Linking soil communities and tree species
in high elevation forests
Ayres E*, Steltzer H, Berg S, Wall DH
Natural Resource Ecology Laboratory and Department of Biology, Colorado State University, Fort Collins, CO 80523-1499, USA. *edayres@nrel.colostate.edu
Introduction
Field experiment
Leaf traits differ
among species
Why might home-field advantage occur?
Leaf litter traits differ among plant species (e.g. litter quality or shape).
Litter is a source of energy and nutrients for soil organisms.
Competition among soil biota for litter resources may lead to selection for
soil species that are highly efficient at decomposing leaf litter derived from
the plant species above them.
Trembling
aspen
Soil biota
consume litter
Specialization of
soil biota
Faster litter
decomposition
Additional mass loss at
home (% initial mass)
Using these trees we investigated whether soil biota beneath a tree species specialize in
decomposing leaf litter from that tree species, which we call ‘home-field advantage’.
Mass loss (%)
Litter mass loss
Aspen (Populus tremuloides), Lodgepole pine (Pinus contorta), and Engelmann spruce (Picea
engelmannii) are common species in high elevation Rocky Mountain forests.
50
Aspen litter
25
Pine litter
Spruce litter
0
200
400
4
Home-field
advantage - All
species
2
0
Aspen litter lost ~35% of its mass after 1 year
(across stands of each tree species), while pine and
spruce litter lost ~22%.
Support for home-field advantage
Litter decomposed faster at home (i.e. in a stand of
the same tree species).
Mass loss of litter decomposing at home was ~9%
faster than litter decomposing in different stands.
-2
200
400
Experiment day
Engelmann
spruce
Lab experiment design
Aspen
Soil from beneath each tree species was mixed
and sterilized to kill all biota.
Lodgepole pine
A similar experiment was performed in the lab to test whether differences in the soil community
were responsible for home-field advantage.
Initial leaf litter quality
C:N
Litter quality
140
b
70
b
a
c
50
Pine Spruce
Aspen
Rotifers
b
Pine Spruce
Collembolans
40
50
b
6
a
a
Aspen Pine Spruce
20
Aspen
Pine
Spruce
Biota
400
Respiration rate
Lab experiment
Aspen litter
Respiration rate was greatest in microcosms
containing aspen litter and lowest in microcosms
containing spruce litter.
Spruce litter
200
Pine litter
0
100
50
100
Soil only
150
80
40
20
Home-field advantage All species
Cumulative respiration was ~3% greater at home
after 133 days.
0
-20
50
100
Experiment day
Support for home-field advantage
Respiration was greater when litter was incubated
with its ‘home’ soil biota.
60
150
Soil biota associated with a tree species specialize in decomposing leaf litter from that species,
which results in faster decomposition rates.
The annual carbon flux through terrestrial ecosystems is 10 times larger than human CO2
emissions. Therefore, if home-field advantage stimulates decomposition by ~8% in many
ecosystems it could represent a significant flux of carbon to the atmosphere.
Soil biota
12
Sterilized
Conclusion
a
Aspen
Abundance (1000s/kg)
lignin:N
100
b
Litter quality and the abundance of rotifers,
collembolans, and mesostigmatid mites
differed among the tree species.
Respiration rate
(µmol CO2 jar-1)
In Oct 2006, leaf litter (3g) was placed in 10 x 10 cm litter bags (1 mm mesh) and litter from each
species was placed in each stand (i.e. reciprocal transplant experiment). 216 litter bags were
deployed and half were collected over 3 dates (May, July, and Sept 2007).
Additional respiration
at home (µmol CO2 jar-1)
Four sites where aspen, pine and spruce occurred in near-monotypic stands and close to each
other (<200 m apart) formed the replicate blocks. Aspect, soil type, and other abiotic conditions
were similar for stands within a block, but varied among blocks.
Soil
Respiration, a measure of decomposition, was
monitored over time.
Materials and methods
The study was located in the San Juan Mountains, Colorado (37°43’N; 107°43’W ).
Spruce
Subsamples were re-inoculated with soil biota
found beneath each tree species to create 3 soils
that were identical except for their soil biotic
community.
Litter from each tree species was incubated with
each soil in a reciprocal transplant experiment.
Near-monotypic stands of aspen, pine and spruce in close proximity to one another in southwest Colorado.
Pine
ab
25
Mesostigmatid
mites
b
ab
a
a
Aspen Pine Spruce
Aspen Pine Spruce
Microbial biomass did not
differ among tree species.
Neither did the abundance of
most nematode families,
tardigrades or other mites.
Implications
Environmental disturbances (e.g. beetle outbreaks, fire, and climate change) are altering tree
composition in forests, which may disrupt home-field advantage by separating soil biota from their
associated tree species.
If soil communities are unable to quickly adapt to changes in tree composition these disturbances
may reduce decomposition rates and increase carbon sequestration in forests.
Acknowledgements The Mountain Studies Institute provided logistical support. Grace Li, Breana Simmons, Matt Wallenstein, Lisa Smith, Matt Territ, Mike Brown, Jill Oropeza, Chrissy Cook, Ali
Morse, and Colin Pinney assisted with sample collection or analysis. This study was funded by a British Ecological Society Early Career Project Grant awarded to EA and HS.