Transcript PowerPoint-Präsentation

Effects of water-soluble organic substrates on the stabilization
and mineralization of lignin and peat
Ute Hamer and Bernd Marschner
Soil Science and Soil Ecology, Geographical Institute, Ruhr-University Bochum, D-44780 Bochum, Germany
http://homepage.ruhr-uni-bochum.de/Ute.Hamer
Introduction
Materials and Methods
Dissolved organic matter continuously enters the soil solution through leaching, root
Computer
exsudation, desorption or decay processes. It is available for microorganisms and may
DOM-typical substrates (14C-labeled):
have a high potential in triggering priming effects. Lignin and peat are organic substances
0000,00
 glucose, fructose, glycine, alanine,
oxalic acid, acetic acid, catechol
that can be relatively resistant to biodegradation.
mS
Conductometer
 addition: 80 µg C g-1 sand or 400 µg
C g-1 sand and approx. 3000 Bq
priming effects (schematic)
Multiplexer
1
96
Respicond
positive
CO2 [mg kg-1]
14CO
Objective
20 °C
2
Identification of DOM-typical sub-
negative
strates
14CO
12CO
12CO
2
that
accelerate
(positive
Model system:
priming) or retard (negative priming)
2
 50 g sand + lignin or peat (3 % Corg)
the decomposition of the model
2
12CO
control without substrate A
substrate
 pH: 6.5
substances.
2
Incubation for 26 days in the Respicond
(Nordgren 1988)
 nutrient solution: NPK
 measurement of total CO2-evolution hourly
 inoculum: batch extract from
O-horizon of a forest soil
substrate B
 measurement of 14CO2-evolution at days 4, 6,
12, 19 and 26
 water content: 60 % of WHC
Dynamics of priming
peat-CO2-C [% of control d-1]
Lignin and peat mineralization
50
lignin
CO2-C [mg]
40
30
20
peat
10
0
0
10
20
100
Priming effects for peat
200
glycine
alanine
glucose
50
80 µg substrate-C g-1
400 µg substrate-C g-1
150
fructose
100
0
50
-50
30
0
10
20
0
30
glucose
time [d]
time [d]
fructose
glycine
alanine
oxalic acid
acetic acid catechol
Fig. 1: Cumulative CO2-C evolution from the unamended
peat and lignin system (initial carbon content of 1500 mg C).
Fig. 2: Dynamics of priming effect intensity after high
substrate addition (400 µg C g-1) to the peat system in
percent of control.
Fig. 3 a: Peat mineralization after substrate addition compared to control after 26
days of incubation.
 after 26 days of incubation lignin mineralization
 strongest priming occurred during the first 4
 only positive priming effects or no priming occurred
(2.8 %) was nearly fourfold higher than peat
to 10 days of incubation
 80 µg oxalic acid-C caused the strongest positive priming effect
mineralization (0.7 %)
 the low addition of glycine and oxalic acid caused stronger effects than
 lignin mineralization started after a lag-phase of
the high addition
5 days
Priming effects for lignin
lignin-CO2-C [% of control]
60
80 µg substrate-C g-1
400 µg substrate-C g-1
Possible Mechanisms of positive priming
Summary
 cometabolism
Most substrates stimulated the degradation of
 degradation of microbial biomass
the model substances (positive priming effects).
Possible Mechanisms of negative priming
40
20
oxalic acid
catechol
addition.
 change of nutrient source from lignin to easier
occurred in the peat system with the oxalic acid
fructose
glycine
alanine
acetic acid
The
strongest
positive
priming
addition of 80 μg C g-1 where 1.8 % of the peat
degradable substrates
 rearrangement in the lignin structure to more stable
glucose
lignin system with oxalic acid and catechol
 inhibition of microbial activity or enzymes
0
-20
Negative priming effects only were found in the
units in the presence of substrate molecules
were mineralized after 26 days, compared to
0.7 % in the control. Most substrates caused
the strongest effects during the first 4 to 10 days
of incubation. The extent of priming depended
Fig. 3 b: Lignin mineralization after substrate addition compared to control after 26
days of incubation.
Future research
 Can
 oxalic acid and catechol caused negative priming effects
 400 µg alanine-C caused the strongest positive priming effect
 compared to high substrate addition the low addition is in most cases
more effective
priming
effects
on substrate type, substrate concentration, and
be
triggered
through
repeated substrate addition ?
This project is financial supported by the DFG. It is part of the programm “Soils as source and sink of
CO2 – mechanisms and regulation of organic matter stabilization in soils”.
model
substance
(Hamer
and
Marschner 2002).
 Are priming effects influenced by soil organic
matter quality ?
 Can priming effects be triggered with “real” DOMsolutions ?
Acknowledgment
organic
 Are priming effects associated with changes in
microbial biomass and population ?
Literature
Hamer, U., and B. Marschner (2002): Priming effects of sugars,
amino acids, organic acids and catechol on the mineralization of
lignin and peat. J. Plant Nutr. Soil Sci. 165, 261-268.
Nordgren, A. (1988): Apparatus for the continuous, long-term
monitoring of soil respiration rate in large numbers of samples. Soil
Biol. Biochem. 20, 955-957.