INTERACTIONS BETWEEN KALMIA HUMUS QUALITY AND CHRONIC LOW C INPUTS INCONTROLLING MICROBIAL AND SOIL NUTRIENT DYNAMICS

Glucose-C was repeatedly added to organic Kalmia humus from two sites of contrasting spruce productivity (i.e. rich and poor) and basal resp iration, microbial biomass and metabolic quotient (qCO(2)) were measur ed over a 438 day incubation and compared to post-incubation soil mine ral-N pools, anaerobic N mineralization rates, the nutritional deficie ncy index (NDI) of soil microbial communities and final soil weights. Repeated measures analysis of variance revealed a strong overall soil effect on basal respiration and microbial biomass and a strong overall glucose effect on microbial biomass and qCO(2), whereas the analysis of within-subjects effects revealed strong interactions of the time fa ctor with both soil and glucose on all three measurements. In the poor soil, glucose supported high microbial biomass and therefore low qCO( 2), until the end of the incubation, whereas in the rich soil, glucose also supported high microbial biomass and low qCO(2), but these conve rged towards control (i.e. no glucose) values before the end of the in cubation. Mineral-N pools were high in the rich control treatment only , whereas the NDI was high only in the rich + glucose treatment. Anaer obic N mineralization rates did not differ statistically among treatme nts. Glucose significantly decreased mass loss in the rich soil but no r in the poor soil. The data support the conclusion that glucose addit ion to the rich soil inhibits microbial utilization of nutrient-contai ning soil OM for maintenance energy thus exacerbating nutritional defi encies, whereas glucose addition to the poor soil does not affect soil N cycling. Based on results of analytical pyrolysis performed on soil subsamples prior to the incubation, we hypothesize that higher amount s of tannins measured in the poor humus may have chemically immobilize d and ultimately controlled availability of N. (C) 1997 Elsevier Scien ce Ltd.