Responses ofLeptospermum scopariumandL. ericoides(Myrtaceae) to waterlogging

Abstract

Field observations of the contrasting tolerances and adaptations to permanently waterlogged habitats of the two widespread indigenous species of Leptospermum (Myrtaceae) were tested experimentally. Seedlings of two populations of manuka, L. scoparium (inland semi-arid and coastal forested regions of Otago), and one of kanuka, L. ericoides (coastal), were partially submerged in either stagnant or running fresh water. Anatomical and morphological responses of the submerged portions were followed and compared between species, populations, and treatments. In both species the rhytidome (bark complex) consists of zones of non-suberised cells separated by suberised layers one cell in width, which were found to be persistent phellogens (cork cambia). After its origin from phloem parenchyma each new phellogen, while still in an active state, becomes rapidly suberised. Submergence resulted in the appearance of a specialised ventilating tissue, aerenchyma, which arose by an increase in the number and radial extension of the non-suberised products of the currently active phellogen. Aerenchyma development was significantly more pronounced in the two populations of L. scoparium than in L. ericoides and was somewhat larger in the coastal than in the inland population of L. scoparium. Vigorous growth, including strong root development, ferric iron staining on the surfaces of both the plastic pots and the larger roots, lack of sulphide odours, and relatively high redox potentials in the rhizosphere of waterlogged plants of L. scoparium contrasted with the weakened responses in similarly treated plants of L. ericoides. These results accord with the differential tolerances to permanently waterlogged habitats revealed by the ecology of these two species.