Home / Anomalous_Items / Aquatic_Macrophytes / Floating_Leaves / Wolffia
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Classification:
Wolffia Horkel ex Schleid. Order Arales; Family Lemnaceae Monocot. Araceae. Related (same family) to Amorphophallus titanum (Araceae), the world’s largest unbranched florescence.
Morphology:
Wolffia is the world's smallest flowering plant, extremely reduced from its ancestors even more than its duckwee relative Lemna. Thallus is elliptical, flattened dorso-ventrally, and <1 mm in length. Actively growing plants are bright green. Moribund plants turn orange to yellow as chlorophyll bleaches, and finally white as carotenes bleach. The life expectancy if ~14 days, and doubling time has been recorded from < 1 day (16 hrs) in the lab, to nearly 14 days. Reproduction is primarily asexual by vegetative budding, limited to one bud at a time per plant. Flowering is not uncommon, with complete flowers (one pistil, one stamen) occurring in a dorsal pit. Pistils are dark red to purple, and mature before stamens, enhancing cross-fertilization. Stamens have bilobed anthers. Wolffia microscopica is a short-day plant, i.e. flower induction occurs in periods of prolonged darkness. However, induction can occur during long days and short nights, by salicylic acid and related organic compounds (Khurana and Maheshwari 1983). More than 50 elongate stomates populate the dorsal (upper) surface of the thallus, oriented parallel to the long axis of the thallus. Also located in the upper epidermis are red spots known as idioblasts (Hegelmaier 1968) and pigment cells (Hillman 1961) that are the result of UV radiation that converts colorless flavans into "red-brown phlobaphene-like compounds" (Witztum 1974). Floatation and upright orientation is aided by a concentric ring of hydrophobic cuticle on the adaxial surface of the thallus, taking advantage of water surface tension. An excellent review of Wolffia and other duckweeds, (Lemna, Spirodela) that includes many copyrighted photogrphic images as well as classroom teaching activities can be found online (Waynesword ).
Habitat :
Epineustonic “floaters” (thallus) on small ponds where wind disturbance is minimal, and benthic “sinkers” (turions) during the winter when surface ice occurs. Wolffia Columbiana has been shown to switch between these two separate anatomic and physiologic forms (Witty 2009). Two states have been observed also in Spirodela polyrhiza, Lemna gibba, L. minor, and L. turionifera, as reviewed by Witty. Transition from sinkers to floaters occurs in hours. Floatation is initiated by accumulation of O2 in the thallus parenchyma “small air pockets” through photosynthesis at medium light intensity (~50 µmol m^-2 s^-1), then assured by the development of substomatal “large air pockets” and accumulation of a thick cuticle (Ibid.). Low intensity (19 µmol m^-2 s^-1) induced a slow conversion to floaters, coming to an equilibrium of half floaters after 10 days incubation (Ibid.) Apparently transition to “sinkers” occurs at low light levels, but not in darkness, indicating that photosynthesis is involved, as well as accumulation of starch. Witty (2002) suggests the likelihood of an unknown factor. It seems likely that the cold air and water temperatures prior to freeze-up would slow or stop bud initiation, and lead to starch accumulation. Loss of the hydrophobic cuticle also occurs during the transition. Optimal pH for at least some duckweeds is somewhat acidic -- Wolffia arrhiza is 5.0, Lemna minor is 6.2 (McLay 1976).
Wolffia Metabolism and Nutrition:
Photoautotrophy. Wolffia can grow by photosynthesis alone, but not as fast as when it has access to labile dissolved organic carbon (DOC). Mixotrophy. Wolffia is both photosynthetic and heterotrophic, the latter by absorbing dissolved organic carbon (DOC)(Landolt and Kandeler 1987). Growth in 1% sucrose is five times higher than in 1% CO2 and twice as fast as in 10% CO2 (Bykova et al. 1998). Heterotrophy. Wolffia arrhiza can grow entirely without photosynthesis in habitats rich in DOC and with insufficient light for photosynthesis (Czerpak et al. 2002). Wolffia is a C3 plant with photorespiration, excreting intermediary products such as glycolate and glycine. Also significant ammonia is secreted (Ibid.). All of these secretions can enhance growth of phytoplankton, although shading and uptake of P and N by Wolffia is inhibitory. After death Wolffia mineralizes rapidly, returning inorganic ions to the environment much more rapidly than larger plants including Lemna sp., Salvinia sp., Cabomba sp., Scirpus cubensis, and Eichhornia azurea (Bitar and Bianchini Jr. 2002), Its rapid turnover of both organic and inorganic solutes stimulates growth of bacteria and phytoplankton.
