Soil biological properties of a montane forest sere: Corroboration of Odum's postulates

Abstract

Changes in organic C content, N component pools, Shannon-Weaver diversity index ( H′) of microbial populations, nitrification potential, and ATP and dehydrogenase activities were examined in soils along a montane meadow-aspen-fir-spruce sere. Along the sere organic C increased from 2.15 to 26.8%, total N from 0.13 to 0.98%, C: N ratios from 17 to 27, total NH 4 + from 103 to 850 μg g −1, total NH 4 +:NO 3 − ratios from 69 to 326, and microbial diversity index, H′, from 0.87 to 1.28. Coefficients of determination, r 2, for H′ vs organic C and total N in A-horizons, were 0.99 and 0.98, respectively, and H′ vs combined O- and A-horizons 0.68 and 0.70, respectively, indicating the presence of different microbial communities in the mineral and forest floor soils. Radiocarbon dating of humic acids and humin showed the longest mean residence times (920 and 1050 yr BP) in the meadow soils, suggesting a more efficient organic matter turnover and selective accumulation of recalcitrant organic components than in soils of more mature stages. The ATP content and dehydrogenase activity values were not statistically different in the forest sequence soils. Rates of nitrification potentials measured in vitro increased along the sere in the surface soils. Information obtained from seral soil variables supported hypothesized successional trends relating to organic matter content, species diversity, nutrient cycling, nutrient exchange rate and nutrient conservation. Nitrification potentials of soils, however, contradicted the postulate that nutrient conservation increases as an ecosystem matures.