5 mg/g (n=131) in a thermic-wet region (Georgia). Higher mean annual temperature resulted in consistently greater basal soil respiration (1.7 vs 0.8 mg CO2-C/g SOC/d in thermic compared with frigid regions), greater net N mineralization (2.8 vs 1.3 mg inorganic N/g SOC/24 d), and greater SMBC (53 vs 21 mg SMBC/g SOC). Higher mean annual precipitation resulted in consistently lower basal soil respiration (1.1 vs 1.3 mg CO2-C/g SOC/d in wetter compared with drier regions) and lower SMBC (31 vs 43 mg SMBC/g SOC), but had inconsistent effects on net N mineralization that depended upon temperature regime. Although thermic regions are not able to retain as high a level of SOC as frigid regions, biologically active soil fractions appear to be as high per mass of soil and even 2- to 3-times greater per unit of SOC.