Plant and Soil 263: 183–190, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands.
183
Naphthenic acids affect plant water conductance but do not alter shoot Na+ and Cl− concentrations in jack pine (Pinus banksiana) seedlings Kent G. Apostol1, Janusz J. Zwiazek1,3 & Michael D. MacKinnon2 1 Department
of Renewable Resources, 4-42 Earth Sciences Building, University of Alberta, Edmonton, T6G 2E3, Canada. 2 Syncrude Canada Ltd., Edmonton Research Centre, 9421 17 Avenue, Edmonton, T6N 1H4, Canada. 3 Corresponding author∗ Received 4 July 2003. Accepted in revised form 24 November 2003
Key words: jack pine, naphthenic acids, salinity, salt uptake, root hydraulic conductance
Abstract Solution culture-grown, six-month old jack pine (Pinus banksiana Lamb.) seedlings were treated with naphthenic acids (NAs) (150 mg l−1 ) and sodium chloride (45 mM NaCl) which were applied together or separately to roots for four weeks. NAs aggravated the effects of NaCl in inhibiting stomatal conductance (gs ) and root hydraulic conductance (Kr ). Naphthenic acids did not affect needle and root electrolyte leakage in the absence of NaCl. However, in plants treated with NaCl, NAs further increased electrolyte leakage from needles and NaCl induced electrolyte leakage from needles, but not from roots. Both NaCl and NAs treatments resulted in a reduction in root respiration. The measured Na+ and Cl− concentrations in the shoots for combined NaCl + NAs treatments were lower than in NaCl-only treatments. These decreases were correlated with a reduction in water conductance. The accumulation of Na+ and Cl− in shoots was accompanied by an increased in needle electrolyte leakage. However, greater concentrations of Cl− compared with Na+ were present in shoots and in the xylem sap suggesting that roots had relatively lower capacity for Cl− storage compared with Na+ .
Introduction In north-eastern Alberta, Canada, extraction of bitumen from oil sands by the large oil sands plants (Syncrude Canada Ltd., Suncor Energy Inc. and Albian Sands Energy Inc.) generates large volumes of tailings containing elevated levels of naphthenic acids (NAs). NAs are complex mixtures of acyclic and polycyclic aliphatic carboxylic acids (Fan, 1991; Holowenko et al., 2002). NAs are cytotoxic and are used as wood preservatives (Brient et al., 1995) as well as emulsifying agents in the production of agricultural insecticides, and as additives and emulsion breakers in the oil industry (Hatch and Matar, 1977). NAs are natural constituents in nearly all crude oils (Brient et al., 1995) and are present in the bitumen of the oil sands from western Canada (Schramm et al., ∗ FAX No: 1 (780) 492-1767.
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2000). These naturally occurring surfactants have been suggested to play an important role in the successful separation of the bitumen during extraction processes that are based on caustic hot water digestion and flotation (Schramm et al., 2000). Under these conditions, large volumes of aqueous tailings are produced with NAs, in the sodium naphthenate form, at concentrations greater than 50 mg l−1 (MacKinnon and Boerger, 1986; Schramm et al., 2000). In the oil sands operations, the process-affected waters are released or contained within the pores of the tailings materials, in which some attenuation will be expected (Holowenko et al., 2002). However, through selected evaporation zones, it has been reported that soil concentrations in some of the oil sands reclamation sites would be expected to contain NAs concentrations higher than 100 mg l−1 (Kamaluddin and Zwiazek, 2002). Despite the commercial use of NAs and their presence in reclamation areas, little is known about the potential impacts of NAs on plants. NAs have been repor-
184 ted to cause injury to aquatic organisms (MacKinnon and Boerger, 1986; CONRAD, 1998). A recent study also showed that NAs inhibited leaf growth, stomatal conductance and net photosynthesis in aspen (Populus tremuloides) seedlings (Kamaluddin and Zwiazek, 2002). In addition to elevated levels of NAs, in most cases the process-affected waters associated with oil sands reclamation areas will display high salinity relative to the pre-disturbance conditions. In certain tailings management options, electrical conductivity of the resulting materials are in excess of 4 dS m−1 (MacKinnon et al., 2001), which is considered detrimental to plants (Singer and Munns, 1996; Renault et al., 1998, Howat, 2000). Since both increasing salinity (Munns and Termaat, 1986) and NAs (Kamaluddin and Zwiazek, 2002) inhibit water uptake and reduce plant growth, there is concern that the combined effects of NAs and salinity may aggravate plant water uptake efficiencies in reclamation areas, where both stress factors could be present. Salinity can have dramatic effects on plant water relations (Bolanos and Longstretch, 1984). NaCl was found to decrease root hydraulic conductivity of Zea mays (Aizazeh et al., 1992; Evlagon et al., 1992), which could affect transpiration rates. Transpiration was demonstrated to influence the rate of ion transport to the shoot and the accumulation of ions in several salt-stressed plants (Lauter and Munns, 1987; Salim, 1989). Often the injury observed in plants exposed to salt is correlated with reduced ability of roots to store Na+ and Cl− , and with the resulting accumulation of Na+ and Cl− in the shoots (Yeo et al., 1977; Grieve and Walker, 1983, Apostol and Zwiazek, 2003). This accumulation has been explained as partly due to the injury of root cell membranes (Kuiper, 1968; Mansour, 1997). Since NAs have surfactant properties, they could potentially affect salt tolerance of plants by disrupting membrane integrity and altering ion transport processes (van Overbeek and Blondeau, 1954; Quinn, 1976). In the present study, we used jack pine (Pinus banksiana Lamb.) to examine the hypothesis that NAs exacerbate inhibition of water conductance to shoots and membrane leakiness caused by NaCl and increase salt uptake in jack pine. Jack pine is a dominant tree species in the boreal forest surrounding the oil sands mining areas. Since the oil sands reclamation objectives are to restore the original forest ecosystems with native plants, jack pine is among the main species to be used for the reclamation of oil sands mining areas.
