Grapevine Root
Growth Dynamics
and Effects of
Drought
Markus Keller
Grapevine root system
• Cuttings: Primary roots grow from cambium
• Branching into secondary, tertiary etc. lateral roots
• Number and placement of lateral roots is not
predetermined; growth depends on soil properties
• Roots detect resource availability and grow preferentially
in water- and nutrient-rich patches
• Young, fine roots (<12 wk) are responsible for resource
acquisition, take up most of a vine’s water and nutrients
• Older, woody roots provide anchorage, transport, and
storage for water and nutrients
5 m (>16 ft)
Huglin & Schneider (1998)
Root anatomy
• Apical meristem: Cell division → Root
elongation growth
• Root cap: Protects meristem from
abrasion, but requires constant renewal.
Contains starch grains as gravity sensors
• Endodermis: Divides root into cortex and
stele. Impregnated with Casparian band
• Cortex: Nutrient uptake and starch
storage
• Stele (vascular cylinder): Xylem and
phloem for water and nutrient transport
• Pericyle (below endodermis): Produces
lateral roots in root elongation zone
• Absorption zone behind growth region:
Water and nutrient uptake
Root anatomy and development
• Suberization (light-blue staining) in grapevine fine roots
• Mainly in endodermis (Casparian band, + lignin) and
exodermis (root/soil boundary)
• Impregnates cells for control of water and nutrient access
Gambetta et al. (2013)
Primary and secondary growth
• Primary growth from apical meristem → Root length 
• Secondary growth from vascular cambium (lateral meristem)
starts ~4” behind tip → Xylem + phloem → Root diameter 
• Pericycle forms
cork cambium
→ Periderm
(Secondary cortex +
cork cambium + cork)
• Exodermis + cortex
+ endodermis are
sloughed off
Xylem = wood
Gambetta et al. (2013)
Root distribution
Roots are concentrated in the top 2-3 ft of soil but can grow
to >30 ft depth
Soil depth (cm)
Root weight (%)
V. cordifolia
V. rupestris
V. riparia
V. berlandieri
Huglin & Schneider (1998)
Plumbing system priming
• Bleeding (sap flow) before budbreak
• Exudation of xylem sap (0.1 – 1 L/day)
• Starts at soil temperature >45°F
• Caused by root pressure (0.2 – 0.4 MPa):
Remobilized nutrient reserves → Xylem
osmotic pressure  → Soil water uptake 
• Restores xylem function: Dissolves air
bubbles (cavitation) formed during freezethaw cycles in winter
• Rehydrates buds:
<50% → 80% water content
• Requires moist soil
Gone too far: Trouble at budbreak
• Dry winter → Vines cannot initiate sap flow
• Delayed budbreak, stunted shoot growth,
aborted clusters, poor fruit set
• Measure soil moisture before budbreak
• Irrigate if soil is dry (>3-4% below FC)!
Shoot vigor (cm/d)
Days to budbreak
45
2.0
Sand
Loam
40
35
1.5
Sand
Loam
30
25
1.0
20
15
0.5
10
5
0.00
6
8
22 24
10 12
12 14
14 16
16 18
18 20 22
10
Soil moisture
moisture (%)
Soil
(%)
Seasonal root growth
• Growth requires auxin from shoot tips and sugar
from leaves or reserves
• Growth throughout growing season (mostly
prebloom – veraison); even in winter in warm soil
• Roots have no winter dormancy, do not seal
phloem with callose nor convert starch to sugar
• Fine roots (<1 mm) are short-lived → Replacement
• White → Brown (5 wk) → Black (8-11 wk)
• Browning = End of ‘functional’ period (metabolism),
but root can still serve as water pipe
• Lifespan is shorter prebloom, with heavy pruning,
or in shallow soil
• Shoot hedging temporarily arrests root growth via
auxin elimination
Temperature and root growth
•
•
•
•
•
•
Temperature  → Root growth 
Lower temperature threshold: 43°F
Optimum temperature: 86°F (almost never in vineyards!)
Higher temperatures kill fine roots within days
Soil buffers temperature fluctuations
Dry and sandy soils have lower buffering capacity
59°F
77°F
Smith, 2004
Erlenwein, 1965
Soil moisture and root growth
• Roots grow downward, following path of
least resistance (soil pores, cracks), but
grow towards moist soil regions
• Hydrotropism: Roots grow away from high
osmotic pressure (can override gravitropism)
• Roots grow preferentially in moist soil
patches → Concentration beneath drip lines
• Roots may find water below
bedrock → Root zone 
→ Vigor control?
How roots cope with stress
• Roots can grow at lower water potential (Ψ) than shoots
• Some ABA → K+ release into xylem  → Root Ψ 
→ Phloem water import 
• More ABA → Root growth 
• Osmoregulation: Root tips accumulate sugar and amino
acids → Root Ψ  → Water uptake continues
• Hydraulic redistribution: Wet roots supply water to dry roots
• Water deficit reduces root growth but favors root over shoot
growth → Root:shoot ratio 
• Water deficit reduces radial root growth more than root
elongation → Root thickness 
• Severe deficit (drought) → Phloem flow and root growth
stop, storage reserves (starch)  → Spring growth 
• Extreme deficit (prolonged drought) → Root death
The good news: It’s in the book!
www.amazon.com/Science-Grapevines-Anatomy-Physiology/dp/012374881X