Do changes in carbon allocation account for the growth response to fertilization in tropical Eucalyptus plantations?

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Do changes in carbon allocation account for the growth response to fertilization in tropical Eucalyptus plantations?

Daniel Epron, Yann Nouvellon, Jean-Paul Laclau, Antoine Kinana, Jean-Claude Mazoumbou, Julio Raposo de Almeida, Raphael Romao, Laurent Saint- André, Philippe Deleporte, Jose Leonardo de Moraes

Gonçalves, Irae Guerrini, Jean Pierre Bouillet

AGU Fall meeting 13-17 December 2010

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Introduction

Eucalypts are among the most widely planted species in the tropics (20 millions ha)

Rapid expansion of eucalypt plantations (300 000 ha/year in Brasil) to fulfil wood demand

This expansion concerns mainly marginal lands

Cost of fertilizer is increasing

Potassium is limited in most tropical weathered soils

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Introduction

K fertilization is known to stimulate wood production in eucalypt plantations

Little is known about the mechanism

Stimulation of GPP ?

Change in C allocation ?

In nutrient-limited environment

The amount of carbon allocated belowground is higher =>

efficient resource acquisition

The leaf life span is longer =>

efficient resource conservation

Na can partly replace K=>

efficient resource substitution

GPP

Leaf prod.

Wood prod.

Leaf resp.

Wood resp.

Root prod. Root resp.

Symbiotic µ

µ respiration Exudation

The tested hypotheses were that

 Leaf life span decreases in response to K fertilisation

 Belowground C allocation decreases in response to K addition

 Na can be a substitute to K for Eucalyptus

Partitioning ANPP between wood and leaf production

Estimating TBCF from soil respiration and litterfall

Estimating and partitioning GPP

GPP

Leaf prod.

Wood prod.

Leaf resp.

Wood resp.

ANPP

Symbiotic µ

Objective

TBCF

GPP

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Seedlings of E. grandisplanted in 2004 on site afforested since more than 60 years

 Control (standard fertilisation except K)

 + K (4.5 kmol ha^-1of KCl fertilizer applied)

 + Na (NaCl was applied instead of KCl)

Tree census (height and dbh) every six months

Tree biomass on 8 trees per treatment each year up to year 6 (2010) => allometric relations

Leaf litter fall in litter trap

Experimental design

^Control

+ K

+ Na

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Above ground net primary production

0 5 10 15 20 25 30

0 12 24 36 48 60 72

Age (month)

H ( m )

Control + K + Na

For each age : Fert. ***

Bloc (Fert.) ns + K > + Na > Control

Height growth was stimulated by both Na and K fertilization at all ages

The effect of K was higher than the effect of Na

Control + 3 m

+ 6 m

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Leaf production was slightly stimulated by both K and Na fertilization

There was no difference in leaf litter fall

Higher standing leaf biomass in the + K treatment

Above ground net primary production

0.0 0.2 0.4 0.6 0.8 1.0

Leaf P (kg m-2 y-1 )

0.0 0.2 0.4 0.6 0.8

0 12 24 36 48 60 72

Age (month) Leaf L (kg m-2 y-1 )

Control + K + Na Fert. ***

Age ***

F x A ***

+ K, + Na > Control

Fert. ns Age ***

Fert. x Age ***

0 1 2 3 4

Cont. + K + Na

Cumulative leaf production (kg m-2 ) litter

total

Therefore, leaf biomass of fertilized trees was higher than in control

The effect of K was much higher than the effect of Na

Increase in leaf life span in response to K fertilization but not to Na fertilization

K increases leaf life span with a strong consequence for leaf biomass and leaf area index

Higher GPP

Above ground net primary production

0.0 0.2 0.4 0.6 0.8

Leaf B (kg m-2 )

0 100 200 300 400 500

0 12 24 36 48 60 72

Age (month)

LLS (days)

Control + K + Na Fert. ***

Age ***

F x A ***

+ K > + Na, Control Fert. ***

Age ***

F x A ***

+ K > + Na > Control

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Above ground net primary production

The increase in wood production in response to K and Na

fertilisation is both due to

an increase in ANPP

a change in allocation

increasing partitioning to wood growth instead of leaf

production

0%

20%

40%

60%

80%

100%

6 18 30 42 54 66

(% ANPP)

Wood Leaf

Control 72%

6 18 30 42 54 66 Age (month) 81%

+ K

6 18 30 42 54 66 75%

+ Na

Fert. ***

Age ***

F x A ***

+ K > + Na > Control 0.0

1.0 2.0 3.0 4.0 5.0

0 12 24 36 48 60 72

Age (month)

ANPP (kg m-2 y-1 ) ^Control

+ K + Na

Fert. ***

Age ***

F x A ***

+ K > + Na > Control

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Total belowground carbon flow

Coarse root biomass was measured at age 5 and 6

Litter amount on the forest floor was also measured at age 5 and 6

Soil CO₂efflux was measured every two weeks during one year between age 5 and 6

GPP

Leaf prod.

