carbon turnover in the rhizosphere and why plants release ...kuzyakov/root-c-soil.pdf · intro...

1

Carbon turnover in the rhizosphere and

why plants release carbon in soil

Yakov [email protected]

Soil Scienceof Temperate Ecosystems

Georg-August-UniversityGöttingen

3http://kfrserver.natur.cuni.cz/globe/others.htm

Units: Petagrams (Pg) = 10 15 gC– Pools: Pg– Fluxes: Pg/year

Intro Rhizo-C Time Lag Hotspots Priming Elevated CO 2Global C cycle

4

Element contents in soils (mg/kg), the Earth crust and sediments (Sparks 2003)

2,20026030-1,600700S6701,00035-5,300800P47025200-5,0002,000N33502-25030Cu52802-75050Ni21.50.1-401.2Mo95751-90090Zn

77095020-10,0001,000Mn5,70023,000150-25,0005,000Na20,00021,00080-37,00014,000K14,00023,000400-9,0005,000Mg66,00041,000700-500,00015,000Ca29,4004807,000-500,00020,000C (total)41,00041,0002,000-550,00040,000Fe72,00082,00010,000-300,00071,000Al

245,000277,000250,000-410,000330,000Si486,000474,000-490,000O

Sediments(mean)

Earth crust(mean)

SoilsMedian Range

Element

Intro Rhizo-C Time Lag Hotspots Priming Elevated CO 2

5

Main differences between soils and soil parent material

• High C and N content � 2 biophilic elements• High content of chemical energy available for microorganisms• High activity of microorganisms• Nutrients are available for plants• … … …

Fertility!the ability of soil to maintain plant growth:– Water

– Nutrients

– Oxygen


6

Very high C and N content!

Haplic Phaeozem

Fertility!

Importance of roots

7

Sources of organic C in soils

Plants ( ∑ > 99%)

• Dead / Litter:– Above ground

• Leaves• Shoots

– Below ground • Roots

• Living:– Rhizodeposition

(organic C released by living roots)

Other sources ( ∑ << 1%)• Algae • CaCO3• Organic C of some rocks (shist)

Contribution of root-C to soil-C is ~ 2.5 timeshigher than of shoot-C(Rasse et al. 2005 Plant and Soil)

Intro Rhizo-C Time Lag Hotspots Priming Elevated C O2

9

Functions of root C in the rhizosphere• Modification of soil chemistry

– pH and redox– Organic acids composition– Chelating substances for nutrient solubilizaiton – Detoxication of Al3+ and Fe3+ (at low pH)

• Symbiosis with soil microbes– N2 fixing bacteria:

• Symbiotic: Rhizobia, Frankia, ... • Associated: Klebsiella, ...• Free-living: Azospirillum, ...

– Mycorrhiza fungi– Rhizosphere microorganisms– Plant growth promoting bacteria

• Defense against pathogens (allelopathics)• Improving of soil structure• Lubricator to decrease soil impendance• .......

Substrate and energy for symbiosis


10

Trade: C for N

Plants provide C as energy for

• Rhizobia and Frankia to fix atmospheric N2

• Associative bacteria to fix atmospheric N2

• Mycorrhizal fungi to acquire N and P from soil

• Rhizospheric bacteria to accelerate SOM mineralization for Nmin release

• ... ... ... ... ... ...

C costs of N aquisition


11

Legumes:N2 fixation and

shoot dry matter

Herridge et al., Plant & Soil 2008

Trade: C for N

15 kg N / Mg DM

25 kg N / Mg DM

50 g DM for 1 g N

Vance & Heichel 1991

1 g N ~ 6 g C1 Mol N ~ 7 Mol C

1 g N ~ 2.5-4 g CWarembourg & Roumet 1989

Symbiotic N 2 fixation

20 g C for 1 g N


12

Trade: C for N






• ... ... ... ... ... ...


13

Mycorrhiza of young pine

Smith & Read 14

Trade: C for N






• ... ... ... ... ... ...

C and N cyclesin the rhizosphere


16

Rhizosphere:Opposite directions of C and N fluxes

C release

Nuptake

C and N fluxes in opposite

directions

Yaalon 2002

Limitations for microorganisms: • in root-free soil: available C• in rhizosphere: available N

TradeC for N

Continuous input = continuous decomposition

17

Labeling: Approach to study processes under steady state

Pulse labeling• Pulse addition of a tracer (13C, 14C, 15N, …)• Chasing of the tracer in various pools

13CO214CO2

13C14C

15N

15N

Parameters• Time lag between assimilation and any flux• C and N flow rates through any pools• Residence time in pools • Dynamics of C, N, … in individual pools:

– turnover times– flux rates � modelling

• known C input � C budget, high resolution & sensitivity

C/N


19

Bangor, Wales, UK 2005C input and turnover

of organics in the rhizosphere

21

Fichtelgebirge 2009

Foto: S Heinrich

Drought effects on C fluxes in the rhizosphere

microorganisms of spruce

23

Budget of assimilated Cfor some grasses and crops

in % of total assimilated C

Below ground:

• Roots 10 – 30%

• Root respiration 3 – 6%

• Soil organic matter 1 – 3%

• Microorganisms 1 – 5%

• Rhizodeposition 5 – 15%

Above ground:

• Shoots 25 – 55%

• Shoot respiration 20 – 35%

Kuzyakov & Domanski 2000 JPNSS

Available substrate for microorganisms!