Materials and methods Plant material and growth conditions Jack pine (Pinus banksiana Lamb.) seeds were collected from trees approximately 60 km north of Fort McMurray, Alberta (57◦05.95 N 111◦38.90 W). The seeds were germinated and seedlings grown for six months in Spencer-Lemaire root trainers (350 ml volume, Steuwe and Sons, Inc., Corvallis, OR, USA) filled with a mixture of peat moss and coarse washed sand (2:1, v/v). The seedlings were grown in a growth room under the following environmental conditions: day/night temperature, 22/18 ◦ C; relative humidity, 70 ± 10%; 18-h photoperiod, and photosynthetic photon flux density of approximately 300 µmol m−2 s−1 at the seedling level. After 6 months, roots were rinsed in water and the seedlings were transferred to 10 L containers filled with aerated mineral nutrient solution as previously described (Apostol et al., 2002). Seventy-two seedlings were grown in solution culture for two weeks before the commencement of treatments, and the solution was replaced weekly. Sodium chloride and naphthenic acids treatments Salinity treatment was imposed by adding 15 mM NaCl to the nutrient solution daily for three days, to reach a final concentration of 45 mM NaCl. Naphthenic acids were prepared by mixing stock solution of sodium salt of NAs (ACROS Organics, NJ, USA) with nutrient solution until the desired concentration of 150 mg NAs l−1 was achieved. We chose this relatively high concentration of NAs due to the relatively short duration of treatments and because the concentrations of NAs in oil sands tailings are expected to increase over time. Based on analysis by electrospray ionization mass spectrometry (ESIMS), the composition (molecular weight and z-value distribution) of the ACROS naphthenic acid standard was comparable to materials in Syncrude’s process waters (MoralesIzquierdo, 1999). NaOH was added to adjust the pH of each treatment and control nutrient solutions to 7.8 to avoid NAs precipitation (Kamaluddin and Zwiazek, 2002). High pH is characteristic of the oil sands reclamation sites, which raises the concerns of potential NAs uptake by plants as well as mineral deficiencies (Renault et al. 1998, 1999). In the present study, six seedlings were placed in each container, in three replicated containers with 18 seedlings per treatment. A total of 72 seedlings were
185 treated for four weeks. This treatment duration was also used in our other studies investigating the phytotoxicity of chemical components of oil sands tailings (Apostol et al., 2002, Apostol and Zwiazek 2003). The treatments were arranged in a 2 × 2 (two levels of NaCl; 0 and 45 mM NaCl and two levels of NAs; 0 and 150 mg l−1 ) factorial randomized design. Growth, stomatal conductance (gs ) and root hydraulic conductance (Kr ) After four weeks of treatments, six seedlings from each treatment were randomly harvested for fresh and dry weight measurements (n = 6). Dry weight was obtained after freeze-drying the samples for 72 h. Stomatal conductance (gs ) measurements were made on the other randomly selected seedlings between 3 and 4 h after the onset of the photoperiod. The measurements were conducted on the upper 30-mm portion of the shoot of 6 seedlings for each treatment using a steady-state porometer LI-600 (Li-Cor Inc., NE, USA) and expressed on the needle area basis following computer scanning (Sigma Scan 3.0, Jandel Scientific, San Rafael, CA, USA). Root hydraulic conductance (Kr ) was measured on the same six seedlings as those used for stomatal conductance measurements using a high pressure flow meter (HPFM) (Dynamax Inc., Houston, TX, USA), as described by Tyree et al. (1995) and expressed in kg s−1 MPa−1 . Whole intact root systems, immersed in either control or treatment solutions, were connected to the HPFM system through the shoot excised 20 mm above the root collar. Root systems were gradually pressurized to 0.4 MPa to obtain a pressure-flow relationship. Root respiration Root respiration was measured as oxygen uptake using an oxygen electrode (Yellow Springs Instruments, Yellow Spring, OH, USA). Intact roots were placed in a 250-ml airtight cuvette filled with aerated treatment or control solutions that were continuously stirred with a magnetic stirrer. Root respiration was monitored for 20 min by recording the oxygen uptake every 2 min. Root respiration rates were calculated as a mean of oxygen uptake over time, and values were expressed in mmol O2 root system−1 min−1 .
