Transpiration of Antirrhinum majus L. ‘Panama’ as Influenced by Soil Temperature1

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Abstract

The rate of transpiration of Antirrhinum majus L. ‘Panama’ increased as the daytime temp was increased in the range 20°C to 35°C while vapor pressure deficit (v.p.d.) and night temp were held constant in a controlled environment chamber. Transpiration rates declined when day temp was 20 or 25°C after nights of 15°C, but remained steady during days of 30 or 35°C following 15°C nights. The slower rates of soil warming with 20 and 25°C days after 15°C nights influenced the rate of transpiration by causing early morning wilting and by increasing stomatal resistance (R_s). The decline in transpiration at 20 and 25°C was similar to that observed when soil water suction was increasing and slowing water flow. Total daily transpiration was one-third less when rhizosphere temp was controlled at 10°C in contrast with 25°C when plants were grown in either a gravel-peat-vermiculite medium or nutrient solution. Plants in 25°C soil responded to increasing evaporative demand by increasing transpiration, but those in 10°C soil wilted under even low v.p.d. and transpired at a low rate under any condition tested. The declining rate of transpiration at 20 and 25°C during the day when soil temp was not controlled was due to cold soil. This work suggests that under glass culture, where wilting can be identified as a result of cold soil, soil heating may be necessary as a preventative treatment.

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