Wood prod.

Leaf resp.

Wood resp.

Symbiotic µ

TBCF

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Total belowground carbon flow

0 2 4 6 8

May Jul Sep Nov Jan Mar May Jul F

S

(µ mo l m

-2

s

-1

)

Control K+

Na+

Annual cumulative F_S: Control 1.24 ± 0.17^akg_Cm^-2 + K 1.45 ± 0.23^b

+ Na 1.39 ± 0.22^b

Fert. **

Bloc (Fert.) * + K , + Na > Control

Seasonal

fluctuations in soil CO₂efflux with greater values during the wet/warm season than during the dry/cold season

Annual soil respiration is higher in fertilized plots than in the control plots

no difference between K and Na fertilization

dry/cool wet/warm

Total belowground carbon flow

The amount of litter aboveground first decreased during 3 years and increased again thereafter

There was no difference among the different fertilization treatment

There was no change between year 5 and 6 0.0

0.5 1.0 1.5 2.0

0 12 24 36 48 60 72

Age (month) Aboveground litter (kg m-2 )

Control + K + Na

a ab b c c c

Fert. ns Age ***

F x A *

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0 1 2 3

control + K + Na control + K + Na

Root mass (kg m-2 ) Coarse

Medium 60 months

72 months

Total belowground carbon flow

The total root biomass is higher in + K plots and lower in control plots

The biomass of medium and coarse roots increased between age 5 and 6.

Fert. ***

Age ***

F x A ns

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Total belowground carbon flow

We checked

 Constant aboveground litter on the forest floor at this age

We assumed

 Constant fine root biomass and necromass at this age

 No change in SOM after more than 60 years of afforestation with eucalypts

 No exportation of carbon (CH₄, leaching or erosion)

 

E P

R TBCF

E P

P R

R

P R

TBCF

SOM beglitter

abglitter abglitter

soil root

SOM beglitter

beglitter soil

root

beglitter root

root

















































heterotrophic respiration

≈0

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Total belowground carbon flow

 

E P

R TBCF

E P

P R

R

P R

TBCF

SOM beglitter

soil root

SOM beglitter

beglitter soil

root

beglitter root

root

















































heterotrophic respiration

≈0

0.20±0.04^c 0.23±0.06^a

1.39±0.22^b 1.36±0.23^b

+ Na

0.26±0.09^b 0.23±0.01^a

1.45±0.23^b 1.48±0.25^b

+ K

0.12±0.07^a 0.23±0.02^a

1.24±0.17^a 1.13±0.18^a

Control

Δroot L

FS TBCF

(kg_Cm^-2y^-1)

A higher amount of carbon is allocated belowground in the fertilized plots

There was not significant difference between K and Na fertilization

Differences in TBCF are less than differences in ANPP

 we assumed similar and constant CUE (0.48) among treatment to estimate above ground respiration from ANPP Ryan et al. 1996 Tree Physiol.

Giardina et al. 2003 GCB

GPP = ANPP + Rabg +TBCF

GPP

Leaf prod.

Wood prod.

Leaf resp.

Wood resp.

ANPP

Symbiotic µ

GPP partitioning

TBCF

GPP Rabg

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Carbon allocation

Pleaf, 10%

Pwood, 28%

Rab, 41%

TBCF,

21% Pleaf, 4%

Pwood, 37%

Rab, 45%

TBCF,

14% Pleaf, 7%

Pwood, 31%

Rab, 42%

TBCF, 20%

Control + K + Na

Age 5 to 6

0 1 2 3 4 5

control K Na

C flow (kgC m-2 y-1)

Pleaf Pwood Rab TBCF GPP = 5.4 ± 0.5

10.3 ± 0.9

6.8 ± 0.6

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Conclusions

GPP was strongly enhanced by K fertilisation while Na has a much smaller effect

K fertilization:

 Higher GPP and lower C allocation belowground lead to an enhanced ANPP

 A higher leaf life span account for a lower allocation to leaf growth

 A higher ANPP and a lower in C allocation to leaf growth account for an enhanced wood production

 Is there an effect on stomatal conductance? What is the water cost of the increase in productivity?

Na fertilization

 Stimulation of GPP, ANPP and wood production

 But Na cannot fully substitute for K.

 This is especially the case for leaf life span.

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Do changes in carbon allocation account for the growth response to fertilization in tropical Eucalyptus plantations?

Daniel Epron, Yann Nouvellon, Jean-Paul Laclau, Antoine Kinana, Jean-Claude Mazoumbou, Julio Raposo de Almeida, Raphael Romao, Laurent Saint-André, Philippe Deleporte, Jose

Leonardo de Moraes Gonçalves, Irae Guerrini, Jean Pierre Bouillet

Thank you

Tree Physiology invited issue ‘Carbon Allocation of Trees and Forests’