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Paraheliotropic Leaf Movements in Mature Alfalfa Canopies 1
Author(s) -
Reed R.,
Travis R. L.
Publication year - 1987
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1987.0011183x002700020036x
Subject(s) - leaflet (botany) , biology , cultivar , vapour pressure deficit , xylem , diurnal temperature variation , growing season , arid , horticulture , agronomy , botany , ecology , transpiration , geography , photosynthesis , meteorology
The relationship between plant water potential and midday sunavoiding leaf movement was studied in mature alfalfa ( Medicago sativa L.) canopies. Diurnal solar tracking patterns were determined for three cultivars representing different germplasm sources: ‘African’, a nondormant type introduced from the arid regions of Africa; ‘Lahontan’, a semidormant type of Turkistan origin; and ‘Norseman’, a dormant type introduced from the Ladak province of northern India. Solar tracking was measureduring four regrowth cycles beginning in early spring and concluding in early fall. Early and late season regrowth cycles for African and Lahontan were typified by patterns in which leaflet surfaces were positioned perpendicular to incident radiation (diaheliotropism) throughout the day. Late spring and midsummer diurnal diaheliotropic patterns were interrupted by midday sun‐avoiding paraheliotropic (PHT) movement in both cultivars. Conversely, diurnal tracking in Norseman was interrupted by PHT movement in all cycles. Leaflet PHT movement is generally presumed to be a stress‐avoidance mechanism induced by changes in plant water status. However, regression analyses of PHT activity data for alfalfa showed no clear relationship between diurnal PHT patterns and xylem water potential (XWP) either among cultivars or with the onset of and recovery from PHT activity. Rather, in all three cultivars, cupping was consistently related to ambient vapor pressure deficit (VPD). African and Lahontan did not exhibit midday leaflet PHT movement during the late season regrowth cycle even when the daily ambient VPD and XWP profiles were similar to the midseason patterns.