Tree Growth and Carbon Sequestration

Photosynthesis — the planet altering cellular process you likely learned about in school at various points. While some of us might be fuzzy on the details since we learned it, many researchers are trying to understand how we can manipulate the process to combat climate change. For example, our featured scientist from December reprograms plant cells to be better and faster at carbon fixation. So what exactly IS carbon ‘fixation’ and why does it impact our atmosphere? To answer this question we need a quick refresher on photosynthesis…

photosynthesisPhotosynthesis requires energy, water (H2O), and carbon dioxide (CO2). Plants can use special pores in the surface of their leaves (called stoma) to take in  CO2 from the air and the water gets absorbed from the soil by a plant’s root system. Plants need to break apart and reassemble these two molecules into sugar that it can use for food, but breaking the bonds in molecules takes energy, so plants gather these ingredients in the leaves where special green pigments (aka chlorophyll) can capture energy from the sun. The energy is used to take apart the CO2 so plants can use the C or carbon from the molecule to create long sugar molecules which are comprised of mostly carbon, hydrogen, and some oxygen. This is why we say that carbon is ‘fixed’! Finally, extra oxygen from this process gets expelled by the plant back into the atmosphere, and the carbon in the completed sugar molecule is stored in the plant’s body (more than half a plant’s dry weight is carbon!).

Now that we understand photosynthesis, you can see that by speeding up this process or making it more efficient, we would be removing more CO2 from the atmosphere and creating more atmospheric oxygen. In particular, there is a great deal of interest in using trees, which are long lived and large, to mitigate the greenhouse effect because trees can store more carbon than herbaceous plants. Perfect solution to climate change, right?! Not necessarily…

tree1
WI DNR

New research published in Science magazine indicates that faster tree growth stimulated by excess carbon dioxide available in the atmosphere DOES NOT translate to more carbon being stored in the wood of trees and in forests as a whole. The paper is appropriately titled ‘A matter of tree longevity’ and indicates that long life in trees is better for total carbon sequestration than purely rapid growth. This is likely because a tree’s biological goal is to absorb nutrients and sunlight so it can grow tall and produce lots of offspring while using as little precious energy and resources as it can. Essentially, more ‘nutrients’ or faster growth doesn’t mean more efficient growth.

So if there is so much potential but faster growth doesn’t seem to work, what can we do? Well, scientists like Pamela Silver are trying to create bionic plant leaves that can preform this photosynthesis process to clean the atmosphere without the need of real plants. This could prove highly useful in areas where plants can not easily grow (e.g. large cities, buildings, outer space!). However, as citizens and perhaps landowners, we can impact carbon sequestration and therefore our atmosphere by:

(1) Promoting stewardship of private forest lands.
(2) Reducing unnecessary deforestation though conscientious consumption, purchasing and resource management.
(3) Adding forest, especially in urban areas.
(4) Increasing the use of sustainable forest management to keep forests healthy.

 

Featured image credit: Elvis Kennedy

 

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