Changes in aromaticity and carbon distribution of soil organic matter due to pedogenesis

The Science of the Total Environment, 81/82 (1989) 179-186 Elsevier Science Publishers B.V., AmsterdRm - - Printed in The Netherlands

CHANGES

IN

MATTER

W.

AROMATICITY

AND

CARBON

DISTRIBUTION

179

OF

SOIL

ORGANIC

DUE TO P E D O G E N E S I S

ZECH,

L.

Institute Bayreuth,

I. K O G E L - K N A B N E R

HAUMAIER,

of P.O.

Soil Science and Soil Geography, University Box 101251, D 8580 B a y r e u t h (F.R. Germany)

of

SUMMARY C h a n g e s in a r o m a t i c i t y and c a r b o n species d i s t r i b u t i o n of eight soil p r o f i l e s were s t u d i e d u s i n g CPMAS 13C NMR spectroscopy. In soils of cooler c l i m a t e s and with C/N ratios of u s u a l l y more than 20, p r o p o r t i o n s of alkyl c a r b o n i n c r e a s e and those of a r o m a t i c c a r b o n d e c r e a s e or r e m a i n c o n s t a n t with soil depth. In soils of w a r m e r c l i m a t e s and w i t h C/N ratios u s u a l l y less than 20, alkyl carbon decreases and a r o m a t i c c a r b o n i n c r e a s e s with soil depth. Concomitantly, signals a r o u n d 130 ppm appear in the N M R spectra, indicating the formation of stable, C-substituted, probably condensed aromatic substances. The s t a t i s t i c a l i n t e r p r e t a t i o n of the data shows that 73~ of the v a r i a t i o n of the a r o m a t i c i t y and 75~ of the v a r i a t i o n of the a l i p h a t i c c a r b o n c o n t e n t s of the deepest soil horizons can be expl~ned by the ratio of precipitation/temperature.

INTRODUCTION Carbon substances carbon

NMR

studies

indicate

species

However,

(alkyl,

little

variation.

The

is

exerts of soil

soil

depth I~C

in

matter

of

aromatic, the

an

influence

and

factors

of this p a p e r was

organic

on

soil

humic

(ref.

carboxyl

for

to investigate,

aromaticity

1)

and

carbon).

responsible

this

whether

and

carbon

matter.

aromaticity

were

studied

and c a r b o n

in

eight

distribution

uncultivated

spectroscopy.

Table

1

profiles

investigated

(soil

nomenclature

Of

surface

layer,

horizon,

and

aromaticity

NMR

litter,

were

organic

AND M E T H O D S

Changes soil

about

objective

distribution

CPMAS

soil

variation

O-alkyl,

known

pedogenesis

MATERIALS

of

a great

= fermentation

Bhs

Ah

= spodic

determined

layer,

= humified

0~01 for

surface

By = cambic M

CaCI2

mineral

soil

some

=

1/2.5

soil

0048-9697/89/$03.50

©

1989 Elsevier Science Publishers B.V.

profiles

ref.

a

Ae

the L

=

organic =

albic

The pH values

glass

horizons

using of

2;

humified

horizon,

horizon).

with

(soil/solution

increasing

properties see

= completely

mineral

horizon,

in

Oh

shows

with

and

electrode i/i0

for

180

organic

horizons).

combustion Kjeldahl

soil

group

(mean

presence

A

20

(profiles

thick and

than

surface

7°C)

profile

annual

with

are

CPMAS

'3C

spectrometer

NMR

the

=

=

1.5

For (ref.

the

ppm),

cool

high

below

climates by

C/N

mineral

temperatures

20.

According

from

Its organic from

the

ratios

B because

range

i0

24,

to

organic to

surface

16 to

21.

layers

and

mean

range

spectral

from

of a r o m a t i c

the s t a t i s t i c a l

MAS

Bruker

CXP

at

300

least

a

width

=

spinning

time

=

10.0

into

four

31.25

rate s,

=

kHz,

3.5-4.5

acquisition

angle.

divided

order

to

(50-110

(160-200

a

allowing

of the spectra:

recycle

were

in

with

conditions,

pulse

O-alkyl

carbon

shift

groups.

comprises

group

recorded

MHz,

ms,

spectra

as the r a t i o

B.

3,000-6,500,

NMR

chemical

or

range

two

annual

ratios

group

75.47

=

integrated

(0-50

6-8)

soil

C/N

were

The

carboxyl

and

interpretation

time

IsC

near

of

with

(mean

to

following

90 d e g r e e

and

layers

C/N ratios

ms,

and

dry

by

characterized

(profiles

ratios

time = 40-150

ranges

B

into

profiles 6°C),

c l im a t e s

to soil

transients

contact

than

6 belongs

the

frequency

of

group

spectra

under

observation

alkyl

by

nitrogen

is 25°C.

semi-quantitative

KHz,

determined

and

subdivided

surface

lacking

thick,

temperature

number

were

8

comprises

less

C/N

7 belongs

3 cm

roughly

warmer

profile

layers

are only

be

1-5)

Soil

from

definition

Also

contents

Carmhomat

organic

50.

profiles

higher

can

temperatures

of

between

this

carbon

W6sthoff

profiles

annual

soil

a

procedure.

