Soil moisture is the major factor influencing microbial community structure and enzyme activities across seven biogeoclimatic zones in western Canada
Brockett, B. F. T.,C. E. Prescott and S. J. Grayston. 2012. Soil Biology and Biochemistry 44:9-20
Abstract
Although soil microorganisms play a central role in the soil processes that determine nutrient availability
and productivity of forest ecosystems, we are only beginning to understand how microbial communities
are shaped by environmental factors and how the structure and function of soil microbial communities
in turn influence rates of key soil processes. Here we compare the structure and function of soil microbial
communities in seven mature, undisturbed forest types across a range of regional climates in British
Columbia and Alberta, and examine the variation in community composition within forest types. We
collected the forest floor fermentation (F) and humus (H) layers and upper 10 cm of mineral soil at 3 sites
in each of seven forest types (corresponding to seven Biogeoclimatic zones) in both spring and summer.
Phospholipid fatty acid analysis was used to investigate the structure of soil microbial communities and
total soil microbial biomass; potential activities of extra-cellular enzymes indicated the functional
potential of the soil microbial community in each layer at each site.
Multivariate analysis indicated that both structure and enzyme activities of soil microbial communities
differed among the forest types, and significantly separated along the regional climate gradient, despite
high local variation. Soil moisture and organic matter contents were most closely related to microbial
community characteristics. Forests in the Ponderosa Pine and Mountain Hemlock zones were distinct
from other forests and from each other when comparing potential enzyme activities and had the most
extreme moisture and temperature values. Forest floors from the hot and dry Ponderosa Pine forests
were associated with enzymes characteristic of water-stress and high concentrations of phenols and
other recalcitrant compounds. The wet and cold Mountain Hemlock forests were associated with low
enzyme activity.
An influence of tree species was apparent at the three sites within the Coastal Western Hemlock zone;
high bacterial:fungal biomass ratios were found under western redcedar (Thuja plicata) which also had
high pH and base-cation levels, and under Douglas-fir (Pseudotsuga menziesii), which had high N
availability. Potential activities enzymes differed among soil layers: potential activities of phenol oxidase
and peroxidase were highest in mineral soil, whereas phosphatase, betaglucosidase, NAGase, sulfatase,
xylosidase and cellobiohydrolase were highest in the forest floors.
Key Words
forest, enzymes, PLFA, soil moisture, soil microorganisms, climate
