Canadian Forest Service Publications
Labile C, humus form and N cycling in forests: Concepts and methods. 1997. Bradley, R.L.; Fyles, J.W.; Titus, B.D. Recent Research Development in Soil Biology and Biochemistry 1: 63-76.
Issued by: Pacific Forestry Centre
Catalog ID: 4893
Availability: Order paper copy (free)
Respirometry techniques, as well as a new kinetic parameter that assesses the potential energy supply to soil microbes, are described. We discuss the potential and limitations of substrate-induced respirometry for deriving ecophysiological indices describing the energy and nutrient limitations of soil microbial communities. The salient points of recent investigations on the interactions between labile-C and humus forms in controlling microbial and nutrient dynamics are reviewed.
A bioassay study demonstrated that the rhizosphere of paper birch (Betula papyrifera Marsh.) seedlings increased available-C and microbial biomass in a mull soil but decreased microbial nutrient limitation. These results suggested an alternative conceptual model for microbial N acquisition termed co-metabolic N mineralization. In another study, the presence of birch and other seedlings lowered the N flux in a mor humus, probably as the result of changes in microbial community structure following the introduction of roots into microsites dominated by ligninolytic organisms. In a third study, humus from two sites colonized by the ericaceous shrub Kalmia angustifolia L. were treated with chronic small doses of glucose and the evolution of microbial biomass, basal respiration and metabolic quotient (qCO2) were compared to indices of N cycling and humus chemical quality. Results suggested that phenolic compounds in Kalmia humus could play a key role in sequestering N and restricting microbial activity, thereby overriding the effects of labile C additions on N cycling. In a fourth study involving the growth of black spruce (Picea mariana (Mill.) B.S.P.), paper birch, and Kalmia on three humus forms from central Newfoundland, it was found that complex soil x species interactions controlled the physiology of microorganisms and gross N process rates. Results were interpreted in terms of the growth strategy and competitive ability of each species.