Ecology of creeping macrophytes with special reference to Ludwigia peploides (H.B.K.) Raven

Abstract

Growth strategies are described of five emergent macrophytes, Ludwigia peploides (H.B.K.) Raven, Myriophyllum aquaticum (Vellozo) Verdcourt, Nasturtium officinale R. Br., Hydrocotyle verticillata Thunb., and Oenanthe sarmentosa Presl, which commonly occur in nutrient rich pools, sloughs, and irrigation and drainage canals throughout central and southern California. Because of their creeping mode of growth, the term ‘creeping emergents’ is suggested. These plants are characterized by rapid growth, high nutrogen accumulation, allocation of most biomass and nitrogen into aboveground plant parts, and rapid decomposition. Experiments on L. peploides showed it to be capable of producing up to 50 g dry weight m −2 day −1. In natural stands its average biomass is usually in the range 500–700 g dry weight m −2. In cultivation, with an artificial stem support, it attained a positive growth rate even at high densities, and a biomass corresponding to 1900 g dry weight m −2. It grew well in a broad range of nitrogen concentrations, its biomass production staying approximately the same through the range 20–140 mg l −1 of nitrate-nitrogen in water. Whole plant nitrogen content reached a maximum of 4.5%, leaf nitrogen 6.8%. The rate of photosynthesis decreased in leaves with nitrogen concentrations > 5.5%. L. peploides regenerated well after 95% of the stem length was removed, regaining 67% of biomass of the uncut control in 45 days. Creeping emergents have good potential for use in waste water treatment.