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Chlorella vulgaris and Chlorella pyrenoidosa were compared relative to their abilities to grow at osmotic potentials of -0.1, -0.5, -1.0, -1.5, -2.0 MPa, [polyethylene glycol(PEG)-induced], and for osmotically-induced changes in lipid composition. C. vulgaris growth was inhibited as osmotic potentials decreased, while C. pyrenoidosa growth was moderately inhibited at -2.0 hPa. C. vulgaris produced increasing concentrations of triglycerides and sterol esters and decreasing levels of polar lipids and sterols as osmotic concentrations increased. Polar lipids, triglycerides, and sterols declined in C. pyrenoidosa while steryl esters remained constant. Ratios of free sterols to polar lipids were 10-fold greater in C. pyrenoidosa and were unaffected by reduced osmotic potentials. In C. vulgaris the sterol to polar lipid ratio declined. Decreasing osmotic potentials in a continuous culture of C. vulgaris, lowered cell lipid concentration, and had no effect on chlorophyll concentrations. The greatest decrease occurred as the osmotic potential decreased from -0.1 to -0.5 HPa. Decreasing osmotic potential caused the phospholipid concentrations to decline. Saturation of triglycerides and free fatty acids increased and decreased, respectively, while polar lipids remained fairly constant. However, the sterol to phospholipid ratio increased as the osmotic potential was lowered. BAS 13-338 (4-chloro-5-(dimethylamino)-2-phenyl-5- 3(2H)pyridazinone) had no effect on C. vulgaris resistance to osmotic stress, but caused growth inhibition as concentrations increased. However, BAS 13-338 was effective in decreasing growth inhibition of C. vulgaris grown in inhibitory levels of ethanol. BAS 13-338 had differing effects on the lipid composition of C. vulgaris when grown in PEG at an osmotic potential of -1.5 MPa compared to -0.1 MPa with 0.33% ethanol. The greatest effects were observed in the ethanol treatments where the qualitative composition of precursor sterols increased as the level of BAS 13-338 increased. This investigation confirmed the important role of lipids in responding to environmental stress through observations of lipid responses to osmotic stress and by manipulation of lipid concentrations using BAS 13-338. Resistance to ethanol inhibition but not osmotic inhibition was achieved in the investigation. / Ph. D.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Renosterveld of the Western Cape region is often seen as a natural occurring veld type that will very easily re-establish itself wherever land is left unattended. In this study it was firstly noted that where wheatlands of the Berg River catchment (BRC) is left bare for a number of years, the renosterbos as a pioneer is slow in its re-growth response and when it does, certain patches in the landscape are preferred. This study therefore firstly focussed on the soil restrictions that widely determined the positions in the Berg River landscape where the renosterbos will re-establish itself. Secondly we needed to know whether some of the soil restrictions encountered could be alleviated and was possibly due to cultivation of this land. Through aerial observation it was found that a general patchiness does exist in the naturally occurring Renosterveld of the Voëlvlei area and hill tops of the region and was described by others as the true nature of this veld type. Closer investigation of the soils in the Voëlvlei reserve however showed that soil type played a major role in the patchiness found here. When re-growth of the renosterbos in previously cultivated areas was investigated, it was found that the soil type played the major role in the patchiness that occurred. The most commonly found soil restriction was soil density of the lower horizons. Any soil form that prevented the renosterbos to access the perched water table, to about 15m depth could not support the renosterbos. It is however our belief that soil could be prepared for the re-growth of renosterbos and through this action; renosterbos could also be used to alleviate the salinity problems found in this region. Additionally we investigated the impact of land-use change on the soil water balance and soil salinity by comparing a mature re-established stand of Renosterveld with an adjacent wheatfield. From the results, large differences in salinity and soil water behaviour were detected between the Renosterveld and wheatfield. Modelling of soil and plant water relations was done and the results were correlated well with field observations. This research also