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Monday, June 7, 2021

What's Going on Underground--The Rhizosphere

We are totally focussed on what is happening with our vines above ground but there are important things happening underground with the root system of a vine. Here is just a short list of what the root tip does:1
  • this region is the most physiologically active and has a highest risk of early mortality
  • water and inorganic nutrient uptake
  • synthesis of growth regulators
  • site for the initiation of mycorrhizal associations
  • root hairs and root cap also release organic nutrients into the soil, promoting the development of a unique microbial flora on and around the root
  • development of a unique rhizosphere microbial flora on and around the root tip
What intrigued me about what I was reading was the mycorrhizal associations that the grapevine root tip makes creating a zone called the rhizosphere:
  • grapevines are among the more than 80% of plant species that develop mycorrhizal associations
  • only vesicular–arbuscular fungi invade grapevine roots
  • Glomus species are the primary vesicular–arbuscular fungi associated with grapevines, although Acaulospora, Gigaspora, Scutellospora and Sclerocystis are occasionally involved
  • root hairs are generally short-lived, and their collapse provides additional nutrients for microbial activity
  • mycorrhizal roots are strong sinks for plant carbohydrates
  • mycorrhizal hyphal extensions absorb and translocate minerals and water back to the root
  • mycorrhizal fungi are more effective at mineral absorption than the root itself by producing hydroxyamates (peptides) that combine with and facilitate nutrient uptake
  • mycorrhizal hyphae also secrete oxalate, citrate, and malate that mobilize various mineral elements
  • mycorrhizal hyphae in mineral uptake is especially notable with poorly soluble inorganic nutrients, such as phosphorus, zinc, and copper
  • mycorrhizal associations also appear to protect the vine from the toxic effects of soil contamination with lead and cadmium
  • mycorrhizal fungi augment water uptake and transport to the host under drought conditions, enhance stomatal conductance and transpiration, and accelerate recovery from stress
  • both root and mycorrhizal exudates appear to influence soil texture and the soil flora
  • mycorrhizal associations also tend to reduce vine sensitivity to salinity and mineral toxicities

References:
1. . Ronald Jackson, Wine Science Third Edition, Elsevier, 2008, pg. 53-54.

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