Who lives in the soil ?? The Furrow

Soil is an archive of life on earth!

Quantifying Biodiversity Group Known Species Estimated Total Species Percentage Known Vascular plants 220,000 270,000 81% Algae 40,000 60,000 67% Fungi 69,000 1,500,000 5% Bacteria 3,000 30,000 10% Most occur in soil (Hawksworth, 1991)

Soil organisms vary widely in size Most are tiny !!! Soil organisms vary widely in size Viruses Bacteria Fungi Algae Protozoa Nematodes Microarthropods Enchytraeids Earthworms Ants, termites, spiders Mollusks Others: rodents, snakes, voles, amphibians, etc. Body size increasing Microflora Microfauna Mesofauna Macrofauna Megafauna Abundance

Body sizes and shapes are adaptations to the many different spatial niches in soil                                                                                 

BACTERIA have many different shapes cocci bacillus filamentous SSSA filamentous spirilla

Typically > 10 billion bacteria per gram of soil

What do bacteria do in soil ? Colonize aerobic and anaerobic environments Decompose labile substrates Mediate redox transformations Nourish bacterivores Fix N

N-fixing nodules on a cowpea plant

Legume love affair Sarrantonio

FUNGI have many different life forms Yeasts Mycelia Fruiting bodies Spores

What do fungi do in soil ? Decompose recalcitrant organic compounds Penetrate residues Stabilize soil structure Nourish fungivores Form symbioses with plant roots and soil fauna Compete with plant pathogens Parasitize plants and soil animals Produce toxins e.g. aflatoxin produced by Aspergillus flavus on peanut Photo credit: No. 48 from Soil Microbiology and Biochemistry Slide Set. 1976. J.P. Martin, et al., eds. SSSA, Madison WI. File name: SSSA48

Mycorrhizal diversity Ectomycorrhizae AM endomycorrhizae Arbutoid mycorrhizae Ericoid endomycorrhizae Orchid endomycorrhizae Lavelle and Spain (2001)

Mycorrhizal Networks: Connecting plants intra- and interspecifically Many plants are connected underground by mycorrhizal hyphal interconnections. Mycorrhizal (AM) fungi are not host specific. Illustration by Mark Brundrett

Increase nutrient (P) uptake suppress pathogens Mediate plant competition Improve soil structure Increase nutrient uptake N, K, Cu, Zn, and esp. P Enhance water acquisition Increase resistance to pathogens Mediate plant competition Improve soil structure through glomalin All of these benefits are situation dependent Glomalin Superglue of the soil ??

PROTOZOA Important bacterivores Ciliates Amoebae Flagellates Largest of the protozoa Move by means of hair-like cilia Amoebae Also large Move by means of a temporary foot (pseudopod) Include testate amoebae (with shell-like covering), and naked amoebae Flagellates Smallest of the protozoa Move by means of flagella (1-2) Important bacterivores

Soil-Dwelling “Vampires” Vampyrellids are a group of amoebe that eat fungi by drilling round holes through the fungal cell wall and consumes the fluid inside. In this picture, they attack Gaeumannomyces graminis, the fungus that causes “take-all disease” in wheat. File name: vampraid.jpg, 451K (Also: E-4 at 1500KB, shows whole Bug Biography.) Photo credit: Homma, Y. et al. 1979. Phytopathology 69:1118-22. (Photo is in the public domain.) Vampyrellid amoebae attacking Gaeumannomyces graminis, the fungus that causes “take-all disease” in wheat.

NEMATODES Most abundant of the soil fauna Functionally diverse Bacterivores Fungivores Herbivores Predators Omnivores File name: large todes LR.jpg, 262K Credit: Elaine R. Ingham, Oregon State University, Corvallis. Most are beneficial - promoting decomposition and nutrient recycling http://nematode.unl.edu/hdigonic.htm

Nematode diversity Bacterivore Fungivore Predatory Plant parasitic Top left is the bacterial-feeding nematode, Elaphonema. Bottom right is a fungal-feeding nematode. Photo credits: (for both) Elaine R. Ingham, Oregon State University, Corvallis File names: BFTODE FFTODE Predatory Plant parasitic

Galled root system of tomato infected with root-knot nematode, Meloidogyne sp., compared with non-infected root system Root knot juvenile penetrating a tomato root http://www.agnr.umd.edu/users/nrsl/entm/nematology/images/eis143.jpg

Arthropods exoskeleton segmented body jointed legs

Arthropod diversity Litter Shredders Fungivores Predators Herbivores Collohmannia sp. Photo credit: Roy A. Norton, State University of New York at Syracuse. File name: M12 Predators Herbivores

