Irrigation water of poor quality can have deleterious effects on soils. However, the effect of drip irrigation on seasonal and long term (e.g. over 50 years) changes in soil chemical properties is poorly understood, complicated by the two-dimensional water flow patterns beneath drippers. Field and laboratory experiments were conducted, along with computer modelling, to evaluate morphological and physio-chemical changes in a typical Barossa Valley Red Brown Earth (Palexeralf, Chromosol or Lixisol) when drip irrigated under various changing management practices. This work focused on the following two management changes : (i) switching from long-term irrigation with a saline source to less saline water and (ii) gypsum (CaSO₄) application. A literature review (Chapter 1) focuses on the distribution, features, properties and management of Red Brown Earths in the premium viticultural regions of the Barossa Valley and McLaren Vale, South Australia. The effects of irrigation method and water quality on the rate and extent of soil deterioration are emphasised. The review also discusses the irrigation of grapes (Vitis vinifera) and summarises previous research into the effect of sodicity and salinity on grape and wine characteristics. This chapter shows the importance of Red Brown Earths to Australian viticulture, but highlights their susceptibility to chemical and physical degradation. Degradation may be prevented or remediated by increasing organic matter levels, applying gypsum, modifying cropping and through tillage practices such as deep ripping. Chapter 2 provides general information on the two study sites investigated, one in the Barossa Valley and the other at McLaren Vale. Local climate, geology, geomorphology and soils are described. Chapter 3 details laboratory, field and sampling methods used to elucidate changes in soil chemical and physical properties following irrigation. The genesis of the non-irrigated Red Brown Earth in the Barossa Valley is described in Chapter 4, and is inferred from geochemical, soil chemical, layer silicate and carbonate mineralogical data. Elemental gain and loss calculations showed 42% of original parent material mass was lost during the formation of A and A2 horizons, while the Bt1 and Bt2 horizons gained 50% of original parent material mass. This is consistent with substrate weathering and illuviation of clay from surface to lower horizons. The depth distributions of all major elements were similar ; the A horizon contained lower amounts of major elements than the remainder of the profile, indicating this region was intensely weathered. This chapter also compares the non-irrigated site to the adjacent irrigated site (separated by 10 m) to determine if the sites are pedogenically identical and geochemical changes from irrigation. Many of the differences between the non-irrigated and irrigated sites appear to be correlated with variations in quartz, clay, Fe oxide and carbonate contents, with little geological variation between the sample sites. In Chapter 5 morphological, chemical and physical properties of a non-irrigated and irrigated Red Brown Earth in the Barossa Valley are compared. Alternating applications of saline irrigation water (in summer) and non-saline rain water (in winter) have caused an increase in electrical conductivity (EC [subscript se]), sodium adsorption ratio (SAR), bulk density (ρ b) and pH. This has resulted in enhanced clay dispersion and migration. Impacts on SAR and ρ b are more pronounced at points away from the dripper due to the presence of an argillic horizon, which has greatly influenced the variations in these soil properties with depth and distance from the dripper. Dispersion and migration of clay were promoted by alternating levels of EC, while SAR remained relatively constant, resulting in the formation of a less permeable layer in the Bt1 horizon. Clay dispersion (breakdown of micro-aggregate structure) was inferred from reduced numbers of pores and voids, alterations in colouring (an indication that iron has changed oxidation state) and increased bulk density (up to 30 %). Eleven years of irrigation changed the soil from a Calcic Palexeralf (non-irrigated) to an Aquic Natrixeralf (irrigated) (Soil Survey Staff, 1999). These results, combined with data from Chapter 4, were used to develop a mechanistic model of soil changes with irrigation. Chapters 6, 7 and 8 describe field experiments conducted in the Barossa Valley and McLaren Vale regions. This data shows seasonal and spatial variations in soil saturation extract properties ( EC [subscript se], SAR [subscript se], Na [subscipt se] and Ca [subscript se] ). At the Barossa Valley site (Chapter 6) non-irrigated soils had low EC [subscript se], SAR [subscript se], Na [subscript se] and Ca [subscript se] values throughout the sampling period. The irrigated treatments included eleven years of drip irrigation with saline water (2.5 dS / m) and also gypsum application at 0, 4 or 8 