Species functional traits and the response of populations to disturbance govern the rate and trajectory of succession, and the functioning of high latitude ecosystems.

Consequently, climate change will alter successional dynamics and ecosystem function primarily through its effects on disturbance regime and on those species that govern successional/ecosystem processes.

Actinorhizal plants25 genera

220 perennial dicotyledonous plants (mostly woody) within 8 families:

(Betulaceae, Casuarinaceae, Coriariaceae, Datiscaceae, Elaeagnaceae, Myricaceae, Rhamnaceae, Rosaceae)

Associated with the filamentous actinomycete: Frankia

Thin-leaf alder (Alnus incana subsp. tenuifolia) Green alder (Alnus viridis subsp. fruticosa)

Autoregulation

The down-regulation of nodule production andnitrogenase activity via a N-sensitive, phloem-transported signal inhibitor

Factors that influence plant growth and plant demand for N, also influence N fixation rates

Climate (temperature, ppt.)

Resource supply (light, water, nutrients)

Phenology & ontogeny

Disturbance (herbivory)Plant Growth Rate

Plant N Demand (N:P ratio)

Nodule production and growth

Nitrogenase activity

Whole-plant N2-fixation rate

Ecosystem N Inputs

Plant density

Nodule biomass/plant

Alnus incana subsp. tenuifolia

160 180 200 220 240 260 280

Julian Day

0

2

4

6

8

10

Sp

ecif

ic A

RA

(m

ol

C2H

4 g

dw

t n

od

ule

-1 h

r-1)

EarlyMidLate

(Uliassi and Ruess 2002)

Mitchell and Ruess (in prep)

Alnus viridis subsp. fruticosa

N Fixation = (julian day, soil temperature, soil moisture)

0

10

20

30

40

No

du

le B

iom

ass

(g m

-2)

0

50

100

150

N I

np

uts

(kg

ha-1

yr-1

)

single (sl)sl - 1cm1-2 cm2-3 cm3-4 cm5-6 cm

Control +P Control +P

Alnus incana subsp. tenuifolia

(Uliassi and Ruess 2002)

Ruess et al. (submitted)

Woolly alder sawfly, Eriocampa

ovata

1 2 3 4 5 6 7 8

RF Pattern

0

10

20

30

40

50

60

Spe

cifi

c N

Fix

atio

n Rat

e (

mo

l N

g n

od

ule

-1 h

r-1)

abc

ab

ab

ab

b

c

a

bc

RF Frequencies; Early FP; All AT

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10

RF

Fre

qu

ency 1A

1B

1C

RF Frequencies; Late FP; All AT

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1 2 3 4 5 6 7 8 9 10

RF

Fre

qu

ency 4A

4B

4C

Anderson et al. (in prep)

Effects of Frankia genetic structure on N fixation rates

Early Successional Stands White Spruce Stands

RF Pattern RF Pattern

Phylogeography of Frankia

545,550 545,600 545,650 545,700 545,750

UTM East

7,176,300

7,176,400

7,176,500

7,176,600

7,176,700

7,176,800

7,176,900U

TM

No

rth

Skookum Pass Genotype Distributions

232

242

253

263

274 284

2

13

2

2 2

13

03

1 1

1

2

How will alder expansion in the arctic (Sturm et al. 2001) affect ecosystem function??

pictures stolen from Ken Tape

Increase in Alnus pollen percentages from 10% to 70% circa 8000-7000 BP.

Hu et al. (2001)

Mack et al. (2004)

1

2

3

4

5

6S

oil

C C

on

ten

t (%

)

A C

Early Shrub

CanopyOpen

Effects of A. crispa on Soil C

OOO AA CC

Birch/Aspen White Spruce

*

*

Mitchell and Ruess (in prep)

0 25 50 75 100 125 150 175 200

N Fixation Rate (mol N g nodule-1 hr-1)

2.0

2.5

3.0

3.5

Le

af

N C

on

ten

t (%

)

015%25%40%

Y = 2.5512 + 0.0023*X

r2 = 0.12, P < 0.01

So what's the quick and dirty way to assess N fixation inputs at the ecosystem scale??

Anderson et al. (2004)

Ruess et al. (submitted)

-3 -2 -1 0 1 2

15N Leaf

10-2.00

10-1.00

100.00

101.00

102.00

9

23468

23468

23468

23468

234

Nit

rog

en F

ixat

ion

Rat

e (

mo

l N g

-1 h

r-1)

Brooks RangeSeward PeninsulaAnderson et al. (in prep)Anderson et al. (2004)

Research/Monitoring Tasks:

1) Establish long-term vegetation monitoring plan for tracking the expansion of alder (low-level aerial photography).

2) Among landscapes where alder is know to be expanding, can we model/predict hot-spots for N fixation? (e.g. climate, soil P, pH, soil 15N)

3) What are the long-term consequences of N inputs to ecosystem structure and function in landscapes where alder is expanding? (changes in vegetation composition, NPP and forage quality; soil C and N stocks; watershed biogeochemistry).

4) Monitor outbreaks of herbivorous insects and plant pathogens.