Fruit production in three masting tree species does not rely on stored carbon reserves
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Fruiting is typically considered to massively burden the seasonal carbon budget of trees. The cost of reproduction has therefore been suggested as a proximate factor explaining observed mast-fruiting patterns. Here, we used a large-scale, continuous 13C labeling of mature, deciduous trees in a temperate Swiss forest to investigate to what extent fruit formation in three species with masting reproduction behavior (Carpinus betulus, Fagus sylvatica, Quercus petraea) relies on the import of stored carbon reserves. Using a free-air CO2 enrichment system, we exposed trees to 13C-depleted CO2 during 8 consecutive years. By the end of this experiment, carbon reserve pools had significantly lower δ13C values compared to control trees. δ13C analysis of new biomass during the first season after termination of the CO2 enrichment allowed us to distinguish the sources of built-in carbon (old carbon reserves vs. current assimilates). Flowers and expanding leaves carried a significant 13C label from old carbon stores. In contrast, fruits and vegetative infructescence tissues were exclusively produced from current, unlabeled photoassimilates in all three species, including F. sylvatica, which had a strong masting season. Analyses of δ13C in purified starch from xylem of fruit-bearing shoots revealed a complete turn-over of starch during the season, likely due to its usage for bud break. This study is the first to directly demonstrate that fruiting is independent from old carbon reserves in masting trees, with significant implications for mechanistic models that explain mast seeding.
Keywords13C isotope labeling Branch autonomy Carbon relationships Reproduction Swiss Canopy Crane
The authors would like to thank Catharina Lötscher for starch extraction and 13C analyses, Erwin Amstutz for operating the crane, Daisuke Kabeya for helping in the field and his valuable discussions on tree reproduction, and Olivier Bignucolo, Susanna Riedl and Gabrielle Schaer for litter trap collection and fruit biomass analyses. We further thank the two anonymous referees for their valuable comments and their helpful suggestions to improve the text. This study was partially supported by grants from the Japanese Society for the Promotion of Science (No. 18580155, No. 21380103 to Q.H.) and a research fellowship to Q.H. from the Co-operative OECD Research Program. The CO2 enrichment and crane infrastructure at the SCC site were funded by grants to C.K. from the Swiss National Science Foundation (SNF, No. 3100-059769.99, No. 3100-067775.02) and NCCR-Climate (No. 5005-65755). During the time of writing this manuscript, G.H. received funding from European Research Council (ERC) grant No. 233399 (project ‘TREELIM’ to C.K.).
- Eschrich W, Burchardt R, Essiamah S (1989) The induction of sun and shade leaves of the European beech (Fagus sylvatica L.): anatomical studies. Trees Struct Funct 3:1–10Google Scholar
- Ichie T, Nakagawa M (2012) Dynamics of mineral nutrient storage for mast reproduction in the tropical emergent tree Dryopalanapos aromatica. Ecol Res (in press)Google Scholar
- Kozlowski TT, Pallardy SG (1997) Physiology of woody plants, 2nd edn. Academic, San DiegoGoogle Scholar
- Kozlowski TT, Davis WJ, Pallardy SG (1991) The physiological ecology of woody plants. Academic, San DiegoGoogle Scholar
- Landhäusser SM (2011) Aspen shoots are carbon autonomous during bud break. Trees 25:531–536Google Scholar
- Miyazaki Y (2013) Dynamics of internal carbon resources during masting behavior in trees. Ecol Res, doi: 10.1007/s1284-011-0892-6
- Sala A, Hopping K, McIntire EJB, Delzon S, Crone EE (2012) Masting in whitebark pine (Pinus albicaulis) depletes stored nutrients. New Phytol 196:189–199Google Scholar
- Shibata M, Tanaka H, Nakashizuka T (1998) Causes and consequences of mast seed production of four co-occurring Carpinus species in Japan. Ecology 79:54–64Google Scholar