Lecture 3Soil Engineers

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.

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

Organisms that make major alterations to the physical environment that influences the habitats for many other

organisms within the ecosystem

Ecosystem Engineers

• 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

What Do Earthworms Do?

1. 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

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

2. Mix and aggregate soil

What Do Earthworms Do? (cont)3. Increase infiltration4. Improve water holding capacity

http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html

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

What Do Earthworms Do? (cont)1. Stimulate microbial activity2. Mix and aggregate soil3. Increase infiltration4. Improve water holding

capacity5. Provide channels for roots

growth6. Bury and shred plant residue

http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html

Pulling corn leaf into burrow

Earthworm Functional Diversity

http://www.nrri.umn.edu/worms/identification/ecology_groups.html

EpigeicSurface soil and

litter species

EndogeicUpper soil species

AnecicDeep burrowing

species

Earthworm Video

www.bbc.co.uk/nature/life/lumbricidae#p00thgkz

Abundance and Distribution

Native Earthworm Distributions

(Proulx 2003 risk assessment of non-indigenous earthworms)

The majority of temperate and many tropical soils

support significant earthworm populations

Abundance and Distribution

Native Earthworm Distributions

(Proulx 2003 risk assessment of non-indigenous earthworms)

L. terrestrus and L. rubellus

Invasive Earthworm Distributions

Active Invasion on Local Scales

(Bohlen et al. 2004, Ecosystems) L. rubellus in Cornell’s Arnot Forest, NY Box 10.1

in text

Smithsonian Forest

3 old forest sites (120-150 y)

3 young forest sites (50-70 y)

Macroinvertebrate activityLitter decayOrganic matter inputs

Dominant earthworms

Late

Mid

• Consume litter layer, can leave 60% of soil surface bare

• Even when native earthworms are present, invasives make major alterations to the soil environment

Earthworm biomass (g/m2)

Successional Stage(Filley et al. 2008, Global Biogeochemical Cycles)

L. rubellus

10

20

30

40

50

60

0

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

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

Putting Invasives to WorkBUG 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,” Lumbricus terrestris 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

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

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.

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

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)