Dynamics in the Microbial Transformation of Organic C in Soil

Dynamics in the Microbial Dynamics in the Microbial Transformation of Organic C in SoilTransformation of Organic C in Soil

Jinshui WuJinshui Wu

Institute of Subtropical Agriculture,

the Chinese Academy of Sciences

Outlines

Concepts of soil microbial biomass and soil organic C transformations

Methodology for quantifying soil microbial biomass

Case studies on dynamics in the microbial transformations of organic C in soil

Outlines




土壤生物Microbial

CommunityOC

(N/P/S)CO2/CH4/NxO…HM/Minerals

Biogeochemical functions of the soil microbial community


CommunityOC



Assumption: The soil microbial community mediate the transformation of all organic materials exiting in soil.


CommunityOC



Assumption: The soil microbial community mediate the transformation of all organic materials exiting in soil.

Key issue: In which community levels can the fluxes (rates) of C and nutrients be quantified (single cells, species, functional groups, or the whole) ?

Soil microbial community: Population

Bacteria (No g-1)

108 - 109

Fungalhyphae (m g-1)

10–1000

Bacterial species: > 104 g-1 soil (Data from Prof. P. C. Brookes)

The concept of soil microbial biomass(Jenkinson and Brookes)

The sum of the masses of all the soil micro-organisms (as a single pool) Providing a definitive entity for the bio-chemical assessments of the soil microbial community (e.g. the pool size), and the fluxes of C and nutrients through the biomass pool.

Compositions Arable Grasslandkg ha-1

Dry matter 1100-3300 1600-7500C 500-1400 750-3500N 80-230 125-500

Soil microbial biomass (per ha)

50-350 sheep

=

Soil microbial community: Biomass


CommunityOC/

N/P/SCO2/CH4/NxO…

HM/Minerals

Quantity of the microbial biomass

Quantifying the dynamics parameters (the flux rates of OC/N/P/S, and the ratios of the products)

Defining the functional groups involved


Outlines




nucleus

extraction

chemicalanalysis

Microbial C, N, P, S

cytoplasm

lipidcellmembrane

Soil

CHCl dissolves cell membranes3

● Lyses > 95% cells.

● Does not alter the solubility and mineralizing activity of organic materials.

The fumigation-extraction method

Powlson & Jenkinson (1976), SBB

TOC

Reliable chemistry procedures Rapid and high accuracy analysis Suitable for large numbers of samples


Automatic instrument analyses for the extracted biomass C, N, P, and S

(Wu et al., 1990, SBB; Shen et al, 1985, SBB; Wu et al., 1994, SBB; Wu et al., 2000, BFS)

Flow injection analyzer


SBB selected papers of the Citation

Classics

Vance, Brookes and Jenkinson (1987). An extraction method for measuring soil microbial biomass C. Soil Biology & Biochemistry 19, 697-702.

Wu, J., R.G. Joergensen, B. Pommerening, R. Chaussod and P.C. Brookes (1990). Measurement of soil microbial biomass by fumigation-extraction - an automated procedure. Soil Biology and Biochemistry 22, 1167-1169.

Organic C

(14C)Biomass 14C

Metabolic-14C (humic substances)

14CO2

Turnover

Turnover

Combined the automated analysis procedures with 14C labelling technique

14C-labeling

Outlines




Yt=Y0 e-kt

ln(Yt) =ln(Y0) - kt

Case 1: The turnover rates of soil microbial biomass C and P

Assumption: The turnover of 14C-labelled biomass C follows the first-order kinetics

k: The turnover rate

1/k: The turnover time (days)

Changes in soil microbial biomass C labelled with 14C (by the amendment with 14C-lablled glucose and incubation at 25 oC)

(Wu et al., 2012, JSFA)

（μ

g g-1

）

Incubation time （ d ）

Paddy soil Upland soil

Turnover rate of microbial biomass C in subtropical upland and paddy soils (China)

培养条件下 20 ~ 100 d 土壤

表观速率常数

（k， 10-3 d-1）

相关系数

（r）

周转时间

（d）

田间条件下

周转时间

（yr）

旱地 2.7 0.1 -0.92 370 13 2.2

稻田 8.1 0.9 -0.98 123 14 0.7

Site 1

Upland

Paddy

Turnover rate Turnover time

Field conditions

Wu et al., 2012, JSFA

At 25℃

The turnover time of biomass C affected by soil clay content and management

％ Clay Turnover time at 25℃ Field conditions

39 383 4.022 201 2.115 126 1.3

Management Turnover time

at 25℃ Field conditionsGrassland 212 2.2

FYM 193 2.0Nil 178 1.9

Fallow 175 1.8

(22% clay)

(NPK)

Organic C Biomass C

Metabolites (humic substances)

