Ecosystem flip-flops in response to anthropogenic N...
Transcript of Ecosystem flip-flops in response to anthropogenic N...
Ecosystem flip-flops in response to anthropogenic N deposition: The
importance of long-term experiments George L Vourlitis, Biological Sciences
Department, California State University San Marcos
2003
2017
• Chaparral can receive up to 35 kgN ha-1 y-1 and coastal sage scrub (CSS) can receive up to 20 kgN ha-1 y-1; however, values can vary with elevation and degree of exposure.
• 90% is dry deposition.
• N accumulates in the summer and fall and becomes available as a large pulse following the first rainfall event. Fenn et al. (2010)
Atmospheric N deposition
• Chaparral and CSS productivity are thought to be N limited. N enrichment has the potential to alter chaparral and CSS C and N storage.
Research objectives and approach
We used a long-term field experiment to assess how dry-season N inputs altered chaparral and CSS C and N storage and cycling. We hypothesized that N addition would significantly
(1) increase rates of C and N accumulation.
(2) increase the cover and dominance of exotic annuals
Research objectives and approach
We used a long-term field experiment to assess how dry-season N inputs altered chaparral and CSS C and N storage and cycling. We hypothesized that N addition would significantly
(1) increase rates of C and N accumulation.
(2) increase the cover and dominance of exotic annuals
• N-fertilizer (50 kgN/ha) is added in the fall of each year since September 2003.
• Samples were collected seasonally (March, June, September, and December).
• Soil (0-10 cm), surface litter pool, litter production, root biomass (0-10 cm), plant tissue, aboveground biomass and plant cover, leaching (1 m).
• C and N content of tissue, litter, soil, roots, extractable N, pH.
Experimental design
10m
10m
• N-fertilizer (50 kgN/ha) is added in the fall of each year since September 2003.
• Samples were collected seasonally (March, June, September, and December).
• Soil (0-10 cm), surface litter pool, litter production, root biomass (0-10 cm), plant tissue, aboveground biomass and plant cover, leaching (1 m).
• C and N content of tissue, litter, soil, roots, extractable N, pH.
Experimental design
10m
10m
• N-fertilizer (50 kgN/ha) is added in the fall of each year since September 2003.
• Samples were collected seasonally (March, June, September, and December).
• Soil (0-10 cm), surface litter pool, litter production, root biomass (0-10 cm), plant tissue, aboveground biomass and plant cover, leaching (1 m).
• C and N content of tissue, litter, soil, roots, extractable N, pH.
Experimental design
10m
10m
• N-fertilizer (50 kgN/ha) is added in the fall of each year since September 2003.
• Samples were collected seasonally (March, June, September, and December).
• Soil (0-10 cm), surface litter pool, litter production, root biomass (0-10 cm), plant tissue, aboveground biomass and plant cover, leaching (1 m).
• C and N content of tissue, litter, soil, roots, extractable N, pH.
Experimental design
10m
10m
Chaparral site description
•Evergreen chaparral: Adenostoma fasciculatum, Ceanothus greggii. •Ambient atmospheric N deposition 2-3 kgN ha-1 y-1. •53 cm of precipitation (rain and snow) annually. •Burned in July 2003
May 2002
March 2004
Fenn et al. (2010) JEMA 91: 2404-2423
Sky Oaks Field Station
• Added N rapidly acidified surface (0-10 cm) soil
• Soil extractable soil N increased significantly after 1 year of addition.
• N addition significantly increased NO3
- leaching during the first 3 years of N addition (Vourlitis et al. 2009).
Chaparral extractable N and pH
Mean + se; n = 4 plots/treatment Vourlitis and Hentz (2016) JGR-B
2003 2005 2007 2009 2011 2013 2015
Precipitation (m
m)
0
200
400
600
800
1000
pH
5.0
5.5
6.0
6.5
7.0
2003 2005 2007 2009 2011 2013 20150
200
400
600
800
1000
Ext
ract
able
N (g
N/m
2 )
0
2
4
6
8
10
N1,6 = 96.9***T12,72 = 35.4***NxT12,72 = 20.8***
N1,6 = 22.2**T12,72 = 3.2***NxT12,72 = 3.0**
Control+N
Aboveground biomass production During the first 6 years, N plots had significantly lower aboveground biomass than control plots.
