Download Drought and Elevated CO2 Impacts On Soil Structure and

Drought and Elevated CO2 Impacts N-Cycling Microorganisms in a Soybean
Agroecosystem.
Engil Isadora Pujol Pereira1*, Kate Scow2, Andrew A.B. Leakey3 and Johan Six1
1
Plant Sciences Dept., Univ. of California, Davis, One Shields Ave, 95616 Davis, CA.
2Land, Air, and Water Resources Dept., , Univ. of California, Davis, One Shields Ave, 95616 Davis, CA.
3Univ. of Illinois, Urbana, IL.
Introduction
Carbon dioxide (CO2) is one of the most
important anthropogenic greenhouse gas and its
atmospheric concentration is projected to increase from
the current 384.78 ppm (September, 2009, Mauna Loa
Observatory) about 550 ppm by 2050 (IPCC, 2007).
In addition, drought-affected areas have
expanded and the severity of droughts is expected to
increase, which will have adverse impacts on agriculture,
water supply, energy production, and health (IPCC, 2007).
Since the nitrogen (N) cycle is driven by biological
processes, it is very likely to be affected by the climate
change.
Material and Methods (cont.)
Results (cont.)
•Gravimetric soil moisture;
•Total soil N;
•Mineral N (Nitrate and Ammonium);
•Nitrifiers and denitrifiers gene abundance (amoA and nosZ respectively).
Retractable
awning
Conclusion
Objectives
Fig.2: Automated system for the drought
treatment.
Fig.1: Layout of plots at the SoyFACE
facility.
Results
Hypotheses
a
16
14
12
10
8
6
4
4.0
-Soil samples (0-15cm depth) were collected at full pod
plant phenological stage and cooled to 4oC and transported
overnight on ice to UC Davis where the following
parameters were assessed:
Drought
- Since bacteria abundance usually show fast
responses to stresses, it is possible that changes on
the mineral N content would be observed in a later
period of the growing season. However, at this point,
only the nitrifiers and denitrifiers abundances were
responsive to such stress.
1.5
-Elevated CO2 tend to ameliorate the effect of
drought on the abundance of N-transformers and
soil moisture.
1
0.5
Ambient
CO2+Drought
(c) Nitrate
a
a
a
3.0
2.5
2.0
1.5
1.0
0.5
CO2
0.0
CO2+Drought
Acknowledgements
a
6
5
Drought
(d) Ammonium
7
NH4 (µg N g-1 soil)
NO3 (µg N g-1 soil)
CO2
a
3.5
a
a
a
Ambient
CO2
Drought
We would like to thank Charlotte Decock
and Chau Minh Khoi for collecting the soil samples.
We also would like to thank Haegeun Chung for her
support and guidance during the soil processing
and microbial analysis.
4
3
2
1
0
CO2
Drought
CO2+Drought
CO2+Drought
Fig.3: Soil Moisture, total N, nitrate and ammonium content.
(a) Nitrifiers
1.E+07
amoA (copies g-1 soil)
-Moderate drought is achieved by an automated system
which controls the extension and retraction of awnings,
blocking about 20% of the rainfall (Fig. 2);
a
-Although changes were observed under drought
conditions, the total soil N was not affected. It is
possible that no changes were observed due to the
large size of the total soil N pool.
0
Ambient
-This study was carried out during the 2008 growing season
randomized complete block design with factorial
treatments of elevated CO2 and drought (n = 4) (Fig.1).
2
0
Material and Methods
-Atmospheric levels of CO2 were increased to 550 ppm,
~180 ppm above ambient conditions.
a
a
2
Ambient
-This study took place in a soybean (Glycine max)
agroecosystem at the University of Illinois Soybean Free Air
Concentration Enrichment (SOYFACE) experiment.
(b) Total N
2.5
Total N (g Kg-1 soil)
-Since the stomatal conductance is reduced under elevated
CO2 concentration (long et al., 2004), which decreases
overall plant water demand, elevated CO2 is expected to
mitigate the stresses caused by drought.
(a) Soil moisture
18
Soil Moisture (%)
-Bacterial activities are reduced under water stress
conditions. Thus, it is expected drought to reduce the
abundance of the N-transformers population.
a
a
b
4.E+06
0.E+00
Ambient
CO2
Science
0543218.
This study was supported by the National
Foundation through Research Grant
4.E+06
a
8.E+06
(b) Denitrifiers
Drought CO2+Drought
nosZ (copies g-1 soil)
To expand the current understanding of the links
between microbial community functioning and the impacts
of elevated CO2 and drought on N cycling processes, this
study aims to investigate the changes in N transformers
population and mineral N pool size .
- The drought treatment decreased 25% of the
gravimetric soil moisture (Fig.1a);
-Total N and mineral nitrogen (NO3 and NH4) were
not affected by the treatments (Fig. 1);
-The amoA gene abundances was reduced by
drought (p=0.02) (Fig.2);
- Elevated CO2 reduced the stress caused by
drought on the nitrifier population abundance.
- Although not statistically significant (p=0.07),
drought reduced the denitrifier bacterial
population.
3.E+06
References
a
a
2.E+06
a
1.E+06
a
0.E+00
Fig.4: Nitrifiers and denitrifiers gene abundance
Ambient
CO2
Drought CO2+Drought
- Intergovernmental Panel on Climate Change
(IPCC).2007. Climate Change 2007: The Physical
Science Basis. Geneva, Switzerland. 18 pp.
- Long S.P., Ainsworth E.A., Rogers A. & Ort D.R.
(2004) Rising atmospheric carbon dioxide: plants
FACE the future. Annual Review of Plant Biology 55,
591–628.
* Corresponding author: [email protected]