Abstract
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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Acknowledgements
This research was facilitated by the A.W. Mellon Foundation research grant to C. K. in cooperation with K. Winter, through the Smithsonian Tropical Research Institute, Panama City and Washington D.C. and by Freie Akademische Gesellschaft, Basel. We are grateful to the Smithsonian Tropical Resarch Institute for the use of the canopy crane and for logistic support. We would also like to thank Monica Mejía, Milton García and Pilar Angúlo for field assistance, and Paul Jordan for statistical consultations.
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Würth, M.K.R., Peláez-Riedl, S., Wright, S.J. et al. Non-structural carbohydrate pools in a tropical forest. Oecologia 143, 11–24 (2005). https://doi.org/10.1007/s00442-004-1773-2
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DOI: https://doi.org/10.1007/s00442-004-1773-2
Keywords
- Biodiversity
- Carbon balance
- Global change
- Seasonality
- Wood reserves