Seedling growth in relation to seed size among species of arid Australia

It has been reported that species from environments where seedlings are prone to drought during establishment tend to have larger seeds. One proposed reason for this is that larger-seeded species might be able to allocate a larger proportion of mass to roots rather than shoots during early growth. Seedlings of 32 species from arid central Australia were grown in coarse sand under standard conditions in a glasshouse, and harvested 10 days after germination. Seedlings from heavier-seeded species did not allocate relatively more resources to roots than lighter-seeded species. Experiments confirmed this result for plants grown on sandy loam, in drying as compared to well-watered soil, and under shaded conditions. Seedlings of heavier-seeded species tended to survive longer than seedlings from lighter-seeded species when grown in the absence of any mineral nutrients other than those in the seed. Seedlings of heavier-seeded species tended to be able to emerge from greater depths in the soil than lighter-seeded species. Seedlings from heavier-seeded species had a slower relative growth rate than lighter-seeded species during the first ten days after germination. Nevertheless, among these species, seed size was more important than relative growth rate or germination speed in determining seedling size ten days after seeds were wetted.