Download Measuring complexity in soil ecosystems

Measuring complexity in soil
ecosystems
Monika Gorzelak
November 24th 2014
Objectives
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How can I ask a CAS question in my research?
Soil is complex
Should behave as a complex adaptive system
Explore whether that is measurable in my
experiments/research
Outline
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Revisit “response diversity”
Historical context Tilman Cedar Creek
Current theory
Introduction to mycorrhizal networks
My experiment(s) + CAS
Response diversity
Definition
• Diversity of responses to environmental
change among species that contribute to the
same ecosystem function
• Diversity within functional groups is important
to the adaptive capacity of ecosystems; not
just species richness
Concepts of diversity in plant
ecosystems
• Tilman 2001
• Hector 1999
• Large scale field experiments that
manipulated diversity and measured fitness
outcomes
• Debate
Cedar Creek
• Long term experiment
• Temperate grasslands, in Minnesota
• 16 species, chosen at random into plots in
increasing species richness
• Measure productivity (biomass)
• Increased diversity = increased productivity
BIODEPTH
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Europe experiment
Same design, 32 plants
8 sites across Europe
Hector et al. (2002)
Same results: increased diversity results in
increased productivity (biomass)
(Loreau, 2010)
Mechanisms
• Complementarity effect: functional niche
complementarity, permanent association of
species leads to better collective performance
• Selection effect: trait variation as initial effect
upon which selective process promotes
dominance of a particular species
• Both at work (Loreau et al. 2001);
complementarity more likely (Cardinal et al.
2007)
What functions?
• Root depth and architecture (Dimitrakopoulos
and Schmid 2004)
• Nutrient use efficiency (van Ruijen and
Berendse 2005)
• Increase input and retention of nitrogen
(Fargione et al. 2007)
• ***grasslands only!
Bonfante and Anca 2009
More functions, more interactions
Mutualisms
• Nitrogen-fixing bacteria (classic example
affecting plant diversity, fix nitrogen, facilitate
co-existence of other species by generating a
nutrient source)
• Mycorrhizas. Symbiosis between soil fungi and
plant. Plant provides fixed carbon, soil fungus
provides mineral nutrient uptake
Microscopic structure
Colonized root tips
• Potential for different types of connections
because different species
Scales of complexity in soil
• Spatial
– Roots create heterogeneous structure*
– Networks
• Temporal
– Within a trophic level
– Between trophic levels (different time scales
apply)
Root architecture
Networks
(Beiler et al. 2010)
Scale-free network
(Beiler et al. 2010)
Temporal (within trophic level)
• Behaviour* (within life span, quick changes)
• Adaptation (positive/negative feedbacks)
– Expression of genes to exploit resources
– Improve fitness
– Adaptive niche construction (Callahan 2014), vs.
homogeneous medium environmental
modification
• Evolution (“permanent” changes to genome)
– Longer term
Growth curve example
Medium term (mal) adaptation
Adaptive niche construction
• “Opposite” of a growth curve experiment
• More likely in a heterogeneous environment
• Modification of a local environment to confer
fitness advantage, passing the local improved
environment onto offspring
• Recently demonstrated in a lab setting using
bacteria (easier to do with bacteria because
they have short generation times)
Soil trophic levels
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1st level: primary producers (plants)
2nd level: decomposers, mutualists, pathogens
3rd level: shredders, predators, grazers
4th level: higher level predators (carni)
5th level: even higher level predators (?)
Also: food webs, organisms can play at
different levels (nematodes eat fungi and are
eaten by other fungi...next slide)
Fungi eat nematodes!
© George L. Barron
Temporal scales across trophic levels
• Plants interact with mycorrhizas (2 trophic
levels)
• Bacteria interact with both
• Reaction times differ between these 3
components (scale: years, months, days)
• (Food webs: there are other players, I’m
ignoring them)
Seasonal changes in fungi
(Pickles et al. 2010)
My project: what we know
• Douglas-fir connect with mycorrhizas which
form networks
• Douglas-fir can transfer resources and signals
through its mycorhizal network
• Douglas-fir preferentially transfers carbon to
kin
• Douglas-fir transfers defense signals via the
mycorrhizal network in response to herbivory
My project: what we want to know
• Do Douglas-fir transfer defense signals
preferentially to kin in response to herbivory?
• Need to look at 3 factors:
– Mycorrhizal network (yes and no)
– Kin vs stranger
– Herbivory (insect, manual defoliation, no)
Treatments
MN
defoliation
Kin vs stranger
insect
Kin vs stranger
control
Kin vs stranger
no-MN
Kin vs stranger
no mesh
Kin vs stranger
Kin vs stranger
Kin vs stranger
Kin vs stranger
Kin vs stranger
MN=mycorrhizal network, using mesh bags that allow fungi to pass, but not roots
No-MN=mesh bags exclude roots and fungi, eliminating the mycorrhizal network, while
allowing the passage of water and bulk soil flow including nutrients
No mesh=control for unknown impacts of including the mesh**changes to spatial
heterogeneity I hope to be able to detect by considering complexity of the soil
in the design and trying to quantify it under these conditions
Design: Two recipient
D = donor
Rs = recipient,
stranger
Rs = recipient,
kin
Design: Tripartite
D = donor
Rs = recipient,
stranger
Rs = recipient,
kin
Thoughts on design
• Tripartite is more complex
• Should I expect different results? Its
essentially the same experiment...
• Dilution of label added to Donor
• Change to the spatial heterogeneity of the soil
structure (can I see this change by monitoring
the bacteria...if they change, will they impact
the system and possibly alter responses to
treatments?)
Complexity in soil: Relevant concepts
• Spatial heterogeneity causes adaptive
radiation in bacteria (increase diversification)
• Priority effects (first bacteria arriving takes
priority, impacts habitat in the future)
• Time-scale differential between plants, fungi,
and bacteria
Apply treatments:
Herbivory, mycorrhizal networks
Bacteria
• Productivity (measure
biomass)
• Diversity
• species diversity
• Functional diversity
• Time-scale comparisons
•Bacteria at start
•Bacteria at finish
Diversity and Productivity
• Aboveground plant diversity unchanged
• Soil spatial structure is altered, allowing for
adaptive radiation
• Parallel to Tilman: will productivity increase with
increased diversity (in bacteria rather than
plants?)
• Plant stress response have different effects on
bacterial community systems (is high diversity
system more resilient?)
• Will kin vs stranger change the
diversity/productivity of bacteria in the system?
Questions
• Does the bacterial community change in
response to
– the presence/absence of a mycorrhizal network?
– herbivory (with and without a mycorrhizal network)?
– Density of seedlings (and therefore changes to root
architecture)?
– Can these changes be seen temporally over the
duration of the experiment?
– If layered on top of the original experiment, can these
measures inform signal transfer through a MN?
Thoughts on measuring complexity?
• What should I add?
• Is there a better measure of soil complexity
(bacteria will be most responsive)?
• Change the experiment to include explicit
measures of complexity
• Do a separate experiment to tease out the
factors
– Consider no plant pot, single plant pots etc
Functional diversity in bacteria
• Too much going on in the design? Simplify
with a lab experiment?
• mimic Tilman experiment, but upside down.
Keep above-ground constant, inoculate the
soil with known species, use fake roots, fake
soil (simplify the system), look for productivity
increases and changes in diversity
The end.