IRCEB Project:
Interannual climate variability and ecosystem processes
Global climate is predicted to include increased
variability in temperature and precipitation, i.e. more periods of
drought and extra precipitation, more heat waves and unexpected frosts.
This experiment was designed to monitor ecosystems processes during an
experimentally produced anomalously warm, wet or dry year and to see if
the unusual climate year had effects that carried over into the
following year.
The experimental infrastructure was installed in 2002
with data gathering beginning in the summer of 2002. Warming and extra
precipitation treatments were added for one year, from Feb. 20, 2003 to
Feb. 20, 2004. Data gathering ended in early spring of 2005.
Experimental Design
The experiment utilized a completely randomized block
design with 2 levels of warming (ambient and +4 oC) and 2
levels of precipitation (ambient and doubled). Twenty 3 x 2 m plots were
placed 1.5 m apart in two rows 3 m apart. Every other plot had two 165
cm by 15 cm radiant infrared heaters suspended above it at a height of
1.4 m (Kalglo electronics Inc., Bethlehem, Pennsylvania, USA). Previous
experimentation determined that, at this height, two heaters, each with
a radiation output of 100 watt/m2 would warm the soil surface
approximately 4oC (Wan et al. 2002). Rigorous testing has
shown that the infrared radiation from the heater does not generate any
visible light affecting photosynthesis (Kimball 2005). The remaining 10
plots each had two “dummy” heaters, the same size and shape as the
infrared heaters, constructed of metal flashing, suspended over the
plots at the same height and position as in the warmed plots.
Five of the warmed plots and five of the unwarmed
plots had attached “water catchments,” an angled sheet of corrugated
plastic the same size as the plots. During a rainfall, these catchments
directed precipitation onto the plots via three 12.5 mm diameter PVC
pipes that distributed the water evenly over the plots. All plots were
fitted with the PVC pipes whether or not they were attached to water
catchments. With this design, extra precipitation was only supplied to
the doubled precipitation treatment plots during natural rain.
Heaters, dummy heaters, water catchments, and PCV
pipes were in place and functional for one year, from February 20, 2003
to February 20, 2004 (the treatment year). Soil temperature in the
middle of each plot was monitored hourly with automated thermocouples
(Campbell Science Equipment, Logan, Utah, USA). Soil water content
(volumetric) was logged at the same frequency using segmented TDR probes
(time domain reflectometry, ESI Equipment, Victoria, British Columbia,
Canada). Temperature was measured at 15 cm above the ground and at
depths of 7.5, 22.5, 45, 75, and 105 cm. Soil water content was measured
over five depth intervals, 0-15 cm, 15-30 cm, 30-60 cm, 60-90 cm, and
90-120 cm. For most of the study period, 11 of or 12 the TDR probes were
functioning properly.
Plots were assigned to treatments as follows:
Control = plots # 2, 6, 10, 14, 18
Double precip = plots # 4, 8, 11, 16, 20
Warmed = plots # 3, 7, 12, 15, 19
Warmed & Double Precip = plots # 1, 5, 9, 13, 17
In addition to temperature and soil moisture,
above-ground biomass and community structure were measured three times a
year. Soil respiration and soil nutrient availability were measured once
a month, and more often at critical periods. Detailed phenology data on
twelve species was taken in 2003 and 2004. Root ingrowth cores were
installed in 2002 and extracted in 2003 and again in 2004. Root growth
was also monitored with a minirhizatron camera.
Total annual precipitation at the site during
the observation period was 854, 622, and 965 mm, for the years 2002,
2003 and 2004 respectively (Oklahoma Climatological Survey).
2003 being a drought year with an
especially dry fall. Detailed Oklahoma climate data from the Washington
mesonet site (~100 yds away from the experiment) are available from the
Oklahoma Climatological Survey (http://climate.ok.gov/)
through their Oklahoma Mesonet Program (http://www.mesonet.org/).
Complete air and soil temperature data from the
experiment is given here. This is raw thermocouple data, default numbers
and "bad" data have not been removed. Soil moisture and biomass data are
to follow soon.
