1. Root Function Framework of relatively large, woody, long-lived roots
Supporting a mass of small, short-lived non-woody absorbing roots

2. Root Growth Can grow as much as 1 cm/day Controlled by Temperature
0.36 mm/day at 5C
3.4 mm/day at 20C
Water, Nutrients
More nutrients => fewer roots
On infertile sites, more photosynthate goes to the roots – WHY?

3. Root Growth
Total root production can be 50-70% of Net Primary Productivity (NPP)
Fine root growth, respiration & loss
Seasonal Root Turnover
Begins at snowmelt
Declines at budburst
Restricted by water stress
Root death is a MAJOR part of nutrient and carbon cycling!

4. Seasonal Root Turnover
LUKAC, M., CALFAPIETRA, C. & GODBOLD, D.L. (2003) Production, turnover and mycorrhizal colonization of root systems of three Populus species grown under elevated CO2 (POPFACE). Global Change Biology  9 (6),  doi: /j x

5. Growth: Root vs. Shoot
Angiosperms – roots typically grow in synchrony with the shoots
Gymnosperms produce new roots primarily in the spring & fall

6. Root : Shoot Ratios
Figure 3.21: Variations in seasonal shoot & root growth characteristics for eight species of forest trees. Shading indicates shoot growth and solid black represents root growth. Seasonal initiation and cessation of growth are indicated by arrows. From Lyr & Hoffman (1967).
Important for survival on dry sites
Competition for carbon

7. Root Hairs

8. Root Hairs 1 cell wide, last hours to weeks
Continually form just behind root tip
Increase surface area for absorption of water and mineral nutrients
Attachment for soil-borne microbes
Increase adhesion between roots & surroundings
Sensitive to desiccation
Most are produced in the spring (95%) and are seasonal

9. Root Water Uptake (primary function)
Controlled at the endodermis
Temperature = f(viscosity, membrane phase change)
Water – lack of potential gradient
Nutrients – some selective absorption, active uptake

10. How do plants get water and nutrients?

11. Rhizosphere Absorbing root – soil interface
About 1 mm in width, it surrounds the
Epidermis of the living root hairs
Boundary cells of mycorrhizae
Hyphae growing out from some mycorrhizae
This is where all the action takes place
Water absorption
Nutrient absorption

12. Mycorrhizae (Myco = fungus; rhiza = root)
Formed by invasion of fungus (5000 species); 90% of all plants in nature
Symbiotic relationship with tree
Symbiotic
fungus gets organic nutrients from plant
tree gets increased surface area for mineral (phosphate)
and water uptake
fungus may help prevent disease in tree
Most plants have them
some do not (not native to N.A. – tropical, shrubs)
e.g., Silk Oak (Australia), grown as ornamental
in TX, CA, nrn FL

13. Mycorrhizae
                                                                                      

14. The Effect of Mycorrhizae on Redwood Seedlings
                       

15. Nitrogen Fixation in Trees
Symbiotic relationship between the tree and bacteria
Bacteria gets steady food supply
Tree gets steady nitrogen source
Important in N-limited systems and impoverished sandy soils
Occurs often in black locust and alder
Black locust / Rhizobium can produce
kg N / ha / yr (53-89 lb N/acre/yr)

16. Root Nodules Modified roots
Continue to grow and divide
Nodules contain a certain class of bacteria (actinomycetes)
Symbiotic relationship
Nitrogen for the plant
Food supply for the bacteria

17. Root Grafting Relatively common in woody plants
most frequent in pure stands
(e.g., pines, spruces, other conifers)
Connection of phloem & xylem allows food, water
growth substances & pathogens to be
transported between trees
Can help girdled trees remain alive
water transport tends to be unaffected by girdling
food supplied to roots via connections with
intact trees

18. From The Living Stump Discovery Project website

19. The Living Stump The Natural Bridge, Upper Rogue River, Southern Oregon