Lecture 3 Soil Engineers

2. Lecture 3Soil Engineers

3. Learning Objectives • Lecture 3 – Soil Engineers • Explain why earthworms, ants and termites are called soil engineers • Describe earthworms as an example for the importance of functional diversity and the impact of invasive species (both negative and positive) • Discuss the benefits of managing soil to encourage a healthy, diverse soil community.

4. Lecture 3 - Topics • Intro Soil Engineers • Earthworms • Summary of Soil Organisms

5. Ecosystem Engineers Organisms that make major alterations to the physical environment that influences the habitats for many other organisms within the ecosystem • Microorganisms that create impermeable surface microbiotic crust that spatially concentrates scarce nutrient and water supplies in certain arid and semi-arid ecosystems. • Burrowing animals that create air and water movement in soil as well as create root passages through dense surface soils. Earthworms are “nature’s tillers”. Ants and termites create passage ways and mounds. • Humans

6. What Do Earthworms Do? • Stimulate microbial activity • Earthworms derive nutrition from microbes • Organic matter is fragmented and inoculated in gut • Greater microbial biomass in feces and casts than in surrounding soil – microbial hotspot http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html

7. What Do Earthworms Do? (cont) • Soil passed through the earthworm gut is expelled as “casts”. • During the passage through the gut, organic materials are shredded and mixed with mineral soil materials. The casts enhance the aggregate stability of the soil. • Carry organic matter down into deeper soil layers • Mix and aggregate soil

8. What Do Earthworms Do? (cont) • Increase infiltration • Improve water holding capacity Burrow • Increase porosity • Burrows become preferential flow paths • Help minimize surface water erosion • By fragmenting organic matter and increasing soil porosity and aggregation - earthworms improve water holding capacity http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html

9. What Do Earthworms Do? (cont) • Stimulate microbial activity • Mix and aggregate soil • Increase infiltration • Improve water holding capacity • Provide channels for roots growth • Bury and shred plant residue Pulling corn leaf into burrow http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html

10. Earthworm Functional Diversity Epigeic Surface soil and litter species Endogeic Upper soil species Anecic Deep burrowing species http://www.nrri.umn.edu/worms/identification/ecology_groups.html

11. Earthworm Video www.bbc.co.uk/nature/life/lumbricidae#p00thgkz

12. Abundance and Distribution Native Earthworm Distributions The majority of temperate and many tropical soils support significant earthworm populations (Proulx 2003 risk assessment of non-indigenous earthworms)

13. Abundance and Distribution Native Earthworm Distributions Invasive Earthworm Distributions L. terrestrus and L. rubellus (Proulx 2003 risk assessment of non-indigenous earthworms)

14. Active Invasion on Local Scales Box 10.1 in text L. rubellus in Cornell’s Arnot Forest, NY (Bohlen et al. 2004, Ecosystems)

15. Smithsonian Forest Macroinvertebrate activity Litter decay Organic matter inputs 3 old forest sites (120-150 y) 3 young forest sites (50-70 y)

16. Mid Late Dominant earthworms • Consume litter layer, can leave 60% of soil surface bare • Even when native earthworms are present, invasives make major alterations to the soil environment L. rubellus 60 50 40 30 Earthworm biomass (g/m2) 20 10 0 SuccessionalStage (Filley et al. 2008, Global Biogeochemical Cycles)

17. Invaded Forests • Biomass and density was high • Species diversity was low • Functional diversity was low

18. Earthworms and Agriculture • Croplands in the US can contain 50-300 earthworms/yd2 • Grasslands and temperate forests can have 100-500 earthworms/yd2 • Based on total biomass, earthworms predominate the soil invertebrates • Lumbricidae is the most important family of earthworms enhancing agricultural soils*. • Only 2 species are native, • the rest are from Europe and Asia

19. Putting Invasives to Work BUG BIOGRAPHY:  Night Crawlers and Tillage The substitution of conventional tillage by no-till or conservation tillage is increasingly common and widely adopted in the United States and elsewhere. In these situations, earthworms, particularly the “night crawler,” Lumbricusterrestris L., are especially important. Earthworms become the main agent for incorporating crop residue into the soil by pulling some into their burrows and by slowly burying the remainder under casts laid on the soil surface. In reduced tillage systems, surface residue builds up and triggers growth in earthworm populations. Earthworms need the food and habitat provided by surface residue, and they eat the fungi that become more common in no-till soils. As earthworm populations increase, they pull more and more residue into their burrows, helping to mix organic matter into the soil, improving soil structure and water infiltration. http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html

20. Summary – Ecosystem Engineers • Organisms that make major alterations to the physical environment that influences the habitats for many other organisms within the ecosystem • Earthworms dominate the soil invertebrates, occur at every trophic level • Native populations are biodiverse, species and functional diversity • Invasive populations are more likely to have greater biomass but less diversity • Invasive earthworms can be damaging in forest floors but beneficial in some agricultural systems

21. Summary – It’s Alive • Soil is a complex, diverse ecosystem • Organisms incorporate plant residues into soil, return CO2 to the atm where it can be re-fixed into plants. In the process, soil organic matter is formed and essential plant nutrients are released. • 80-90% of metabolic activity in soil food web is bacteria and fungi • The activity of organisms is more important than the identity. Functional diversity vs. species diversity.

22. Summary – Beneath the Surface • Rhizosphere • Hyphae • Mycorrhizae • Biological N fixation • Inoculants to be sure that crops have the right symbiosis cost $3 /ha; fertilizer costs $87 /ha • Nearly as much N fixed into fertilizers than BNF annually

23. Summary – Soil Organisms • In every healthy system or watershed, the soil food web is critical to major soil functions • Sustaining biological diversity • Regulating flow of water and dissolved nutrients • Storing and recycling nutrients and elements • Filtering, buffering, degrading, immobilizing, detoxifying potential pollutants • Complexity, that is, interactions among organisms and high functional diversity within the soil food web, enhances these functions • Microorganisms and earthworms dominate the life of most soils (Table 10.4)