The general aim of this thesis was to investigate the mechanisms that determine variation in Al accumulation among tropical woody plants. The focus of the study variation among populations of the well-studied Al accumulator Melastoma malabathricum, but this was coupled with sampling 50 tree species growing on the 50 ha forest dynamics plot at Pasoh Forest Reserve in Peninsular Malaysia in order to gain a perspective on Al accumulation at a community scale. I sampled mature leaves and seeds of M. malabathricum from 20 populations growing in six habitats across Peninsular Malaysia. Concentrations of Al, N, P, K, Ca and Mg were determined in air-dried leaves and the soil from each site. The seeds were used to generate cohorts of seedlings that were grown in hydroponic solutions amended with Al in the form of 1.0 mM AlCl3. Foliar Al concentrations varied significantly among populations, but were not consistently different among plants growing in different habitats and showed no relationship to total or exchangeable Al concentrations in soils collected at the 20 sites. Similarly, foliar Al concentrations in seedlings grown in the presence of Al differed significantly among source populations, but values did not correlate with foliar Al concentrations in wild plants from parent populations. Mean foliar Al concentration in wild plants was positively correlated with foliar Ca concentration, and with total soil Ca and Mg concentrations, across the 20 populations. Furthermore, total dry mass and relative growth rates were significantly greater for seedlings that had received Al in the growth medium than for seedlings that had received no Al. The growth response to Al addition varied among populations of M. malabathricum, and relative growth rate in response to Al addition was greater for populations that accumulated higher foliar Al concentrations. In a further experiment, increasing Al concentrations from In a further experiment, increasing Al concentrations from 0 to 2.0 mM in the nutrient solution increased rates of growth, but growth declined at 5.0 mM Al. The responses to Al addition varied among populations for growth, photosynthesis, respiration, carbon allocation, and foliar P, Ca, and Mg concentrations. The rates of photosynthesis and respiration, and total nonstructural carbohydrate concentrations, were higher for seedlings grown in the presence of 2.0 mM Al in the nutrient solution than in the absence of Al, while lignin concentration in roots decreased. These results suggest that Al addition stimulate growth stimulation by increasing rates of photosynthesis and respiration, resulting in higher non-structural carbohydrate concentrations. Increased allocation of photosynthate to root systems coupled with their lower lignification results in enhanced nutrient uptake (particularly P, Ca and Mg), which contributes to enhanced whole-plant growth. To test the prevalence of Al accumulation at the community scale I sampled 50 tree species growing on the 50 ha Forest Dynamics Plot at Pasoh Forest Reserve in Peninsular Malaysia. Twenty two species possessed foliar Al concentrations that exceeded a value of 2.3 mg g-1 Al dry mass, which is a suitable threshold for detecting Al accumulators in Southeast Asian forests. A phylogenetic signal was detected for foliar concentrations of Al and other elements, suggesting that more closely related species have more similar values of these traits. A canonical correspondence analysis (CCA) revealed that soil Al concentrations have limited influence on the fine-scale distribution of the tree species sampled at Pasoh. I conclude that the distribution of differences in the expression of Al accumulation among populations of M. malabathricum and the distribution of Al accumulator species within a tree community growing at one site are uncoupled from soil Al concentrations, but may be linked to other soil properties such as Ca and Mg concentrations. When supplied in nutrient solutions, Al promotes the growth of the Al accumulator M. malabathricum through a physiological mechanism that includes up-regulation of photosynthetic and respiration rates. The functional significance of this growth response for plants growing under natural conditions in the field requires further investigation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:731649 |
| Date | January 2017 |
| Creators | Mahmud, Khairil |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=235553 |
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