HC 9: Microbial Ecology of the rhizosphere:

-“spheres” (4)

• The rhizosphere: the soil zone that surrounds and is influenced by the roots of plants.

• Endorhizosphere: inside of the root.

• Ectrorhizospere: soil outside of the root.

• Rhizoplane: the surface of the root in contact with the soil.

The role of plants in driving microbial diversity

Plants drive microbial diversity by creating different microhabitats and resources that select for specific microbes

• Through root exudates (such as sugars, amino acids, and signaling molecules), plants feed and attract certain microorganisms

• Their immune systems and root chemistry filter out others

Bulk soil vs. rhizosphere

Bulk soil generally has higher microbial diversity than the rhizosphere

• it is less strongly influenced by plant selection

• a wide range of stable and varied microhabitats supports many different microbial lifestyles, including slow-growing and specialized organisms.

Rhizosphere: plant immune responses that strongly favor a limited group of fast-growing, root-adapted microbes, reducing overall diversity

“Soil memory via the microbiome”

refers to the idea that previous plants, management practices, or pathogen exposures leave a lasting imprint on the soil’s microbial community

• These microbial shifts can persist over time and influence how future plants grow, either by improving functions like disease suppression or by altering nutrient cycling and plant performance.

• But this is also trade-off; e.g. Reducing ethylene improves growth under low stress conditions, but decreases ability to cope with stress.

Adaptive microbial partners

microbes that consistently increase plant fitness in a given environment

• for example by promoting nutrient uptake, producing growth hormones, or protecting against pathogens
  »so their presence benefits the plant under those conditions.

Maladaptive microbial partners

microbes that form associations with plants but reduce plant fitness

• such as by acting as weak pathogens, over-consuming resources, or prioritizing functions like pathogen competition at the expense of plant growth

how plants influence the diversity and composition of the rhizosphere microbiome

Planten drijven microbiële diversiteit aan door microhabitats en hulpbronnen te creëren die specifiek bepaalde microben selecteren (selectieve druk)

Understand the different modes of action of so-called plant-growth-promoting (rhizo)bacteria (PGPR)

1.       directe remming: f.e. bacterie die pathogeen direct remt door productie van antibiotica

2.       induceren van afweer: ze kunnen de eigen afweermechanismen van de plant activeren (ISR)

3.       hormoonregulatie: door ethyleenniveaus in de plant te verlagen à bevordert groei (bij weinig stress)

4.       voedingsstoffen: kunnen helpen bij opname van nutriënten (f.e. stiikstoffixatie)

the evolutionary forces that help maintain plant-microbe interactions (role of other interactions)

-      Mutualisme blijft alleen bestaan als de voordelen opwegen tegen de kosten

-      mechanismen tegen “cheaters” door f.e. hun toevoer van zuurstof of suikers te beperken

-      de opbouw van het microbioom is een combi van verticale – en horizontale transmissie