Comparative Pre‐floral Growth of Flue‐cured Tobacco in Field and Controlled Environments1

Abstract

AbstractThe use of controlled‐environment facilities in agronomic research has raised questions about the comparability of plant growth in controlled and field environments. The objective of this study was to compare leaf area, leaf and stem dry weights, and stem height at several intervals during the exponential growth phase of tobacco plants (Nicotiana tabacum L. ‘NC 2326’) in field and phytotron environments. Since photosynthetically active radiation (PAR) in growth rooms usually is less than occurs in the field, the study included a range of accumulated daily PAR of 11.4, 17.9, and 25.0 E m−2day−1 in the growth rooms and 24.9 and 42.2 E m−2day−1 in the field. The lower PAR in the field was obtained by shading with open mesh fabric. For each PAR level in the growth rooms, plants were grown at day/night temperatures of 22/18 and 26/22 C.In the growth rooms, there was not an interaction between PAR and temperature on growth characteristics. During the exponential growth phase, there was little difference between PAR levels of 17.9 and 25.0 E m−2day−1 in growth characteristics measured at the five individual sample dates or relative growth rate (RGR) and relative leaf area growth rate (RLGR) calculated over all sampling dates. There was a consistent reduction in growth when PAR was reduced to 11.4 E m−2day−1, although the differences were seldom significant.In the comparisons of leaf weight and area growth between field and phytotron‐grown plants, growth of leaves was generally enhanced, though usually not to significant levels, for full sunlight. However, growth at the maximum growth room PAR of 25.0 E m−2day−1 tended to be greater than at 24.9 E m−2day−1 for the shaded field plots. Leaf growth at the lowest growth room PAR of 11.4 E m−2day−1 was nearly identical to that in the shaded plots. This apparent inefficiency of PAR utilization in field plots is postulated, on the basis of other experimentation, to be due to the seasonal pattern of temperature variations in the field rather than to a difference in the quality of light between field and phytotron. Stem height increased in the growth rooms at nearly twice the rate as in the field, regardless of PAR level. This difference in growth also is postulated to be the result of the temperature variations in the field.