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Structure and Functions of the Soil Food Web: Understanding Healthy Soils. The organisms involved How they interact What they do Monitoring food web condition Food web management. Howard Ferris Department of Nematology University of California, Davis [email protected] November, 2005. - PowerPoint PPT Presentation
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Structure and Functions of theSoil Food Web:
Understanding Healthy Soils
Howard FerrisDepartment of Nematology
University of California, Davis
November, 2005
The organisms involvedHow they interactWhat they doMonitoring food web conditionFood web management
Soil Food Web Structure – Resource Effects
Organic Source
Resources
•Carbon is respired and Energy is used by each organism in the web
•The amounts of Carbon and Energy available determine the size and activity of the web
Heat and CO2
Linear Food Chains
Linear Food Chainsand Trophic Cascades
But consider.. Bottom up effects Omnivory
A more likely structure…
The Trophic NetworkOr Food Web
Roots
Detritus
PhytophagousNematodes
SaprophyticFungi
Bacteria
Collembolans
Noncrypto-stigmatic Mites
CryptostigmaticMites
FungivorousNematodes
Bacteriophagous
NematodesBacteriophagous
Earthworms
Mites
Flagellates
Amoebae
PredaceousNematodes
PredaceousMites
PredaceousCollembolans
NematodeFeeding Mites
Functional Guilds
Soil Food Web Structure – Biotic Effects
Positive and Negative Feedback in Food Web Structure
Sinorhizobium meliloti and bacterivore nematodes
With twenty nematodes
0 nematodes 5 nematodes
Fu et al. 2005
0
20
40
60
80
100
0 5 10 20 40 80 160
Nematode Abundance
Bact
eria
l Cel
lsPositive feedback Overgrazing
0
20
40
60
80
100
0 5 10 20 40 80 160
Nematode Abundance
Bact
eria
l Cel
ls
0
20
40
60
80
100
0 5 10 20 40 80 160
Nematode Abundance
Bact
eria
l Cel
lsPositive feedback Overgrazing
Environmental heterogeneity
Zones andGradients:
texturestructuretemperaturewaterO2
CO2
NO3
NH4
minerals
Soil Food Web Structure – Environmental Effects
Separatemetacommunities?
•Resource distribution•Spatial heterogeneity•Organism motility•Omnivory•Strong and weak links•Microsite asynchrony•Viewing resolution
Food Web Structure - Patchiness
Structure and Function: Abundance and Diversity
Strength ofFunction
orService
Functional Group Diversity
Functional Redundancy
Functional Group Diversity
Functional Complementarity
Loreau, Oikos 2004
resource
consumers
Soil Food Webs - Function
• Decomposition of organic matter
• Cycling of minerals and nutrients
• Reservoirs of minerals and nutrients
• Redistribution of minerals and nutrients
• Sequestration of carbon
• Degradation of pollutants, pesticides
• Modification of soil structure
• Community self-regulation
• Biological regulation of pest species
Soil Food Web Structure and Function - the need for indicators
The Nematode Fauna as a Soil Food Web Indicator
HerbivoresBacterivoresFungivoresOmnivoresPredators
• Occupy key positions in soil food webs
• Standard extraction procedures
• Identification based on morphology
• Clear relationship between structure and function
• The most abundant of the metazoa
• Each sample has high intrinsic information value
Why nematodes as bioindicators?
Functional Diversity of Nematodes
RhabditidaePanagrolaimidae
etc.
Short lifecycleSmall/ Mod. body sizeHigh fecunditySmall eggsDauer stagesWide amplitudeOpportunistsDisturbed conditions
AporcelaimidaeNygolaimidae
etc.
Long lifecycleLarge body sizeLow fecundityLarge eggsStress intolerantNarrow amplitudeUndisturbed conditions
Enrichment Indicators Structure Indicators
CephalobidaeAphelenchidae,
etc.
Moderate lifecycleSmall body sizeStress tolerantFeeding adaptationsPresent in all soils
Basal Fauna
Ba2
Fu2
Fu2
Ba1
Ba3
Fu3
Ca3
Ba4
Fu4
Ca4
Om4
Ba5
Fu5
Ca5
Om5
Enriched
Structured
Basal
Basalcondition
Structure index
Enr
ichm
ent i
ndex
•Disturbed•N-enriched•Low C:N•Bacterial•Conducive
•Maturing•N-enriched•Low C:N•Bacterial•Regulated
•Matured•Fertile•Mod. C:N•Bact./Fungal•Suppressive
•Degraded•Depleted•High C:N•Fungal•Conducive
Testable Hypotheses of Food Web Structure and Function
Ferris et al. (2001)
0
50
100
0 50 100
Structure Index
Enr
ichm
ent I
ndex Prune
OrchardsYuba Co.
MojaveDesert
TomatoSystemsYolo Co.
Redwood Forest and
GrassMendocino
Co.