24

Janssens et al. 2002 Forest Ecol & Management

Budget of assimilated Cfor trees

in % of total assimilated C

Time scale of the links

between above and below?


25

Photosynthesis is the main source of available substrates in soil

C

C/N

CO2

Knohl et al., 200525032.55Fagus sylatica

Ekblad et al., 200468226Picea abies

Steinmann et al., 20041003410Mixed temperate

25353-4Mixed broadleaf decid.

Mortazavi et al., 20052517.23-4Pinus taeda

152,573;10Juniperus occidentalis

147,5215Pinus ponderosa

30235;9Pseudotsuga menziesii

Bowling et al., 20021585Pseudotsuga menziesii

Ekblad & Hogberg, 2001150231-4Mixed coniferous

Keel et al., 200610032,521Mixed diverse

Andrews et al., 1999157Pinus taeda

Olsson et al., 20054014Picea abies

B.Singh et al., 200350205Pinus sylvestris

Johnsen et al. 2007203Loblolly pine

Carbone et al., 20073444Picea mariana

Mikan et al., 200021Populus tremuloides

Horwath et al., 1994232Populus eumericana

Liu et al., 200615150Liquidambar styraciflua

Ekblad et al., 200468221Picea abies

5021.65Picea abies

Moyano et al., 2008125.5244Fagus sylatica

Baldocchi et al., 20069.40.21;14savanna

ReferenceAverage age, yrHeight, mTime-lag dSpecies

Time lag vs. height and age of plants


26

R2 = 0.07

R2 = 0.15

R2 = 0.48

R2 = 0.13

0

3

6

9

12

15

0 50 100 150 200 250

Age, yr

TSA of CO2

Labeling

Interruption13C natural

0

10

20

30

40

0 20 40 60 80 100

DAS, d

Grasses

Herbs

Time lag between photosynthesis and soil CO 2 for

trees and grasses depending on age

~ 4…5 days

Tim

e la

g (d

ays)

Kuzyakov & Gavrichkova 2010 Global Change Biology

~ 10…15 hours

Trees

Tim

e la

g (h

ours

)

Very short link between above-

and belowground

Localizationof C input


27

Ryegrass Autoradio-gramm 6 hours after

14C assimilation

5-15% of total assimilated C

10-25% of net-assimilated C=

Hotspots of- C availability- microbial activity


28

Maize

Localization of root exudates

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Life time of hotspots?

Maize

Localization of root exudates

30

Life time of Hotspots

Changes of hotspots on Lolium roots after 14C labeling: 6 h, 2 d, 11 d.

6 hours 2 days 11 days

Time after 14C labeling

Relative 14C

activity

Pausch & Kuzyakov 2010 JPNSS

What are these Hotspots?


31

Microbial Hotspots in soil:• Rhizosphere• Detritusphere • Drilosphere• … …

Soi

l vol

ume

Hotspots in soil

Hotspots are small soil volumes with much higher process rates and intensive interactions compared to the „average“ soil conditions

Rich in:carbon, energy, and nutrients compared to the surrounding soil

�� prefered habitat formicroorganisms

Process rate (h-1)

MeanHotspots“Dead”

soil 10…1001Process rate

110…100Relat. volume

Hotspots„Dead“ soil


32

Organism abundances in the rhizosphere

12601 × 105126 × 106Denitrifiers

1254 × 10650 × 107Ammonifiers

210 × 10224 × 102Protozoa

121 × 10512 × 105Fungi

245 × 107120 × 107Bacteria

CFU × g-1

R/S Soil (S)Rhizosphere (R)Group

Rouatt et al. 1960, Kennedy 1996

Carex riparia - root capMagnification 630

Fluorescens staininggreen: living bacteria

red: dead bacteria

Photo: E. Jüschke

Properties of hotspots

• Activity of microorganisms

• Rates of – SOM decomposition

– Nutrient mobilization

Rhi

zosp

here

effe

ct


33

0

5

10

15

20

0 100 200 300 400 500 600µg C glucose

µg C

O2-

C*g

-1*

h-1

0

20

40

60

80

0 3 6 9 12 15 18h

µgC

O2-

C*g

-1*h

-1

rhizosphere soilroot free soil

Microorganisms in the rhizosphere

µ (h-1) = 0.38±0.01

µ = 0.3±0.02

Respiration and growth rates of microorganisms

Mineralization potential

Blagodatskaya et al. 2008 Applied Soil Ecology

� specific growth rates increase for > 25%,

� shift to r strategists

Higher input + higher mineralization

� faster turnover� priming effects� nutrient mobilization

Kmax > 2.5 times


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Priming effects: changes of SOM decompositionby addition of available substrates

