8/3/2019 Poster Statuskolloqu 2009klein

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Introduction

The detritusphere is one of the hot spots in soil

that show a high microbial activity due to an

enrichment of readily available substrates.

The use of 4-chloro-2-methylphenoxy-acetic

acid (MCPA) and phenanthrene (PHE) offers

the opportunity to follow the microbial use

and the transport of two compounds that

differ in sorptive properties, but show similar 

decay rates under laboratory conditions. In a

first microcosm experiment, we tested the

overall effect of maize litter on the degra-

dation of MCPA and PHE in soil.

Results

Holger Pagel1, Christian Poll2, Omar Saleh2, Rieke Trittin2, Marion Devers3, Fabrice Martin-Laurent3,

Joachim Ingwersen1, Ellen Kandeler 2 & Thilo Streck 1

SPP 1315 Biogeochemical Interfaces in Soil

Does maize litter stimulate the microbial degradation of

MCPA and Phenanthren in soil?

Conclusions

The addition of maize litter stimulates the degradation of MCPA,

but not of PHE.

Stimulation of MCPA degradation at high amendment of the

pesticide was accompanied by high abundance of bacteria

carrying the specific tfdA genes.

Fungi benefit more from the addition of maize litter than bacteria.

Most likely they substantially contribute to the microbial

degradation of MCPA via cometabolism.

In conclusion, MCPA degradation of the Luvisol is sensitive to

positive priming, whereas priming effects do not seem to beimportant for PHE degradation.

Fig. 2 Cumulative CO2 production during incubation,

mean of 3 replicates ± standard deviation

Fig. 3 Remaining MCPA/ PHE in soil and first order degradation kinetics:

C=C0e-kt; with C0 - initial conc. in soil, k - degradation rate,

t - incubation period

mean of 3 replicates ± standard deviation

Abb. 4 Concentration of selected PLFAs after 7, 21 or 42 days incubation,

mean of 3 replicates ± standard deviation

Fig. 5 Abundance of the functional gene tfdA in soil

in relation to the abundance of 16S rDNA in soil

Fig. 2 + 3

Addition of litter increased CO2

production. MCPA and PHE treat-

ments without litter addition did only slightly enhance CO2

produc-

tion after an incubation period of 25 days.

Litter stimulated MCPA degradation only at high amendment,

whereas litter did not modify the degradation of PHE.

Fig. 4

The addition of maize litter had a positive effect on microorganisms,

in particular on fungi.

MCPA reduced the content of bacterial PLFAs.

Fungal PLFA increased with MCPA addition, especially in combi-

nation with litter.

PHE reduced bacterial and fungal PLFAs up to 21 days.

Fig. 5 The relative abundance of MCPA degraders increased significantly

in the 50 mg kg-1 treatment.

1 Institute of Soil Science and Land Evaluation, Biogeophysics, University of Hohenheim2 Institute of Soil Science and Land Evaluation, Soil Biology, University of Hohenheim

3 Laboratory of Soil Microbiology and Geochemistry, INRA-University of Burgundy

Material & MethodsSoil

Luvisol from a research farm in Scheyern (Germany)

Plough horizon 0-30 cm, passed through 2 mm sieve and

homogenized

Experiment

0, 10, 50 mg kg-1 MCPA or PHE

0, 10 or 20 g kg-1 maize litter 

Incubation at 20°C in microcosms: 7, 21, 42 days

Methods

CO2-production in microcosms (CO

2-sorption in NaOH)

MCPA/ PHE-contents in soil (HPLC-UV and GC-MS)

Analysis of phospholipid fatty acids (PLFAs)

Abundance of tfdA functional genes (DNA extraktion, quantitative PCR, see Fig. 1)

Fig. 1 The tfdA gene encodes a a-keto-

glutarate(a-KG) dependent dioxy-

genase which catalyses the initial

step in the degradation of MCPA.

Tab. 1 Soil properties

Special thanks go to Sabine Rudolph for PLFA analyses and DNA

extractions as well as to Thomas Wendel and Renate Seelig from

the Center for Applied Geoscience (University of Tübingen) for

assistance with PHE GC/MS measurements.

Texture pH (CaCl2) C

orgC/ N

40% sand

45% silt

15% clay

5,3 1,4% 10,3

k=0,1047 - 0,1212 day-1

R2=0,99

k=0,0071 day-1; R2=0,79

k=0,0251 day-1; R2=0,99

k=0,0324 day-1; R2=0,97

k=0,0593 - 0,1293 day-1

R2=0,87 - 0,99