Relationships between Seed Mass, Seed Nutrients, and Seedling Growth in Banksia cunninghamii (Proteaceae)

We examined relationships between seed mass, seed nutrients, and seedling growth in two populations of Banksia cunninghamii to determine whether large seed mass provided an advantage for seedling establishment on nutrient-poor soils. N and P content of seeds increased more than proportionally with increasing seed mass, indicating that large seeds had greater concentrations of these nutrients than small seeds. K content of seeds increased either proportionally or more than proportionally with seed mass, depending on population. In a common garden, larger seeds produced larger seedlings, although seed mass had little effect on seed germination, seedling survival, root:shoot ratios, or relative growth rate. In a nutrient-deprivation experiment, seedlings were smaller under low nutrients than under high nutrients. Under low nutrients in one population, the increase in seedling size with seed mass was greater than proportional, indicating that large seed mass minimized the effect of nutrient deprivation. Under high nutrients in this population and under both nutrient regimes in the other population, the increase in seedling size with seed mass was only proportional. Overall, our findings highlight the advantage of large seed mass on nutrient-poor soils, probably by rendering seedlings less reliant on soil nutrients.