How does a Tree grow? (feat fungal friends)

How the first trees grew: This video demonstrates how scale trees figured out how to grow tall - they had to rip themselves apart!!!

So...this is pretty awesome!

This video provides some basic terms when looking at wood. It is a great practical first look!

• layers of tree - outer bark, inner bark, cambium (living part responsible for growth), sapwood (active vascular transport), pith (original embryo tissue for initial growth), heartwood (dead internal)

• Tree rings - early wood/late wood delineated by differences in vascular structures, medullary rays (parenchyma cells that enhance strength)

Watch this video for an introduction into how trees grow (secondary growth) with the added wrinkle of "pulsating" growth

• Take a look at the animation of how trees grow from the cambium

• Trees swell and shrink with daily update and transpiration of water - heat and cloud cover modulate this relationship

Detailed video showing primary and secondary growth

• primary growth - primary meristem - lengthening of stems and roots

• secondary growth - increase in girth of stem and roots

• secondary meristems = vascular cambium and cork cambium

  • • Wood is produced by vascular cambium (intrafascicular cambium) - found in a vascular bundle between primary xylem and primary phloem - is patchy when stem is young but forms the uninterrupted cambrial ring as developed

      • • medullary ray cells next to intrafasicular cambium become meristematic and produce interfascicular cambium to complete the ring

      • Once cambrial ring is formed - primary xylem is on its inner surface and primary phloem is on its outer surface - cell division happens on both sides of cambrial ring - secondary xylem and phloem are formed on inner and outer surface respectively...this is essential how a tree grows!

      • The cambial ring is more active on the inside than the outside...as the tree grows the phloem on the outside of the cambrial ring gets crushed while the xylem on the inside does not - eventually resulting in the formation of wood inside the cambrial ring

      • Secondary medullary rays are formed by parenchyma produced by cambrial ring

      • Wood formation (and tree rings affected by: defoliation, light, diseases, drought, temperature) - rings formed because some conditions/seasons result in active cambial division (spring) while others (winter) do not in temperate regions

      • tanins, resins, gums, and essential oils are deposited in wood to discourage insect attack

  • Bark is produced partially by cork cambium (phellogen) - cell growth on both sides - inner = secondary cortex (phelloderm), outer = cork (phellem) -- all together these three layers are called the periderm

  • Secondary phloem and periderm together make up the bark

  • Lenticels - openings in bark to allow gas exchange between tree stem and atmosphere

  • Secondary growth also occurs in roots by a similar process

  • monocots do not have secondary growth - palm trees, corn, grasses, etc.

Dendrochronology - cross-dating trees and using tree rings to generate paleoclimate data

• used as a climate record from before the instrumental record

• information directly useful to managers to forecast drought, flood, etc.

A great video showing how trees are connected through fungi

• Trees share food, supplies, and wisdom

• Mycorrhizae - symbiotic fungi partnering with plant roots - fungal hyphae form mycellium to extend root network

• Mycorhizal networks - pass nutrients and signaling molecules from tree to tree

• Oldest trees have the largest and most connected networks - they are very complex and hard to trace

• 100 species of mycorihizal fungi!

• Mycohirizal fungi either surround (ectomycorizae) or penetrate (endomycorhyizae) plant root cells - fungi can process organic matter (plants can't) so the fungi are able to more readily access nutrients and pass them to the tree root system

• plants provide sugars to fungus through root exudates of sugars

• sugars pass through hyphae, some are absorbed by fungus but others are passed through networks to other trees

• This symbiotic relationship between fungi and plant makes sense...both parties benefit...but......

• We don't completely understand why fungi would pass sugars to other trees but here are some ideas:

  • • fungus could benefit by having as many connections between trees as possible and gains the most connections by shuttling materials between trees

    • perhaps trees reduce interactions with fungi that don't facilitate connections between trees

• Trees can tell if info is coming from their own species, or even their own relatives within a population!

• Drought or insect attack info is also passed through the fungal network

More descriptions about this fungal network system

• Mother trees protect and nurture seedlings through wood wide network

• Sick and dying trees dump resources into the network before they die to help their neighbors

• If attacked plants send messages to neighbors to warn them to ready their defenses

• Orchids hack the system to steal resources from nearby trees

• Black walnuts send hazardous chemicals through network to poison rivals (allelopathy)

Very cool REAL video of fungal hyphae carrying nutrients around.