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Changes in the Microbial Biomass and Metabolic Quotient During Leaf Litter Succession in Some New Zealand Forest and Scrubland Ecosystems
D. A. Wardle
Vol. 7, No. 3 (Jun., 1993), pp. 346-355
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2390215
Page Count: 10
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1. The soil microbial biomass and microbial metabolic quotient (respiration:biomass ratio) was measured in 16 forest and scrubland ecosystems throughout New Zealand, on materials representing successional stages of plant litter and its subsequent incorporation into the F-H and mineral soil layers. 2. Microbial biomass usually peaked in the L1 layer and then declined. The microbial carbon:organic carbon ratio decreased sharply between the F-H layer and the underlying mineral layer, indicating that a stress factor (possibly pH) reduced the proportion of organic matter immobilized in the microbial biomass at this stage. 3. The microbial respiration:biomass ratio declined between the L1 and F-H stages. This was then followed by a statistically significant (and sometimes very large) increase in this ratio upon reaching the mineral layer, for 10 of the 16 sites. This increase is in contrast to the predictions of Odum's theory of ecosystem succession and probably occurs because increasing levels of stress (in the absence of disturbance) in the latter stages of this succession reduce microbial efficiency. 4. When the 16 sites were classified according to early- and late-vegetation successional stages, there was no difference between the two categories with regard to microbial biomass, respiration or the metabolic quotient, although the microbial biomass carbon:organic carbon ratio was significantly higher for the early-successional sites. However, the variance for the microbial biomass:carbon ratio and metabolic quotient was substantially lower for the late-successional than early-successional sites, indicating that as vegetation succession proceeds these variables both converge to a narrower range of values.
Functional Ecology © 1993 British Ecological Society