Patterns in forest soil microbial community composition across a range of regional climates in Western Canada
Brockett, B. 2008. M.Sc Thesis. Dept. of Forestry, University of British Columbia, Vancouver, Canada
Abstract
Soil microbial communities can be characterized by community structure and function
(community composition) across a spectrum of spatial scales, and variation in soil
microbial composition has been associated with a number of environmental gradients.
This study investigates the structure and function of soil microbial communities under
mature, undisturbed forested sites across a range of regional climates in British
Columbia and Alberta, and also examines the variation in community composition within
sites.
Phospholipid fatty acid analysis was used to investigate the structure of soil microbial
communities and total soil microbial biomass at each site. Extra-cellular enzyme assays
established the functional potential of the soil microbial community at each site.
Multivariate analysis of the data showed that the soil microbial communities under
different forest types did significantly separate along the regional climate gradient by
both community structure and function, despite high local variation in the communities.
Soil moisture content and soil organic matter concentration consistently exhibited the
strongest relationship with microbial community characteristics, although the functional
and structural responses to the external drivers were different. Microbial community
function and structure also changed with soil depth but not with time of sampling.
Microbial community function was related to the regional annual average precipitation
gradient. Most of the locations exhibited unique microbial community functional profiles
in their soil layers; however the enzyme activities in the samples from the driest
(Ponderosa Pine) and wettest (Mountain Hemlock) locations were notably different from
each other and from those of the other locations, especially in the organic layers.
The moist maritime-influenced Coastal Western Hemlock (CWH) forest exhibited
microbial community structural characteristics which were unique from those of the other
forest locations. The higher abundance of bacteria relative to fungi in the CWH forest
soils may be related to the significantly higher available nitrogen concentrations at this
site.
