Growth phenology, biomass, and vine recruitment potential of the invasive plant Dioscorea bulbifera in Florida

Background/Question/Methods

 Dioscorea bulbifera L. (air potato, Dioscoreaceae) is an herbaceous twining vine introduced to Florida in 1905. Since then it has aggressively invaded and smothered vegetations in various natural and manmade plant communities in Florida and beyond. It has displaced native plants and disrupted ecological functions. Dioscorea bulbifera primarily spreads via bulbils (vegetative propagules) produced annually at the leaf axils. Detached bulbils sprout and produce vines and underground tubers from which new vines emerge every year.  Both brown (rough-surface) and tan (smooth-surface) bulbil producing morphotypes of D. bulbifera occur in Florida. A biological control program is underway. Data on D. bulbifera growth phenology and biomass (tuber, vine, foliage, and bulbil) producing potential will be needed to quantify impacts to the plant populations following the field-release of selected biological control agents. Herein, we examined growth trends and biomass production potential of D. bulbifera from Florida. It was hypothesized that the biomass production and vine recruitment potential of D. bulbifera is directly related to the mass of the propagules (bulbils). To test this hypothesis, bulbils of both morphotypes were planted in common garden plots. Vine length was measured and bulbils were enumerated weekly and the whole plant was harvested following complete senescence of vines. Tubers, vines, leaves and bulbils were sorted by plant, oven dried at 70^oC and weighed. 

 Results/Conclusions

Weight of the planted bulbils (propagules) showed a significant positive correlation with the tuber, vine, leaf, bulbil, and root biomass produced during the entire growth season; both tan and brown bulbil morphotypes showed a similar trend. Also, fresh weight of the propagules had strong positive correlation with total vine length and seasonal growth rates. Proportion of root, tuber, vine, leaves and bulbils produced during the growth season was 2:22:11:31:34 for tan and 1:17:11:33:38 for brown morphotypes, respectively.  Number of bulbils per plant was higher in tan (mean 53, range 0-138) compared to brown (mean 49, range 0-172) morphotypes; total dry biomass of bulbil per plant was higher in brown than in tan morphotypes. Vine growth rate was higher (9.5 cm/day) in tan than in brown (8.4 cm/day) morphotypes. These results show that both morphotypes of D. bulbifera allocate greater proportion of their annual biomass to aerial bulbils and underground tubers; higher bulbil quantities ensure massive recruitment potential to invade new areas while underground tubers ensure persistent vine emergence every year during February-April to replace the old vines that die off during November-December in Florida.