Macrofaunaeg moles, earthworms, ants, millipedes,spiders, beetles– The ‘structural engineers’ of the soil– Create aeration– Earthworms incorporate organic material into the soil

– Earthworms provide channels for root growth

Mesofaunaeg mites, springtails (collembola)– Eat dead plant material and fungi

– Break down decaying matter– Help nutrient cycling

Microfaunaeg protozoa, nematodes– Protozoa, for the most part, feed offsoil bacteria

– Nematodes are a diverse group,including plant parasites and predatorsthat feed on bacteria, fungi or othernematodes

– Microfauna releasenutrients thatplants canuse

Microorganismseg bacteria, fungi, viruses– Microorganisms perform a varietyof functions, including:> soil stability (aggregate formation)> decomposition of organic matter> nutrient cycling> nutrient uptake by plants> disease suppression> induced systemic resistance> plant growth promotion> production of antibiotics and hormones> toxin breakdown (pesticides, pollutants)

– Microorganisms that interact directly with roots can affect planthealth and/or productivity in either a positive or a negative way

– Viruses can be transmitted by plant-feeding nematodes orcertain groups of fungi that infect plant roots

Summer 2016

Not to scale

An introduction tosoil biology

Organisms in the soil

© Agriculture and Horticulture Development Board 2016. All rights reserved.

While the Agriculture and Horticulture Development Board seeks to ensure that the information contained within this document is accurate at thetime of printing, no warranty is given in respect thereof and, to the maximum extent permitted by law, the Agriculture and Horticulture DevelopmentBoard accepts no liability for loss, damage or injury howsoever caused (including that caused by negligence) or suffered directly or indirectly inrelation to information and opinions contained in or omitted from this document.

Reference herein to trade names and proprietary products without stating that they are protected does not imply that they may be regarded asunprotected and thus free for general use. No endorsement of named products is intended, nor is any criticism implied of other alternative butunnamed products.

AHDB Cereals & Oilseeds is a part of the Agriculture and Horticulture Development Board (AHDB).

Further informationAmanda Bennett, AHDBamanda.bennett@ahdb.org.uk

cereals.ahdb.org.uk

Soil-borne pathogens and pestsSoil-borne pathogens and pests may not causeobvious above-ground symptoms, although there maybe stunting or areas of the field showing poor plantperformance; rotting roots will impair root functioning.

Damage occurring below ground can have asignificant impact, particularly when the harvestedproduct is a root crop (symptoms may not be noticeduntil harvest).

Disease in the field can be patchy rather than uniform.

Control of soil-borne pathogens and pests is notsimple and chemical options are not really viable.

Spores of most soil-borne pathogens can survive formany years.

DeleteriousmicroorganismsMicrobial interactions inthe root zone(rhizosphere) that have adetrimental effect on theplant without visiblesymptoms are not wellunderstood. However, theimpact of deleteriousmicroorganisms on plantgrowth and productivityhas been demonstratedby soil sterilisation or soiltransfer experiments, andvarious modes of actionhave been implicated.

Beneficial microorganismsBiological controlBiological control is important in eitherstopping pathogens from infecting roots,weakening the pathogens or making theplants more resistant to pathogen attack.

Modes of action include direct parasitism,competition for space or nutrients, productionof antibiotics, or inducing the plant to switchon its resistance mechanisms.

Mycorrhizal fungi

Example – DirectparasitismConiothyrium minitanscolonises the restingstructures of the soil-bornepathogen, Sclerotiniasclerotiorum, preventinggermination of the sclerotiumand the subsequent releaseof pathogenic spores.

Example – CompetitionPhialophora sp. is a naturalantagonist to the take-allpathogen. It either directlycompetes for space/nutrientsin the root tissue orstimulates the plant'sdefence mechanisms.

Plant growth-promoting rhizobacteria (PGPR)PGPRs are bacteria that colonise plant roots and benefit plants through mechanisms such as suppression ofplant disease, production of antibiotics, improved nutrient acquisition, or phytohormone production.

Induced systemic resistanceDefence responses to foliar pathogens canalso be triggered by root-associatedmicroorganisms.

Nitrogen-fixingrhizobiaBacteria thatassociate with theroots of leguminousplants fixatmospheric nitrogeninto a form that isuseable by the plant.

Ectomycorrhizal fungi form asheath around the root, extendingthe volume of soil that can be‘tapped’ for nutrients.

Arbuscular mycorrhizal fungi formassociations with most plant species,and live within the root tissue itself.Benefits to the plant include improvednutrient uptake, particularly phosphorus.