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Title: Why are wetland plants limited to waterlogged soils?
Author: Smith, Susanna Lucy
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 1992
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The growth of the wetland plants, Phragmites communis, Mentha aquatica, Phalaris arund. nacea, Juncus effusus, and Oenanthe crocata were all significantly reduced when grown in dry soil and/or with competition from L. perenne in a glasshouse. The interaction of water stress with competition caused the greatest reduction in growth. Nitrate reductase activity was highest in those wetland plants grown in soil with minimum watering. Results from field trials, indicated that the spread of M. aquatica and P. arundinacea was restricted because of competition from other naturally occuring species, whereas P. communis was not. Levels of nutrients in glasshouse grown plants did not vary with watering regime or competition from L. perenne. In the field, levels of N and P were lower in the wetland species from drier soils. Particle size of the soil did not restrict the growth of the above wetland species in comparison to a mesophyte (Zea mays). Increased bulk density restricted root growth of Z. mays to a greater extent than the wetland species. When the above wetland plants and Z. mays were grown in tubes that were slowly droughted, Z. mays was less affected by water stress compared to the wetland species. Z. mays had lower stomatal conductance, greater photosynthetic rates, and less negative leaf water potentials than the wetland species. Z. mays also had much faster and deeper root growth. In contrast root growth of P. communis and M. aquatica were restricted by a relatively small drop in soil water potential. P. arundinacea had greater root growth rates than the other wetland species, but its roots were restricted to the surface soil layers. Few adventitious roots formed on the wetland species even in fully watered controls. Leaf water potentials were more negative than expected in the wetland species and in particular P. communis, in comparison to usual values for mesophytes. Investigations showed that this was not an artifact of the psychrometer measurements. Calculated hydraulic resistance was high in P. communis. Metaxylem vessels had smaller diameters and were less abundant in many parts of the wetland species compared to Z. mays. P. communis had more negative leaf water potentials in intact plants compared to excised leaves or stems suggesting existance of high hydraulic resistance in the root or rhizome system. In addition this species showed a loss of water from the leaves at night. The above factors were thought to contribute to the negative leaf water potentials of the wetland species.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Botany Botany Ecology