Physiological responses of Atherosperma moschatum to day length, night length and photosynthetic photon fluence rate.

Abstract

Young, non-reproductive plants of Atherosperma moschatum Labill, were conditioned to a range of day lengths, night lengths and photosynthetic photon fluence rates (PPFRs). The plants conditioned to the shorter of the two day lengths grew more slowly. On protein specific bases, the leaves of these plants had greater PPFR-saturated CO2 exchange rates (CERs), steeper initial slopes to the CER-PPFR plots, and greater chlorophyll concentrations than did the leaves of the long day length plants. The rates of leaf respiration, and the rates of leaf carbon export and /or incorporation into structural leaf products (E+ I) were similar under the two day lengths. The plants conditioned to the shorter of the two night lengths grew more quickly. The leaves ot these plants had smaller PPFR-saturated CERs, shallower initial slopes to the CER-PPFR plots and smaller chlorophyll concentrations than did the leaves of the long night length plants, but greater rates of leaf respiration and E + I. In a separate experiment A. moschatum was shown to be vegetatively sensitive to night breaks of far-red irradiation. The plants conditioned to the higher of the two PPFRs grew more quickly. The leaves of these plants had greater PPFR-saturated CERs, greater rates of leaf respiration, and greater rates of E+I than did the leaves of the lower PPFR plants, but shallower initial slopes to the CER-PPFR plots, and smaller chlorophyll concentrations. Acclimation to photosynthetic period (day length/night length) can be as marked as that to PPFR, and is quite different in character.