-30

0

30

60

90

120

150

0 30 60 90 120

Lolium

Wheat

Maize

Lettuce

plant age (days)

SO

M-d

eriv

ed C

O2

efflu

x (k

g C

ha

-1 d

-1)

reta

rdat

ion

ac

cele

ratio

n Additionalnutrient

mobilization

Kuzyakov 2002 JPNSS

Priming effects in rooted soil

Prim

ing

effe

ct (

kg C

ha

-1d

-1)

Faster turnover of soil Cin rooted soil


Release of Nby microbes (for plants)

35


SOM

Chain of processes:

long-term

winners

1. Release of C substrate

3. Microbial activation ( Priming )

4. N mineralization from SOM

5. Competition for N min :- MO �� short-term winners, but ...- Plants �� long-term winners

C

MO MO

MON

P

NN

short-term

winners

Plants

SOM

Micro-organisms

Nmin

N

Live cycle3-5 days

3-5 months

2. Triggering ?

Importance of rhizosphere

hotspots and priming effects

in future?

slow

slowfast

37

Control Elevated CO 2, (+150 ppm CO 2) Ambient CO2

Fotos: S. Marhan

δδδδ13CCO2 = -8.0‰ δδδδ13CCO2 = -8.0‰ δδδδ13CCO2 = -22.0‰

MiniFACE Hohenheim

Prof. A. Fangmeier

FACE in Hohenheim

Soil:Soil: GleyicGleyic CambisolCambisol9% sand, 69% silt, 22% clay; pH 6.8

+150 ppm CO 2

canola, wheat


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200

250

300

350

400

450

500

550

bulk > 2mm 0.25-2mm <0.25mm

Amb Elev

Act

ivity

(nm

ol g

-1 h

-1)

• No changes of pools :– SOM fractions

– microbial biomass

• Changes of microbial activity:– Growth rates– Enzyme activities: β-Glucosidase,

Chitinase , Sulphatase, Phosphotase

C and N turnoverunder elevated CO 2

Dorodnikov et al. 2007 Soil Biology Biochemistry 2009 Global Change Biology

• Elevated CO 2 leads to:1. Higher C input by plants in the soil2. Activation of microbial biomass3. Faster C and N turnover4. Higher nutrient mobilization

� Acceleration of element cycles

Chitinase

Microbail growth rates

Aggregate classes


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C and N turnover under elevated CO 23 FACE experiments

Hohenheim+150 ppm CO2

canola, wheat

Braunschweig +150 ppm CO2

sugar beet, wheat

Biosphere 2+400/+800 ppm CO2

poplar

FACECO2

plant


40

R2 = 0.76

0.15

0.25

0.35

0.45

300 600 900 1200

Atmospheric CO 2 (ppm)

Spe

cific

gro

wth

rat

e (h

-1)

Braunschweig, Beta vulgarisBraunschweig, Triticum aestivumHohenheim, Brassica napusBiosphere-2, Populus deltoides

1.0

1.2

1.4

1.6

Brassica napus

540 ppm

Triticum aestivum550 ppm

Beta vulgaris 550 ppm

Populus deltoides800 ppm

Populus deltoides

1200 ppm

Rat

io: µ

ele

vate

d C

O 2

/ µ

am

bien

t CO

2

Rhizosphere soil

Root free soil

Microbial growth ratesdepending on

CO2 concentration

Elevated CO 2

Blagodatskaya et al. 2010 Global Change Biology

Rhizosphere hotspots and priming will be more

important in future because of acceleration

of biogeochemical cycles


41De Graaff et al. 2006 Global Change Biology Kuzyakov 2011 Nature Climate Change

Priming

Relative increase of

fluxes & pools

22%

in soil:• no changes of pools• strong increase of fluxes


42

C sequestration in soil after 5 (♦), 10 (■), and 15 (▲) months. Means for 6 plants expressed as % of ambient CO2 with no added nutrients∆ 15-month harvest, added nutrients

C sequestration in soil

� Soil microbial respiration after 15 months. Means for 6 species expressed as % of the ambient CO2 control with no added nutrients. ▲ no added nutrients; ∆ added nutrients

Microbial respiration

�� C sequestration in soil decreases


43

Photosynthesis:• is the main source of available substrates in soil• links above ground and C turnover in soil• affects belowground processes in short time

• trees: days grasses: hours• initiation of hotspots

N

P

Priming:• mobilization of extra nutrients for plants

N

N

Conclusions

Rhizodeposition is the most important process linking:• above and belowground processes• plants and soils• roots and microorganisms• nutrients and C

Hotspots:• especially in the rhizosphere life time: few days• increase of microbial activity ��

• acceleration of SOM turnover �� priming effectC

C/N

Release of C in soil by living roots:• ecological importance for symbiosis with microbes

Thanks!


carbon turnover in the rhizosphere and why plants release ...kuzyakov/root-c-soil.pdf · intro...

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