Question:
What is the source of carbon that is assimilated in photosynthesis?
Solar radiation
Atmospheric CO2
Soil water
Soil nutrients
Response:
The effect of light on photosynthesis has a clear saturating pattern: more light results in more photosynthesis but eventually leaves cannot take full advantage of all the extra light.
Early spring is a tricky time for plants due to the combination of sunny but still quite cold days.
Photosynthesis of a tree canopy is driven or influenced by
the total leaf area (LAI).
photosynthetically active solar radiation (PAR).
soil moisture (REW).
air humidity (VPD).
air temperature (T).
atmospheric CO2.
When there is low soil moisture, plants close its stomata pores which then decreases photosynthesis.
In some part of the stems, some photosynthesis may also occur.
As plants respire, they release
carbon dioxide.
oxygen.
High soil moisture leads to decreased photosynthesis.
In boreal upland forests, low soil moisture decreases the rate of photosynthesis.
De-hardening in spring involves gradual re-hydration of the cells, recovery of photosynthetic capacity and a tight control of water loss.
Almost half of the total biomass of a tree may be allocated to the roots.
Plant respiration captures CO2.
Unlike photosynhesis, plant respiration captures atmospheric oxygen and releases carbon dioxide.
The rate of respiration decreases with temperature.
Leaf area increases with stand age, resulting in a decreasing rate of photosynthesis in the stand.
An increment in leaf area increases also the photosynthesis of a tree stand. However, the relationship is saturating.
In general, the more carbon dioxide that is available to the plant, the faster the rate of photosynthesis - if other factors are favourable.
A complex microbiota lives belowground, releasing carbon dioxide to the soil.
