Leaf gas exchange response of 'Arapaho' blackberry and six red raspberry cultivars to moderate and high temperatures

Abstract

Leaf gas exchange of six red raspberry (Rubus idaeus L.) and one blackberry (Rubus L. subgenus Rubus Watson) genotypes growing in 12-L containers was measured at four temperatures (20, 25, 30, and 35°C) once a month for 3 months in growth chambers by infrared gas analysis. Measurements were taken on three successive leaves on the same primocane between the third and seventh nodes (≈75% to 85% of full leaf expansion). The plants were grown in ambient (field) conditions except when measurements were taken. Maximum daily ambient temperatures rose as high as ≈37°C during this period. Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (gs) were measured during June, July, and August. Significant differences (P ≤ 0.01) in A were found among the seven genotypes. 'Arapaho' blackberry displayed the highest mean A rate at all temperatures. Only in the raspberry cultivars Nova and Reveille did the rate of A drop significantly when temperature increased from 20 to 30°C. 'Reveille' was also the only cultivar in which A significantly declined between 30 and 35°C. The ET increased significantly over the four temperatures in four cultivars ('Arapaho', 'Heritage', 'Nova', and 'Southland'). The ET rate at 35°C was higher for 'Arapaho' than for all other cultivars. 'Autumn Bliss', 'Dormanred', and 'Reveille' did not change significantly as the temperature rose from 20 to 35°C. Stomatal conductance of 'Heritage' and 'Arapaho' did not change significantly between 20 and 35°C, whereas that of 'Autumn Bliss' and 'Reveille' declined almost 50% when temperature increased to 30 or 35°C.