title: Aquatic adventitious root development in partially and completely submerged wetland plants Cotula coronopifolia and Meionectes brownii.
abstract: OBJECTIVE
  A common response of wetland plants to flooding is the formation of aquatic adventitious roots. Observations of aquatic root growth are widespread; however, controlled studies of aquatic roots of terrestrial herbaceous species are scarce. Submergence tolerance and aquatic root growth and physiology were evaluated in two herbaceous, perennial wetland species Cotula coronopifolia and Meionectes brownii.
  
  
  METHODS
  Plants were raised in large pots with 'sediment' roots in nutrient solution and then placed into individual tanks and shoots were left in air or submerged (completely or partially). The effects on growth of aquatic root removal, and of light availability to submerged plant organs, were evaluated. Responses of aquatic root porosity, chlorophyll and underwater photosynthesis, were studied.
  
  
  RESULTS
  Both species tolerated 4 weeks of complete or partial submergence. Extensive, photosynthetically active, aquatic adventitious roots grew from submerged stems and contributed up to 90 % of the total root dry mass. When aquatic roots were pruned, completely submerged plants grew less and had lower stem and leaf chlorophyll a, as compared with controls with intact roots. Roots exposed to the lowest PAR (daily mean 4.7 ± 2.4 µmol m(-2) s(-1)) under water contained less chlorophyll, but there was no difference in aquatic root biomass after 4 weeks, regardless of light availability in the water column (high PAR was available to all emergent shoots).
  
  
  CONCLUSIONS
  Both M. brownii and C. coronopifolia responded to submergence with growth of aquatic adventitious roots, which essentially replaced the existing sediment root system. These aquatic roots contained chlorophyll and were photosynthetically active. Removal of aquatic roots had negative effects on plant growth during partial and complete submergence.
authors.affiliation: School of Plant Biology (M084), Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA 6009, Australia. sarah.rich@grs.uwa.edu.au
authors.forename: Sarah Meghan
authors.initials: SM
authors.lastname: Rich
authors.forename: Martha
authors.initials: M
authors.lastname: Ludwig
authors.forename: Timothy David
authors.initials: TD
authors.lastname: Colmer
mesh_terms: D059001:Aquatic Organisms / Q000254:growth & development; D019659:Asteraceae / Q000254:growth & development* / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D008027:Light; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism*; D018547:Plant Stems / Q000378:metabolism*; D053833:Wetlands
chemical_list: D002734:Chlorophyll