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 Though
plants are very important sinks for atmospheric carbon dioxide on
both land and in aquatic environments, uptake by aquatic plants
is included in the discussion of oceanic carbon dioxide uptake elsewhere
on the site. See Carbon dioxide Sinks
- Oceans.
On land, plants themselves represent a global mass
equivalent to about 1500 billion tonnes of carbon at any one time.
Plants utilize carbon dioxide during photosynthesis, but also produce
it during respiration. The net effect is an uptake of carbon dioxide
from the atmosphere equivalent to around 60 billion tonnes of carbon
each year.
Human Impact
Our primary impact on the terrestrial plant life carbon dioxide
sink has been through our alterations in the vegetation types and
land-use commonly occurring around the world. A switch from forested
land to agricultural crops means that carbon dioxide incorporated
into plant tissues is taken out of the atmosphere for a much shorter
time and so the effectiveness of the plants as atmospheric carbon
dioxide sinks is much reduced.
Potential for control
Much has been made of the potential for plants to increase their
rate of carbon dioxide use in response to elevated atmospheric carbon
dioxide concentrations, so providing a negative feedback on greenhouse
gas increase and global warming. However, in depth studies of this
'carbon dioxide fertilization' effect indicate that any such response
will be rather limited, with any initial increase in the plant based
carbon dioxide sink disappearing within only a few years.
Certainly, it seems that relying on existing vegetation to simply
sap up increasing atmospheric carbon dioxide would be ill-founded.
Instead, planting of new forests and better land-management practice
offer the potential for the creation of significant carbon dioxide
sinks.
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