Microarthropods

EARTHWORMS Members of phylum Annelida, earthworms and annelids best known soil inhabitants. More advanced than nematodes because they have a circulatory system- 3-4? hearts Earthworm mass- Photo credit: Clive A. Edwards, The Ohio State University, Columbus. File name: CD1 ew bunch Giant earthworm from Australia; can get up to 11 feet. Also very endangered/rare

~ 35 species of earthworms have been found in Illinois soils anecic ~ 35 species of earthworms have been found in Illinois soils ~ half are exotic species from Europe and Asia endogeic epigeic

Contact Ed Zaborski at (217) 265-0330, or zaborski@uiuc.edu by e-mail A new earthworm parasite has arrived in IL Before earthworms invaded After earthworms invaded A new earthworm predator has arrived in IL The geographic distribution of Bipalium adventitium in Illinois is unknown. Home gardeners and nursery workers may see these exotic land planarians under boards and stones or crawling on the soil surface after rains. They are up to 2.5 inches long and 1/8 of an inch wide when crawling. They are pale brown or tan with a thin dark brown line running down their back. Scientists would appreciate receiving reports of any observations of these creatures. Contact Ed Zaborski at (217) 265-0330, or zaborski@uiuc.edu by e-mail

Epigeic species can be used for vermicomposting

Earthworm cocoons http://soils.usda.gov/sqi/soil_quality/soil_biology/images/CE8a-cocoon_LR_small.jpg

How do earthworms move through soil ? Loose soil They insert their anterior tip into a pore, extend their setae to anchor most of their body and then exert radial and longitudinal pressure. A cycle of alternating contractions and relaxations thrusts their body forward. Dense soil They invert their pharynx, exude lubricating mucus and suck obstructive soil into their body.

How do earthworms eat ? Earthworms eat by pulling food into their mouth with their prostomium (mouth) and pharynx which creates a very strong suction. The food is stored in the crop and then ground up into small digestible pieces in the gizzard. Earthworms need a gizzard because they do not have any teeth. Nutrients are absorbed in the small intestine.

Where are the soil organisms ??

Soil organisms are concentrated in HOT SPOTS ! drilosphere porosphere The rhizosphere is the narrow region where roots and soil meet. Soil biological activity is concentrated here. This photo shows cells, proteins, and sugars being released by the young root tip. Credit: No. 53 from Soil Microbiology and Biochemistry Slide Set.1976 J.P. Martin, et al., eds. SSSA, Madison, WI. File name: SST detritusphere aggregatusphere rhizosphere Adapted from Coleman et al. (19??)

casts middens Drilosphere Zone of earthworm influence

Which burrows were made by an endogeic ? Capowiez et al. 2003)

In 1881, Darwin reported that healthy earthworms sometimes leave their burrows at night and embark on a “voyage of discovery” Surface migration is a routine activity aimed at dispersal and finding a mate. Surface migration usually occurs during cloudy moist conditions. Both anecic and endogeic earthworms are active surface migrants.

Rhizosphere < 10 % of soil volume Zone of root influence

Navigating the rhizosphere Rhizoplane End of the rhizosphere Endo-Rhizosphere Root free soil Ecto-Rhizosphere > 90% of soil volume < 10% of soil volume (Lavelle and Spain, 2001)

Detritusphere surface residue zone

The soil matrix presents its inhabitants with many challenges Tortuous, loosely connected and highly constricted porosity Structural rigidity The soil matrix presents its inhabitants with many challenges Low quality nutritional resources Moisture fluctuations

Microorganisms have very limited ability to move within the soil matrix.

For their prince charmings to arrive ! As a result, most soil microorganisms are in a dormant state For their prince charmings to arrive ! waiting…

There are many types of prince charmings Rain Roots There are many types of prince charmings Organic amendments Tillage

Soil fauna have a disproportionate impact on nutrient cycling, energy fluxes and plant growth >90% metabolic activity

Soil fauna are relatively mobile but have limited digestive ability 3 main types of digestive interactions occur between soil fauna and microflora Soil microflora are relatively immobile but have almost unlimited digestive ability

I want some bacteria for lunch ! Microbivory NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ I want some bacteria for lunch ! Microfauna (e.g. protozoa and nematodes) harness the microflora’s digestive abilities by grazing on them

External rumen digestion The fecal pellets of many mesofauna contain shredded, moistened and mixed but largely undigested residues Reingestion of fecal pellets after a few days of microbial activity greatly increases assimilation

Soil macrofauna are ecosystem engineers Rumen digestion greatly enhances utilization of complex substrates by soil macrofauna Soil macrofauna are ecosystem engineers

Impact of tillage on the soil food web Adapted from Hunt et al. (1986)

Soil organic matter fuels the soil food web

Active OM energizes biologically mediated processes

Biologically active SOM SOM is a complex mixture Living organisms Biologically active SOM Recent residues Recalcitrant SOM HUMUS Adapted from Magdoff and Weil (2003)