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

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?

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!

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), 838-848. doi: 10.1046/j.1365-2486.2003.00582.x

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

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

Root Hairs

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

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

How do plants get water and nutrients?

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

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

Mycorrhizae                                                                                       

The Effect of Mycorrhizae on Redwood Seedlings                        

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 60-100 kg N / ha / yr (53-89 lb N/acre/yr)

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

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

From The Living Stump Discovery Project website http://pfranc.com/projects/LSD/

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