Temporal and spatial patterns of carbon allocation in the canopy of white oak

Abstract

The fate of photoassimilated 14C was followed by measuring 14C incorporation into leaf and branch tissues (≤ 5 years old) of two forest-grown white oak trees. Fate of 14C-labelled photosynthate was examined 7 days after 14CO2 uptake on live dates (April–October) during the growing season. Both upper and lower canopy positions were sampled. Incorporation of 14C into foliage was significant throughout the growing season. It ranged from 95% of the total 14C retained in April to 50% in October. Incorporation of 14C-labelled photosynthate into the canopy was highest in June and averaged 33% of gross photosynthetic production over the entire growing season. Higher retention of photosynthate in branches versus leaves was noted in the upper canopy than in the lower canopy during the middle and late growing season. Activity levels in tissues indicated that within-canopy sink strength was in the order acorns ≈ buds > leaves > branches. Translocation of initial 14C-labelled photosynthate from both leaves and branches was calculated based on 14C retention and estimated respiratory losses of leaf and branch tissues. These calculations indicate that leaves were still importing significant amounts of photosynthate in April when expansion was two-thirds complete. Translocation of 14C from the canopy during the remaining growing season amounted to 25–45% of gross photosynthesis. Our data indicate that seasonal demands of growth and maintenance of the forest canopy constitute a substantial sink for photosynthate allocation by white oak.

Net Photosynthesis and Early Growth Trends of a Dominant White Oak (Quercus alba L.)

“…Even when leaves were approximately 60% expanded (average Phn between 0500 and 1800 h = 4.7 mg C02/dm2.h) (Fig. 9), no translocation would be expected from them (17) (17). It was only then that stem cambiaL root, and acorn growth increased dramatically (Fig.…”

“…9). In addition, two recent studies have described the relationship between translocation and phenology in white oak trees in eastern Tennessee (17,18). Because of the similarity in white oak phenology in Tennessee and Missouri (11,12,17,18), we have used these data on translocation to link net carbon exchange and phenology in the following discussion.…”

“…Even during a drought, when root growth had slowed and stem growth had ceased, acorn growth continued or actually increased because the acorns constitute a major sink (Fig. 9) (17).…”

Phenological and growth patterns of the Mediterranean oak Quercus suber L.

“…According to McLaughlin and McConathy (1979), most of the carbon was probably incorporated into new leaves and shoots during this period. Later, it might have been supplied to the developing acorns (Mooney and Hays 1973), which would explain the decrease of specific leaf weight values observed for some trees during the fruit maturation period (Fig.…”

Effects of SO2 and O3 on Allocation of 14C-Labeled Photosynthate in Phaseolus vulgaris

“…A number of possible mechanisms related to the known metabolic effects of air pollutants can be postulated for these responses. They include both reduced photosynthetic production (reduced energy) and inhibition of enzymic pathways (7,16,27,28) ( 13), and it can be expected that this on-site demand would require a higher fraction of available photosynthate-a demand which would be additionally augmented by increased metabolic demand of injured tissues. While reduced photosynthesis may contribute to reduced translocation, it does not appear to be a prerequisite for this process to occur (8,14).…”