Pollution remediation and toxin accumulation:
Wolffia acts as a bioremediator of excess phosphorus and nitrogen through its rapid growth and uptake of these elements, containing 1-2% P and 6-7% N of total dry weight, with uptake rates estimated to be 38 mg P d^-1 and 126 mg N d^-1 per frond in continuous culture at 30 C and >8,000 lux light (Fujita et al. 1999). Highest efficiency of P removal (100%) was achieved with a 10-day hydraulic retention time (HRT). Maximum efficiency of N removal (80%) was at 5 days, diminishing at 10 days. Wolffia is used in Thailand to treat shrimp farm effluent (Suppadit et al. 2008). General reviews ( Zhirsky and Reed 1988, Körner et al. 2003) conclude that Wolffia and larger duckweeds show promise for use in sustainable wastewater treatment systems. Wolffia accumulates toxic heavy metal such as lead, cadmium (Piotrowska et al. 2009), chromium (Boonyakookana et al. 2002), and arsenic (Zhang et al. 2009) as well as cyanotoxins such as microcystin (Mitrovic et al. 2005). Because of its mixotrophic ability, including organotrophy (uptake of DOC) Wolffia also accumulates exotic molecules including sex steroids and corticosteroids found in human sewage discharge, helping to reduce their concentration and downstream consequences. At the same time such substances enhance growth of Wolffia through stimulation of DNA and RNA, and increase its production of proteins and sugars (Szamrej and Czerpak 2004).
Use as food or food supplement:
High protein (20% if dry weight) and carbohydrate (44% of dry weight) content, fast growth rate (doubling in less than 2 days under ideal conditions), and ease of harvest suggest Wolffia is a potential major food source for humans (Bhanthumnavin, and McGarry 1971). Wolffia is estimated to produce 60 times more protein per hectare per year than soybeans. Wolffia arrhiza is cultivated and eaten as a vegetable in Burma, Laos, and Thailand, where it is harvested twice a week during nine months of the year (November through July). Its calculated annual yield (265 tons fresh weight (10.5 tons dry weight) ha-^1 yr^-1 is more than convential crops in Thailand. Wolffia is eaten by herbivorous fish as well as a variety of waterfowl. It is also used both as fodder for cattle and pigs, and as a fertilizer because of its high phosphorus and nitrogen accumulation, in Africa, India, and Southeast Asia (National Academy of Sciences 1976). Yearling carp prefer Wolffia over 29 other aquatic plants, more than twice more than the next most preferred plant (Theriot and Sanders Sr. 1975), and increase carp yield (Kumudranjan at al. 1986). Wolffia has been successfully tested as an additive for tilapia feed, replacing up to 15% of soybean content (Chareontesprasit and Jiwyam 2001). Quail have been successfully raised on a diet containing up to 50% crude protein from Wolffia globosa, and the remainder from soybean meal (Chantiratikul et al. 2010).
Use as food cycle for space travel
A closed plant and animal system has been tested with Wolffia arrhiza because of its rapid rate of biomass production. The system is designed to function for a period of two years (Blum et al. 1998).
Epineustonic “floaters” (thallus) on small ponds where wind disturbance is minimal, and benthic “sinkers” (turions) during the winter when surface ice occurs. Wolffia Columbiana has been shown to switch between these two separate anatomic and physiologic forms (Witty 2009). Two states have been observed also in Spirodela polyrhiza, Lemna gibba, L. minor, and L. turionifera, as reviewed by Witty. Transition from sinkers to floaters occurs in hours. Floatation is initiated by accumulation of O2 in the thallus parenchyma “small air pockets” through photosynthesis at medium light intensity (~50 µmol m^-2 s^-1), then assured by the development of substomatal “large air pockets” and accumulation of a thick cuticle (Ibid.). Low intensity (19 µmol m^-2 s^-1) induced a slow conversion to floaters, coming to an equilibrium of half floaters after 10 days incubation (Ibid.) Apparently transition to “sinkers” occurs at low light levels, but not in darkness, indicating that photosynthesis is involved, as well as accumulation of starch. Witty (2002) suggests the likelihood of an unknown factor. It seems likely that the cold air and water temperatures prior to freeze-up would slow or stop bud initiation, and lead to starch accumulation. Loss of the hydrophobic cuticle also occurs during the transition. Optimal pH for at least some duckweeds is somewhat acidic -- Wolffia arrhiza is 5.0, Lemna minor is 6.2 (McLay 1976).
