A comparison of pressure chamber, leaf-press, and canopy temperature for four species under humid conditions

SOJKA R. E., SADLER E. J., CAMP C. R. and ARNOLD F. B. A comparison of pressure chamber, leafpress, and canopy iemperatureforfror species under humid conditions. ENVIRONMENTAL AND EXPERIMENTAL BOTANY 30, 75-83, 1990.—Numerous techniques are currently available for measurement of plant water status in field environments, including pressure chambers and indices based upon infrared-determined canopy temperatures. The Campbell-Brewster (J-14) leaf press has been promoted as a compact alternative to the pressure chamber for plant water potential determination. In-depth comparisons of the J-14 ('P J) with the pressure chamber ('P) or with canopy temperatures (T) and crop water stress index (CWSI) have been limited, and an evaluation of the technique in a humid environment was needed. All three J-14 end points [exudation from cut (T R) or uncut leaf edges (T N) or darkening of interveinal areas (T N)] were highly correlated among themselves for the four species studied. Correlations of J-14 end points with other stress indicators from unstable diurnal periods were poor. None of the water status indicators correlated well with leaf diffusive resistance. Our data showed a species-related reliability of the J-14. The J-14 produced r 2 values above 0.7 for soybean [Glycine max. (L.) Merr.] for all but comparisons with CWSI or T, minus air temperature (ST), and for corn (Zea mays L.) for '11„ only. The J-14 did not perform well for tomato (Lypersician esculentum Mill.) or rapeseed (Brassica napes L.), and is probably best regarded only as a relative indication of plant water status in the absence of calibration with other techniques. Failure of 'P„ or J-14 to correlate well with CWSI underscores difficulty with CWSI measurement under humid conditions.