Vol 31, Part I - forums.sou.edu • Index page - Southern Oregon ...

ABSTRACTS – Symposia
years. Soils were collected from directly beneath plants and
from plant-interspaces, after which they were fractionated
into macroaggregates, free microaggregates and free silt and
clay fractions. Further, macroaggregates were separated into
particulate organic matter (POM), microaggregates and silt
and clay fractions. We measured the relative abundance of
soil fractions, and SOC within the fractions. Results showed
that increased precipitation decreased SOC in all treatments,
but not in soils underneath sagebrush, where SOC incorporation
into more stable soil fractions was enhanced. Our data
suggest that precipitation in semi arid ecosystems deplete
SOC contents, and that plant species mediate the impact of
precipitation on soil C dynamics.
38 Influence of Precipitation Regime on Microbial Decomposition
Patterns and Community Structure in Semi-Arid
Ecosystems: Altered Roles of Bacteria and Fungi, KEVIN
FERIS 1 *, CARRIE JILEK 1 , DAVID HUBER 2 , KEITH
REINHARDT 2 , MARIE-ANNE de GRAAFF 1 , KATH-
ERINE LOHSE 2 , and MATT GERMINO 3 ( 1 Department
of Biological Sciences, Boise State University, 1910 University
Dr. Boise, ID 83725; 2 Department of Biological Science,
Idaho State University, Pocatello, ID; 3 USGS FRESC, Boise
ID, 83725; kevinferis@boisestate.edu).
In water-limited semi-arid sagebrush steppe ecosystems
changes in climate may manifest as a shift from historically
winter/snow-dominated precipitation regimes to
one dominated by spring rains. In these ecosystems soil
microorganisms play a vital role in linking the effects of
water availability and plant productivity to biogeochemical
cycling. Patterns of soil microbial catalyzed organic matter
decomposition patterns (i.e. patterns of extracellular enzyme
activity (EEA)) and soil community structure may respond
both directly and indirectly to climate-induced changes in
precipitation regime. For example, EEA patterns are thought
to depend upon the quantity and quality of soil organic matter
(SOM), pH, and mean annual precipitation. However,
sagebrush-steppe plant communities respond strongly to
changes in the timing and magnitude of precipitation, and
preliminary findings by our group suggest that corresponding
changes in SOM quantity, quality, N-cycle dynamics,
and soil structure are occurring. Other groups have demonstrated
shifts from a bacterial to fungal dominated community
as precipitation regime shifts from winter to summer
precipitation. We hypothesized: 1) Shifts in the timing and
magnitude of precipitation indirectly affect soil microbial
decomposition patterns via responses in the plant community
structure and subsequent effects on soil organic matter
quantity/quality; and 2) Changes in precipitation patterns
may both directly and indirectly affect soil community structure,
potentially uncoupling interactions between plant and
soil community structure. We tested these hypotheses in a
long-term (> 15 year) precipitation manipulation experiment
in the sagebrush-steppe. Results are presented in the context
of biotic responses to climate and subsequent alterations in
C and N cycling.
39 Effects of Climate Shifts and Plant-Community Transformations
on Carbon and Nitrogen Cycling in Semi-Arid
Rangelands, DAVID P HUBER 1 *, KATHERINE LOHSE 1 ,
MATT HERMINO 2 , KEITH REINHARDT 1 , KEVIN
FERIS 3 , and MARIE-ANNE de GRAAFF 3 ( 1 Department
of Biological Science, Idaho State University, Pocatello, ID,
83207; 2 USGS FRESC, Boise ID, 83725; 3 Department of
Biological Sciences, Boise State University, 1910 University
Dr. Boise, ID 83725; hubedavi@isu.edu).
Semi-arid rangelands are being impacted by climate
shifts and plant-community transformations. However, little
is known about how these ecosystems will respond to longterm
changes in climate or how shifts in vegetation will modulate
ecosystem processes. We used an established long-term
ecohydrologic experiment (Est. 1993) in southeastern Idaho
to evaluate ecosystem response to altered precipitation patterns
and changing plant communities (sagebrush vs. Crested
Wheatgrass (CWG)). We also assessed how response patterns
varied due to landscape heterogeneity (i.e. inter-plant
vs. under-plant patches and shallow vs. deep soils).
Preliminary results show increased precipitation altered
available N pools, with NH 4
+
increasing and NO 3
-
decreasing
relative to controls. Surprisingly, vegetation dynamics,
not precipitation patterns controlled overall N pools and
processes. Sagebrush systems have greater NO 3
-
pools than
CWG, which reflects the high rates of N mineralization and
nitrification under sagebrush vs. high rates of N immobilization
under CWG. These patterns may make sagebrush systems
more vulnerable to invasive plant species and nutrient
losses.
Inter-plant patches responded to precipitation treatments
more strongly than under-plant soils, showing increased
nutrient pools and process rates and reducing landscape
resource heterogeneity. Deep soils had greater carbon pools
and available N than shallow soils. Shallow soils showed differential
control on C and N pools for sagebrush vs. CWG
systems, exaggerating N transformation rates for sagebrush
but muting rates for CWG.
Overall, these results suggest that plant community
dynamics and landscape heterogeneity may play a larger role
in dictating ecosystem response to future changes in climate
than expected previously.
40 Identifying Holocene Relationships among Climate, Vegetation,
Fire and Fire-related Erosion using Alluvial Charcoal
and Fossilized Woodrat (Neotoma) Middens at City of
Rocks National Reserve, Idaho, KERRIE WEPPNER 1 *,
JEN PIERCE 1 , and JULIO BETANCOURT 2 ( 1 Department
of Geosciences, Boise State University, 1910 University
Dr. Boise, ID 83725; 2 USGS NRP, 1955 E 6th St., Tucson,
AZ 85719; kwepp@yahoo.com).
58