GROWTH AND CARBON UTILIZATION BY SPROUTED PROPAGULES OF 2 SPECIES OF SUBMERSED ROOTED AQUATIC PLANTS GROWN IN DARKNESS

Hydrilla verticillata (L.f.) Royle tubers from monoecious plants and P otamogeton gramineus L. winter buds were sprouted and allowed to grow in the dark for 120 days. We measured plant length and counted the num ber of leaves at 2-3 day intervals. Hydrilla grew most rapidly during the first 16-17 days and Potamogeton grew most rapidly during the firs t 16-25 days. Measurement of propagule carbon content over time indica ted that cessation of rapid growth coincided with depletion of tuber c arbon by one-half for Hydrilla. For Potamogeton, growth was reduced af ter 16 to 25 days while the winter bud C half-life was 37 days. Calcul ations indicated that Hydrilla mobilized 49% and Potamogeton 39% of th e initial propagule carbon to support growth. In a second experiment, in which plants were grown in substrate the plants grew taller and pro duced slightly more leaves per plant. Potamogeton removed from darknes s after specified time periods, and allowed to grow for 21 days in a g reenhouse recovered from 20-30 days in the dark. Similarly treated Hyd rilla plants recovered from up to 80 days in the dark. Potamogeton had mobilized 79% of initial C by the time it was unable to recover from the dark treatment. Combined results for both species indicate that th e majority of propagule C was utilized in the first 16 to 30 days foll owing sprouting. In conjunction with an understanding propagule sprout ing requirements, this information will be useful in the timing of app lication for management techniques.