meet the cast:

soil biology

rhizosphere

the rhizosphere is a bustling metropolis with billions of organisms in a single teaspoon! it's the area of soil that is in close contact with plant roots, where biological activity and turnover provides available nutrients right where plants needs them most!

rhizosphere

roots release carbon-rich sugars, amino and nucleic acids that attract bacteria and fungi......high concentrations of bacteria and fungi attract protozoa and nematodes......and high concentrations of protozoa and nematodes attract arthropods and earthworms.

soil food web

soil is home to 1/4 of the world's biodiversity with billions of organisms -- 10's of 1,000's of species -- in a single teaspoon. the soil food web serves as the foundation of every (terrestrial) food web on the planet!

plants:the “sugar daddy”and“mixers”fungi:“connectors”insects:“shredders”animals:the “fertilizers”archaea: “extremophiles”protozoa: “grazers”bacteria:“decomposers”

symbioses

nitrogen fixation

legumes (i.e. soybeans, alfalfa) release signaling compounds, known as flavonoids,which attract nitrogen fixing bacteria called rhizobia.in response, rhizobia release nodule factors,which help the rhizobia enter the root hair. the root hair curls, cells divide rapidly, and a nodule forms around the rhizobia.this process,which pulls nitrogen out of thin air and into the soilvia plant-microbe symbiosis accounts for65%of the nitrogen used to growfoodworldwide. creating more “tightly coupled” nutrient cycles can lead to less nitrogen loss, saving farmers money and protecting our groundwater!biologicalnitrogen fixationNPKmineral fertilizer

fungal networks

common mycelial networks allow plants tocommunicate with one another,requesting nutrientswhen there is a deficiency,warning of a pestwhen there is an attack,and providing extra protection against disease.

plants release compounds to attract mycorrhizal fungi, stimulating the growth of thread-like hyphae, which connect within or outside the roots, extending their reach 100-1000x. the root provides sugars which feed the fungus and in turn, its hyphae spread throughout the soil in search of water, nitrogen, phosphorus, and other nutrients.

plant growth promotion

different bacteria and fungi release different types of organic compounds that can promote plant growth, regulate hormones, and protect against disease and environmental stress.

sesquiterpenes attract insect-feeding nematodesflorigenauxins:promote root initiationgibberellinstimulates cell elongationcytokinininduces shoot growthprimarymetabolitesprovide nutrients for plant-growth promoting bacteriatriggers blossoming

biocycling

from photosynthesis to metabolism, organic materials move up and down the food chain — eaten and excreted by microbes, insects and animals, which are eaten and excreted by other organisms. as they decompose, nutrients are made available for new growth and the cycle continues.

bioturbationnitrogen fixationplant respirationCCCCCplant uptakeKMgdecompositionCrespirationCphotosynthesisplant roots extend into deeper horizons to access water and nutrients

biodegradation

microbes in the soil also have the ability to break down organic compounds, considered toxic to humans. they can even transform heavy metals into less toxic or less mobile forms.

so what's with all the pollution?

a microbe's ability to degrade toxic substances is controlled by:

(physical)(biological)pollutantsenvironmentorganismsbiodegradabilityavailabilityphysiologicalfitness(chemical)

soil: the final frontier