HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Peoples, T. R. Articles by Koch, D. W. Search for Related Content PubMed Articles by Peoples, T. R. Articles by Koch, D. W. Agricola Articles by Peoples, T. R. Articles by Koch, D. W.

Physiological Response of Three Alfalfa Cultivars to One Chilling Night¹

Most studies involving photosynthetic efficiency have compared species or cultivars that were grown under fixed day/night temperature regimes. Researchers attempting to improve photosynthetic efficiency and productivity of a crop may also need to consider genotype response to adverse factors, such as temporary chilling, which have been shown to reduce subsequent photosynthetic rates.

Three alfalfa (Medicago sativa L.) cultlvars, representing a range of environmental adaptation, were grown in a greenhouse at 22/18 C (day/night), and then were exposed for one night to 5 or 18 C to determine the effect of low temperature on physiological processes the following morning. The CO₂ exchange rate (CER) of all three cultivars was reduced following a 5 C night. A greater reduction in CER occurred in ‘Mesa-Sirsa’ and ‘Saranac’ (69.1 and 60.2% less than 18 C, respectively) than in ‘Kane’ (36.7% less than 18 C). Transpiration rates were significantly reduced following chilling exposure of Mesa-Sirsa only (75.5% less than 18 C). This reduction in transpiration was associated with a 50% increase in leaf diffusive resistance and a 4.3 bar decrease in xylem water p6tential. Increased leaf diffusive resistance was not observed in Saranac and Kane following a chilling night. A greater leaf carbohydrate concentration and reduced ^l4C-photosynthate translocation from leaf tissue was noted in all cultivars following a 5 C night.

These data suggest a feedback inhibition of CER in alfalfa following one 5 C chilling night. A water stress inducing an increased leaf diffusion resistance and decreased transpiration was found in Mesa-Sirsa only.

Key Words: Medicago sativa L. • CO₂ exchange rate • Transpiration • Stomatal resistance • Water stress • Photosynthate translocation

² Graduate assistant and associate professor, Dep. of Plant Sci., Univ. of New Hampshire, Durham, NH 03824.

Received for publication December 20, 1976.