Resource transfer dynamics during early seedling development of 23 species in a species-rich tribe, Ingeae (Fabaceae), from two Neotropical forests

Background/Question/Methods

During the initial developmental stage, seedlings are expected to allocate resources stored in the seed in a manner to optimize growth and survival. Variations in seed size and how seedlings allocate seed nutrients and biomass may reflect intrinsic growth rates and life history strategies of the species. Our objective was to use seed mass as a key trait to compare 23 co-occurring Ingeae (Fabaceae) species’ seed and young seedling resource allocation traits. We asked the following questions: (1) How do dry mass, N and P contents of seeds and seedlings co-vary across related taxa within Ingeae? (2) What are the proportions of mass, N and P reserves in the seed retained in individual seedlings? Seeds were collected at Barro Colorado Nature Monument, Panama and La Selva Biological Station, Costa Rica. Seeds were either dried, then biomass and nutrient content determined, or geminated. Seedlings were grown in a shade house and harvested when their first leaf was green and fully expanded. Seed and seedling dry mass and nutrient data were used to determine allocation patterns within seedlings. Ingeae species were also used in a community-wide comparison of seed traits to determine how trait patterns may differ with increasing phylogenetic diversity.

Results/Conclusions

Seed mass varied substantially (0.02-1.84 g) across species in the tribe Ingeae, which was narrow compared to the community-level diversity in seed mass (0.15 mg to 4.01 g). Large seeds transferred a smaller proportion of their resources to the seedling than small seeds. Seed N and P concentrations were not correlated with seed mass, however, seed nutrient concentrations were positively correlated with seedling stem and root nutrient concentrations. Leaf nutrient concentrations were high (4-9 %N, 0.2-0.5 %P). Interestingly, seedling leaf nutrient concentrations were not correlated to adult leaf concentrations or any other trait we examined. We conclude that within the tribe Ingeae some seed and seedling traits do not follow certain traits correlations previously observed across a broad range of phylogeny, such as increasing seed N concentration with decreasing biomass. Furthermore, it appears that traits such as seed N concentration and proportional transfer of nutrients from seed to seedling may be conserved within and among some genera in this tribe, though they do differ among species.