tonnes/hectare in 2001 and 2002. Salts in the profile increased with gypsum application rate, with high levels occurring midwinter 2002 prior to rainfall leaching salts. SAR has declined with gypsum application, particularly in the A horizon and at 100 cm from the dripper in the Bt1 horizon ; this has the potential to reflocculate clay particles and improve soil hydraulic conductivity. Chapter 7 presents further results from the Barossa Valley site, this treatment had been irrigated for 9 years with saline water (2.5 dS / m) prior to switching to a less saline water source (0.5 dS / m). The soil also received gypsum at 0, 4 or 8 tonnes / hectare in 2001 and 2002. It was found that the first few years are critical when switching to a less saline water source. EC declines rapidly, but SAR requires a number of years, depending on conditions, to decline, resulting in a period during which the Bt1 horizon may become dispersed. Gypsum application increased the EC [subscipt se] but not to the EC [subscript se] levels of soil irrigated with saline water. Chapter 8 examines soil chemical properties of a McLaren Vale vineyard, irrigated with moderately saline water (1.2 dS / m) since 1987 and treated with gypsum every second year since establishment. This practice prevented the SAR (< 8) rising and a large zone of the soil profile (20 to 100 cm from dripper) has a high calcium level (> 5 mmol / L). However, irrigation caused the leaching of calcium beneath the dripper in both the A and B horizons (0 to 20 cm from dripper) (< 4 mmol / L). Chapters 9 and 10 interpret and discuss results from continuous monitoring of redox potential (Eh) and soil solution composition in the Barossa Valley vineyard, irrigated with saline or non-saline water, and gypsum-treated at 0 and 4 tonnes / hectare. Soil pore water solution (Chapter 9) collected by suction cups is compared to results obtained in chapters 6 and 7. The soil has extended zones and times of high SAR and low EC. This was particularly evident in the upper B horizon, where the SAR of the soil remained stable throughout the year while the EC was more seasonally variable with EC declining during the winter months. The A horizon does not appear to be as susceptible to clay dispersion (compared to the B horizon) because during periods of low EC the SAR also declines, which may be due to the low CEC (low clay and organic matter content) of this horizon. Chapter 10 presents redox potentials (Eh) measured using platinum redox electrodes installed in the A, A2 and Bt1 horizons to examine whether Eh of the profile varies with irrigation water quality and gypsum application. Saline irrigation water caused the B horizon to become waterlogged in winter months, while less saline irrigation water caused a perched watertable to develop, due to a dispersed Bt1 horizon. Application of gypsum reduced the soil Eh particularly in the A2 horizon (+ 500 to + 50 mV) during winter. Thus redox potential can be influenced by irrigation water quality and gypsum applications. Chapter 11 incorporated site data from the Barossa Valley non-irrigated site into a predictive mathematical model, TRANSMIT, a 2D version of LEACHM. This model was used to predict zones of gypsum accumulation during long-term irrigation (67 years). When applied over the entire soil surface, gypsum accumulated at 60 to 90 cm from the dripper in the B horizon; higher application rates caused increased accumulation. When applied immediately beneath the irrigation dripper, gypsum accumulated in a 'column' under the dripper (at 0 to 35 cm radius from the dripper), with very little movement away from the dripper. Also, the zone of accumulation of salts from high and low salinity irrigation water was investigated. These regions were found to be similar, although concentrations were significantly lower with low salinity water. In low rainfall years salts accumulated throughout the B horizon (35 - 150 cm), while in periods of high rainfall (and leaching) the A, A2 and Bt1 horizons (0 - 60 cm) were leached, although at greater depths (80 - 150 cm) salt concentrations remained high. Chapter 12 summarises results and provides an understanding of soil processes in drip irrigated soils to underpin improved management options for viticulture. This study combines results from redox and soil solution monitoring, mineralogy, elemental gains and losses, and seasonal soil sampling to develop a mechanistic model of soil processes, which was combined with computer modelling to predict future properties of the soil. Major conclusions and recommendations of this study include : - Application of saline irrigation water to soil then ameliorated with gypsum - The first application of gypsum was leached by the subsequent irrigation from extended regions of the soil. As Na continues to enter the system via irrigation water, gypsum needs to be regularly applied. Otherwise calcium will be leached through the soil and SAR increases. - Application of