Microbial Processes and
Plant Nutrient Availability in Arctic soils
Introduction
¡§Several characteristics of arctic soils influence
microbial activity, nutrient mineralization, and nutrient
availability to plants and will certainly figure prominently in
changes in these processes in a warmer arctic climate.
Arctic soils are generally overlain by a dense mat of
organic matter and vegetation, wet for at least part of the year
and permanently frozen at some depth. These factors combine to lower summer soil temperatures,
impede the progression and decrease the depth of seasonal
thawing, and maintain relatively high soil moisture content.
Cold, wet soil environments and short summers slow
organic matter decomposition and nutrient mineralization and
severely restrict nutrient availability to plants.
The accumulation of organic matter in arctic soils is
determined largely by the combined effects of temperature and
moisture on decomposition and primary production.
Because of climatic variation among arctic regions, the
amounts of organic matter and nutrients in tundra soils vary
across broad geographic scales.
Organic matter often accumulates at depth in permanently
frozen peats in relatively wet arctic regions such as the
coastal plain no northern Alaska.¡¨
>Organic carbon increases with moisture, from low amounts in
well-drained beach-ridge ecosystems with cushion plant-lichen
communities. Such an overall patter ¡V of organic carbon
increasing with moisture from well- to poorly ¡Vdrained
ecosystems ¡V also occurs in Alaska¡¦s coastal and foothill
tundra regions
¡§Well-drained soils are less common in patterned ground
regions with little relief, such as the Alaskan coastal plain,
where more than 85% of soils are moist to poorly drained.
Moist soils with dense organic mats(5-40cm thick),
intermediate thaw depths, and divers plant communities dominated
by tussock-forming sedges occupy gently sloping land in much of
the Low Arctic¡K
Organic matter and moisture content are important
determinants of soil temperature, thaw depth, cation exchange
capacity, aeration, redox potential, and other properties
affecting biological processes in soils.
Decomposition rates and soil moisture balances will
likely be affected by the warmer temperatures predicted for the
Arctic The
resulting changes in soil organic matter, moisture and microbial
processes in ecosystems will alter the amounts, seasonality, and
forms of mineral nutrients available to plants.
A warmer climate will likely have different overall
effects on soil properties and on nutrient cycling in dry,
moist, and wet arctic ecosystems.¡¨
(Source:
CHAPIN, F.S., JEFFERIES, R.L., REYNOLDS, J.F., SHAVER, G.R.
Arctic Ecosystem in a Changing Climate: An Ecophysiological
Perspective, 1991. P. 281-283)
Microbial and soil Processes
Nutrient cycling and fertilization studies in arctic
ecosystems show that plant growth is strongly limited by
nutrient availability. Primary
production is often nitrogen-limited, but phosphorus (especially
in organic soils) or nitrogen and phosphorus together can also
limit production.
Arctic ecosystems are generally conservative of nutrients
accumulating large amounts in soil organic matter pools with
very long turnover times. Because
of these characteristically slow turnover rates and, in some
ecosystems, the gradual burial of organic matter in permafrost,
nutrients become available to plants at very low rates.
Long turnover time result from slow decomposition, which
can become a bottleneck in nutrient cycling rates.
Differences among ecosystem types in soil microclimate
and decomposition may explain the inverse relationships between
soil nutrient stocks and nutrient cycling rates or primary
productivity as reported, for example, on Alaska¡¦s northern
coast. Slow
decomposition leads to greater accumulation of organic matter in
soil and can lower nutrient mineralization rates, thereby
decreasing primary productivity.
(Source:
CHAPIN, F.S., JEFFERIES, R.L., REYNOLDS, J.F., SHAVER, G.R.
Arctic Ecosystem in a Changing Climate: An Ecophysiological
Perspective, 1991)