confirmed that the renosterbos through its deep rootedness is crucial in the conservation of other species found in the Renosterveld resulting from its ability to keep the water table down and with that the salts that is so often a problem in this area. / AFRIKAANSE OPSOMMING: In die Wes-Kaap word Renosterveld gesien as 'n veld tipe wat natuurlik voorkom en maklik sal hervestig in areas waar land sonder toesig gelaat word. In hierdie studie is dit eerstens opgemerk dat waar koringlande in die Berg Rivier opvanggebied kaal gelaat word vir 'n aantal jare, is die renosterbos as pionier stadig in sy hervestiging en wanneer terug groei wel plaasvind is dit selektief. Die studie fokus dus eerstens op grondbeperkinge wat die areas bepaal waar Renosterveld sal hervestig. Tweedens wou ons vasstel of die grondbeperkings wat voorkom in die grond en wat heel moontlik die oorsaak is van landbewerking opgehef kan word. Deur lugfoto-waarneming is dit gevind dat algemene leë kolle wel opgemerk is in die natuurlik plantegroei van die Renosterveld, in die Voëlvlei area, asook teen die berg hange. Dit word beskryf as 'n algemene kenmerk van die Renosterveld. Nadere ondersoek in die verskillende grondtipes van die area het egter gewys dat die grond tipe 'n belangrike rol speel in die voorkoms en groei van die renosterbos en uiteindelik die (her-)vestiging van Renosterveld. Die terug groei van die renosterbos is ondersoek in voorheen bewerkte lande. Dit is gevind dat die grond tipe 'n belangrike rol speel in die voorkoms van die leë kolle in die Renosterveld. Die mees algemene grond beperking wat opgemerk is, was die verdigte sub-horisonte. Enige grondvorm wat toegang van die renosterboswortels tot by die grondwatertafel (tot by 'n diepte van 15m) beperk, is nie voldoende om die groei van 'n volwasse renosterbos te onderhou nie. Dit is egter ons oortuiging dat die grond voorberei kan word vir die hervestinging van die renosterbos en deur dit te bewerkstellig sal grondversouting beheer kan word. Die impak van landgebruikverandering op die grondwaterbalans en grondversouting is ook ondersoek, deur 'n volwasse stand van Renosterveld te vergelyk met 'n nabygeleë koringveld. Die resultate het getoon dat daar groot verskille in die grondwatervlakke, asook die soutinhoud tussen die Renosterveld en die koringland voorkom. Modellering van die grond-en plantwaterverhouding is uitgevoer en data het goed gekorreleer met veld waarnemings. Die studie het bevestig dat die natuurlike bewaring van die diep gewortelde renosterbos noodsaaklik is vir die voortbestaan van blom- en skilpadspesies wat slegs in die Renosterveld voorkom asook die vermoë van die renosterbos om stygende watertafels en versouting te beheer waar dit dikwels 'n probleem in hierdie area is.

Thesis (MscAgric (Viticulture and Oenology))--Stellenbosch University, 2008. / The effect of various irrigation strategies on grapevine water relations during the berry ripening period was investigated in a Shiraz/Richter 99 vineyard. Comparisons between different irrigation strategies (full/seasonal, véraison+post véraison, post véraison and no irrigation) were made. During the day, the seasonally irrigated vines experienced less water stress than the deficit treatments. Non-irrigated vines seemed to maintain higher diurnal leaf water potentials. Lower leaf water potentials indicated lower water contents in the vegetative and reproductive tissue. Full irrigation seemed to stimulate primary shoot length. Longer water deficit induced earlier and more complete shoot maturation (reserve accumulation). Re-distribution of leaf area on the shoot may occur when vines are subjected to water deficit. Extended water deficit seemed to induce earlier and restricted water loss from vegetative tissue. The water relations were reflected in the berry size. Irrigation during ripening seemed to induce a continuation of berry water loss. Transpiration losses were apparently much higher in fully irrigated vines whereas stomatal control efficiently maintained water relations in non-irrigated vines. Water deficit seemed to have enhanced the soluble solid accumulation. Irrigation treatments did not seem to affect the titratable acid and pH. The post véraison irrigation in particular seemed to favour a wide window for harvesting. Irrigation at post véraison and especially véraison+post veraison seemed to have a greater effect on the synthesis and extraction of phenolics, anthocyanins and tannins in the berry skins. Different irrigation strategies may affect grapes in such a way that different wine styles are obtained.

Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 219-235.

Irrigation in 1980 accounted for approximately 52 per cent of the water consumed in Southern Africa. The need for planning water resources in the agricultural sector is therefore apparent. Much of Southern Africa's arable farming is carried out on land which, in terms of soil moisture availability to crops, can be described as marginal. Information on soil moisture is therefore valuable to the agriculturalist for planning irrigation schemes and for dryland farming. The objectives of this study were to provide the information mentioned above. This was achieved by producing a detailed delimitation of 712 zones throughout Southern Africa, of more or less homogeneous climate and by providing estimates of crop water requirements under dryland and irrigated conditions in each zone. At the same time the bulk of information which is normally forthcoming from such an analysis involving a large number of combinations of possible input, i.e. crops, soils and planting dates, was reduced, whilst the essential information content was retained. The study provided inter alia an estimate of the frequency of non-exceedance of certain levels of irrigation requirement, based on analyses of soil moisture budgets using long daily rainfall records. The soil moisture budgeting models which were used to estimate the above information were verified inter alia using field measurements of soil moisture. The irrigation analysis was designed such that the results should not became redundant when the inevitable improvement occurs in the estimation of crop factors or soil moisture variables nor if the farming practices change with respect to planting dates. A dryland soil moisture budget analysis for a range of crops and soils was performed in addition to the abovementioned irrigation analysis. The need for this latter study stemmed from the belief that irrigation should not be considered in isolation but rather as one of a range of options, many of them involving dryland farming, facing the agriculturalist. In addition to the dissertation, this study produced a map of Southern Africa on which the 712 homogeneous climate zones are depicted. For each of these zones four pages of computer printout were produced. These pages contain the results of the crop water requirements study for irrigated conditions and the crop water requirement deficit, runoff and an index of stress days for a range of crops, soils and planting dates, under dryland conditions. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.

The increasing human population, industrialization, urbanisation and climate change challenges have resulted in an increased demand for already scarce water resources. This has left the agricultural sector with less water for production. Sustainable water management strategies would therefore require accurate determination of water-use. In agriculture, water-use can best be determined from total evaporation which is the loss of water from soil and vegetation to the atmosphere. Accurate quantification of total evaporation from vegetation would require a thorough understanding of water transport processes between vegetation and the atmosphere, especially in a water-scarce country like South Africa. Several methods for estimating total evaporation have been developed and are in use today. Some of the common methods used today are: the Bowen ratio energy balance, eddy covariance, scintillometry, flux variance and surface renewal. However, various methods have advantages and disadvantages. Considerations include the cost of equipment and level of skill required for use of some of the methods. A number of methods involve indirect or direct estimation of sensible heat flux then calculating latent energy flux and hence total evaporation as a residual of the shortened energy balance equation. The main objective of this study is to determine the effects of grassland management practices on the energy balance components as well as on the surface radiation balance. Eddy covariance and surface renewal methods were employed to investigate the effects of grassland management practices (mowing and burning) on the micrometeorology of naturally occurring grassland. A 4.5-ha grassland site (Ukulinga, Pietermaritzburg, South Africa) was divided into two halves: one area was initially mowed (cut-grass site) to a height of 0.1 m while the other was not mowed (tall-grass site). The tall-grass site was later treated by burning and hence referred to as the burnt-grass site. Two eddy covariance systems were deployed, one at each of the cut-grass and the tall-grass sites. The systems each comprised a three-dimensional sonic anemometer to measure high frequency sonic temperature, orthogonal wind speeds and directions and the eddy covariance sensible heat flux (W m-2). Latent energy