Seasonal changes in net carbon dioxide exchange rates of autumn bliss, a primocane-fruiting red raspberry (Rubus idaeus L.)

Abstract

Seasonal changes in leaf net carbon exchange rate (NCER), stomatal conductance (g(S)), and intercellular CO2 (c(i)) were determined for 2-yr-old potted Autumn Bliss (Rubus idaeus L.) plants grown under field conditions. NCER varied inconsistently between leaves which subtended fruiting lateral branches (laterals) and those that did not. In leaves with fruiting laterals, it was lower on three dates, similar on three other dates and once greater than in leaves without fruiting laterals. Evidence of nonstomatal inhibition of photosynthesis was also apparent as leaf NCER and g(S) fluctuated during the season while c(i) remained relatively constant. The leaf chlorophyll content increased when fruiting laterals were present, but this did not produce a consistently higher leaf NCER. The SPAD-501 meter provided a rapid and accurate, nondestructive estimate of leaf chlorophyll content for Autumn Bliss red raspberry leaves. Under uniform environmental conditions, all healthy, fully expanded leaves along the primocane had the same photosynthetic potential. Also, leaf age did not influence leaf gas exchange until the leaves started to senesce. Therefore, good light interception throughout the canopy is needed to optimize dry matter production in primocane-fruiting red raspberries.