References:
Bhanthumnavin, K., and M.G. McGarry 1971. Wolffia arrhiza as a possible source of inexpensive protein. Nature 232:495. Bitar, A.L., and I. Bianchini Jr. 2002. Mineralisaton [sic] assays of some organic resources of aquatic systems. Braz. J. Biol. 62:557-564. Blum, V., M. Andriske, K. Kreuzberg, U. Paassen, M.P. Schreibman, and D. Voeste 1998. Novel laboratory approaches to multi-purpose aquatic bioregenerative closed-loop food production systems. Acta Astronautica 42:25-35. Bykova, N.V., I.V. Popova, and A.U. Igamberdiev 1998. Photorespiratory metabolism of Wolffia arrhiza. In: Photosynthesis: Mechanisms and Effects. G. Garba, ed. Vol. 5. Kluwer: Dordrecht, pp. 3715-3718. Chantiratikul, A., A. Chantiratikul, A. Sangdee, U. Maneechote, C. Bunchasak, and O. Chinrasri. Performance and carcass characteristics of Japanese quails fed diets containing Wolffia meal [Wolffia globosa (L). Wimm.] as a protein replacement for soybean meal. Int. J. Poultry Sci. 9:562-566. Chareontesprasit, N., and W. Jiwyam 2001. An evaluation of Wolffia meal (Wolffia arrhiza) in replacing soybean meal in some formulated rations of Nile Tilapia (Oreochromis niloticus L.). Pakistan J. Biol. Sci. 4:618-620. Czerpak, R., P. Dobrzyn, A. Krotke, and E. Kicinska 2002. The effect of auxins and salicylic acid on chlorophyll and carotenoid contents in Wolffia arrhiza (L.) Wimm. (Lemnaceae) growing on media of various trophicities. Polish J. Environ. Studies 11:231-235. Fujita, M., K. Mori, and T. Kodera 1998. Nutrient removal and starch production through cultivation of Wolffia arrhiza. J. Biosci. and Bioeng. 87:194-198. Körner, S., J.E. Vermaat, and S. Veenstra 2003. The capacity of duckweed to treat wastewater: Ecological considerations for a sounds design. J. Environ. Qual. 32:1583-1590. Hegelmaier, F. 1868. Die Lemnaceen - eine monographische Untersuchung. Wilhelm Engelmman, Leipzig. Hillman, W.S. 1961. The Lemnaceae or duckweeds -- a review of the descriptive and experimental literature. Bot. Rev. 27:221-287. Landolt, E., and R. Kandeler 1987. The family of Lemnaceae – a monographic study. Geobot. Inst. Veröffentlichungen, Zürich. McLay, C.L. 1976. The effect of pH on the population growth of three species of duckweed: Spirodela oligorrhiza, Lemna minor, and Wolffia arrhiza. Freshwater Biology 6:125-136. Mitrovic, S.M., O. Allis, A. Furey, and K.J. James 2005. Bioaccumulation and harmful effects of microcystin-LR in the aquatic plants Lemna minor and Wolffia arrhiza and the filamentous alga Chladophora [sic] fracta. Ecotoxicology and Environmental Safety 61:345-352. National Academy of Sciences 1976. Making aquatic weeds useful: Some perspectives for developing countries Piotrowska, A., A. Baiguz, B. Godlewska-Zylkiewicz, and E. Zambrzycka 2009. Changes in growth, biochemical components, and antioxidant activity in aquatic plant Wolffia arrhiza (Lemnaceae) exposed to cadmium and lead. Arch. Environ. Contamination and Toxicology 58:594-604. Szamrej, I.K., and R. Czerpak 2004. The effect of sex steroids and corticosteroids on the content of soluble proteins, nucleic acids and reducing sugars in Wolffia arrhiza (L.) Wimm. (Lemnaceae). Polish J. Environ. Studies 13:565-571. Suppadit, T., W. Phoochinda, S. Phutthilerphong, and C. Nieobubpa 2008. Treatment of effluent from shrimp farms using watermeal (Wolffia arrhiza). www.scienceasia.org Witty, M. 2009. Wolffia Columbiana can switch between two anatomically and physiologically separate states: Buoyant for invasion and starch rich for colonization. Int. J. Bot. 5:307-313. Zhang, X., F.-J. Zhao, Q. Huang, P.N. Williams, G.-X. Sun, and Y.-G. Zhu 2009. Arsenic uptake and speciation in the rootless duckweed Wolffia globosa. New Phytol 182:421-428. Zirschky, J., and S.C. Reed 1988. The use of duckweed for wastewater treatment. J. Water Pollut. Control Fed. 60:1253-1258.