Mycorrhizal
colonization of giant sequoia
Cathy Fahey and Rob York
Acknowledgements
• Teresa Pawlowska‐
Cornell University
• John Battles‐
UC Berkeley
Sequoias: long‐lived pioneer species
A bad-ass species
Giant sequoia and Achilles: Both formidable but flawed
Bad heel Bad regeneration
Giant sequoia age structureToo few recruits in last 100 years
1800’s
1900’s
from Nate Stephenson
Fire Return Interval Departure (FRID)
Index = number of maximum fire
free intervals that have been skipped
1 = Extreme (5+ max return intervals passed)2 = High (2 ‐
5 max intervals passed)3 = Moderate (0 ‐
2 max intervals passed)4 = Low (last fire occurred within the max
interval time period)
As of end of 2009 fire season
63 of the 70 groves had high or
extreme FRID values
Average for all groves = 1.5
Zero groves had an index of 4
What we need to do
Active adaptive management•Treatments that create canopy gaps for
regeneration•Do uncertainty silviculture
instead of
restoration silviculture
– Learn more about the factors of giant sequoia regeneration under different conditions
Arbuscular
mycorrhizae
Bonafante
and Genre (2010)
Assimilated carbon
Nutrient supplementation
Mark Brundrett
(2008)
fungus plant
50 100 150 200 250 300 350 400
Hoeksema
et al. (2010)
Context of study: ‐
Cool, socially
‐
Bad‐ass, ecologically ‐
Vulnerable
‐
Need info about treatments that can increase resilience
‐
Mycorrhizae
may be key
Study Objectives• Assess interaction between mycorrhizae
and giant sequoia saplings in canopy gaps
By Measuring effects of:• Canopy gap size• Sapling position within gaps• Soil versus burned substrate
Canopy gaps
Experimental Design
Hypotheses• Higher AM colonization at the edges of gaps
– greater access to inoculum– higher resource stress from competing adult trees
• Higher AM colonization on bare
mineral soil than on ash
– reduced inoculum from burn treatment
– greater nutrient stress on bare soil
Tree‐crutch hypothesis
Field Collections
6 year old saplings
Root Processing
• Cleared with KOH and bleach and stained with
trypan
blue• Scored percent
colonization– AM hyphae– AM vesicles– AM coils– Non‐AM hyphae
Colonization ResultsColonization (per unit root length) 34.4%
Vesicle abundance 3.7%
AM hyphae
abundance 30.5%
AM coils abundance 10.8%
Non‐AM fungi abundance 10.2%
Colonization Across Gaps
Highest colonization at gap centers, lowest at south edges
Colonization correlated with light availability
Colonization negatively correlated with non‐AM fungi
Substrate
Biom
ass
(g)
0
50
100
150
200
Mean= 60g
Mean=138g
Ash Mineral soil
Bars = 95% Confidence Intervals
Soil substrate‐
no difference
Despite obvious differences in seedling growth,
colonization was similar on ash and bare soil.
Conclusions‐
academic version• AM colonization was correlated positively
with light rather than negatively with belowground resources (driven by carbon
availability).
• Overall functioning of the symbiosis is high at the centers of gaps.
• Crutch hypothesis rejected• There is a highly diverse group of fungi harbored in giant
sequoia
roots.
Conclusions –
baseball analogy version AM is like a third base coach
• Not absolutely necessary
• Usually helpful, but only when things are going
well
• Sometimes a hindrance
• Every champion has one