non-saline irrigation water to soil then ameliorated with gypsum - The soil was found to only require one application at 8 tons / ha as this reduced SAR sufficiently. As less salt is entering the soil, subsequent gypsum applications can be at a lower rate or less frequently than required for saline irrigation water. - Gypsum applied directly beneath the dripper systems distributes calcium to a narrow region of the soil, while large regions of the soil require amelioration (high SAR) and are not receiving calcium. Therefore, gypsum application through the drip system or only beneath the dripper should be combined with broad acre application. - A range of methods to sample vineyards is recommended for duplex soils, including the use of saturation extracts, sampling time, sampling location (distance from dripper) and depth of sampling. This work is critical for vineyard management and may be applicable to other Australian viticulture regions with Red Brown Earths. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

Graduation date: 1963

Ice formed from seawater, called sea ice, is both an important actor in and a sensitive indicator of climate change. Covering 7% of the World Ocean, sea ice damps the atmosphere-ocean exchanges of heat, radiation and momentum in polar regions. It also affects the oceanic circulation at a global scale. Recent satellite and submarine observations systems indicate a sharp decrease in the extent and volume of Arctic sea ice over the last 30 years. In addition, climate models project drastic sea ice reductions for the next century, in both hemispheres, with potentially large consequences on climate and ecosystems. Contrary to what is commonly believed, sea ice retains about 25% of the oceanic salt when it forms. As salt cannot lock in the ice crystalline lattice, it accumulates in liquid inclusions of salty water (brine). Under a temperature change, the inclusions freeze or melt and release or absorb huge amounts of latent heat. This affects heat transfer through and storage in sea ice, which may affect the mass balance of sea ice at a global scale. This is the central hypothesis of this work. In order to address this problem, the author develops two sea ice models and assesses their ability to simulate the recent evolution of the sea ice mass balance. Then, the physics of brine uptake and drainage are included in the models and sea ice desalination is investigated. Finally, the impact of sea ice salinity variations on the global sea ice mass balance is studied. The roles of sea ice thermal properties, of ice-ocean salt / fresh water fluxes and of oceanic feedbacks are evaluated. The new salinity module improves the simulation of ice and ocean characteristics compared to observations. Including salinity variations increases ice growth, reduces vertical mixing in the ocean and the ocean-to-ice heat flux. In conclusion, salinity variations should be included in future sea ice models used for climate projections.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisors: Steven K. Dentel and Pei C. Chiu, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Increasing salinity has been a growing concern for users of waters from the Pecos River and the reservoirs it feeds in the Texas portion of the River's watershed. Irrigation water diverted from the river in the northern reach of this watershed is often only suitable for a limited number of crops, reducing harvesting options for local farmers. In the south, the Pecos feeds into the International Amistad Reservoir along the border with Mexico. During the 1990s, total dissolved solids concentrations in the reservoir rose as much as 10 mg/L per year and often approached the drinking water standard for potable water (1000 mg/L). Since this time, control efforts have focused on reducing the river's salinity, requiring the identification of salt sources. Hydrologic trend analysis and geochemical identification methods were used to determine these sources for the reach of the river between Red Bluff Reservoir and Brotherton Ranch. Between Red Bluff Reservoir and Coyanosa, flow diversions remove much of the flow that carries the salts, resulting in decreased salt loads, but also making the river more sensitive to evapotranspirative concentration. This sensitivity is evident in the river between Coyanosa and Girvin, where salinity begins to increase to the highest levels within the study area. However, salt loads increase here as well, indicating external salt sources as a contributor. The most substantial increase in bromide ions and the Br-/Cl- ratio appears between Grandfalls and Imperial, although no conclusion could be drawn regarding the identity of the source. The ratio continues to increase up to Girvin, where it appears that evapotranspirative concentration again has a significant effect. Here, several points drifted to the right of the groundwater mixing zones, plotting at values that were uncharacteristic of these sources.

