P1254503556JLyjk

1
Variation in species responses to species
richness, CO2, and N the role of unique
functional attributes
Tali D. Lee
2
BioCON - Free-air CO2 enrichment
CO2 ambient (368 ppm) elevated (560 ppm)
Soil N unamended enriched N (4 gN m-2y-1)
Ring 5, Elevated CO2
3
Functional groups
C3 grasses C4 grasses Legumes Forbs
4
Methods leaf-level gas exchange

• Net photosynthetic rates
• Leaf N concentrations

5
Variation in functional group responses?
CO2 effect
CO2 effect
CO2 effect
CO2 effect
CO2 effect
CO2 effect
CO2 effect
CO2 effect
15
15
15
15
15
15
15
15
10
10
10
10
10
10
10
10
change in photosynthesis
5
5
5
5
5
5
5
5
Forb Legume C3 grass C4 grass
0
0
0
0
0
0
0
0
6
Link between carbon and nitrogen
CO2
CO2
N2
N2
CO2
N2
N
N
N
N
Individual plant community levels
7
Results
Photosynthetic performance in mixtures vs.
monocultures
L. perennis
A. gerardii
40
40
20
20
0
0
difference in photosynthesis (16-spp vs.
monoculture)
-20
-20
-40
-40
-60
-60
98 99 00 01 02 03 04 05
98 99 00 01 02 03 04 05
Year
Species responses differ and change over time
8
Results
B. inermis
40
20
0
-20
-40
-60
difference in photosynthesis (16-spp vs.
monoculture)
98 99 00 01 02 03
A. millefolium
40
20
0
-20
-40
-60
98 99 00 01 02 03
Year
9
Results
Andropogon gerardii
700
1998
600
500
400
300
200
100
improved performance of Andropogon in mixtures
explained largely by ? leaf N
Photosynthesis (nmol g-1 s-1)
0
1
1.5
2
2.5
3
3.5
Leaf N
10
Results
1999
1.0
soil
soil
N in Lupinus plant
0.5
fixation
fixation
0.0
Ambient CO2 Elevated CO2
Lupinus - N derived from fixation ? in elevated
vs. ambient CO2
11
Results
2002
1.2

ambient CO2 ? elevated CO2
1.0
0.8
Proportion of N derived from fixation
0.6
0.4
0.2
0.0
Dalea
Lupinus
Amorpha
Lespedeza
Legume species
West et al. (2005)
Legume species differ in N2 fixation response to
CO2
12
Summary
performances of some species in mixtures are
changing over time these changes may be related
to functional traits such as an ability to fix N2
or to compete effectively for soil
N implications for community responses to global
change?
13
Acknowledgements
Peter Reich Numerous interns and the rest of the
BioCON team Susan Barrott Kally Worm Ann
Karpinski Lauren Losek Doreen Hoover Emily
Hockman Wiyanna Morris Funding National
Science Foundation National Institute for Global
Environmental Change Minnesota Agricultural
Experiment Station UWEC office of research
programs UMN and NSF fellowships
14
Photosynthetic acclimation to ? CO2
Ambient CO2
CO2
Net Photosynthesis
Measurement CO2
15
Results
Lupine
0.5
0.4
0.3
0.2
0.1
Proportion of total aboveground biomass in mixture
0.0
1998
1999
2000
2001
2002
2003
2004
Andropogon
0.5
0.4
0.3
0.2
0.1
0.0
1998
1999
2000
2001
2002
2003
2004
Year
16
Results
Soil solution N
1.5
1.0
mg N/kg soil
0.5
0.0
Non-fixers
Lupinus
monocultures
17
Results
Plant N concentration in mixtures
1.5
ANOVA Plt0.0001
1.0
N
0.5
0.0
absent
present
Lupinus
18
Results
Legume presence ? N status photosynthesis, but
this did not result in stronger responses to
elevated CO2