Poster PDF - INI 2016
Microdialysis
An sensitive method for estimating plant-available N released during litter decomposition Scott Buckley*, Richard Brackin, Susanne Schmidt
The University of Queensland, School of Agriculture and Food Sciences, St Lucia, QLD, Australia. [email protected]
@musoscienti�ic
Introduction
Given the importance of nitrogen (N) availability in controlling N acquisition in plants and microbes, estimating soluble and exchangeable N forms in soil is vital to understanding these processes. However, we have relied on extraction methods that severely disrupt the soil environment, biasing estimates of soil N. Microdialysis offers an alternative method of sampling soil N with minimal disturbance, and here we compare it with traditional KCl and H2O extractions, in the context of litter decomposition, and expected microbial processes.
Methods
Sugarcane and soybean litter was added to soil microcosms at 10%, 70% and 200% of organic C content of soil. mg N per g Soil
Sugarcane 0 0.01 0.08 0.23
Treatment Control Lo (+10% C) Mid (+70% C)
Hi (+200% C)
2. Probe is positioned in situ. Soil solutes passively diffuse across probe membrane.
a
40 b
b
b
b
b
b
% Total LMW-N
H2O
60
% Total LMW-N
a
80
KCl
60
b
b
b
b
b
b
NH4+
a
Diffusive Flux
1.0 c
b
bc
c
c
c
Results
Co nt ro Ca ne l Lo Ca w ne Ca Med ne Hi gh So y Lo w So y M So ed y Hi gh
Treatment
Colourmetric Griess Method
Ultra Pressure Liquid Chromotography
Such patterns were not apparent in KCl or water extractions, both showing uniform N concentrations and N species across treatments, with the exception of Hi Soybean treatments.
80
Conclusions
60 40 20 0
0.0
3. Sieved soil is shaken in 1M KCl or H2O for 1 hour, then centrifuged, with supernatant collected for N analysis.
Diffusive �luxes (measured via microdialysis) provided a high-resolution snapshot of N availability at day 30, highlighting N cycling processes that were insuf�iciently resolved using salt or water extractions. Patterns of N immobilisation were observed in sugarcane treatments; signi�icant N mineralisation was found in soybean treatments. Each pattern increased with litter concentration, and was consistent with observed microbial activity and current concepts of N cycling.
Co nt ro Ca ne l Lo Ca w ne Ca Med ne Hi gh So y Lo w So y M So ed y Hi gh
1.5
NH4 Total AAs +
20
100
Analyses NO3
40
2.0
2. Soil is passed through a 2mm sieve.
-
60
0
1. Soil is destructively harvested.
Total AA
80
0
% Total LMW-N
(mol N g-1 DW)
3. Refridgerated fraction collector collects the dialysate, ready for N analysis.
20
100
Total LMW-N Flux (mol N cm-2 h-1)
Extractions
40
100
0.5
NO3-
14.8
After 30 Days
60
0
20
63.1
80
0
40
C:N
100
80
(mol N g-1 DW)
Total LMW-N Concentration
1.0
100
20
C:N
Microdialysis
1. Pump pushes perfusate (dH2O) through to the probe.
Total LMW-N Concentration
Soybean 0 0.05 0.35
Treatment
Figure 1. Proportion (%) of Total Low Molecular Weight Nitrogen (LMW-N) and total LMW-N concentration of water (H2O) and Potassium Chloride (KCl) soil extractions (top and middle rows); % of Total LMW-N Flux and Total LMW-N Flux of diffusive �lux (microdialysis) measurements (bottom row), of soils incubated for 30 days with sugarcane and soybean litter.
These �indings challenge the effectiveness of conventional soil extraction techniques to suf�iciently estimate plant-available N, and to resolve N cycling processes in soil environments. Conversely, microdialysis represents a sensitive method for estimating soil nitrogen, with potential for providing genuine insight into spatial and temporal factors affecting N cycling in situ within undisturbed soil.