Upstream oil and gas production has caused soil salinity problems across western Canada. In this work we investigated the use of ACC (1-aminocyclopropane-1-carboxylate) deaminase-producing plant growth-promoting rhizobacteria (PGPR) and the arbuscular mycorrhizal fungus (AMF) Glomus intraradices to enhance the efficiency and feasibility of phytoremediation of saline soils. This work involved laboratory and field research for three sites in south east Saskatchewan, Canada. The three research sites were Cannington Manor South (CMS), Cannington Manor North (CMN) and Alameda (AL). CMS and AL were highly saline, while the CMN site had moderate salinity. Indigenous PGPR were isolated from these sites and tested in greenhouse experiments using authentic salt-contaminated soils taken from the research sites. Increased plant biomass by PGPR and/or AMF was observed. This growth promotion effect varied with plant species, soil salinity and soil fertility. The combination treatment of two previously isolated PGPR Pseudomonas putida UW3 and UW4 (noted as UW3+4) from farm soil in Ontario consistently promoted shoot growth of both barley and oats grown in saline soils by approximately 100%. The indigenous PGPR Pseudomonas corrugata (CMH3) and Acinetobacter haemolyticus (CMH2) also promoted plant growth on par with UW3+4. In addition, in one experiment where alfalfa was tested, UW3+4, CMH2 and CMH3 treatments not only enhanced shoot biomass but also increased root nodulation. For AMF effects, G. intraradices enhanced biomass of oats and barley. Furthermore, the AMF+CMH3 was effective in promoting growth of Topgun ryegrass, while AMF+CMH2 was beneficial for Inferno tall fescue growth in salt impacted soils. The concentration of NaCl in the plants grown in salt-impacted soils ranged from 24 – 83 g/kg. There was no evidence of an increase in NaCl concentrations of plant tissue by PGPR and/or AMF treatments. In addition, to determine the importance of nutrient addition to research sites, liquid fertilizer was applied to 2-week old plants. Results demonstrated that fertilizer effectively increased biomass, and more importantly the biomass of PGPR treated plants supplied with fertilizer was approximately 20% higher than that of plants treated with fertilizer alone. Therefore, research sites were then amended with compost before planting of the 2007 field trial. Plant growth promotion by UW3+4 and CMH3 was tested in the summer of 2007 in the field. Prior to planting, soils were sampled from each site for soil salinity analysis. Barley, oats, tall fescue and ryegrass treated with and without PGPR were sown in plots. The plant coverage condition, NaCl concentrations and biomass of plant shoots were assessed to evaluate the PGPR effect. The results showed that PGPR promoted shoot dry weight by 30% - 175%. The NaCl concentrations of barley, oats and tall fescue averaged 53 g/kg, 66 g/kg and 35 g/kg, respectively. There was no evidence of an increase in NaCl concentrations of plant tissue by PGPR in the field. The salt removal of the CMN site was the highest among three sites due to the large amount of shoot biomass produced. The amount of salt accumulated in the shoots on the CMN site is estimated to be 1580 kg per hectare per year when both barley and ryegrass are planted together as a mix and treated with PGPR. Based on the field data, the estimated time required to remove 50% salt in the top 50 cm soil is seven years with PGPR treatments, while it takes fifteen years to do so without PGPR. In conclusion, PGPR-promoted phytoremediation was proven to be a feasible and effective remediation technique for soils with moderate salinity.

