Microbial control of litter decay The goal of this research is
to explore the role of the microbial community in the conversion of
litter to humus, a critical process affecting rates and quantities of
soil carbon sequestration. We will investigate the functional links
between decomposer microorganisms, litter chemistry, and nitrogen (N)
using experiments that manipulate carbon (C) and N availability over
the course of litter decomposition. To accomplish this we will set up
laboratory incubations of deciduous leaf litters of contrasting
chemical composition and add pulses of isotopically labeled C and N at
different stages of decomposition. This will enable us to quantify C
and N effects on the breakdown of the different chemical constituents
in litter as decomposition proceeds. To determine how patterns of
microbial community behavior are linked to decomposition we will
monitor the activities of a variety of microbial enzymes associated
with decomposition throughout the experiment.
The Changing Seasonality of Tundra Plant-Soil Interactions
Tundra
soils are key regulators of many aspects of the Arctic System. Arctic
soils have large stores of carbon (C) and may act as a significant CO2
source with warming. The key to understanding tundra soil processes is
nitrogen (N), though, as both plant growth and decomposition are
severely N limited. However, current models of tundra ecosystems and
their responses to climate change assume that while N limits plant
growth, C limits decomposition. In addition, N availability is strongly
seasonal with relatively high availability early in the growing season
followed by a pronounced crash. We need to understand the controls on
this seasonality to predict Arctic System responses to climate change,
but there are multiple questions that need answers: 1) What
causes the seasonal nutrient crash? 2) Does microbial activity switch
seasonally between C and N limitation? 3) How will a lengthening of the
growing season alter overall ecosystem C and N dynamics, as a result of
differential extension of the periods before and after the nutrient
crash? 4) What will be the larger impacts of these patterns on the
Arctic system?
This research addresses these questions by: 1)
Varying the length and timing of the growing season in the field by
advancing snow melt and warming the ecosystem; 2) Establishing the fine
scale seasonal time-courses of soil N availability, plant N content,
leaf expansion, root growth and rhizodeposition, ecosystem respiration,
microbial biomass and enzyme activity; 3) Conducting lab experiments to
determine the extent to which microbial activity is limited by
temperature, and C and N availability before and after the crash; 4)
Determining how the timing of the nutrient crash and plant growth vary
across a latitudinal transect; 5) Refining models developed for arctic
ecosystems to better handle how plant and microbial systems respond to
N limitation; and 6) Testing the large-scale spatial and temporal
effects of the seasonality of nutrient availability and how it may
change in a warming Arctic with a lengthening growing season.
The below ground effects of invasive speciesIt has been
previously found that invasive plants can gain a competitive advantage
against other plants by altering belowground processes such as
decomposition and nutrient cycling. We are conducting a region wide
comparison of soil N availability, C availability, microbial biomass
and enzyme activity in soils beneath invasive plants that are a problem
in our region (e.g. garlic mustard, glossy buckthorn, cow vetch,
multiflora rose) and the native plants that occur in the same soils to
determine the extent to which important terrestrial ecosystem processes
are affected by invasive plants, and to gain insight into what makes
these plants effective invaders, so that we will ultimately have the
knowledge required to eliminate these noxious invasive plants and
restore native plant communities.
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The biogeochemical importance of extra-cellular enzymes on plant rootsPlant
roots are known to produce extracellular enzymes that can mineralize
organic nutrients, such as phosphatases, but little is known about the
variety of different enzymes that roots can produce, and how important
these root enzymes are in biogeochemical cycling. The goal of this
research is to use fluorescent staining techniques to screen roots from
a range of different plant species for a variety of different
extra-cellular enzymes, to determine the activities of the enzymes we
find, and compare their activities to enzymes produced by
microorganisms in the same soil environment.
Enzymatic Controls on N Mineralization
Nitrogen mineralization
is the conversion of organic N to mineral N. This process involves the
decomposition of a variety of different organic N forms, including
proteins, chitin and peptidoglycan, and DNA and RNA. The goal of this
research is to determine how much these organic N forms contribute to N
mineralization in different places and times, and why. For this project
we will measure the activities of a variety of microbial enzymes
responsible for degrading different organic N forms in soils from a
variety of environments, all collected several times a year, and
compare the enzyme activities to overall N mineralization rates. We
will also perform a variety of basic soil chemical characterizations to
try and determine the factors that control N mineralization.
To view past research projects, please click here.
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