Mangrove forests are subjected to many environmental factors which influence species distribution, zonation patterns as well as succession. Important driving factors in these forests are salinity, water level fluctuations and available light. This study investigated the response of red mangrove (Rhizophora mucronata Lam.) seedlings to these factors in controlled laboratory experiments. Increase in salinity and prolonged inundation within estuaries are predicted impacts resulting from sea level rise due to climate change. The study investigated the effect of five salinity treatments (0, 8, 18, 35 and 45 ppt) with a semi-diurnal tidal cycle on seedling growth. In a separate experiment the effect of different inundation treatments: no inundation, 3, 6, 9 hour tidal cycles and continuous inundation (24 h) were investigated. Both morphological and physiological responses of R. mucronata seedlings were measured. There was a decrease in growth (plant height, biomass and leaf production) with increasing salinity. Seedlings in the seawater, hypersaline and no inundation treatments showed symptoms of stress, having increased leaf necrosis ("burn marks"). The highest growth occurred in the low salinity (8 ppt) treatment, but the highest photosynthetic performance and stomatal conductance occurred in the freshwater treatment (0 ppt). The typical response of stem elongation with increasing inundation was observed in the 24 hr inundation treatment. In the light and salinity combination study there were ten different treatments of five different light treatments (unshaded, 20 percent, 50 percent, 80 percent and 90 percent shade) combined with two salinity concentrations (18 and 35 ppt). In this study the seedling growth: plant height, biomass, leaf surface area and leaf production were higher in the moderate salinity (18 ppt) treatments compared to the seawater (35 ppt) treatments. Biomass in the 35 ppt experiment decreased with increasing shade as well as in the unshaded treatments. Photosynthetic performance and stomatal conductance were lower for the unshaded treatment in both 18 and 35 ppt salinity compared to all other treatments with the same salinity. This suggests that R. mucronata more shade than sun tolerant, but overall it can be concluded that the species has a broad tolerance range. The results may be relevant in mangrove rehabilitation and predicting responses to climate change. This is important as mangrove ecosystems may adapt to changing sea levels and in order to restore areas it will be necessary to choose the mangrove species which will grow best. The results may also help to increase the protection of existing mangrove habitats.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nmmu/vital:10616 |
| Date | January 2009 |
| Creators | Hoppe-Speer, Sabine Clara Lisa |
| Publisher | Nelson Mandela Metropolitan University, Faculty of Science |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc |
| Format | viii, 103 leaves : col.ill, pdf |
| Rights | Nelson Mandela Metropolitan University |
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