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Mineral nutrient influxes and additions and their effects in a Banksia woodland ecosystem in South Western Australia

Smith, Russell Stephen (1990) Mineral nutrient influxes and additions and their effects in a Banksia woodland ecosystem in South Western Australia. Honours thesis, Murdoch University.

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The objectives of this study were to gain information on the environmental effects of fertilizer drift. This was achieved by undertaking two separate investigations 1 firstly soil nutrient levels and vegetation composition along transects from farmland into a Banksia woodland were analysed to see how they co-varied. Secondly the effect of agricultural fertilizers on the growth, and nutrient and carbohydrate levels of selected shrub species from a Banksia woodland was investigated to determine if fertilizer stimulated shoot growth led to a reduction in root reserves which might diminish post-fire resprouting ability.

The first investigation, into fertilizer drift at Dardanup Block, a conservation reserve, found that most invasive exotic pasture species were restricted to physically disturbed areas at the edge of the reserve with only Hypochaeris glabra a small wind dispersed composite being common away from the edge. Total phosphorus values were highest in the paddock and declined with increasing distance into the reserve, levels were significantly higher in samples taken 0.5 m, 10 m and 20 m into the reserve than they were from those taken 60 m from the fence. Although potassium had been applied to the paddock for over twenty years there was no apparent effect on soil available potassium values at the edge of the reserve. The levels of this mineral and also total nitrogen within the woodland were correlated with native vegetation composition.

In the fertilization study the shrubs Kunzea ericifolia and Leucopogon conostephioides increased their mean biomass per new shoot in response to NPK fertilizer but not to superphosphate alone. The NPK fertilized 11 Kunzea plants connnenced shoot elongation earlier in the season than did the control plants. Increased growth was associated with higher proportions of phosphorus and potassium per unit of shoot nitrogen in Kunzea and increased K:N ratios in Leucopogon.

Levels of root non-structural carbohydrates in Kunzea and Leucopogon were not affected by increased shoot growth and the relatively low root reserves in these plants and their low root:shoot ratio are consistent with their lack of resprouting ability. Stir lingia which did not significantly increase its shoot growth in response to fertilization, had substantially higher root polysaccharide levels in the NPK plots which indicates that the added nutrients stimulated a higher rate of photosynthesis. The relatively high root: shoot ratio and root non-structural carbohydrate levels of Stirlingia are probably the reason for its strong resprouting ability.

From the results of these studies it is proposed that although superphosphate influx increases the levels of phosphorus on roadsides and at the edges of reserves it alone probably doesn't adversely affect the life strategies of native species, though it may favour exotic species. Longer term studies would be needed to separate the effects of continuing nutrient influx on vegetation composition from those of overfrequent burning and various other environmental changes and disturbances associated with "edge" habitats.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Ladd, Phil
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