Autumn Leaf FallTrees thatkeep theirleaves areevergreens,trees thatlose theirleaves aredeciduous. Abscission zone– area at the base of the petiole that breaks down and causes leaf (or fruit) drop
Autumn Leaf FallDeclining intensity of sunlight triggers theprocesses leading up to leaf fall in autumn. Chlorophyll reduces, unmasking carotenoids. Clogged phloem veins trap sugars in the leaf and promote production of anthocyanins.
Mycorrhizae Is a symbiotic relationship- mutually beneficial- with a tree and a fungus Fungus increases surface area of roots Facilitates uptake of minerals that are otherwise unavailable Fungus gets to share the tree’s carbohydrates.
Photosynthesis & Respiration
Tree Growth & DevelopmentTree shape, height, etc, are determined by genetics, but its environment plays a part as well.
Tree Growth & Development Plant growth regulators are hormones that work in concert. ◦ auxin, cytokinins, gibberelins, ethylene, abscisic acid…etc. Environmental triggers ◦ Budbreak ◦ Leaf fall ◦ Seed germination ◦ Geotropism ◦ Phototropism
Tree DefensesChemical – to dissuade animal/insect feeding, stop pathogen infection, or help prevent rotMechanical – Thick bark, thorns, leaf hairs, thick cuticles – Shiny wax, leaf hairs – CODIT (Compartmentalization of Decay In Trees)
Palms- StemPalm stem-monocot Tree stem- diocot
Palms- Roots Root initiation zone Root mat
Image credits: Dr. Ed Gilman and Scott Jones, University of Florida Sharon Lilly, ISA Arborists’ Certification Study Guide Natural Resources Canada website www.nrcan-rncan.gc.ca Kathy Ripke, University of Minnesota Department of Horticultural Science Taiz and Zeiger, 1998. Plant Physiology, 2nd ed.