Deeper Bulbs Are Larger

Premise of research.Belowground bud placement generally offers plants protection from aboveground disturbances, such as frosts and fires. However, deeper bud placement requires more reliance on stored resources for emergence. The aim of this study is to examine the relationship between the size of an underground storage organ and its depth within the soil across taxa. Methodology.We measured bulb diameter and bulb depth in the soil for 44 distinct species of Ledebouriinae (Scilloideae, Asparagaceae) found in Zambia and South Africa. Pivotal results.Across species, we found that larger bulbs are positioned deeper in the soil. At the individual level within species, a positive relationship between bulb diameter and bulb depth was generally found, except for in a few instances where larger and smaller bulbs appeared to be found at similar depths. Conclusions.Overall, our study suggests that deeper renewal bud positioning requires greater energetic costs (as indicated by larger bulbs) for emergence across species. Our within-species results could be interpreted as showing that older bulbous plants generally have larger, deeper bulbs. These characteristics are likely interrelated, where older plants have grown relatively larger bulbs that then allow for deeper bud placement, resulting in more protection from aboveground disturbances.