Structure and Functions of the Soil Food Web

Structure and Functions of the Soil Food Web: Understanding Healthy Soils Howard Ferris The organisms involved Department of Nematology How they interact What they doof California, Davis University Monitoring food web condition hferris@ucdavis. edu Food web management November, 2005

Soil Food Web Structure – Resource Effects Heat and CO 2 Organic Source • Carbon is respired and Energy is used by each organism in the web Resources • The amounts of Carbon and Energy available determine the size and activity of the web

Linear Food Chains

Linear Food Chains and Trophic Cascades But consider. . Bottom up effects Omnivory

A more likely structure… The Trophic Network Or Food Web

Functional Guilds

Soil Food Web Structure – Biotic Effects

Positive and Negative Feedback in Food Web Structure Sinorhizobium meliloti and bacterivore nematodes 0 nematodes Fu et al. 2005 5 nematodes With twenty nematodes

Soil Food Web Structure – Environmental Effects Environmental heterogeneity Separate metacommunities? Zones and Gradients: texture structure temperature water O 2 CO 2 NO 3 NH 4 minerals

Food Web Structure - Patchiness • Resource distribution • Spatial heterogeneity • Organism motility • Omnivory • Strong and weak links • Microsite asynchrony • Viewing resolution

Structure and Function: Abundance and Diversity consumers resource Functional Complementarity Functional Redundancy Strength of Function or Service Functional Group Diversity Loreau, Oikos 2004 Functional Group Diversity

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 Herbivores Bacterivores Fungivores Omnivores Predators

Why nematodes as bioindicators? • • 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

Functional Diversity of Nematodes

Enrichment Indicators Rhabditidae Panagrolaimidae etc. ¨Short lifecycle ¨Small/ Mod. body size ¨High fecundity ¨Small eggs ¨Dauer stages ¨Wide amplitude ¨Opportunists ¨Disturbed conditions Structure Indicators Aporcelaimidae Nygolaimidae etc. Basal Fauna Cephalobidae Aphelenchidae, etc. ¨Moderate lifecycle ¨Small body size ¨Stress tolerant ¨Feeding adaptations ¨Present in all soils ¨Long lifecycle ¨Large body size ¨Low fecundity ¨Large eggs ¨Stress intolerant ¨Narrow amplitude ¨Undisturbed conditions

• Disturbed • N-enriched • Low C: N • Bacterial • Conducive Ba 1 Enriched • Maturing • N-enriched • Low C: N • Bacterial • Regulated En ric hm en t in de x Testable Hypotheses of Food Web Structure and Function • Degraded • Depleted • High C: N • Fungal Basal • Conducive Fu 2 Basal condition Structured Fu 2 Ba 2 Ca 3 Fu 3 Ba 3 Om 4 Ca 4 Fu 4 Ba 4 Structure index Ferris et al. (2001) Om 5 Ca 5 Fu 5 Ba 5 • Matured • Fertile • Mod. C: N • Bact. /Fungal • Suppressive

Food Web Analyses Enrichment Index Tomato Systems Yolo Co. Mojave Desert 100 Prune Orchards Yuba Co. 50 0 0 50 Structure Index Redwood Forest and Grass Mendocino Co. 100

Management of Food Web Structure: Carbon Pathways and Pools Herbivore Fungal Omnivory Decomposition Bacterial channelized reticulate

Carbon Channel Management Bacterivore Channel • “Fast Channel” • Moisture • Low C: N, labile substrates • High respiration and turnover • Mineralization of nutrients • Major predators are protozoa and Herbivore Channel • “Intermediate Channel” nematodes • Host status and defense mechanisms • Damage to host • Substrate respiration and immobilization, excretion and defecation Fungivore Channel • “Slow • Major predators are. Channel“ fungi and nematodes • High C: N, lignin, cellulose, resistant substrates • Conservation of carbon, greater web structure • Major predators are microarthropods and nematodes

Structure and Function Regulatory function P Nutrient function F B O P Pr F B O Pr

Inflow Channel Analysis

Succession C supplied Resource transformation Community structure shifts Ferris and Matute (2003)

Resource transformation Channel Index: • a weighted ratio of fungivore and bacterivore nematodes • higher CI indicates more fungal Ferris and Matute (2003)

Food Web channel management: Nature and timing of carbon sources Data adapted from Mc. Sorley and Frederick. 1999. what if?

Food for the Soil Food Web external sources rhizodeposition old root death C external sources rhizodeposition herbivory old root death herbivory C

Soil Food Web Management - Experiment and Observation Mineralization potential of fungal- and bacterial-feeding nematodes C: N = 4: 1 C: N = 8. 5: 1 C: N = 8. 3: 1 C: N = 6: 1

Sustainable Agriculture Farming Systems Project 1988 -2000

Soil Food Web Management - experiment Cover crop Irrigation temperature moisture T 0 activity M 0

How Fragile is the Food Web? Sampled 2000 Organically-managed for 12 years Enrichment index 100 Sampled 2001 After Deep Tillage 100 50 50 Structure index Berkelmans et al. (2003) 100 0 50 Structure index 100

Standardized Counts Nematode Sensitivity – Mineral Fertilizers Ammonium sulfate 200 Nematode guild 150 100 c-p 1 c-p 2 c-p 3 c-p 4 X c-p 5 X 50 X X 0 0 0. 02 0. 05 0. 1 X X 0. 5 1 Concentration (m. M-N) Tenuta and Ferris (2004)

Disadvantages: ↓Productivity ↑Continuous ↑Monitoring ↑Rotation ↑Risk ? Equipment ? Economics ? Labor ? Knowledge base Transplant inoculants: Entomopathogenic nematodes Rhizobia Flourescent pseudomonads Nematode-trapping fungi Advantages: Surface mulch with ↓Tillage designed C: N ratio Pestfuel ↓Fossil resistance/tolerance ↓Dust Undisturbed ↓Leaching Buried drip ↑Soil structure ↑Porosity ↑Food web structure ↓Pesticides ↓Mineral fertilizers ↓Weeds and herbicides ↓Water ↓Costs ↑Sustainability

Some References • 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 CO 2 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: 8594. • 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