- Title
- Metals in saltmarsh ecosystems: an assessment from global to local scales
- Creator
- Alam, Md Rushna
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2024
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Urbanised estuarine saltmarshes are often subjected to a wide range of anthropogenic pressures due to their presence in close vicinity to urban and industrial development. One such threatening process is anthropogenic inputs of metals and metalloids in the saltmarsh sediment from various sources, which poses significant threats to saltmarsh ecosystem integrity worldwide, including Australia. There is therefore a recognised crucial need to monitor and manage such impacts within estuarine ecosystems. In this context, the overall aim of the thesis is to explore the metal accumulation and partitioning pattern in the tissues of saltmarsh halophytes and also to explore halophyte offspring metal tolerance in response to parental metal stress. These would aid in understanding and identifying taxa particularly adept at bioindication and/or phytoremediation for metal-contaminated estuaries and contribute to saltmarsh tolerance responses to metals. Firstly in Chapter 2, I amassed a dataset of saltmarsh taxa globally to explore the pattern of metal (Cu, Zn, Cd and Pb) root uptake and distribution in the plant quantitatively in a phylogenetic framework, and further, to explore the relationship of these patterns with halophytes’ life-history attributes. Most halophytic saltmarsh species exhibited greater root uptake for essential metals (Cu and Zn) and their subsequent higher mobility from roots to shoot was at or above unity (≥1). Patterns of uptake to roots and translocation to leaves were broadly similar among plant type, plant form, habitat and photosynthetic mode. Zinc is lower in the leaves of salt-secreting species for some closely related taxa, suggesting some species co-excrete sodium (Na+) and Zn2+ through glands in leaf tissue. Na+ accumulation and consequent salinity tolerance to maintain osmoregulation have no relationship to metal uptake and translocation, likely because Na+ and metal transport are facilitated by different transporter assemblages. Patterns of accumulation to roots and limited translocation in leaf tissue mean that saltmarsh, as a group, could be classified as effective phytostabilisers rather than hyperaccumulating phytoextractive species. Secondly, in chapters 3 & 4, I explored the pattern of uptake and partitioning of metal(loid) (Cu, Zn, Cd, Pb, Se and As) in the common halophytic saltmarsh species, Austral seablite (Suaeda australis) and Spiny rush (Juncus acutus); collected from highly urbanised estuaries (Georges river, Sydney Olympic park, Lake Macquarie and Hunter wetlands) of NSW, Australia. The field experiments were designed to create a metal exposure gradient to the candidate plants. Both candidate species exhibited greater root uptake of essential metals Cu and Zn along with the non-essential metal Cd. Substantial barriers for translocation from roots to shoots were identified for all metal(loid)s (TFs < 1). Despite limited uptake and translocation of As species across the tissues of J. acutus, inorganic As (As(III) and As(V)) were predominantly accumulated in the roots and As(III) appeared more mobile than As(V). S. australis and J. acutus may be applicable as a bioindicator for examined metal(loid)s as root metal(loid) concentration significantly correlated with sediment metal(loid) load, and both species were found to be effective as phytostabilisers as metal(loid)s were mostly accumulated in underground tissues with limited transfer to above-ground parts. Finally, in Chapters 5 & 6, I examined the hypotheses that elevated sediment Zn and Pb could induce tolerance to the halophyte J. acutus inhabiting metal-contaminated estuaries and whether such tolerance may be transferred to F1 offspring. I also assessed if antioxidative enzymes may be implicated in conferring tolerance to the F1 offspring of metal-exposed parents. These chapters revealed that J. actus F1 offspring exhibited enhanced tolerance to essential metal Zn, as the Zn medium effective concentration (EC50; % germination) increased with the incremental parents’ plant tissue Zn (culm and capsule) accumulation; and seedlings (F1 offspring) originated from contaminated estuary locations displayed significantly greater inclines in early growth parameters (i.e. biomass and root length) with Zn addition in growth media compared to seed from non-contaminated locations. Further, significant upregulation of the antioxidative enzymes i.e. catalase (CAT) and glutathione peroxidase (GPx) in the seedlings’ tissues derived from parents of contaminated locations suggests Zn-induced oxidative stress alleviation and a contribution to enhanced seedling fitness. Observed offspring metal tolerance was most likely due to maternal physiological acclimation as Zn was more mobile across J. acutus tissues and greater accumulation and dispersion of the metal was found in the seed. Overall, this thesis concludes that metal(loid) accumulation patterns are broadly similar across saltmarsh taxa, and exhibited very little relation with plant salt tolerance. Essential metals are more mobile across the plant parts than non-essential metals and halophyte F1 offspring from contaminated wetlands enjoy better fitness in subsequent offspring metal (i.e. Zn) exposures. Halophytes could be employed as phytostabilizers for metal phytoremediation and showed to limited accumulative bioindicator utility for metal-contaminated estuaries.
- Subject
- metals; saltmarshes; halophytes; phytoremediation; bioindicator; metlal tolerance; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1506620
- Identifier
- uon:55911
- Rights
- Copyright 2024 Md Rushna Alam
- Language
- eng
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