Black spruce (Picea mariana [Mill.] B.S.P.) boreal ecosystems : how tree-length and full-tree harvesting affects soil microbial populations

Abstract

To evaluate the hypothesis that microbial populations are affected by organic biomass removals, a study was designed to complement ongoing work in a black spruce {Picea mariana [Mill.] B.S.P.) Boreal ecosystem. The treatments included a control (uncut) and two harvest levels, tree-length (TL) and full-tree (FT). Soil samples from the organic and mineral horizons were taken from nine plots, representing three each ofthe treatments. Samples were taken once a month for four consecutive months; May through August during 1998. Soil respiration on two dates in September was estimated using the soda-lime technique. Bacterial cultures were prepared from the soil samples and pure strains identified using morphological and substrate utilization characteristics (specifically API 20E). Soil descriptors, including pH, total nitrogen, total phosphorus, organic matter content, and moisture content, were measured to investigate relationships with microbial biomass. Microbial biomass carbon (MBc) and nitrogen (MBN) were estimated using chloroform fumigation extraction. The data were statistically analyzed, using ANOVA, Pearson and Spearman correlations and, in the case ofthe MBc and MBN, ANCOVA, to determine if there were any treatment or seasonal effects. Soil respiration demonstrated a significant treatment effect where the efflux was significantly greater on the control treatment compared to the harvest treatments. Five bacterial cultures were identified from the soil samples, Chryseomonas luteola, Aeoromonas salmonicida, Serratia marcescens, Syntrophomonas multifilia, and Pseudomonasfluorescens. MBc and MBN values measured were in agreement with other published values for boreal coniferous soils. The MBc in the organic horizon was significantly affected by the interaction ofthe treatment and month factors. There was a significant treatment effect on the MBc in the mineral horizon, with the control mean significantly higher than those ofthe harvest treatments. The MBN revealed no significant effects in either the organic or the mineral horizons. The author concludes that soil moisture and temperature did affect the values for microbial biomass and that these environmental conditions were likely impacted by the level of harvest.