The Soil

Organic

with

determine ppm),

ppm).

0 to ii0 ppm,

calculations

we

percentages

aromatic

Aliphatic

C/nonaromatic

chemical-shift

the

(110-160

carbon

ppm),

comprises

and a r o m a t i c i t y

of

the

is d e f i n e d

C x 100. used

the

SPSSx

2.2

program

3).

RESULTS The carbon

integration distribution

belonging with

soil

increasing

constant Table

to

or

i).

characterized

the soil

group

A

decrease

spectra A

reveals

and

B

alkyl

aromatic

carbon

from L to O h / A

profiles of alkyl

belonging carbon

differences

(Table

increasing

Their

slightly

contrast, by

NMR

groups show

soil depth.

decrease In

of of

Profiles

carbon

contents

contents

(profiles to

soil

contents

in

i).

and

remain

2, 4 and group

B

increase

5, are of

181

o 40

O~ O

O~ 0O k o

cD 0 0 LO ~-I 0 o

0 J LO O~1 C~I

E 0 co

8)

n u)

Z

LO

t.) Ce)

0

C~

CD

EE

0

{.O

f-4 4a 4-4

U

O CD

Z

c~l ,q" r-. oO ~'-

0~1 ~ " O

~-.t O~

OD c ~ kO p-.

oO CD (.O LO

E

O3

¢,-~

.

.

.

.

.

.

.

.

.

.

.

.

.

.

o)

tO

0.1

"O

O N

0

0

{.~

(

;

I

CDO

I

I

~) r-

I

I

I

I

____lq.4 r" ~

I

~0

I

I

I

_.lq.4

r"

O

I

I

.

"

0

4~33

O

~ ' ~ O

0

-

•

~33

.

~4

-

t-

.ri "

~.~C~

I

•

OCD~

I

I

..-I k,-I ~- ~-

O

o

.,

I

182

.M

0

m i

N

~

O

O

~

l l l l

I

I

I

I

I

I

i

l

l

l

l

I

I

I

I

0 N

0

C3L~O

~' = ~ ,,.., .,.,

~ooog

~

.H

~

~

~'"': ~o

183 aromatic alkyl

carbon contents with soil depth.

carbon

decreases

from

the

In both soil groups,

surface

layer

downwards,

Oand

carboxyl carbon contents increase. Since the surface horizons of these uncultivated soils are less humified

than

of

carbon

the

processes

the subsurface

layers,

distribution

during

the

give

an

above-mentioned

overall

humification in undisturbed

changes

picture

soils

of

under

the

aerobic

conditions. They comprise with increasing soil depth: - Predominant

mineralization

of

O-alkyl

carbon

(mainly

polysaccharides) - Relative

accumulation

group A in

the

deepest

relatively root

of

alkyl

carbon

in

the

profiles

of

soil

(mean alkyl carbon content in the litter layers is 18%, horizons

stable

litter

or

phospholipids,

due

fats,

waxes,

alkyl

decrease

the mineral

to

compounds

microbial

degradation in

29%)

alkyl

residues

ref.

compounds

selective

4,

may

preservation

originating

layers of

plant

(cutin,

5).

be

from

Also,

produced

suberin,

during (ref.

the profiles

of and

lignin

6). Their

from

soil group

B is probably the result of more rapid mineralization. - In the profiles of soil group A aromatic constant

or

decrease

slightly

from

cleavage

of

moderately

degraded

by

oxidation

of

side

analyses induces lignin

the

for

profiles

only

slight

(Fig.

constancy

la).

the mineralization in equilibrium

rate

with

of aromatic carbon 1 and

inputs

the

in

2 could be influenced

1

aryl

and by

chemical

features

may

even

and

aromatic

of

by

NMR

lignin

the spodic

Lignin is

linkages

this degradation

typical

root

the

inputs

Oh/Ah.

But

(profiles

of

contents

8).

the

of

to

confirmed

7,

in

aromaticity

L

aryl-ether

as

(refs.

changes

High

of

chains

1-4

carbon contents remain

cause

3)

if

substances

compounds. horizons

of

is

Increase

of

profiles

by leaching of phenolic substances

during podzolization. -

Relative accumulation of aromatic carbon with soil depth in the profiles decrease

of

soil

compounds.

B

of

may

probably

chemical shift of the

where nearly

130 ppm

NMR no

spectra

alteration

of in

due

Fig.