CO2

Turnover

Turnover

Case 2: Quantifying the ratio of CO2 from biomass C and non-biomass organic C

Soil+14C-glucose

Incubation (20 d at 25 )℃

Ad-Rw (5 cycles; incubated for 7 d at 25

)℃

DeterminationsCO2\Bc\DOC

(total\14C-labelled)

0

20

40

60

80

0 7 14 21 28 35

0

500

1000

1500

0 7 14 21 28 35

CO2 evolved from a soil following the amendment of 14C-lablled glucose and 5 drying-rewetting cycles

(Wu et al., 2005, SBB)

Total 14C-labelled

(μg

C g

-1 s

oil)

Incubation time (days)

Proportions of CO2 evolved in a soil following 5 drying-rewetting Cycles (Wu et al., 2005, SBB)

0

20

40

60

80

100

1 2 3 4 5

来自微生物量来自微生物代谢

%

Biomass C (heavily 14C labeled) Organic C (lightly 14C labeled)

Case 3: The mechanisms of “priming effect”

Priming effects: Responses of the mineralization of soil organic C following the inputs of fresh organic materials.

Responses of CO2 evolution and biomass C to glucose (14C-lablled) addition

Mechanism I: Enhanced turnover of the biomass C which results in the ‘replacement’ of native biomass C (unlablled) by the newly formed biomass C (labelled) (Wu et al., 1993, SBB)

PE

Responses of CO2 evolution and biomass C to ryegrass (14C-lablled) addition

Mechanism II: Increased mineralization of the native soil organic C (unlabelled) by the activities of the prolonged increases of the microbial biomass (Wu et al., 1993, SBB)

Case 4: Quantifying the assimilation of atmospheric CO2 by autotrophic micro-

organisms in soils

Soil incubated for 80 d in the growth chamber with 14C-la

beled CO2

Soils (x 8)

(14C-CO2)

Incubate in dark(foam cover, 4 reps)

Incubate in light(no cover, 4 reps)

12 hr light cycle, incubate for 80 days

14C-MBC14C-OC DNARubisCo

cbbL (1A,1C); cbbL (1D)qPCR, cloning and sequencing

Functional micro-organisms

mg

C k

g -1 so

il

% o

f t

otal

SO

C

Microbial assimilation of atmospheric CO2 (14C-labelled) in subtropical soils

(Yuan et al., 2012, AEM; Ge et al., 2012, SBB)

mg

C k

g -1 so

il

% o

f t

otal

SO

C

Annual C assimilation: 100-500 kg C!

Microbial assimilation of atmospheric CO2 (14C-labelled) in subtropical soils

(Yuan et al., 2012, AEM; Ge et al., 2012, SBB)

(nm

ol C

O2 g

-1 m

in -

1）

RubisCO activity in the soils incubated for 80 d(Yuan et al., 2012, AEM; Ge et al., 2012, SBB)

Light

Dark

nd nd

*

*

*

**

*

*

0.0

0.5

1.0

1.5

P1 P2 P3 P4 U1 U2 U3

(×10

8 cop

ies g

-1 )

0.0

0.5

1.0

1.5

2.0

2.5

P1 P2 P3 P4 U1 U2 U3

(×10

6 cop

ies g

-1 )

Bacterial cbbL genes blue-green cbbL genes

0.0

0.5

1.0

1.5

2.0

P1 P2 P3 P4 U1 U2 U3

(×10

6 cop

ies g

-1)

Non-green cbbL genes

Abundance of cbbL genes encoding bacteria, blue-green and non-green algae in the soils(Yuan et al., 2012, AEM)

Light Dark

** *

*

* * *

**

* *

* * *

*

**

*

*

* *nd nd

0.0

0.5

1.0

1.5

2.0

2.5

1 20

2

4

6

8

10

1 2

Thiobacillus denitrificans

Ralstonia eutropha

Bradyrhizobium japonicum Azospirillum lipoferum

Rhodobacter azotoformans Aminobacter sp.

Rhodopseudomonas palustris

U1-lightP1-dark

(×10

7 cop

ies g

-1）

P1-light U1-dark

Rhodopseudomonas palustris

Bradyrhizobium japonicum Thiobacillus denitrificans

Aminobacter sp.Mycobacterium sp.

Bacterial cbbL taxa abundance in soils P1 and U1 (Yuan et al., 2012, AEM)

0

1

2

3

4

1 2 3 4

(×10

6 cop

ies g

-1）

Algal cbbL taxa abundance in soils P1 and U1(Yuan et al., 2012, AEM)

Blue-green algae

Non-green algae

P1-light P1-dark U1-light U1-dark

Oscillatoria sp.

Anabaena sp.

Fischerella thermalis

Tribonema viride

Porphyridium aerugineum

Sellaphora auldreekie

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Dynamics in the Microbial Transformation of Organic C in Soil