Photosynthesis & transpiration from upper & lower surfaces of intact banana leaves

Abstract

The use of modern gas analysis instrumentation makes it possible to obtain continuous recordings of transpiration (3, 6, 8, 12, 13, 23) and photosynthesis (4, 5, 16, 19) from intact portions of higher plants. The high sensitivity and rapid response of these instruments permits one to determine rather subtle effects of various internal or environmental factors on physiological processes involving gas exchanges between the plant and its environment (4, 7, 8, 13). Measurements of photosynthesis and transpiration comparing the rates on the two surfaces of leaves have been made in the past (9, 10, 17, 18, 24), but none of these reports is of very recent origin. In general it was found by these investigators that the rates of photosynthesis and transpiration were dependent upon the stomatal distribution on the two leaf surfaces. Conflicting conclusions have been reached, however, concerning the extent to which these gas exchange processes are limited by the degree of aggregate stomatal opening. Lloyd (14) has concluded that the opening and closing of stomates should be without appreciable effect on the transpiration rate. Conversely, Thoday (22) and Maskell (15) consider that changes in stomatal aperture definitely influence the rate of photosynthesis. Freeland (9) concluded that in some plants, especially those with a thick cuticle, the stomates constitute the only path of entry of CO2 into the leaf; whereas in other plants considerable quantities of CO2 could enter the leaf directly through the epidermis. More recently, Andersson and Hertz (3) have interpreted the periodical oscillations in the transpiration curve of Thunbergia as being due to a periodical opening and closing of the stomates. Andersson and Hertz (3), as well as Allerup (1) and Decker and Wien (8), have observed a temporary stimulation of transpiration from a leaf following its excision from the parent plant. Allerup (2) considers this increase in transpiration rate to be due to an increase in stomatal opening which he has demonstrated to take place following such treatment. The work here reported was undertaken preliminary to an investigation of the effects of various spray materials on the processes of photosynthesis and transpiration in banana leaves. For this purpose it became necessary to devise appropriate facilities to determine the relationship between these two processes and the leaf surface from which they were measured.