Ib).

profile the

to and

the alkyl

the accumulation of stable,

condensed (e.g.

be

polysaccharides

The NMR spectra indicate

C-substituted, la shows

group

(mineralization)

aromatics

with

For comparison, 2

aromatic

~soil range

a Fig.

group

A},

between

ii0

184

Entic Haplorthod,

Fichtelgebirge

Bavaria CPMAS13CNMR spectra of the soil organic matter

Umbrept,

72 7°I~ /I

104

Spain

CPMAS13C NMR spectra of the soil organicmatter

j /I

d"d

65 33

L 174150.,,.116~ /J 3 ~

Ah2

i

., t.k/llt

I

200

t

150

ppm

I

100

I

50

~ ppm I I I I I 0 300 250 200 150 100 50 i

I

0

Fig. i. CPMAS 13C NMR s p e c t r a of an Entic H a p l o r t h o d (profile 2, soil g r o u p A) on the left side (= Fig. la) and of a P a c h i c Haplumbrept (profile 8, soil g r o u p B) on the right side (= Fig. Ib).

and

160 ppm

can

accelerated

be

and a c c u m u l a t i o n occurs

in

mineral

be

In

of

of

carboxyl

7,

soil

to

these

resulting

in

aromatic

horizons

results

the

an

formation

compounds

only

contact

with

due

to

carbon

order

analyses

to

evaluate and

were

aliphatic

contents

the

result

soil

depth

the

carbon

carried

carbon

give

75%

factors

out.

contents

is s u p p o s e d

oxidation

and

73%

of

carbon

(R = 0.87, Aromaticity

of lignin

It

was

(P/T)

found

the

variation

content

= 0.044

Other

The

of

of the d e e p e s t

that

variation

statistical

aromaticity

correlate

only.

explanation.

for the

multivariate

with

factors

following

aliphatic

the

and ratio

like pH and

equations

carbon

ex-

contents

soil horizons:

x P/T + 53.27

R 2 = 0.75)

= -0.049

(R = 0.85;

responsible

significantly

no further

and of the a r o m a t i c i t y

Aliphatic

the

distribution

of p r e c i p i t a t i o n / t e m p e r a t u r e C/N ratio

with

of

8).

aromaticity

plain

According

lignin

C-substituted

mineral

predominantly

(refs.

of

the

of

substances.

- Increase to

observed.

degradation

x P/T + 40.96

R 2 = 0.73)

ACKNOWLEDGEMENT The

authors

Geological

Survey)

Gil

Sotres

the

soil

and

8,

analysed

are

and

to

(University

samples

and

respectively. profiles

The D e u t s c h e

indebted

i,

Dr.

Professor

of

Santiago

results J.

to

C.

of

W.

Dr. de

Grottenthaler Guitian

chemical

Forster,

and

Compostela)

F.

analyses Ziegler,

(Bavarian

Professor for of

and

Dr.

providing profiles R.

6

Bochter

2, 5 and 7.

Forschungsgemeinschaft

(SFB 137)

supported

the

study.

REFERENCES 1

2 3

P.G. Hatcher, M. Schnitzer, L.W. Dennis and G.E. Maciel, A r o m a t i c i t y of h u m i c s u b s t a n c e s in soils, Soil Sci. Soc. Am. J., 45 (1981) 1089-1094. Soil Taxonomy, A g r i c u l t u r e H a n d b o o k 436, US Soil S u r v e y Staff, W a s h i n g t o n , 1975. W. Schub6 and H.M. Uehlinger, SPSSx, Handbuch der Programmversion 2.2, Gustav Fischer Verlag, Stuttgart, New York, 1986.

186

4

5

6

7

8

M. Nip, E.W. Tegelaar, J.W. de Leeuw, P.A. Schenck and P.J. Holloway, A new non-saponifiable highly aliphatic and resistant biopolymer in plant cuticles, Naturwissenschaften, 73 (1986) 579-585. I. K6gel-Knabner and P.G. Hatcher, Characterization of alkyl carbon in forest soils by 13C NMR spectroscopy and dipolar dephasing, Sci. Total Environ., 81/82 (1989) 169-177. K. Haider, Changes in substrate composition during incubation of plant residues in soil, V. Jensen, A. Kjoller and C.H. Sorensen (Eds.), Microbial communities in soil, Elsevier, London, 1986, pp 133-147. I. K6gel, F. Ziegler and W. Zech, Lignin signature of subalpine Rendzinas (Tangel- and Moderrendzina) in the Bavarian Alps, Z. Pflanzenernaehr. Bodenk., 151 (1988) 15-20. F. Ziegler, I. K6gel and W. Zech, Alteration of gymnosperm and angiosperm lignin during decomposition in forest humus layers, Z. Pflanzenernaehr. Bodenk., 149 (1986) 323-331.