Upstream oil and gas production has caused soil salinity problems across western Canada. In this work we investigated the use of ACC (1-aminocyclopropane-1-carboxylate) deaminase-producing plant growth-promoting rhizobacteria (PGPR) and the arbuscular mycorrhizal fungus (AMF) Glomus intraradices to enhance the efficiency and feasibility of phytoremediation of saline soils. This work involved laboratory and field research for three sites in south east Saskatchewan, Canada. The three research sites were Cannington Manor South (CMS), Cannington Manor North (CMN) and Alameda (AL). CMS and AL were highly saline, while the CMN site had moderate salinity. Indigenous PGPR were isolated from these sites and tested in greenhouse experiments using authentic salt-contaminated soils taken from the research sites. Increased plant biomass by PGPR and/or AMF was observed. This growth promotion effect varied with plant species, soil salinity and soil fertility. The combination treatment of two previously isolated PGPR Pseudomonas putida UW3 and UW4 (noted as UW3+4) from farm soil in Ontario consistently promoted shoot growth of both barley and oats grown in saline soils by approximately 100%. The indigenous PGPR Pseudomonas corrugata (CMH3) and Acinetobacter haemolyticus (CMH2) also promoted plant growth on par with UW3+4. In addition, in one experiment where alfalfa was tested, UW3+4, CMH2 and CMH3 treatments not only enhanced shoot biomass but also increased root nodulation. For AMF effects, G. intraradices enhanced biomass of oats and barley. Furthermore, the AMF+CMH3 was effective in promoting growth of Topgun ryegrass, while AMF+CMH2 was beneficial for Inferno tall fescue growth in salt impacted soils. The concentration of NaCl in the plants grown in salt-impacted soils ranged from 24 – 83 g/kg. There was no evidence of an increase in NaCl concentrations of plant tissue by PGPR and/or AMF treatments. In addition, to determine the importance of nutrient addition to research sites, liquid fertilizer was applied to 2-week old plants. Results demonstrated that fertilizer effectively increased biomass, and more importantly the biomass of PGPR treated plants supplied with fertilizer was approximately 20% higher than that of plants treated with fertilizer alone. Therefore, research sites were then amended with compost before planting of the 2007 field trial. Plant growth promotion by UW3+4 and CMH3 was tested in the summer of 2007 in the field. Prior to planting, soils were sampled from each site for soil salinity analysis. Barley, oats, tall fescue and ryegrass treated with and without PGPR were sown in plots. The plant coverage condition, NaCl concentrations and biomass of plant shoots were assessed to evaluate the PGPR effect. The results showed that PGPR promoted shoot dry weight by 30% - 175%. The NaCl concentrations of barley, oats and tall fescue averaged 53 g/kg, 66 g/kg and 35 g/kg, respectively. There was no evidence of an increase in NaCl concentrations of plant tissue by PGPR in the field. The salt removal of the CMN site was the highest among three sites due to the large amount of shoot biomass produced. The amount of salt accumulated in the shoots on the CMN site is estimated to be 1580 kg per hectare per year when both barley and ryegrass are planted together as a mix and treated with PGPR. Based on the field data, the estimated time required to remove 50% salt in the top 50 cm soil is seven years with PGPR treatments, while it takes fifteen years to do so without PGPR. In conclusion, PGPR-promoted phytoremediation was proven to be a feasible and effective remediation technique for soils with moderate salinity.