Food Web Analyses
Management of Food Web Structure:Carbon Pathways and Pools
Omnivory
Decomposition
Herbivore
Bacterial
Fungal
channelized reticulate
Carbon Channel ManagementBacterivore Channel
•“Fast Channel”•Moisture•Low C:N, labile substrates
•High respiration and turnover•Mineralization of nutrients•Major predators are protozoa and nematodes
Herbivore Channel•“Intermediate Channel”
•Host status and defense mechanisms•Damage to host•Substrate respiration and immobilization, excretion and defecation•Major predators are fungi and nematodes
Fungivore Channel•“Slow Channel“
•High C:N, lignin, cellulose, resistant substrates
•Conservation of carbon, greater web structure•Major predators are microarthropods and nematodes
O Pr
B
F
P
O Pr
B
F
P
Structure and Function
Nutrientfunction
Regulatory function
%Fungivore
%Bacterivore%Herbivore
Compromised-Not
Sustained
Fast-Ephemeral
Slow -Sustained
Characteristics of Foodweb Enrichment
Inflow ChannelAnalysis
Plant Materials - Surface
0
20
40
60
80
100
0 300 600 900 1200
DD>10
Enric
hmen
t Ind
ex
C:N High
C:N Low
Control
A
C supplied
Resourcetransformation
Community structureshifts
Ferris and Matute (2003)
Succession
0.00006
0.00008
0.0001
45000 55000 65000 75000Aggregate Enrichment Index
Min
eral
N In
crea
se R
ateA
0.00006
0.00008
0.0001
0.025 0.03 0.035 0.04 0.045 0.05 0.055
Plant Low C:N
0
20
40
60
80
100
0 300 600 900 1200
DD>10 C
Ch
an
ne
l In
de
x
Cont. Undist.
Cont. Incorp.
Pl. Incorp.
Pl. Undist.
0
20
40
60
80
100
0 300 600 900 1200
A
Ferris and Matute (2003)
Resource transformation
Channel Index: •a weighted ratio of fungivore and bacterivore nematodes•higher CI indicates more fungal
0
1000
2000
3000
4000
5000
6000
7000
12/9/
1993
1/28
/1994
3/19
/1994
5/8/
1994
6/27
/1994
8/16
/1994
10/5/
1994
To
tal
Infl
ow
Bio
mas
s Maize
Panicum
Mucuna
Control
Food Web channel management:
Nature and timing of carbon sources
0
1000
2000
3000
4000
5000
6000
7000
12/9/
1993
1/28
/1994
3/19
/1994
5/8/
1994
6/27
/1994
8/16
/1994
10/5/
1994
To
tal
Infl
ow
Bio
mas
s
what if?
Data adapted fromMcSorley and Frederick. 1999.
external sources
rhizodeposition
old root death
C
herbivory
herbivory
external sources
rhizodeposition
old root death
Food for the Soil Food Web
C
Soil Food Web Management - Experiment and Observation
C:N = 8.3:1
C:N = 8.5:1
C:N = 4:1
C:N = 6:1
Mineralization potential of fungal- and bacterial-feeding nematodes
Sustainable Agriculture Farming Systems Project
1988-2000
Soil Food Web Management - experiment
Aug Sep Oct Nov Dec Jan Feb Mar Apr May
Cover cropCover crop
Irrigation
temperature
moisture
activity
T0
M0
Tomato Yields - 1997
0
10
20
30
40
50
60
+I+S+W +I-S+W +I-S-W -I-S+W -I-S-W
Tons
/Acr
eA A
B B B
0
50
100
0 50 1000
50
100
0 50 100
Structure index
En
rich
me
nt in
de
xSampled 2000
Organically-managed for 12 years
Structure index
Sampled 2001After Deep Tillage
How Fragile is the Food Web?
Berkelmans et al. (2003)
Nematode Sensitivity – Mineral Fertilizers
Concentration (mM-N)
0 0.1 1
Sta
ndar
dize
d C
ount
s
0
50
100
150
200
X
X X X X
c-p 1 c-p 2 c-p 3 c-p 4 c-p 5 X
Ammonium sulfate
0.50.050.02
Nematode guild
Tenuta and Ferris (2004)
Transplant inoculants:Entomopathogenic nematodesRhizobiaFlourescent pseudomonadsNematode-trapping fungi
Surface mulch with designed C:N ratioPest resistance/toleranceUndisturbed bedBuried drip
Disadvantages:↓Productivity ↑Continuous↑Monitoring↑Rotation↑Risk ? Equipment? Economics? Labor? Knowledge base
Advantages:↓Tillage ↓Fossil fuel↓Dust ↓Leaching ↑Soil structure↑Porosity ↑Food web structure↓Pesticides↓Mineral fertilizers↓Weeds and herbicides ↓Water ↓Costs ↑Sustainability
•Bongers, T., H. Ferris. 1999. Nematode community structure as a bioindicator in environmental monitoring. Trends Ecol. Evol. 14, 224-228.
•Ferris, H., T. Bongers, R. G. M. de Goede. 2001. A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. Appl. Soil Ecol. 18, 13-29.
•Ferris, H., M.M. Matute. 2003. Structural and functional succession in the nematode fauna of a soil food web. Appl. Soil Ecol. 23:93-110.
•Loreau M. 2004. Does functional redundancy exist? Oikos 104:606-611.
•Neher, D. A., T. R. Weicht, D. L. Moorhead, R. L. Sinsabaugh. 2004. Elevated CO2 alters functional attributes of nematode communities in forest soils. Funct. Ecol. 18:584-591.
•Tenuta, M., H. Ferris. 2004. Relationship between nematode life-history classification and sensitivity to stressors: ionic and osmotic effects of nitrogenous solutions. J. Nematol. 36:85-94.
•Yeates, G. W., R. Cook. 1998. Nematode fauna of three Welsh soils under conventional and organic grassland farm management. Pp. 305-313 in R. de Goede and T. Bongers, eds. Nematode Communities of Northern Temperate Grassland Ecosystems. Giessen, Germany: Focus Verlag.
More information: http://plpnemweb.ucdavis.edu/nemaplex
Some References