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.