Physiological activity in persistent bulbils of Agave vilmoriniana (Agavaceae)

Plants of Agave vilmoriniana are unique members of a reproductively diverse genus since they produce prolific numbers of both bulbils and viable seeds. Bulbils were observed to remain attached to the flowering stalk into a second summer, instead of abscising in the year they developed. Hence, a number of hypotheses were tested to establish the physiological basis for their longevity and evaluate their influence upon the plant's reproductive biology. Bulbils produced following anthesis were abundant (>2000 bulbils), large (0.44 g dry mass per individual), and their combined leaf surface area (one side) could exceed 3 m². Thus, the current-year inflorescence may act as a photosynthate source. Second-year, attached bulbils are healthy-looking, even after leaves of the parent plant have senesced, since maternal roots continue to absorb rain water. Rehydrated 2nd-yr bulbils resume Crassulacean acid metabolism, sometimes demonstrating net daytime tissue acidification. Water conservation by bulbils is very efficient, exhibiting very low cuticular conductances (0.016-0.0035 mm/s). Bulbils detach over all climatic seasons after having formed >3 and >18 root primordia in their 1st and 2nd year, respectively. About one-third of bulbils are capable of forming roots after a 1-yr storage at 35°C, when their water contents averaged 37%. Irrigated bulbils produce water-absorbing roots within 2 d, with de novo chlorophyll synthesis and nocturnal acidification commencing within 4 d. Two bulbils were observed to root and become established in shaded microhabitats during this 2-yr study of 29 plants.