Proven Carbon Capture and Avoidance

Photons to wood and Photons to electricity

Blog #83, CaliforniaGeo 11-16–21 

Fall can be a colorful time of year.  For some, it is the final goodbye to summer’s growing season and for others, a warning that shorter days are already here, with winter fast approaching.  For many of us, coping with Fall is a bit like cutting firewood.  The first load of raked leaves or cut wood might be recreation—after that, it’s all work.

 A different meaning-

The most obvious falling leaves are the annual deciduous ones from trees, although the evergreen conifers will shed some of theirs after a few years’ service.  What is that special service for both?  It’s Photosynthesis.  AKA, to build something using the power of photons from the sun.

The leaves of trees capture sunshine on their surface and open their vents called stoma to take in carbon dioxide—an important building block for the wood they build.  Wood is a complex hydrocarbon molecule with a lot of what chemists recognize as double-bonding, something common for carbon atoms.  Photosynthesis provides power from the sun to pull moisture from roots, split apart water molecules to separate their hydrogen, bond them into long-chained carbon molecules, and dump excess oxygen into the atmosphere through those same stoma.

Trees and shrubs can carry their little solar collectors (photosynthetic leaves) for only a year, or a few, or in the case of my favorite conifer, the Bristlecone Pine—usually over 25 years.  When trees of any kind build up layers of wood (without being burned up in wildfires) we can call this a SEQUESTRATION of atmospheric CO2.  In other words, growing lots of trees works for atmospheric weather and climate stability—if we let it.

Even the removal of trees by logging, milling, and building construction keeps that carbon sequestered and out of the air unless such buildings burn up.  Managing forests for fewer semi-stagnated small trees can increase the overall growth rate of those remaining, and that can also increase sequestration.

Leaf Anatomy-

Nature builds things in certain ways, some of which we don’t understand.  One thing that can be said is that whatever’s still around, botanically, is what works.  It has outlasted other types of plants over thousands of years of competition.  All of our vascular trees and plants use photosynthesis to generate their sustaining energy and to build layers of wood.  Their solar collectors are different.  They are built in different shapes and sizes to get the job done.  Perhaps you’ve heard the term “quaking” Aspen?  Without getting into engineering depth, I’ll share that the structure of leaf attachment to a twig (the petiole) PET-e-oll is supported as a vertical structure with lateral instability.  In a light wind, the leaf quivers horizontally, perhaps minimizing shading from its neighbors while becoming an attention-getter for us.  The petiole has to support not only the weight and motion of the leaf it serves, but it has to carry fluids and chemicals in two directions, from and to the leaf itself.  A tall order. 

Doubtless, you’ve seen the visual of a wilted leaf.  If not, leave a bundle of celery unwrapped and out of the fridge for a day or two.  Wilting happens when fluid pressure to the leaf and all its cells cannot be maintained against the loss of moist vapor through its stoma.  The soft photosynthetic cells, the micro-veins that serve them, and the main veins can no longer support the weight—so they droop.

At left, A represents the petiole, B represents the main vein and its branches.  C represents the main photosynthetic cells, and D represents some of the micro-vein structures which provide chemical access to and from photosynthetic cells.

Seasonal Sequence-

How does a tree know when to shed its leaves?  Trees don’t have a brain like we do so they rely on certain bio-chemical messages.  Most are sensitive to some combination of day length and temperature.  When days are short and temperatures lower, we’re out of the optimum growing season.  It’s time to conserve chemical energy.  These temporary solar collectors aren’t as productive now, so let’s shed them and re-start next Spring.  But how?

There are a layer of cells at the base of the leaf’s petiole where it meets a twig called the abscission layer.  Think of this as a cellular Venetian Blind.  It can remain open during the growing season and respond to that chemical signal to close in fall.  This layer gets waxy and stiff at the same time it restricts fluid flow.  Adhesion to the twig degrades, and gravity, wind, or rain does the rest to make them drop—get out your rake! 

Another kind of collector-

A man-made version of leaves doesn’t sequester carbon by storage within wood, but it does generate DC electricity to help with CARBON AVOIDANCE.  Solar Photo-voltaic panels are widely noticed and convert the power of photons by causing electrons to jump through conductive substrates and produce electrical power.  Arranged in series connection, these panel’s cells deliver much improved conversion efficiency of sunlight than their ancestors that went into space to power satellites in the 1950s.

Unlike green leaves, some of them can track the sun across the sky without shading each other while maintaining efficiency for over 25 years.  They don’t require water and have no moving parts.  And with battery storage technology constantly improving, they can replace most conventional power plants at lower cost and without pollution or carbon emissions. 

Photovoltaics continue to drop in price and can be deployed anywhere.  California’s new residential housing is forced to utilize some measure of them.  They work at a variety of tilt angles and some in Canada are being mounted vertically on outside walls to stay snow-free and to maximize winter “catch.” 

Solar panels are becoming ubiquitous as “distributed energy generation” on our national grids.  Because they are at the outer edges of electric transmission territory (at the point of a building’s use) they do not require upgrading of existing lines and substations.  This is helpful to the reduction of CO2 in the atmosphere, and the reduction of fossil-based electricity generation.  You could say that they are a perfect teammate for all the leaves we see each fall.  Our lives are better as a result of their presence.



—Bill Martin