catherine lovelock variable effects of nutrient enrichment ... c... · enrichment on soil...
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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