Nematode Assemblages as Plant Health Indicators - a soil food web perspective

1. Nematode Assemblages as Plant Health Indicators- a soil food web perspective Howard Ferris Department of Nematology University of California, Davis hferris@ucdavis.edu July, 2007

2. Functional Diversity of Soil Nematodes

3. Soil Food Web Functions - metabolic and behavioral activities • that impact the biotic or abiotic components of the ecosystem • Feeding: Ingestion, assimilation, defecation and excretion • Behavior: Movement, activity, migration • Functions may be classified, subjectively, as Services orDisservices • Disservices: • Damage to plants of agricultural or ornamental significance • Injury to humans and vertebrate animals • Services: • Sequestration and redistribution of minerals • Mineralization of organic molecules • Acceleration of turnover • Regulation and suppression of pests • Substrate alteration providing access to other organisms • Phoretic redistribution of organisms

4. Functional Diversity in relation to Structure of the Soil Food Web P P F O Pr O Pr F B B Effects of: tillage tertilizers pesticides punctuated cropping type and amount of organic input Regulation Mineralization

5. perennial intermediate wheatgrass annual wheat 0 1 Soil Depth (m) 2 Photograph courtesy of Dr. Jerry Glover The Land Institute Soil Food Webs Bottom up effects: Resource availability

6. P F O Pr B Resources Soil Food Web Structure is strongly influenced by nature and frequency of Carbon and Energy Input • Carbon is respired by all organisms in the web • The amounts of Carbon and Energy available limit the size and activity of the web

7. Soil Food Webs – environmental effects on Structure Environmental heterogeneity Zones and Gradients: texture structure temperature water O2 CO2 NO3 NH4 minerals Separate metacommunities?

8. Soil Food Webs – environmental effects on Structure Ammonium sulfate 200 Nematode guild 150 c-p 1 Standardized Counts c-p 2 X 100 c-p 3 c-p 4 50 c-p 5 X X X X X 0 0 0.02 0.05 0.1 0.5 1 Concentration (mM-N) Nematode Sensitivity to Mineral Fertilizer Tenuta and Ferris, 2004

9. Some soil nematodes are Herbivores

10. Herbivory may be a Disservice

11. Or Herbivory may provide Services • It provides resources to the soil food web, often without • measurable plant damage, e.g., Tylenchidae • It may place weed species at a competitive disadvantage • Fiddleneck and Anguina amsinckiae • Silverleaf nightshade and Ditylenchus phyllobia • (but it is difficult to find convincing examples)

12. Observation • A preponderance of herbivores in the nematode assemblage is an indicator that recent soil management has diminished functional diversity in the soil food web.

13. Indices of Structural Diversity are available • Species richness • Simpson’s diversity index • Shannon’s diversity index • etc. From these we infer ecosystem characteristics, e.g., regulation …but they provide no information on food and feeders, prey and predators Functional Diversity is more difficult to assess

14. Cobb Bastian Maupas Ingham Yeates Bongers Wall 19th Century to mid 20th Century discovery of abundance and habitat diversity 20th Century to present functional diversity and bioindicator potential

15. Ingham A milestone contribution: Ingham, R.E., J.A. Trofymow, E.R. Ingham, and D.C. Coleman. 1985. Interactions of bacteria, fungi, and their nematode grazers: Effects on nutrient cycling and plant growth. Ecological Monographs 55:119-140. When feeding on their prey. bacterial- and fungal- feeding nematodes excrete N that is in excess of their structural and metabolic needs.

16. Maturity Index = Bongers Calibration of Ecosystem Function: Colonizer-persister Series opportunism structure enrichment stability 1 2 3 4 5 Bongers, 1990 • Weighting: • should the separations between the classes be equal? Issues of proportions: • If the proportion of opportunists increases, the proportion of sensitive species decreases. • It should be possible to increase structure without decreasing enrichment, and vice versa. The axes should be independent.

17. Nematode Faunal Profiles bacterivores Enriched fungivores • Enrichment index • 100 (w1.cp1 + w2.Fu2) • / (w1.cp1 + w2.cp2 ) Ba1 Enrichment trajectory Structured Fu2 fungivores bacterivores Fu2 Basal Ba2 Om4 Om5 omnivores Basal condition Ca3 Ca4 Ca5 carnivores Fu3 Fu4 Fu5 fungivores Ba3 Ba4 Ba5 bacterivores Structure trajectory • Structure Index = 100 wi.cpi / (wi.cpi + w2.cp2 ) for i = 3-5 Ferris et al., 2001

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

19. Nematode Indicators of Soil Food Web Structure and Function • Disturbed • N-enriched • Low C:N • Bacterial • Conducive • Maturing • N-enriched • Low C:N • Bacterial • Regulated Enriched Ba1 Enrichment index Structured Fu2 • Degraded • Depleted • High C:N • Fungal • Conducive • Matured • Fertile • Mod. C:N • Bact./Fungal • Suppressive Fu2 Basal Ba2 Om4 Om5 Basal condition Ca3 Ca4 Ca5 Fu3 Fu4 Fu5 Ba3 Ba4 Ba5 Structure index Ferris et al., 2001

20. 100 Tomato Systems Yolo Co. Prune Orchards Yuba Co. Enrichment Index 50 Redwood Forest and Grass Mendocino Co. Mojave Desert 0 0 50 100 Structure Index Faunal Analysis of some California Soil Systems

21. Calibration of the N-Mineralization Service of Bacterivore Nematodes

22. C:N = 4:1 C:N = 6:1 Effects of Bacterivore Nematodes onN-Mineralization Rates Ferris, Venette and Lau, 1997

23. Soil Food Web Management – an experiment Sustainable Agriculture Farming Systems Project 1988-2000

24. Soil Food Web Management – an experiment Cover crop Cover crop Irrigation temperature moisture T0 activity M0

25. Ferris et al. (2004)

26. The Importance of Diversity

27. The Importance of Diversity

28. 100 Enrichment Index 50 Woodland 0 0 50 100 Vineyard Structure Index Another Ecosystem Service: • The regulation of opportunistic species

29. Predator: Prey Ratio Density-dependent predation Sánchez-Moreno et al., subm.

30. Managing Input Resources for Food Web Structure and Function: Carbon Pathways and Pools Herbivory Fungal Omnivory Decomposition Bacterial

31. P F O Pr B Structure of the Soil Food Web in relation to Resource Inputs

32. Indices are based on proportions What about biomass?

33. Higher trophic levels - food web shape

34. Higher trophic levels - food web shape

35. Higher trophic levels - food web shape

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

37. Infrequent Resource Input

38. Frequent Resource Input

39. Another Experiment: Soil Food Webs and Carbon Dynamics in Response to Conservation Tillage in Legume Rotations in California Observation: The Structure Index did not increase in two years of organic, no-till, continuous cropping. Conclusion: Increase in Structure Index after changes in management may involve a prolonged period of recolonization by sensitive species, requiring many years. So…. Inoculate nematodes into the vacant niche…. Minoshima et al. (2007)

40. Nematodes are useful bioindicators of soil condition and Plant Health • 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 But we still have much to learn about Soil Food Web Management! More information: http://plpnemweb.ucdavis.edu/nemaplex