flux, from which total evaporation was then determined, was calculated as a residual from the shortened energy balance equation from measurements of sensible heat flux, net irradiance and soil heat flux assuming closure is met. Other microclimatic measurements of soil water content, soil temperature, surface reflection coefficient and reflected solar irradiance were performed, the latter with a four-component net radiometer. An automatic weather station was also set up at the research site for continuous measurements of solar irradiance, air temperature, relative humidity, wind speed and direction and rainfall. Water vapour pressure and grass reference evaporation were also determined online. Energy fluxes from the tall-grass site were measured from March to June 2008. Greater total evaporation rates (2.27 mm day-1) were observed at the beginning of the experiment (March). As winter approached most of the energy balance components showed a constant decreasing trend and the average total evaporation rates for May and June were 1.03 and 0.62 mm day-1, respectively. The tall-grass site had consistently lower soil temperatures that changed diurnally when compared to the cut-grass site. The soil water content at both sites showed no significant differences. Most of the energy balance components were similar between the two sites and changed diurnally. Although there were small differences observed between other energy balance components, for example, latent energy flux was slightly greater for the tall-grass site than for the cut-grass site. The tall-grass site had more basal cover and this may have contributed to the differences in temperature regimes observed between the two sites. However, the plants growing at the cut-grass site showed more vigour than the ones at the tall-grass site as spring approached. Burning of a mixed grassland surface caused significant changes to most of the optical properties and energy fluxes of the surface. Following burning, the soil temperature was elevated to noticeable levels due to removal of basal cover by burning. The surface reflection coefficient measured before and after the burn also presented a remarkable change. The surface reflection coefficient was significantly reduced after the burn but a progressive increase was observed as the burnt grass recovered after the spell of spring rains. The energy fluxes: net irradiance, latent energy flux and soil heat flux also increased following the burn but the latent energy flux was reduced as transpiration was effectively eliminated by the burning of all actively transpiring leaves. As a result, the main process that contributed towards latent energy flux was soil evaporation. An ideal surface renewal analysis model based on two air temperature structure functions was used to estimate sensible heat flux over natural grassland treated by mowing. Two air temperature lag times r (0.4 and 0.8 s) were used when computing the air temperature structure functions online. The surface renewal sensible heat fluxes were computed using an iteration process in Excel. The fluxes, obtained using an iterative procedure, were calibrated to determine the surface renewal weighting factor (a) and then validated against the eddy covariance method using different data sets for unstable conditions during 2008. The latent energy flux was computed as a residual from the shortened energy balance equation. The surface renewal weighting factor was determined for each of the two heights and two lag times for each measurement height (z) above the soil surface. The a values obtained during the surface renewal calibration period (day of year 223 to 242, 2008) ranged from 1.90 to 2.26 for measurement height 0.7 m and r = 0.4 and 0.8 s. For a measurement height of 1.2 m and r = 0.4 and 0.8 s, a values of 0.71 and 1.01 were obtained, respectively. Good agreement between surface renewal sensible heat flux and eddy covariance sensible heat flux was obtained at a height of 1.2 m using a = 0.71 and a lag time of 0.4 s. Total evaporation for the surface renewal method was compared against the eddy covariance method. The surface renewal method, for a height of 1.2 m and a lag time of 0.4 s, yielded 1.67 mm while the eddy covariance method yielded 1.57 mm for a typical cloudless day. For the same day for a measurement height of 1.2 m and a lag time of 0.8 s, eddy covariance and surface renewal methods yielded 1.57 and 1.10 mm, respectively. For a lag time of 0.4 s, the surface renewal method overestimated total evaporation by 0.10 mm while for a lag time of 0.8 s, the total evaporation was underestimated by 0.47 mm. As a result, the surface renewal method performed better for z = 1.2 m and a lag time of 0.4 s. The eddy covariance method gave reliable sensible heat fluxes throughout the experiment and this allowed a comparison of fluxes across all treatment