An effect of gibberellic acid on circumnutation

Gibberellic acid causes a marked increase in the amplitude of circumnutation in dwarf pea seedlings. The effect may be detected within 12 hours from the time of treatment. The relation was investigated between the time at which this effect occurred and the time at which increased growth of the shoot was detected

The biology of Australian seagrasses

Seagrasses are angiosperms which have ventured into the marine environment, where they produce totally submerged flowers which are pollinated under water. They occur in many regions of the world,but the following account is concerned primarily with studies on the biology of these plants in Australian waters. It also attempts to contrast some of the features displayed by the seagrasses with those of more familiar terrestrial plants

Distribution and abundance of benthic microalgae in a shallow southwestern Australian estuarine system

Measurements were made of benthic microalgal biomass (chlorophyll mg m-2) and concentration (chlorophyll, µg g-1 dry weight of sediment) from the Peel-Harvey estuarine system, Western Australia. Most chlorophyll was in the top 1 cm of sediment, and less than 10 % of chlorophyll a was non-functional as determined by hexane extraction. Highest biomass occurred at shallow sites and on coarse sandy sediments. Biomass was higher in Harvey (202 mg m-2) than Peel (107 mg m-2) in summer when there was a large population of microalgae in Peel; biomass was similar in winter (Harvey 163 mg m-2, Peel 151 mg m-2). Biomass increased with the onset of riverine nutrient input and decreased when blooms occurred in the water column. Except during Nodularia blooms, the biomass (chlorophyll) of benthic microalgae greatly exceeded (e g 40 times) the biomass of chlorophyll in the water column above. In summer much of the chlorophyll of the water column was due to wind stirring of benthic microalgae. The possible importance of benthic microalgae to the productivity of shallow systems is emphasized

The nutritional eco-physiology of Chaetomorpha linum and Ulva rigida in Peel Inlet, Western Australia

The uptake rates and critical tissue concentrations of nitrogen and phosphorus were determined for Chaetomorpha linum and Ulva rigida , the dominant algae in Peel Inlet, Western Australia. Both species had rate-saturating mechanisms of phosphate uptake described by Michaelis-menten type functions; C. linum had the faster uptake rate (667 c.f. 272 mu g P g/dwt/h) although U. rigida had a lower half-saturation value. Both species displayed linear relationships between ammonium uptake rates and substrate concentrations with C. linum having the greater slope (4.4 c.f. 1.7). Chaetomorpha linum also had a linear increase in uptake rate with increasing concentration of nitrate, but U. rigida showed rate-saturating kinetics; below 750 mu g/L, U. rigida had the higher rate of uptake. Ulva rigida had critical tissue nitrogen and phosphorus concentrations of 20 and 0.25 mg g/dwt respectively. Corresponding concentrations for C. linum were 12 and 0.5 mg g/dwt. Ulva is frequently nitrogen limited during spring in Peel Inlet, reflecting the high nitrogen requirements of this plant compared to Chaetomorpha as well as the reduced ability of Ulva to store nutrients over winter

Quantitative electron energy-loss spectroscopy (EELS) analyses of lead zirconate titanate

Electron energy-loss spectroscopy (EELS) analyses have been performed on a sol–gel deposited lead zirconate titanate film, showing that EELS can be used for heavy as well as light element analysis. The elemental distributions within the sol–gel layers are profiled using the Pb N<sub>6,7</sub>-edges, Zr M-edges, Ti L-edges and O K-edge. A multiple linear least squares fitting procedure was used to extract the Zr signal which overlaps with the Pb signal. Excellent qualitative information has been obtained on the distribution of the four elements. The non-uniform and complementary distributions of Ti and Zr within each sol–gel deposited layer are observed. The metal:oxygen elemental ratios are quantified using experimental standards of PbTiO<sub>3</sub>, PbZrO<sub>3</sub>, ZrO<sub>2</sub> and TiO<sub>2</sub> to provide relevant cross-section ratios. The quantitative results obtained for Ti/O and Pb/O are very good but the Zr/O results are less accurate. Methods of further improving the results are discussed

The nutrient status of Wilson Inlet 1984-1985

In response to the concern of local residents about the condition of Wilson Inlet, a study of the inlet and its catchment was undertaken during 1982-83. While the results for that study were clear, it occurred during an atypical year; the winter had a particularly low rainfall and the sand bar between the estuary and the ocean was breached for the shortest period of any winter. To obtain some understanding of the variability likely to be encountered in the estuary between years, another, smaller study was undertaken in 1984-85. The main conclusions about nutrient concentrations in plant tissues, the importance of phosphorus, total plant biomass and general ecosystem behaviour were si111ilar to those reached in the earlier study, despite very different winters. Catchment behaviour, in relation to nutrient losses to streamflow was also generally similar, with somewhat higher concentrations of nutrients associated with a winter of higher runoff. The main contrast was the large amount of nitrogen, especially in the form of nitrate, which came from the larger subcatchments during the present study. Rainfall was much closer to the long-term mean in 1984 and there was a 2.8 times increase in streamflow for the whole Wilson Inlet catchment compared to 1982. The phosphorus load of 19 tonnes was lower than the 30 tonnes predicted for an average year on the basis of the 1982 results. The nitrogen load of 340 tonnes was slightly higher than predicted for an average year from the 1982 study. Salinities were lower and nutrient concentrations and water column loads higher in winter in the present study due to the higher streamflows. Chlorophyll 'a' concentrations and water column load were also higher, presumably in response to the higher nutrient loads. Estimates of total plant biomass in winter were similar, and the results of both studies show that Ruppia biomass is one of the major nutrient banks in the Inlet. Sediment nutrient loads were similar in both studies. A nutrient budget was calculated for one cycle of bar opening and closing. There was a net retention of phosphorus of 9 tonnes (49% of total input), and net retention of nitrogen of 217 tonnes (63%). The percentage of total riverine phosphorus load retained by the inlet was similar in both studies. In contrast, it was estimated that there was net export of nitrogen in the previous study

Probing magnetic order in EELS of chromite spinels using both multiple scattering (FEFF8.2) and DFT (WIEN2k)

The electron energy loss near edge structure on the O K-edge from chromite spinels contains fine structure from the hybridisation of the O p-orbitals and the Cr d-orbitals. Unlike the aluminates, a non-spin polarised calculation of this fine structure differs significantly from experimental observations. This is due to the large magnetic moment on the Cr. Calculations using simplified collinear ordering of the spins and the local spin density approximation give much improved agreement. A real space multiple scattering formalism and a reciprocal space density functional formalism give results in substantial agreement. In general, the actual spin arrangement of these chromites is not known since they are typically frustrated magnetic systems with ordering temperatures in the 10–20 K range. The calculations are based on the hypothesis that dynamic short range order persists to room temperature over the time scale of the interaction with the fast electron. However, it is possible that the observed effects are due to the strong paramagnetism present at room temperatures but which it is not possible to simulate accurately at present