Effect of environmental factors and bulb mass on the invasive geophyte Oxalis pes-caprae development

Oxalis pes-caprae is an invasive pseudoannual plant that reproduces exclusively via offspring bulbs in the introduced range. It is most abundant in disturbed, fertile sites such as agricultural fields, but it is also found in undisturbed shrublands and shadier forest habitats. Oxalis infestation depends on long distance bulb dispersal (mainly anthropogenic) and on the ability of bulbs to grow and reproduce successfully. We conducted a greenhouse experiment to test the effects of parent bulb size on Oxalis growth and offspring production as a function of light availability (ambient and shade), planting depth (surface vs. 9 cm deep), and soil volume (full pots and pots with reduced soil volume). Oxalis grew and reproduced prolifically in all treatments. However, plant development and final offspring bulb production were sensitive to environmental conditions. Shading and reduced soil volume reduced maximum plant biomass relative to control and planting depth treatments, which produced either higher number of offspring bulbs (control) or larger offspring bulbs and higher total offspring bulb biomass (planting depth). Parent bulb size and vegetative reproductive organs had little effect on plant growth and offspring production. Our results are consistent with the lower abundance of Oxalis in undisturbed soils and shadier habitats in the field but indicate that even in these marginal habitats Oxalis can reproduce prolifically and contribute to further spread.