areas to be achieved. The short-term analysis of the surface renewal method also gave reliable energy fluxes after calibration. Compared to the eddy covariance method, the surface renewal method is more attractive in the sense that it is easy to operate and use and it is relatively cheap. However, the surface renewal method requires calibration and validation against a standard method such as the eddy covariance method. This study showed that grassland management practices had a considerable effect on surface radiation and energy balance of the mowed and burnt treatment sites. Total evaporation was mainly controlled by the available energy flux, rainfall and grassland surface structure. High total evaporation values were observed during summer when net irradiance was at its highest and grass growth at its peak. Low total evaporation values were observed in winter (dry atmospheric conditions) when net irradiance was at its lowest and most vegetation was dormant. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

The budgeting of water fluxes in the soil is an extremely complex problem, and is compounded by subsurface controls and environmental forces which modify the soil water dynamics. Of the controlling factors, the underlying geology and the soil media are vital components and are often misinterpreted. The geology and soil media components have been neglected mostly because of the difficulty in monitoring the dominant processes that are linked to the water balance in the subsurface. Until recently, hydrometry has been the dominant method of measuring and monitoring the subsurface water balance. Hydrometric measurements have included water content measurement by Time Domain Reflectometry (TDR), soil water potential measurements through tensiometry and groundwater water level monitoring. Hydrometry is still the preferred method of monitoring soil water dynamics, but measurements are generally localised and lateral accumulations and fluxes of water are difficult to interpret. Using geophysical methods and instrumentation to define soil water dynamics could have numerous advantages over conventional hydrometric methods. Among the geophysical techniques dedicated to image the near surface, Electrical Resistivity Tomography (ERT) surveying has been increasingly used for environmental, engineering and geological purposes during the last decade. The aim of this study is to determine if ERT observations could yield the accuracy required to define vertical and lateral soil water dynamics. The ERT instrumentation uses an electrical current that is inserted into the subsurface through various electrode arrangements and a resulting resistance is determined at the take-out electrodes. With the aid of a modelling package these resistance values are reproduced into a pseudosection of underlying resistivity distribution which is influenced by the moisture conditions of the subsurface medium. This geophysical method is primarily used for geological studies but by doing repeated surveys with the same electrode positioning, moisture fluctuation monitoring could be realised. Use of the ERT technique is at the forefront of soil water dynamics monitoring. The main objective of this study is to propose that the ERT instrumentation could be a more efficient and more informative method of studying soil water dynamics than the traditional soil water dynamics monitoring equipment, particularly to define lateral fluxes and accumulation of subsurface water. The study site is a well instrumented transect in the Nkuhlu Exclosures in the Kruger National Park, South Africa, where ongoing soil water dynamics are monitored. The project aims to compare the ERT data to fiR data on a daily basis, over a period of three weeks, during the rain season, monitoring event based wetting and the subsequent drying phases of the soils in a 2-dimensional section. The project and its fmdings are shown to be valuable to the hydrological interpretation of the subsurface water balance. The application is shown to be particularly important to ecohydrology, in the monitoring of soil water dynamics in a 2-dimensional transect and understanding how the natural cycles of water distribution and plant uptake are linked together. The study demonstrates that ERT can be used to observe changes in the water storage and lateral fluxes within a transect which supports varying vegetation and ecologies. The linking of water fluxes in the hydrology cycle to uptakes and controls in the ecosystem has been developed into the research focus known as ecohydrology The use of the ERT instrument can only benefit this research focus in the future. The study demonstrates that ERT instrumentation can be used to provide valuable understanding of subsurface water dynamics and in turn the effects on ecohydrology. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.