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Rhizosphere

Also known as
root zone, rhizosphere microbiome

The rhizosphere is the thin zone of soil immediately surrounding plant roots that is directly influenced by them. Roots release sugars, amino acids and other compounds there, which feed a dense, active community of microorganisms that affects nutrient availability and plant health.

What is the rhizosphere?

The term was coined by the German scientist Lorenz Hiltner in 1904. It describes the narrow band of soil, often only a few millimeters thick, that surrounds living roots and is changed by them. Roots release a mix of compounds, called root exudates, including sugars, amino acids and organic acids, along with sloughed-off cells. These feed microorganisms, so the rhizosphere supports far more microbial activity than the bulk soil farther from roots.

Scientists also distinguish the rhizoplane, the root surface itself, and the endosphere, the inside of the root, where endophytes live.

Why the rhizosphere matters

  • Nutrient cycling. Microbes in the rhizosphere break down organic matter and release nutrients, and some make bound nutrients available, as in phosphorus solubilization.
  • Plant growth. Plant growth-promoting rhizobacteria and fungi such as mycorrhizae interact with roots to improve growth and nutrient uptake.
  • Disease. The rhizosphere is where soilborne pathogens meet roots, and where beneficial microbes can compete with or suppress them.
  • Soil structure. Root exudates and microbial products help bind soil into aggregates.

Managing the rhizosphere

Plants shape their rhizosphere, but so does management. Crop choice, rotation, tillage, fertilization and cover crops all influence which microbes live there. Many agricultural biological products are designed to establish in the rhizosphere, delivered as seed treatments or in furrow so that the organisms are in place as roots grow.

Frequently asked questions

It is typically a few millimeters around each root, but because roots are so extensive, the total volume of rhizosphere soil in a field is large.

The soil microbiome is the community of microbes throughout the soil. The rhizosphere is the zone next to roots, where that community is densest and most influenced by the plant.

  • Endophyte

    An endophyte is a bacterium or fungus that lives inside a plant's tissues for at least part of its life without causing disease. Some endophytes benefit their host, for example by improving nutrient uptake, growth or tolerance to stress.

  • Plant growth-promoting rhizobacteria PGPR

    Plant growth-promoting rhizobacteria (PGPR) are bacteria that live in the soil around roots, on root surfaces or inside roots and benefit plant growth, for example by making nutrients available, producing plant hormones or protecting against disease.

  • Soil microbiome

    The soil microbiome is the community of microorganisms living in soil, including bacteria, archaea, fungi, protists and viruses. These organisms decompose organic matter, cycle nutrients, build soil structure and influence plant health.

Sources

  1. Soil Biology Primer, USDA Natural Resources Conservation Service
  2. The rhizosphere: history and concepts, Peer-reviewed reviews