Growth Responses on Young Wheat Plants to a Range of Ambient CO₂ Levels

Abstract

The growth of wheat seedlings in a closed environment was measured from day 10 to day 24 after germination, in 12 separate and sequential experiments, in which the imposed variable was the ambient CO₂ concentration. CO₂ levels between 200 and 800 volumes per million (vpm) and a daily irradiance of 6.5 MJ m^-2 were used.

The effects of CO₂ concentration on various growth parameters strongly interacted with plant age. For instance, in the 10-day-old plants, relative growth rate and net assimilation rate were increased (by 35 and 55% respectively) by an increase in CO₂ levels from 200 to 800 vpm, whereas these two growth parameters were reduced (by 44 and 16%) in 24-day-old plants over the same interval of CO₂ concentration. Also, increasing CO₂ levels reduced the leafiness (leaf area ratio) of the plant, and increased the dry matter in the leaves (specific leaf weight).

It is suggested that the observed large interactions on plant growth of plant age and CO₂ concentration account for the relatively small enhancement by CO₂ enrichment of total plant biomass and economic yield that are reported in the literature.