How is carbon sequestration of plants calculated? A Gardeners Guide

All plants (and any other photosynthesising being) takes in carbon dioxide from the atmosphere and, whilst it expires the majority though respiration, some is retained, or sequestered by the plant.

Read this article here if you'd like to know how much carbon plants sequester in the soil for the long term.

So how is carbon sequestration of plants calculated?

It is a rather simple process to be honest in a standardised setting

 

How to Calculate CO2 Absorbed by Plants 

To calculate CO2 absorbed by plants in a standardised setting:

1. Remove the plant from where it is growing. For an accurate result you would want to choose a potted plant so that its roots are intact.
2. Clean the plant - all soil residue and any matter that is not part of the plant needs to be removed
3. Dry the plant completely either through several weeks of air drying or in a low temperature oven
4. Weigh the dried plant.
5. Carefully burn it down to ashes, making sure to retain them
6. Weigh the ashes
7. Dry weight - Ash weight = Carbon sequestration in the plant.
8. For example, if the dry weight of the plant was 50g, and the ashes weighed say 26g, then the majority of the lost weight (50g-26g=24g or 48%) was CO2 which literally went up in smoke.

Ok, but how do you go about calculating the carbon sequestration of plants that are growing in the ground? It is very hard to dig up a plant, especially an established plant, without severing some roots. 

How to Measure Carbon Sequestration In Plants

Hmm, this is more difficult as every type of plant has different root biomasses depending on the species. A perennial plant has a much more expansive root system than an annual flower for instance.

In the paper, Root biomass and shoot to root ratios of perennial forage crops in eastern Canada, legume species, such as clover or lupins, stored an average of 25% of their carbon in the roots, and grasses stored an average of 50% of carbon there. Higher nitrogen levels reduce this ratio as the plant puts on green growth above ground.

It should be noted that lawns which are cut regularly will not achieve deep roots. Clumping tall grasses achieve the deepest roots and the most carbon sequestration - and that organic carbon is stored deep underground where it can stay for centuries.

Determine the Biomass, Estimate the Rootmass, Calculate the Carbon

So, now you know how to measure carbon sequestration in plants growing in your herbaceous garden flowerbeds - dry and weigh the above ground growth and estimate the rootmass, from around 25% to 50% of the total dry weight of the plant, depending on the type of plant, it's size and age, then do the calculation at the top of this blog post.

Conclusion - Does this measure how much carbon plants sequester in soil?

In a way though, measuring carbon sequestration in plants is a bit pointless. All the articles extolling the benefits of say fast growing bamboos absorbing carbon from the atmosphere misses the point - the carbon stored in plants that is mainly held above the ground doesn't lock as much into the soil over the long term. Bamboo is harvested and decomposes, woodland is burnt in wildfires or turned into timber (using vast amounts of energy in the process). Grasses won't thrive in heavy clay. Every situation is different and the subject is more nuanced than 'plant trees'.

Locking as much carbon into the soil for as long as possible is what matters. Read this article about the best plants for carbon sequerstration