An sensitive method for estimating plant-available N released during litter decomposition Scott Buckley*, Richard Brackin, Susanne Schmidt
The University of Queensland, School of Agriculture and Food Sciences, St Lucia, QLD, Australia. [email protected]
@musoscienti�ic
Introduction
Given the importance of nitrogen (N) availability in controlling N acquisition in plants and microbes, estimating soluble and exchangeable N forms in soil is vital to understanding these processes. However, we have relied on extraction methods that severely disrupt the soil environment, biasing estimates of soil N. Microdialysis offers an alternative method of sampling soil N with minimal disturbance, and here we compare it with traditional KCl and H2O extractions, in the context of litter decomposition, and expected microbial processes.
Methods
Sugarcane and soybean litter was added to soil microcosms at 10%, 70% and 200% of organic C content of soil. mg N per g Soil
Sugarcane 0 0.01 0.08 0.23
Treatment Control Lo (+10% C) Mid (+70% C)
Hi (+200% C)
2. Probe is positioned in situ. Soil solutes passively diffuse across probe membrane.
a
40 b
b
b
b
b
b
% Total LMW-N
H2O
60
% Total LMW-N
a
80
KCl
60
b
b
b
b
b
b
NH4+
a
Diffusive Flux
1.0 c
b
bc
c
c
c
Results
Co nt ro Ca ne l Lo Ca w ne Ca Med ne Hi gh So y Lo w So y M So ed y Hi gh
Treatment
Colourmetric Griess Method
Ultra Pressure Liquid Chromotography
Such patterns were not apparent in KCl or water extractions, both showing uniform N concentrations and N species across treatments, with the exception of Hi Soybean treatments.
80
Conclusions
60 40 20 0
0.0
3. Sieved soil is shaken in 1M KCl or H2O for 1 hour, then centrifuged, with supernatant collected for N analysis.
Diffusive �luxes (measured via microdialysis) provided a high-resolution snapshot of N availability at day 30, highlighting N cycling processes that were insuf�iciently resolved using salt or water extractions. Patterns of N immobilisation were observed in sugarcane treatments; signi�icant N mineralisation was found in soybean treatments. Each pattern increased with litter concentration, and was consistent with observed microbial activity and current concepts of N cycling.
Co nt ro Ca ne l Lo Ca w ne Ca Med ne Hi gh So y Lo w So y M So ed y Hi gh
1.5
NH4 Total AAs +
20
100
Analyses NO3
40
2.0
2. Soil is passed through a 2mm sieve.
-
60
0
1. Soil is destructively harvested.
Total AA
80
0
% Total LMW-N
(mol N g-1 DW)
3. Refridgerated fraction collector collects the dialysate, ready for N analysis.
20
100
Total LMW-N Flux (mol N cm-2 h-1)
Extractions
40
100
0.5
NO3-
14.8
After 30 Days
60
0
20
63.1
80
0
40
C:N
100
80
(mol N g-1 DW)
Total LMW-N Concentration
1.0
100
20
C:N
Microdialysis
1. Pump pushes perfusate (dH2O) through to the probe.
Total LMW-N Concentration
Soybean 0 0.05 0.35
Treatment
Figure 1. Proportion (%) of Total Low Molecular Weight Nitrogen (LMW-N) and total LMW-N concentration of water (H2O) and Potassium Chloride (KCl) soil extractions (top and middle rows); % of Total LMW-N Flux and Total LMW-N Flux of diffusive �lux (microdialysis) measurements (bottom row), of soils incubated for 30 days with sugarcane and soybean litter.
These �indings challenge the effectiveness of conventional soil extraction techniques to suf�iciently estimate plant-available N, and to resolve N cycling processes in soil environments. Conversely, microdialysis represents a sensitive method for estimating soil nitrogen, with potential for providing genuine insight into spatial and temporal factors affecting N cycling in situ within undisturbed soil.