2003 2005 2007 2009 2011 2013 2015
Abo
vegr
ound
bio
mas
s (g
dw/m
2 )
0
200
400
600
800
1000Control+N
Mean + se; n = 4 plots/treatment Vourlitis and Hentz (2016) JGR-B
pH
2003-09
pH
-0.5
-0.4
-0.3
-0.2
-0.1
0.0Extractable N
2003-09
Ext
ract
able
N (g
N/m
2 )
0.00.20.40.60.81.01.21.41.6
ANPP
2003-09
AN
PP
(gC
m-2
y-1
)
-40
-30
-20
-10
Resulting in significantly lower ANPP for N plots
N-Control: Mean + 95% CI; n = 4 plots/treatment
N-Control: Mean + 95% CI; n = 4 plots/treatment N-Control: Mean + 95% CI; n = 4 plots/treatment
Dry season N addition significantly increased N availability and soil acidity
2003 2005 2007 2009 2011 2013 2015
Abo
vegr
ound
bio
mas
s (g
dw/m
2 )
0
200
400
600
800
1000
1200Control+N
N1,6 = 0.2T11,66 = 51.2***NxT11,66 = 5.3***
Aboveground biomass increment Mean + se; n = 4 plots/treatment Vourlitis and Hentz (2016) JGR-B During the last 6 years, aboveground
biomass of +N plots either equaled or exceeded control plots.
pH
2003-09 2009-15
pH
-1.0
-0.8
-0.6
-0.4
-0.2
0.0Extractable N
2003-09 2009-15
Ext
ract
able
N (g
N/m
2 )
0.0
0.5
1.0
1.5
2.0
2.5
3.0
ANPP
2003-09 2009-15
AN
PP
(gC
m-2
y-1
)
-60
-40
-20
0
20
40
60N-Control: Mean + 95% CI; n = 4 plots/treatment
Resulting in significantly higher ANPP for N plots
N-Control: Mean + 95% CI; n = 4 plots/treatment N-Control: Mean + 95% CI; n = 4 plots/treatment
Extractable N and soil acidification increased by > 2x in N plots
CSS Site description
Coastal sage scrub (CSS) •Santa Margarita Ecological Reserve •Artemisia californica, Salvia mellifera. •Ambient atmospheric N deposition 6-8 kgN ha-1 y-1. •36 cm of precipitation annually. •Has not experienced fire for about 35-40 years.
Wet season
Dry season Fenn et al. (2010) JEMA 91: 2404-2423
• Added N acidified surface (0-10 cm) soil after 4 years
• Soil extractable soil N increased significantly after 2 years of addition.
CSS extractable N and pH
Mean + se; n = 4 plots/treatment Vourlitis (2017) Oecologia
Year2003 2005 2007 2009 2011 2013 2015
0
100
200
300
400
500
600
700
800
900
Soi
l ext
ract
able
N (g
N/m
2 )
0
2
4
6
8
10
12N1,6 = 82.3***T13,78 = 34.9***NxT13,78 = 21.6***
2003 2005 2007 2009 2011 2013 2015
Precipitation (m
m)
0
100
200
300
400
500
600
700
800
900
Soi
l pH
5.0
5.2
5.4
5.6
5.8
6.0
6.2
6.4
6.6
6.8
7.0N1,6 = 122.1***T13,78 = 19.6***NxT13,78 = 16.5***
Control+N
CSS cover and species composition
After 4 years of N addition: Artemisia californica increased significantly in N plots. Salvia mellifera decreased significantly in N plots. Brassica nigra cover was < 1 % in both control and N plots. Drier period (except 2005).
