Ashes to Ashes, Dust to Dust: Decomposition in the Desert...Ashes to Ashes, Dust to Dust:...
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Ashes to Ashes, Dust to Dust: Decomposition in the Desert
Authors Aguillon, Stepfanie
Rights Copyright © is held by the author.
Download date 09/09/2021 21:40:03
Link to Item http://hdl.handle.net/10150/197969
Ashes to Ashes, Dust to Dust: Decomposition in the Desert Stepfanie Aguillon
School of Natural Resources and the Environment, University of Arizona, Tucson, AZ
NSF Research Experience for Undergraduates Scholar
Introduction
Objectives
Study Site
Methods
Conclusions
Results
• Decomposition, the process of breaking down organic material into its physical and chemical
constituents, is a key determinant of soil fertility and an important component in the cycling
of carbon and nutrients through an ecosystem.
• Climatic variables predict decomposition rates in mesic systems reasonably well, but
underestimate the actual amount of decomposition that occurs in drylands. Photodegradation
has been proposed as an important, but overlooked, factor in this discrepancy.
• The importance of solar ultraviolet (UV) radiation in litter degradation is uncertain, some
research shows strong UV effects and others show no UV effects.
• Most decomposition studies are conducted over relatively long timescales (months to years)
and may therefore miss the finer details of mass losses during the first few weeks.
• Quantify the influence of radiant energy exposure (full sun vs. shade) and UV radiation on the
decomposition of Prosopis velutina leaf litter.
• Characterize the rates and dynamics of litter mass loss during the initial stages (first 4 weeks)
of decomposition under field conditions.
• The study was conducted on the Santa Rita
Experimental Range (SRER), a 21,513 ha shrub
savanna site in SE Arizona (~80 km south of
Tucson, AZ).
• Mean annual precipitation ranges from 275 to
400 mm (depending on elevation) and is equally
delivered as summer monsoons and winter rains.
• Litterbags were deployed in the mesquite-
grassland zone at 1,148 m elevation.
Litterbags
• 10 × 10 cm; deployed on 13 July 2011
• Constructed with 20 × 20 mesh (~0.9 mm openings) fiberglass window screen back and a
plastic front; filled with ~1.3 g of dried P. velutina leaflets
• Edges stapled; plastic front perforated (twenty-four 1.6 mm diameter holes) to allow for the
exchange of air and moisture
Sample Manipulation
• UV Environment –
• Aclar – control, UV transparent plastic (= UV present = UV+)
• Mylar – UV-B absorbing plastic (= UV absent = UV–)
• Level of Radiant Energy Exposure –
• Intercanopy Zone – bare ground between shrubs receiving full sun
• Subcanopy Zone – shaded area beneath a P. velutina canopy
• 25 litterbags in each of the experimental treatment combinations: UV+/intercanopy,
UV+/subcanopy, UV–/intercanopy, and UV–/subcanopy
• 5 litterbags from each combination collected at weeks 0, 1, 2, 3, and 4
• Soil-surface temperatures (in litterbags and on bare ground), levels of photosynthetically active
radiation, precipitation, and soil moisture were monitored during the 4-week study
Intercanopy Zone Placement Subcanopy Zone Placement
• Near-surface soil moisture
was statistically comparable
in intercanopy and
subcanopy placements
(Fig. 2; p = 0.7817)
• Litter decomposition rates in
intercanopy zones were
significantly higher than
those in subcanopy zones
(Fig. 2; p = 0.0303)
• Manipulation of UV
radiation had no significant
effect on decomposition
rates (Fig. 2; p = 0.8012)
• Temperatures in UV+ and
UV– litterbags were
statistically comparable
(p = 0.6544)
• Soil temperature (Fig. 1)
and photosynthetically
active radiation (PAR) was
greater in the intercanopy
zone (mean noon PAR =
1,816 μmol m-2 s-1) than in
the subcanopy zone
(PAR = 597 μmol m-2 s-1;
p < 0.0001)
Figure 2 – Mean ( ±1 S.E; n=5) ash-corrected mass loss
(scaled so time 0 values start at 100% and represent
initial litter mass). Numerical values associated with
each harvest date indicate mean (± S.E.) soil moisture
in intercanopy and subcanopy placements. Bars
represent the daily precipitation.
60
65
70
75
80
85
90
95
Perc
ent
ash
-co
rrec
ted
dry
mas
s re
mai
nin
g
100
0
5
10
15
20
25
30
35
40
Pre
cip
itat
ion
(m
m)
2.4±0.004
2.8±0.003
2.8±0.001
2.6±0.002 4.1±0.004
4.6±0.007
1.1±0.0009
0.8±0.0003
7/13/2011 7/17/2011 7/22/2011 7/27/2011 8/1/2011 8/6/2011 8/11/2011
23
25
27
29
31
33
35
37
Tem
per
atu
re (°C
)
7/13/2011 7/20/2011 7/27/2011 8/3/2011 8/10/2011
Figure 1 – Average daily temperature (monitored hourly)
on bare soil in intercanopy and subcanopy zones.
• Traditional decomposition studies quantify decomposition rates over months to years.
However, rapid and extensive mass losses occurred during the first four weeks of this field
trial. Future decomposition studies should thus include short- as well as long-term dynamics
of litter mass loss.
• Rates of litter mass loss were neither gradual nor linear, but rather were erratic and in
response to pulses of rainfall input.
• Levels of radiant energy interacted with precipitation to influence rates of decomposition via
temperature effects. Contrary to expectations, levels of UV radiation had no effect on short-
term mass loss.
Katharine Predick assisted with project logistics, data analysis, and litterbag collection; Eva Levi assisted with
project logistics and helped deploy and collect litterbags; Dean Keller assisted with the construction, deployment,
and collection of litterbags; Steven Archer provided guidance on experimental design, transportation to the field
site, and access to laboratory facilities and sampling equipment in the Savanna/Woodland Ecology Laboratory.
Acknowledgements