Structure and Functions of theSoil Food Web:

Understanding Healthy Soils

Howard FerrisDepartment of Nematology

University of California, Davis

hferris@ucdavis.edu

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