Linking physiological traits and species
abundance to invasion resistance
Jeremy James
Framework
• Plant community composition influences
ecosystem properties
• Much emphasis on effects of functional group
diversity on ecosystem properties
• Invasive plant management can be improved by
managing plant communities based on
functional traits as opposed to functional groups
Outline
• An example of how functional traits influence
ecosystem properties (N capture and invasion)
– Traits related to N capture
– Trait effects on ecosystems are moderated by
species abundance
• What traits might be important to consider when
revegetating areas prone to weed invasion?
– At the seedling stage traits affecting initial growth
rate important
• Conclusions and future directions
Functional group diversity, nitrogen
capture and invasion resistance
Study site
Group
Annual
Annual
Bunchgrass
Bunchgrass
Bunchgrass
Forb
Forb
Code
BRTE
TACA
PSSP
ELEL
POSE
LOTR
CRIN
Common Name
cheatgrass
medusahead
bluebunch wheatgrass
bottlebrush squirreltail
Sandberg’s bluegrass
nineleaf biscuitroot
grey hawksbeard
Scientific Name
Bromus tectorum L.
Taeniatherum caput-medusae (L.) Nevski
Pseudoroegneria spicata (Pursh) A. Löve
Elymus elymoides (Raf.) Swezey
Poa secunda J. Presl
Lomatium triternatum (Pursh) Coult. & Rose
Crepis intermedia Gray
Experimental design
•
15N
was injected into soils around 7 study
species
• Injections were made:
– 3 times during the growing season (April,
May June)
– At 2 soil depth (2-7 cm, 17-22 cm)
– Using 2 forms of N (NH4+, NO3-)
• Removal plots
– Medusahead establishment in plots where different
functional groups removed
April
May
60
40
20
15
N capture (% of each species total)
N partitioning through time
Annuals
Bunchgrasses Sandberg
Forbs
100
2-7 cm
17-22 cm
80
60
40
20
15
N capture (% of each species total)
N partitioning by soil depth
Annuals
Bunchgrasses Sandberg
Forbs
Integrating N uptake patterns and species
abundance
Influence on ecosystem = trait × abundance
Portion of community biomass
Nitrogen uptake
×
annuals
bunchgrasses
Sandberg
forbs
Total N capture
April
May
June
2.0
1.5
1.0
3.0
2-7 cm
17-22 cm
2.0
1.0
15
-2
N capture (mg m )
0.5
NH4
2.0
NO3
1.5
1.0
0.5
0.0
+
Annuals Bunchgrasses Sandberg
Forbs
-
-
T. caput-medusae (plants m 2)
Removal plots
b
300
200
a
a
a
100
Nothing
removed
Annual
forbs
removed
Perennial
forbs
removed
Bunchgrasses
removed
A trait based approach for managing invasives
•
Conventional groupings encompass a wide
range of trait differences
•
Different traits likely influence different
ecosystem properties
•
Effective invasive plant management requires
an understanding of traits allowing invaders to
outperform natives
Trait variation of desirable species
• Do you want to:
– maximize trait variation
– maximize a trait
A
B
D
C
What traits should be considered?
• Relative growth rate (RGR) is a key
trait to consider
Native grass
• Invasives often have a higher RGR
• Seed → seedling stage
– Plant size
– Resource capture
• Influences competitive interactions
and survival
Invasive grass
Components of RGR
• RGR (mg g-1 d-1) has two components
– Leaf area ratio (LAR, m2 kg-1), the amount
of leaf area per unit total plant mass
– Net assimilation rate (NAR, g m-2 d-1), the
rate of dry mass gain per unit leaf area
RGR (mg g-1 d-1) = LAR (m2 kg-1) x NAR (g m-2 d-1)
Decomposition of LAR
Leaf area ratio (LAR, m2 kg-1), the
amount of leaf area per unit total
plant mass, can increase by:
1. Adding more leaf biomass
•
Leaf mass ratio (LMR) amount of
leaf mass per unit plant mass
2. Making more leaf area per unit
biomass
•
Specific leaf area (SLA) amount of
leaf area per unit leaf mass
LAR = SLA x LMR
Decomposition of NAR
• NAR (g m2 d-1) rate of dry mass gain per
unit leaf area
• Is the net balance of:
– Photosynthetic carbon gain
per unit leaf area minus carbon
loss through respiration
– Influenced by how efficiently plants
use nitrogen (leaf N productivity)
and how much N is allocated to leaves.
Traits driving RGR variation
SLA
(m2 kg-1)
LAR
(m2 kg-1)
LMR
RGR
(g g-1)
(mg g-1 d-1)
NAR
(g m-2 d-1)
Leaf N productivity
(g leaf g N-1 d-1)
Leaf N concentration
(g N m-2)
Approach
• Use model to examine RGR traits in 3 invasive
annual grasses, 3 perennial bunchgrasses, 6
invasive forbs, 6 desirable forbs
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-1
0.14
RGR (g g d )
RGR variation among grasses
0.20
0.18
0.16
0.10
0.08
0.06
0.04
0.02
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-1
-1
RGR (g g d )
RGR variation among forbs
0.15
0.10
0.05
Traits driving RGR variation
Invasive
Invasive
vs. desirable
vs. desirable
forbsgrasses
SLA
(m2 kg-1)
LAR
(m2 kg-1)
LMR
RGR
(g g-1)
(mg g-1 d-1)
NAR
(g m-2 d-1)
Leaf N productivity
(g leaf g N-1 d-1)
Leaf N concentration
(g N m-2)
Toward trait-based management of invasives
•
This involves identifying:
1. The specific ecosystem property or processes
that we want to manage/ traits of the invader
2. The traits likely to have the largest impact on the
property or processes
3. Trait variation and abundance in your desirable
species pool
•
May only need to consider a handful of traits to
maximize invasion resistance
Traits to consider in desirable species pool
1. Get biomass established and get it fast
– Target species with high RGR
• High SLA and high nitrogen productivity
2. Select species that differ in phenology
3. Select species that differ in root distribution
Questions and comments