Soil salinity is a serious environmental stress threatening productivity of major crops worldwide. Among the various biotic and abiotic strategies that exist, transgenic technologies provide a promising avenue to reduce yield losses in crops under saline environments. Recently, transgenic technology involving the TMT gene encoding thiol methyltransferase enzyme has been suggested as an effective solution for engineering a chloride detoxification capability into a high value crops to improve tolerance against chloride ion toxicity under saline environments. This proposed mechanism, however, results in the emission of methyl chloride (CH3Cl) from plants, which has deleterious effects on stratospheric ozone. This study was performed to examine the relationship between salt tolerance and chloride volatilizing capacity of transgenic plants containing TMT gene as well as to explore the possibility of generating transgenic rice crop containing TMT gene for salinity tolerance. To achieve these objectives, transgenic tobacco plants containing TMT gene were grown in comparison with wild type tobacco plants under three levels of sodium chloride (NaCl) salinity (0, 100 and 200 mM), three levels of soil water content (40%, 60% and 80% of the field capacity) and their tolerance to NaCl and water stress was studied. Plant growth parameters recorded included plant height, number of leaves, leaf area, stem dry weight, leaf dry weight, root dry weight, plant dry biomass and root/shoot ratio. Similarly, both types of plants were exposed to five levels of NaCl concentrations (0, 50, 100, 150 and 200 mM) and three levels of soil water content (40%, 60% and 80% of the field capacity), and the quantity of CH3Cl emitted was recorded. Significant decrease in plants growth parameters of both types of plants were recorded upon exposure to salinity and water stress. Under 100 mM NaCl, however, transgenic plants showed better tolerance to salinity by suffering less reduction in growth parameters compared to wild type plants. Under 200 mM NaCl, growth of both types of plants was completely inhibited. The interactive effects of salinity and water stress were more pronounced in wild type plants than in transgenic plants. Results also showed that all engineered plants acquired an ability to efficiently transform chloride ion to CH3Cl, and the rate of such transformation was higher under greater NaCl and soil water content compared to lower NaCl concentrations and soil water content. In order to explore the possibility of generating a transgenic food crop using TMT gene, a hypothetical transgenic rice crop was grown over 27 million hectares of the saline coastal areas of south and southeast Asia and the possible emission of CH3Cl from such ecosystem was inferred based on the CH3Cl emission data obtained from transgenic tobacco plants. The estimates showed that the possible CH3Cl emission from such ecosystem would be 219.21 Gg which is equivalent to 5.36 % of the global atmospheric emissions of CH3Cl.

Salinity is one of the most severe environmental factors that limits global crop yield. Enhanced phytoremediation using plant growth promoting rhizobacteria (PGPR) has proven to be an effective and environmentally responsible approach to remove salt from the surface soil and reclaim salt-impacted soil for crop production. PGPR enhanced phytoremediation systems (PEPS) were applied to two research sites, Cannington Manor North (CMN) and Cannington Manor South (CMS) in southern Saskatchewan. The sites were impacted by brine leakage during upstream oil and gas production. A salt mass balance study was performed based on data collected from these two sites. Both sites were planted in June. Soil samples were taken in June 2009 (beginning of the season), August (midseason) and October (end of the season). Soil salinity changes throughout the season were monitored by measuring soil electrical conductivity (EC). The average surface soil ECe decreased from 3.7 dS/m to 3.1 dS/m at CMN, and from 10.2 dS/m to 9.2 dS/m at CMS in 2009 season. Plant samples that were collected in August and October were analyzed for sodium and chloride concentrations. These values were then converted into predicted ECe changes for the soil to compare with the actual changes in soil ECe. Plant uptake of NaCl was calculated to account for 25.2% and 28.1% of the decrease in surface soil ECe at CMN and CMS, respectively. However, plant samples were washed prior to salt content analysis. A considerable amount of salt could have been lost during the washing process. Several plant samples from other salt-impacted sites in Saskatchewan and Alberta were selected to examine salt loss due to tissue washing. The salt ions lost by washing were determined to be 44.4% for Na+ and 63.8% for Cl-. After the adjustment of plant NaCl uptake data by the