h)
2004 2006 2008 2010 2012 2014 2016-5
0
5
10
15
20
25
A. californica
0
20
40
60
80NControl
S. mellifera
Abso
lute
cov
er (%
)
0
10
20
30
40
50
B. nigra
Year
2004 2006 2008 2010 2012 2014 20160
5
10
15
20
25
30
Diff
eren
ce in
cov
er (%
)
-20
-10
0
10
20
30
f)
-30
-20
-10
0
10
20
*
*
Mean + se; n = 4 plots/treatment Vourlitis (2017) Oecologia
CSS cover and species composition
After 8 years of N addition: Artemisia californica cover begins to decline in N plots. Salvia mellifera cover begins to increase in N plots. Brassica nigra cover begins to increase in N plots. Wetter period.
h)
2004 2006 2008 2010 2012 2014 2016-5
0
5
10
15
20
25
A. californica
0
20
40
60
80NControl
S. mellifera
Abso
lute
cov
er (%
)
0
10
20
30
40
50
B. nigra
Year
2004 2006 2008 2010 2012 2014 20160
5
10
15
20
25
30
Diff
eren
ce in
cov
er (%
)
-20
-10
0
10
20
30
f)
-30
-20
-10
0
10
20
** *
*
*
Mean + se; n = 4 plots/treatment Vourlitis (2017) Oecologia
CSS cover and species composition
After 13 years of N addition: Artemisia californica cover is the same in N and control plots. Salvia mellifera cover is significantly lower in N plots. Brassica nigra cover is significantly higher in N plots. Drier period.
Mean + se; n = 4 plots/treatment Vourlitis (2017) Oecologia
h)
2004 2006 2008 2010 2012 2014 2016-5
0
5
10
15
20
25
A. californica
0
20
40
60
80NControl
S. mellifera
Abso
lute
cov
er (%
)
0
10
20
30
40
50
B. nigra
Year
2004 2006 2008 2010 2012 2014 20160
5
10
15
20
25
30
N1,6=1.1T51,306=5.8***NxT51,306=1.0
N1,6=2.1T51,306=3.9***NxT51,306=1.4*
N1,6=2.2T51,306=5.9***NxT51,306=1.9***
Diff
eren
ce in
cov
er (%
)
-20
-10
0
10
20
30
f)
-30
-20
-10
0
10
20
** *
* *
* * **
**
*
CSS cover and species composition
Total cover = 55% B. nigra cover = 20%
SMER: Plot 3 (Control) SMER: Plot 4 (+N)
Total cover = 66% B. nigra cover = 52%
Discussion/conclusions We hypothesized that N addition would significantly
(1) increase rates of C and N accumulation.
Chaparral: Yes, but only after 7 years of N addition
CSS: Yes, but only when rainfall exceeded ca. 400 mm/y (Vourlitis 2012)
(2) Increase the cover and dominance of exotic annuals
Discussion/conclusions We hypothesized that N addition would significantly
(1) increase rates of C and N accumulation.
Chaparral: Yes, but only after 7 years of N addition
CSS: Yes, but only when rainfall exceeded ca. 400 mm/y (Vourlitis 2012)
(2) Increase the cover and dominance of exotic annuals
Chaparral: No, no change in species composition or richness after 14 years of N fertilization.
CSS: Yes, but only after 10 years of fertilization and prolonged drought.
Discussion/conclusions We hypothesized that N addition would significantly
(1) increase rates of C and N accumulation.
Chaparral: Yes, but only after 7 years of N addition
CSS: Yes, but only when rainfall exceeded ca. 400 mm/y (Vourlitis 2012)
(2) Increase the cover and dominance of exotic annuals
Chaparral: No, no change in species composition or richness after 14 years of N fertilization.
CSS: Yes, but only after 10 years of fertilization and prolonged drought.
These data indicate that ecosystem responses to N deposition are complex, may change over time, and interact with other environmental variables.
Long-term studies are needed to understand how N deposition will alter ecosystem structure and function.
Thank you!
Field Stations Program College of Arts and Sciences at San Diego State University