Download Management History, Soil Porosity, and Litter Quality Interact to

2/18/2016
Background
i) Cropping management
Controls soil OM gain vs. loss mainly through: • Amount and quality of litter
• Soil disturbance
• Fertilization
Management History, Soil Porosity, and Litter Quality Interact to
Regulate Organic Matter Stabilization and Greenhouse Gas Emission
Ehsan Toosi:
Jing Yu:
ii) Litter quality (i.e. crop residue)
Affects decomposition, particularly at early stages
Michigan State University
Hubei University, China
Andrey Guber:
Michigan State University
Timothy Doane:
Mark Rivers:
ii) How about Pore characteristics?
University of California, Davis
An important, but overlooked aspect in soil organic matter research
The University of Chicago
Terence Marsh:
• Pore size distribution
Michigan State University
Alexandra Kravchenko:
• Pores connectivity
Michigan State University
• Total porosity (%)
• Pore shapes
500 µm
Importance of pore characteristics is soil OM processes
Pore characteristics specifically regulate decomposition of fresh OM (vs. native soil OM)
(Juarez et al., 2013; Negassa et al., 2015)
• Providing micro-habitats for microbes against predators
• Spatial accessibility of microbes to substrate (OM)
Decomposition
• Transport of gases and solutes
• Oxidation-reduction status
Regulatory effect of pores characteristics
on the soil matrix-pores interacting zone
• Activity of fine roots and fungi
Regulatory effect of pore characteristics
?
Decomposition of fresh OM
GHGs efflux
Pore characteristics regulate the rate at which biotic and abiotic processes occur in the “hotspots”
Priming effect
Accelerated decomposition of native soil C following supply of fresh C
Decomposition of soil native OM
Materials & Methods
The broad research question:
How interactions of contrasting pore characteristics, crop residue quality, land management history, and soil moisture
status regulate efflux of GHGs and C stability?
Soil preparation
Site and sampling
1-2 mm soil fraction was separated and used as
i) Coarse fraction, and
ii) To generate the Fine fraction
• Kellogg Biological Station (Long Term Ecological Research Site)
• Long term management (since 1989)
• 11 land management systems
Coarse (1-2 mm)
SOM loss vs. gain
GHGs emission
Conventional
Cover Crop
?
?
Management
Fertilization
Cover Crop
Cover Crop-N
Conventional
NPK fertilizer
Vegetation
Wheat
N
Decomposition of
plant residue
Clover
Corn
Rye
Fine (0.05-0.1 mm)
Belowground
biodiversity
Soybean
Soil OM
Wheat
Crop residue
quality
Pore
characteristics
Soil moisture
status
Cropping
management
Corn
Soybean
Soil: fine-loamy, mixed, mesic Typic Hapludalf
1
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Materials & Methods
Materials & Methods
Plant materials:
•
13C-labeled corn and
Components of the experiment
soybean
Analyses
Incubation experiment:
• 110 days
• 4 replicates
- Residue quality: Soybean (C/N: 7.4) > Corn (C/N: 13)
- Common crop residues across the Midwest
Independ variable
• Leaf disks were used as a source of plant residue
Level
Porosity
2
Substrate quality
2
Management history
2
Soil moisture status
2
i) Headspace gas analyses
• 110 days
• 11 sampling events
• 13C-CO2 and GHGs (CO2, CH4, N2O)
• 420 samples
Treatment
i) Large (1-2 mm) soil fraction
ii) Small (0.05-0.1 mm) soil fractions
Syringe tube
i) Corn
ii) Microbial community structure
• Sampling events: day 7, 14, 24
• 16S-18SrRNA analysis
ii) Soybean
i) Cover cropping
ii) Conventional cropping
Leaf disk
Soil
(1 g)
i) Field Capacity
ii) Image analysis X-ray computed micro-tomography
• Sampling events: day 7, 14, 24
• 3.2 µm resolution
Teflon support
ii) Capillary Break Point
Argonne National Lab, IL
6.5 mm
Large (1-2 mm) soil fraction
Pore characteristics of the large and small soil fractions
Connectivity
of air-filled
(large) pores
mm
cm3 cm-3
μm
%
1.0–2.0
0.562
104
99
0.05–0.1
0.566
10
<1
960 µm
Start day
size 1-2 mm
2.E-03
size 0.05-0.1 mm
2.E-03
Water
Soil
Air
1.E-03
5.E-04
0.E+00
Leaf loss at day 24 (% of original)
Pore medial axes voxels as a
fraction of total image
voxels
Small (0.05-0.1 mm) soil fraction
Abundance of pore sizes
3.E-03
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
10
100
**
1
900
800
Primed C (Day 24)
Large pores
Small pores
*
**
700
600
500
400
300
200
140
120
100
100
2
Large pores
Small pores
*
60
40
20
0
0
Corn
**
80
Soy
-20
Corn
Soy
Corn
-40
**: P≤0.01
Findings
Findings
Decomposition: Cumulative CO2 efflux during the incubation (110 d)
600
300
0
Soy
*: P≤0.05
Corn
1200
*
Capillary break point
1500
*
900
600
300
0
1200
*
*
900
600
300
0
Soy
Corn
Soy
Large pores
Small pores
*
6
5.5
5
Corn
Corn
Soy
6.5
Effect of soil moisture
6.5
Cover crop
Conventional
*
6
5.5
Log cumulative N2O (ug-N/Kg soil)
900
1500
6.5
Log cumulative N2O (ug-N/Kg soil)
*
Cumulative CO2 (ug C/g)
*
Field capacity
Effect of management history
Effect of pore characteristics
Effect of soil moisture
Cover crop
Conventional
Log cumulative N2O (ug-N /kg soil)
Effect of management history
Large pores
Small pores
1500
Cumulative N2O efflux during the incubation (110 d)
Cumulative CO2 (ug C/g)
Effect of pore characteristics
Cumulative CO2 (ug C/g)
Small pores
1000
Equivalent pore size, mm
1200
Day 7
Decomposed C (Day 24)
Large pores
Soy
1
Start day
Day 7
Loss of leaf (Day 24)
Negassa et al., 2015
3.E-03
Soy leaf
Corn leaf
Primed C (ug-C/g)
Total
Average pore
porosity
diameter
Image analysis – Enabled to visualize and quantify loss leaf
Cumulative CO2 (ug C/g soil)
Fraction
size
Findings
Water
Soil
Air
Field capacity
Capillary break point
*
6
5.5
5
5
Corn
Soy
Corn
Soy
*: P≤0.05
* (P≤0.1)
2
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Research highlights:
Acknowledgement:
1- Combined application of labeled plant materials and X-ray µ tomography allowed us to quantify the
rate of substrate and soil OM decomposition, under contrasting soil pore characteristics.
Under the experimental conditions:
2- In soils with dominance of large pores the rate of leaf loss was greater, primarily due to better
aeration. However, the loss of soil native C (primed C) was lower due to limited movement of
substrate (decomposing leaf) to the ambient soil.
3- Contrary to CO2, emission of N2O tended to be greater from soils with abundance of the large pores.
Questions:
3