Contact for Oklahoma data: Rebecca Sherry,
rsherry@ou.edu
A parallel experiment was carried out on intact
monoliths of prairie in more control conditions at the Desert Research
Institute in Reno, NV (DRI, URL: http://www.dri.edu). The twelve
monoliths were extracted from a site immediately adjacent to the
experiment described above.
Contact at DRI: Jay Arnone,
Jay.Arnone@dri.edu
Data:
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TECO
model
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The
Terrestrial ECOsystem (TECO) model evolves from its precursor model
TCS [Luo and Reynolds, 1999]. It is a process-based ecosystem model
and designed to examine critical processes in regulating interactive
responses of plants and ecosystems to elevated CO2, warming, altered
precipitation. TECO has four major components: canopy
photosynthesis, soil water dynamic , plant growth (allocation and
phenology) , soil carbon transfers.
The canopy
photosynthesis and soil water dynamic sub-models run at the hourly
time step. The plant growth and soil carbon sub-models run at daily
time step. The detailed description of the TECO model is in the
appendix. Here is a brief description. The canopy photosynthesis was
simulated by a multi-layer process-based model, which mainly evolves
from the model developed by Wang and Leuning [1998]. It simulates
radiation transmission in the canopy based on Beer’s law. Foliage is
divided into sunlit and shaded leaves. Leaf photosynthesis is
estimated based on the Farquhar photosynthesis model [Farquhar et
al., 1980] and a stomatal conductance model proposed by Ball et al.
[1987]. |
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Schematic presentation of TECO model.
A. Canopy model; B. Soil water dynamics model; C. Plant growth
model; D. Carbon transfer model. Rectangles represent the carbon
pools. Soil is stratified into three layers. Ra:
autotrophic respiration. Rh: heterotrophic
respiration, NSC: non-structure carbohydrate. |
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The soil water dynamic sub-model stratifies soil into ten layers. The
thickness of the first layer is 10 cm and 20 cm for the other 9 layers.
Soil water content of these layers is determined by mass balance between
water influx and efflux. The water influx is precipitation for the
surface layer and percolation for deeper layers. The water efflux
includes evaporation, transpiration, and runoff. Evaporation is mainly
controlled by the moisture of the first soil layer and evaporative
demand of atmosphere. Transpiration is regulated by stomatal
conductance, soil moisture, and root distribution.
The plant growth sub-model simulates carbon allocation and phenology
following ALPHAPHA model [Luo et al., 1995; Denison and Loomis, 1989]
and CTEM [Arora and Boer, 2005], respectively. Allocation of assimilated
carbon among the leaves, stems, and roots depends on their growth rates,
and varies with phenology. Phenology is represented by annual variation
of leaf area index (LAI). Leaf onset, the start of a growing season, is
determined by growing degree days (GDDs). Leaf senescence is induced by
low temperature and low soil moisture. When LAI is below a certain level
(LAI<0.1), the end of growing season comes.
The carbon transfer sub-model considers the movement of carbon from
plant to soil through litterfall and the decomposition of litter and
soil organic carbon [Luo and Reynolds, 1999; Barrett, 2002]. In this
sub-model, a soil profile is divided into three layers with carbon
movement from upper to lower layers. Carbon inputs to the soil from root
growth and dead root residues are partitioned into these three layers.
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Downloads |
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Please send a email to
Ensheng Weng <wengensheng@yahoo.com>
if you downloaded the model or have any questions. |
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Manual
TECO model (It contains source code and test run data)
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Please cite the following
references if you use TECO model in your studies:
Weng, E. and Luo, Y., 2008.
Soil hydrological properties regulate grassland ecosystem responses
to multifactor global change: a modeling analysis. Journal of Geophysical Research – Biogeosciences,
doi:10.1029/2007JG000539. (in press) . |
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References:
Weng, Ensheng,
Luo, Yiqi, 2008. Soil hydrological properties regulate grassland
ecosystem responses to multifactor global change: a modeling analysis.
“Journal of Geophysical Research – Biogeosciences”,
doi:10.1029/2007JG000539. (in press)
PDF
Zhou, X., E. Weng, Y. Luo, 2008. Modeling Patterns of nonlinearity
in ecosystem responses to temperature, CO2, and precipitation changes.
Ecological Applications, 18, 453~466.
PDF
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