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Shoot growth, chlorophyll concentrations, gas exchange and starch concentrations were studied in lychee (Litchi chinensis Sonn.) seedlings of cultivar "Wai Chee" grown in a heated greenhouse at Nambour in subtropical Australia (27 degrees S). We also examined the effects of shoot defoliation and root pruning on leaf expansion. Shoot growth showed a rhythmic cycle under constant greenhouse conditions, with a mean duration of flushing of 20 days and an interval of 10 days over three cycles. Shoots and leaves expanded in a sigmoidal pattern to about 80 mm and 500 cm(2), respectively, for each flush. Starch concentrations of the lower stem and roots decreased as the young red leaves expanded, and increased as the fully expanded leaves turned dark green. Chlorophyll concentrations and net CO(2) assimilation rate were highest in the fully expanded dark green leaves. Removing 50% of the area of each fully expanded leaf had little effect on the expansion of younger leaves, but total biomass of defoliated plants was only 60% of that of controls. In contrast, removing half the roots just before bud swelling reduced final leaf area by 80%. We conclude that the young shoot has relatively low rates of photoassimilation until the leaves are fully expanded and dark green, and depends on assimilates from elsewhere in the plant. During leaf expansion, translocation of assimilates to the shoot occurred at the expense of the roots.
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PMID:Shoot development, chlorophyll, gas exchange and carbohydrates in lychee seedlings (Litchi chinensis). 1220 51

The pool size of mobile, i.e. non-structural carbohydrates (NSC) in trees reflects the balance between net photosynthetic carbon uptake (source) and irreversible investments in structures or loss of carbon (sink). The seasonal variation of NSC concentration should reflect the sink/source relationship, provided all tissues from root to crown tops are considered. Using the Smithsonian canopy crane in Panama we studied NSC concentrations in a semi-deciduous tropical forest over 22 months. In the 9 most intensively studied species (out of the 17 investigated), we found higher NSC concentrations (starch, glucose, fructose, sucrose) across all species and organs in the dry season than in the wet season (NSC 7.2% vs 5.8% of dry matter in leaves, 8.8/6.0 in branches, 9.7/8.5 in stems, 8.3/6.4 in coarse and 3.9/2.2 in fine roots). Since this increase was due to starch only, we attribute this to drought-constrained growth (photosynthesis less affected by drought than sink activity). Species-specific phenological rhythms (leafing or fruiting) did not overturn these seasonal trends. Most of the stem volume (diameter at breast height around 40 cm) stores NSC. We present the first whole forest estimate of NSC pool size, assuming a 200 t ha(-1) forest biomass: 8% of this i.e. ca. 16 t ha(-1) is NSC, with ca. 13 t ha(-1) in stems and branches, ca. 0.5 and 2.8 t ha(-1) in leaves and roots. Starch alone (ca. 10.5 t ha(-1)) accounts for far more C than would be needed to replace the total leaf canopy without additional photosynthesis. NSC never passed through a period of significant depletion. Leaf flushing did not draw heavily upon NSC pools. Overall, the data imply a high carbon supply status of this forest and that growth during the dry season is not carbon limited. Rather, water shortage seems to limit carbon investment (new tissue formation) directly, leaving little leeway for a direct CO2 fertilization effects.
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PMID:Non-structural carbohydrate pools in a tropical forest. 1557 27

Nonstructural carbohydrates (NSC) are the most important C reserves in the tissues of deciduous and evergreen tree species. Besides NSC, cell-wall hemicelluloses as the second most abundant polysaccharides in plants have often been discussed to serve as additional mobile carbon (C) reserves during periods of enhanced carbon-sink activities. To assess the significance of hemicelluloses as mobile carbon reserves, branches of two deciduous (Carpinus betulus L. and Fagus sylvatica L.) and two evergreen (Picea abies L. and Pinus sylvestris L.) tree species were sampled in a mature mixed forest stand in short intervals before and during bud break to assess NSC and hemicellulose concentrations in response to the increased carbon demand during bud break. Starch concentrations in branch sapwood of deciduous trees strongly decreased immediately before bud break and increased after bud break. In both evergreen species, only small changes of NSC were found in branch sapwood. However, 1-year-old needles exhibited a significant increase in starch concentration shortly before bud break which declined again after flushing. Hemicellulose concentrations (on an NSC-free dry matter basis) in branch sapwood of Carpinus decreased significantly shortly before bud break, but increased again after bud break. Contrarily, in Fagus branch sapwood, hemicellulose concentrations remained constant during bud break. Moderate increases of total hemicellulose concentrations before bud break were found in 1-year-old needles of both conifers, which could be explained by an accumulation of glucose units within the hemicellulose fraction. Overall, cell-wall hemicelluloses appeared to respond in a species-specific manner to the enhanced carbon demand during bud break. Hemicelluloses in branch sapwood of Carpinus and in 1-year-old needles of conifers likely act as additional carbon reserves similar to starch.
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PMID:Short-term dynamics of nonstructural carbohydrates and hemicelluloses in young branches of temperate forest trees during bud break. 1945 84