Submitted to: Journal of Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/1995
Publication Date: N/A
Interpretive Summary: Mt. St. Helen's is a natural ecosystem recovering from a natural disaster. This ecosystem in terms of soil resources is starting from ground zero and slowly developing input to stimulate plant growth. We studied the progression of resource development at Mt. St. Helen's around two plant species with different characteristics. We were able to document how the plants influenced the developing microflora and in turn influenced how nitrogen and carbon were accumulating to develop functioning soils. This study one of the first of it's kind showed the interactions of plants and microorganisms in developing a habitat for further ecosystem development.
Technical Abstract: Legumes like Lupinus lepidus and L. latifolius affect soil C and N concentrations and microbial activity in Mount St. Helen's pyroclastic deposits. Concentrations of total Kjeldahl-N (TKN), total organic-C (TOC) and water soluble-C (H2O-C) were measured in soil from under live L. lepidus (LULE), live L. latifolius (LULA) and dead L. lepidus (DEAD), and in bare soil (BARE). Soil microbial biomass-C (SIR-C), metabolic quotient (qCO2), and C and N mineralization from lupine- biomass amended and non-amended soils were also estimated. The greatest concentrations of TKN, TOC and SIR-C were observed near the surface. In surface soil (0-5 cm), LULA soil contained the highest concentrations of TKN, TOC and SIR-C followed by DEAD, LULE and BARE plant-soil types, respectively. Changes in qCO2 with depth varied with plant-soil type. While TOC was strongly and linearly correlated with TKN, the relationship between SIR-C and both TKN and TOC was curvilinear and suggested a carrying capacity for SIR-C of about 400 kg microbial biomass-C ha-1. In an incubation study, the patterns of cumulative net respiration were similar to those observed for TKN and TOC (i.e., LULA > DEAD > LULE . BARE). Soils amended with L. latifolius biomass had a higher rate of net N mineralization than soils amended with L. lepidus biomass. Low amounts of TOC, TKN and soluble C, together with zero net N mineralization in some amended soils, suggest that microbial populations in Mount St. Helen's soils are N limited.