loss due to washing, plant accumulation of NaCl accounted for 59.9% of the decrease in surface soil ECe at CMN and 56.1% at CMS. When plant uptake of K+ and Ca2+ were also taken into consideration by a simulation study, the decrease in surface soil ECe that was caused by plant uptake of salt ions accounted for 107.5% at CMN and 117.5% at CMS. This indicated that plants can have a significant role in the remediation of salt-impacted soil. The effects of PGPR (Pseudomonas spp. UW4 and Pseudomonas corrugata CMH3) treatment on selected physiological indicators, such as proline, superoxide dismutase (SOD), membrane leakage and photosynthesis, were examined on annual ryegrass (Lolium multiflorum). Plants were grown under three saline conditions: non-saline topsoil, non-saline topsoil spiked with NaCl to 10 dS/m, and high saline soil collected from a salt-impacted site diluted with non-saline topsoil to reach 10 dS/m. The shoot fresh weight of plants grown in spiked salt soil decreased by 74% and in diluted salt soil by 44%, respectively, compared to control soil. Both types of salt soil increased SOD activities by approximately 50%, proline concentrations by 20 to 25 fold, and membrane leakage levels by 1.6 to 2.8 fold. Significant impairment of photosynthetic performances, as indicated by the decreases in the chlorophyll fluorescence parameters Fv/Fm, yield and qP, and a parallel increase in qN, was also observed using Pulse Amplitude Modulation (PAM) fluorometry for plants in diluted impacted soil. PGPR moderately increased fresh weight and SOD activity. Both UW4 and CMH3 significantly increased proline concentration and lowered membrane leakage relative to untreated plants. Therefore, PGPR improve plant performance under salt stress by elevating proline levels, which can act as a quencher of destructive reactive oxygen species. PGPR treatment also restored all the chlorophyll fluorescence parameters nearly to the non-stressed level, indicating protection of photosynthetic tissues of PGPR treated plants under salt stress. Overall, PEPS was successfully applied to the salt-impacted sites. Plant uptake of salt played a major role in the decrease of surface soil ECe. PGPR’s role in enhancing plant performance under salt stress was suggested by the elevated proline concentrations, the decreased membrane leakage levels and the restored photosynthetic activity.

This study has investigated the gene expression of ubiquitin¡B20S proteasome beta subunit type 1 (20s£]1)¡Bubiquitin-conjugating enzyme e2 (ucee2)¡BATP-dependent caseinolytic protease regulatory subunit (clpC) in the marine macroalga Ulva fasciata Delile in relation to the hypersalinity-induced oxidative stress and protein oxidation. During the early stage (0-1 h), the water contents and TTC (2,3,5-tripheny tetrazolium chloride) reduction ability maintained unchanged but recovery ability and photosynthetic ability (PS II activity as indicated by Fv/Fm) were decreased along with accumulated H2O2, suggesting the occurrence of oxidative stress. Only ubiquitin expressed at this stage. During 1-3 h, water lost (approximately 33% of the control) with a further decrease in recovery ability, TTC reduction ability¡BPS II activity but more H2O2 accumulation and protein carbonyl compound. The transcripts of 20s£]1 and clpC and caseinolytic protease activity increased at this stage with the maximum of clpC at hour 3. In the 6-48 h, water lost seriously with high accumulated free amino acid at 6-12 h but low recovery ability. The transcript amounts of ubiquitin¡B20s£]1 and ucee2 increased marked during this stage, in which these might be related to programmed cell death caused by long-term exposure to hypersalinity. Reactive oxygen species (ROS) scavengers inhibited H2O2 accumulation, caseinolytic proteolytic activity increase, carbonyl compound formation and gene expression of ubiquitin¡B20s£]1¡Bucee2¡BclpC, indicating a role of ROS in the regulation of protease genes. A role of polyamines in the regulation of protease gene expression was tested. Spermidine and spermine inhibited the gene expression of ubiquitin¡B20s£]1 and ucee2, the oxidation of proteins (carbonyl groups) and the induction of caseinolytic protease activity in 90‰-treated thalli, whereas putrescine inhibited clpC expression, the oxidation of proteins and caseinolytic protease activity but enhanced the gene expression of ubiquitin¡B20s£]1 and ucee2. In conclusion, the results of the present investigation show that the degradation of oxidatively damaged proteins under hypersalinity conditions by increased caseinolytic protease activity is driven by the up-regulation of clpC gene expression via ROS and polyamines. It seems likely that the induction of ubiquitin¡B20s£]1 and ucee2 gene expression might be associated with the hypersalinity-mediated programmed cell death.