CORRELATIONS BETWEEN ENVIRONMENTAL CO₂ AND O₂ CONCENTRATIONS ON PHOTOSYNTHESIS AND GROWTH OF TOMATO PLANTS UNDER CONTROLLED ENVIRONMENTS.

Short-term (5-,7-day period) controlled-environment studies were conducted to investigate further the effects of ambient CO₂ and O₂ concentrations on net photosynthesis and growth of tomato plants (Lycopersicon esculentum Mill., Eurocross BB, F₁-hybrid). It was found that at 100 w m² photosynthetically active radiation with 17 hours light per 24 hours at day/night temperatures of 25 °C/18 °C, and at 300 cm³ m^-3 ambient CO₂ concentration, 5% O₂ increased the rate of net photosynthesis by about 44%, but had no clear-cut effect on the rate of dark respiration as compared with air-level O₂. The low O₂ enhancement effect was dependent upon the ambient CO₂ concentration.
Increasing the ambient CO₂ concentration decreased the low O₂ effect on photosynthesis.
It was noticeable that the CO₂ uptake process responded to changes in O₂ concentration very quickly, and there was little evidence of any carry-over of the effects of one day’s treatment into the next day at the new O₂ level.
Net assimilation rate gives a clear indication of the interactions, between the environmental CO₂ and O₂ concentrations, because the relative increase in net assimilation rate due to decrease in ambient O₂ level depended upon the ambient CO₂ concentration.
The largest increase in net assimilation rate was found at 100 cm³ m^-3 CO₂, and was negligible at 900 cm³ m^-3 CO₂ concentration.
Conversely the increase in net assimilation rate from increased CO₂ was about 10-fold when the ambient CO₂ changed from 100 to 900 cm³ m^-3 in air-level O₂ concentration.
Results indicates that leaf growth is not related in any simple way to dry matter production.
It appears that cell division and/or cell expansion and consequently plant enlargement do not necessarily depend on the rate of photosynthesis.

Symposium on CO2 Enrichment

R.A. Khavari-Nejad

https://doi.org/10.17660/ActaHortic.1984.162.16