Veterinary and Agricultural Sciences Collected Works - Theses

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    Investigations of seed production potential of indigenous grassland forbs
    Delpratt, Cecil John ( 1999)
    This study investigated the potential for seed production, ex situ, from a range of forbs that were component species of grasslands and other grass-dominated plant communities in south-eastern Australia. Thirty-five species of native perennial forbs were collected from remnant grass-dominated plant communities in southern and western Victoria. All but one species (Tricoryne elatior, which did not germinate) were amenable to propagation and production in bark-based soil-less growing media in a variety of containers. Of 34 species, 29 (85%) flowered and produced seed within one year of propagation, and all species flowered and produced seed within 3 years. Of 20 species planted into field beds in autumn, 15 established successfully. The species generally were not amenable to spring planting in field beds. There was large variation between species in seed production potential due to differences in the number of flowers produced and the number of seeds produced per flower. Seasonal environmental effects on plant development and seed production were investigated in two studies. Firstly, Bulbine bulbosa and Craspedia variabilis were sown outdoors, in containers, at 12 sequential monthly intervals from 2/4/95 to 10/3/96. Both species established from all sowings but most flower and seed production occurred during spring and early summer, regardless of sowing date. For C. variabilis, sowings in January and February produced the most inflorescences per plant in the following spring. B. bulbosa plants produced visible buds approximately one month later than C. variabilis and were harvested 3 months later than equivalent sowings of C. variabilis. The second study investigated the potential for scheduling `out-of-season' production of seed. Seventeen species (that would normally be propagated in autumn) were sown in a greenhouse, and grown outdoors, on three occasions in late winter and spring (6/8/95, 3/9/95 and 1/10/95). Some plants of all but one species (Eryngium ovinum) flowered by April 1996, with 5 species exhibiting complete flowering in one or more sowings (Brachyscome dentata, Leptorhynchos tenuifolius, Velleia paradoxa, Wahlenbergia luteola, and W. stricto). Most species appeared to flower in response to interactions between cool (< 10 C) and warm (> 10 C) temperatures and to changes in photoperiod. It was concluded that to ensure synchronous flowering and, therefore, the potential for panmixis in out-breeding species, most species should be scheduled for flowering in their 'natural' flowering season. A method for improving the harvest efficiency of Bulbine bulbosa was investigated to replace the need for hand-harvesting of individual capsules. The yield, size and germination capacity of seed harvested from inflorescences that had been detached from the parent plant at a range of maturities, and dried at 20 degrees C, were compared to those of seed harvested from intact inflorescences. Seed yield was highest from intact inflorescences but daily harvests were required and harvests spanned a mean of 33 days per inflorescence, double the time needed for detached inflorescences to release all their seed. There was no significant difference between harvest methods in the number of seeds harvested per capsule, but there was a higher proportion of large seeds harvested from intact inflorescences. Germination was greater than 70% for all harvest treatments after 8 months of dry storage. Harvesting and drying inflorescences when one to three capsules had reached harvest maturity appeared to have the potential to increase harvest efficiency in B. bulbosa. The breeding system of Craspedia variabilis was examined in a greenhouse experiment that subjected inflorescences to one of three pollination treatments (none, hand self-pollination and hand cross-pollination). Cross-pollinated inflorescences produced an average of 301 achenes per capitulum, significantly more than either self-pollinated or non-pollinated inflorescences (19 and 15, respectively). It was concluded that C. variabilis is strongly out-breeding and largely self-incompatible. It was concluded that many perennial forb species were amenable to growth in containers but that seed production potential varied between species. For the genetic diversity sampled from remnant populations to be represented in seed produced in cultivated plants, the seed production system must take full account of the breeding system requirements and seasonal influences on flowering and seed production, for each species.
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    Responses of tree roots to post-planting waterlogging and soil compaction
    Smith, Karen D. ( 1997)
    Plants growing in urban soils are frequently subject to waterlogging and changes in soil strength due to compaction and fluctuations in watertables, and variations in texture and bulk density due to the disturbed nature of urban soils. A waterlogging trial was set up to test the ability of recently planted trees to grow new roots under waterlogged conditions and to recover from this period of waterlogging. Corymbia maculata, Lophostemon confertus, Platanus orientalis and Platanus X acerifolia were subjected to a period of waterlogging and then a recovery phase after waterlogging had ceased. Root length was measured at the end of the waterlogging phase, and at the end of the recovery phase. The different species were found to vary considerably in their ability to tolerate and recover from a period of waterlogging. Waterlogging suppressed shoot and root growth in all species trialed. Corymbia maculata, and Platanus orientalis were able to initiate new roots under waterlogged conditions. Platanus X acerifolia and Lophostemon confertus were not able to do this. Compaction trials were set up to test the hypothesis that trees which are able to establish in urban soils will have a higher than average tolerance to soil compaction and to the higher mechanical impedance and soil strength in dry compacted soils. Compaction Trial A tested the ability of the roots of Corymbia maculata, Lophostemon confertus, Corymbia ficifolia and Agonis flexuosa seedlings to penetrate soil cores compacted to bulk density 1.4 and 1.8 Mg/m3 at 13 % gravimetric moisture content. While roots of all species were able to penetrate the soil at the higher bulk density, total root penetration depth was reduced by 60 % across all the species. Compaction Trial B tested the ability of Corymbia maculata and Corymbia ficifolia to penetrate soil compacted at bulk densities 1.4, 1.6 and 1.8 Mg/m3 at two moisture levels, 7 and 10 % gravimetric moisture. At 7 % moisture, both species were able to penetrate soil compacted to 1.4 and i .6 Mg/m3, but neither species was able to successfully penetrate soil compacted to 1.8 Mg/m3. At 10 % moisture, both species were able to penetrate soil compacted to 1.4 and 1.6 Mg/m3. They were also able to successfully penetrate soil compacted to 1.8 Mg/m3, although with significantly less depth of penetration.