Influence of day and night temperature on the growth of young tomato plants
Young tomato plants were grown at different day and night temperature combinations with an average of 21°C. Some combinations with a different average 24-h temperature were included. Day temperature (Td) varied between 16 and 26°C, night temperature (Tn) between 12 and 26°C, while the daylength was 12h. Light intensity was about 26 W m−2 photosynthetic active radiation (PAR).An inversed temperature regime (Td lower than Tn) reduced plant growth (fresh weight, FW; dry weight, DW) and development (number of leaves, number of trusses). Reduction in development was less than reduction in growth. Growth reduction was caused by a lowering of the leaf area ratio (LAR). The decrease in LAR at an inversed temperature regime was caused mainly by a decrease in specific leaf area (SLA). Net assimilation rate (NAR) was not influenced by the temperature regime. For young widely spaced plants a lower SLA (thicker leaves) results in less light interception and thus in growth reduction.It is possible now to explain the different reactions on temperature regime at the same temperature intergral between young plants and closed canopies. In a closed canopy (a producing crop) differences in leaf area index, brought about by differences in leaf thickness, have hardly any influence on light interception because most light has been already intercepted anyway. This explains why a producing crop, in contrast to young plants, shows hardly any reaction to temperature regime at the same temperature integral.A regression analysis indicated that for FW and DW, plant length, leaf area (A), number of leaves, number of trusses, relative growth rate (RGR), LAR and SLA, Td is more important than Tn.
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