Variable Effects of Nutrient Enrichment on Soil Respiration in

Mangrove Forests

Catherine Lovelock

The University of Queensland

Soils are responsible for large C stocks and fluxes

From: Ozcoasts

Coastal wetlands are important in the global C cycle

• C stocks are globally important

• Understanding soil respiration gives insight into other components of carbon budget

Mcleod et al. 2011

Mil

leniu

m E

co

syste

m A

sse

ssm

en

t

Meta analysis of terrestrial systems • N deposition decreased soil respiration

• Reduced allocation to roots

• Microbial community becomes carbon limited

Janssens et al. 2010

Hypothesis

• Soil respiration will decrease with fertilization

Nutrient availability To

tal b

iom

ass

Be

low

gro

un

d C

allo

cati

on

Broad geographic approach – natural gradients and variation

Field sites

IRL Twin Cays Bocas del Toro

Hinchinbrook Channel, QLD

Whangapuoua, NZ

Giralia, WA

Townsville, QLD

Port Douglas, QLD

Exmouth, WA

Methods • Fertilized (> 2 years)

• Growth (stem extension)

• Soil respiration

+N

Control

N N

1.0m

2.0m

Fertilizer N = urea P = triphos

Soil respiration with fertilization

• Scrub forests 8/14 significantly increased

• Fringe forests 1/7 increased

• Phosphorus 3 increased; Nitrogen 5 increased

So

il R

esp

ira

tio

n

mo

l C

O2 m

-2 s

-1

-1

0

1

2

3

4

5

6

Control

N fertilized

P fertilized

Fr

Belize Panama Florida WA Q Q New Zealand Q WA

Fr

Fr

Fr

Fr

Fr Fr

Q

*

*

Why would soil respiration increase?

• Enhancement in soil respiration correlates with above-ground growth (but weak, less sensitive)

Change in Stem Extension(Log %treatment/control)

-0.5 0.0 0.5 1.0 1.5 2.0

Ch

an

ge

in

So

il R

esp

ira

tio

n

(Lo

g %

tre

atm

en

t/co

ntr

ol)

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

N fertilized

P fertilized

X 1.1 controls

X 4.0 control

Changes in soil respiration correlate with specific leaf area

• Specific leaf area is correlated with specific root length • Change in structure of roots? (more, finer roots)

Change in Specific Leaf Area(Log %treatment/control)

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10

Ch

an

ge

in

So

il R

esp

ira

tio

n(L

og %

tre

atm

en

t/co

ntr

ol)

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

P fertilized

N fertilized

Conclusion 1.

• Reduced allocation belowground with fertilization

aboveground growth ≠ soil respiration

• Some evidence fertilization does alter roots

• Why no decrease in soil respiration with fertilization (as observed in terrestrial ecoystems)?

– Mangrove below ground production is nutrient limited in some sites (e.g. scrub forests – McKee et al. 2007)

• Work for the future: increases in nutrient availability gives rise to enhanced stored carbon?

Nutrient availability

Tota

l bio

mas

s B

elo

w g

rou

nd

C a

lloca

tio

n

Conclusion 2

So what about my methods?

– Good for covering a whole range of sites (portable*, flexible, rapid)

Portable*

mangrove

Flexible

Conclusion 2 cont.

So what about my methods?

– Good for covering a whole range of sites (portable*, flexible, rapid)

– Surface films

– Missing what happens in water

– Scaling – e.g. annual rates

Surface films

Tide

• Can’t measure when sites are under water • Rates of metabolism in air and water

correlate (Alongi et al. 2000, Alongi et al. 2001), but variable.

• Issues of scaling

Log sumerged O2 consumption

0.5 1.0 1.5 2.0 2.5 3.0

Lo

g C

CO

2 e

volu

tio

n

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Acknowledgements

• Collaborators and colleagues who indulged me in my soil respiration habit: Candy Feller, Roger Ruess, Bettina Engelbrecht, Ann Chamberlain, Ruth Reef, Don Cahoon, Marilyn Ball, Rachel Tenni, Helen Penrose, Brian Sorrell, Andrew Swales and others

• Smithsonian Marine Science Network and staff at field stations (SMS Fort Pierce, STRI Bocas del Toro, Carrie Bow Cay)

• Giralia Pastoral Station, WA • Australian Institute of Marine Science • National Institute of Water and Atmospheric Sciences (NIWA) New Zealand • Australian Research Council

Abiotic conditions are important

Soil Porewater Salinity (PSU)

20 40 60 80

Soil

respir

ation (

mo

l m

-2 s

-1)

-1

0

1

2

3

4

5

• Soil respiration declines with increasing salinity • No interaction with fertilization

N fertilized

P fertilized