To investigate how seed reserves affect early seedling performance, we conducted a factorial greenhouse experiment using Lithocarpus densiflora (Tanoak). Seedlings were grown from large (5.8±0.7 g) and small (3.2±0.4 g) seeds and, following shoot emergence, seeds were either removed or left attached. Seedlings were harvested for quantification of biomass and δ13C at seven time periods following seed removal (2, 4, 8, 16, 32, 64, 128 days) and seedling photosynthesis was measured three separate time periods (2-4, 49-82, 95-128 days after seed removal). Biomass increased for all seedlings, but the increase was significantly larger for seedlings with attached seeds than with removed seeds. Seed removal just after shoot emergence significantly decreased seedling biomass, but seed removal 64 days after shoot emergence had no effect on seedling biomass. Seedling photosynthesis per unit leaf area varied by time and seed presence, but not by seed size. At the first period, seedlings with attached seeds had significantly higher photosynthetic rates than seedlings with removed seeds, at the second period there was no effect of seed removal, and at the third time period seedlings with attached seeds had significantly lower photosynthetic rates than seedlings with removed seeds. Despite temporal variation in photosynthesis per unit leaf area, seedlings with attached seeds always had significantly greater leaf area than seedlings with removed seeds, resulting in significantly higher total plant photosynthesis at all three time periods. The δ13C values of both the leaves and roots were more similar to that of the seed for seedlings with attached seeds than for seedlings with removed seeds, however, seed removal and seed size strongly affected root δ13C. This study demonstrates that seed reserves have important effects on the early growth, physiology, and δ13C of L. densiflora seedlings.
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Acknowledgements The authors would like to thank the Marin Municipal Water District for use of their land; J. Diaz, J. Hu, K. Peer, V. Schmidt for field and greenhouse assistance; N. Teutsch and V. Schmidt for assistance in preparation of isotope samples; and S. Mambelli for assistance in analyzing the isotope samples at the Center for Stable Isotope Biogeochemistry (CSIB), UC Berkeley. The work was supported by a NSF Graduate Research Fellowship and a CSIB graduate research reward to P.G.K.
- Lithocarpus densiflora
- Seed reserves
- Seedling growth and physiology