Measurements of tissue electrolyte leakage Prior to the electrolyte leakage test, shoots and roots of 6 seedlings for each treatment were washed three times with deionized water, each time for five minutes. The electrolyte leakage test was conducted as described by Apostol et al. (2002). Briefly, shoot and root samples, each approximately 0.45 g fresh weight (FW), were placed in tubes containing deionized water and incubated for 5 h. Electrical conductivities of the solutions (ECL) were measured with an electrical conductivity meter HI 8033 (Hanna Instruments Inc., Woonsocket, RI, USA). Total electrolytes (ECT) were obtained by autoclaving the samples at 121 ◦ C followed by freezing overnight at −85 ◦ C and thawing at room temperature (23 ◦ C) for 5 h. Electrolyte leakage was calculated as the percentage of total electrolytes in the solution after 5 h (ECL /ECT ∗ 100). Osmotic potential and naphthenic acids (NAs) determination Xylem saps were collected for osmotic potential and NAs determinations. The objective of this experiment was to determine whether NAs can penetrate the root tissues and reach the xylem, which would suggest that they can be transported with the transpiration stream into shoots. The xylem saps were collected from the roots of five seedlings that were immersed in the respective treatment and control solutions. Intact roots were placed in a pressure chamber and pressurized to 0.3 MPa for 1 h. These conditions were experimentally determined to give sufficient quantity of xylem sap for the NAs analysis. Osmotic potential of the xylem sap was measured with a thermocouple psychrometer (HR-33T, 5112, Wescor, Logan, UT, USA) and a C52 sensor in the dew point mode. Xylem saps obtained from the pressurized roots were analysed for NAs using a Syncrude Canada Ltd. method based on Fourier transform infrared (FT-IR) analysis of methylene chloride (CH2 Cl2 ) extracts of acidified (pH 2.5) samples (Jivraj et al., 1996). Samples were taken from 2 seedlings of each treatment (n = 2). Analyses of ionic content of plant tissues and xylem saps Shoots and roots, which were not used for the electrolyte leakage test, were used for ion analyses. Freezedried shoots and roots were weighed and ground in liquid nitrogen to a fine powder prior to extractions. Sodium, potassium, calcium and magnesium contents
186 Table 1. Effects of NAs on shoot and root fresh weights in NaCl-treated jack pine seedlings. Values are means ± SE, n = 6
Shoot FW (g) Root FW (g)
NaCl levels
Naphthenic acids − NAs + NAs
Control 45 mM NaCl Control 45 mM NaCl
6.12 ± 0.48 4.57 ± 0.61 2.84 ± 0.29 2.49 ± 0.28
5.40 ± 0.77 3.98 ± 0.36 2.86 ± 0.32 2.55 ± 0.23
were quantified using the ICP-OES method (Vista-RL CCD Simultaneous ICP-OES, Varian Inc., Victoria, Australia) after strong acid (conc. HNO3 ) digestion, as previously described (Renault et al., 1999). Chloride and sulfate were extracted using the hot water extraction technique, as described earlier (Apostol et al., 2002), and were measured by ion chromatography (Dionex-300 Series, Dionex Corp., Sunnyvale, CA, USA). Tissue total N concentrations were determined colorimetrically using the Technicon AutoAnalyzer II (Technicon Industrial Systems, Tarrotown, NY) after digestion with H2 SO4 and H2 O2 at 350 ◦ C (Richards 1993). Ion analyses in the xylem sap were carried out after digesting diluted sap samples in 0.1 M HNO3 using the techniques described for plant tissues. The data were collected from 6 seedlings of each treatment (n = 6 ). Experimental design and statistical analysis Analysis of variance (ANOVA) and correlation analyses were performed using SAS GLM (General Linear Model) (SAS Institute Inc., Cary, NC, USA). ANOVA were determined for the treatment effects by two-way interactions between NaCl and NAs treatments. The model used in the present study is Yijk = µ+ρi +αj +βk +(αβ)jk +εijk where; Yijk = response variable; µ = overall mean; ρi = replication (random factor), i = 1. . .3; αj = sodium chloride effect (fixed factor), j = 1 . . . 2; βk = naphthenic acids effect (fixed factor); k = 1 . . . 2; (αβ)jk = NaCl and NAs treatment interaction effect; and εijk = random error.
Results Shoot fresh weight (Table 1) was significantly inhibited by NaCl (P < 0.02), but not by NAs treatments (P < 0.22). There were no significant effects of NaCl
Figure 1. Effects of NAs on a) stomatal conductance (gs ) and b) root hydraulic conductance (Kr ) of NaCl-treated jack pine seedlings. Each data point represents mean (n = 6) ± SE.
and NAs treatments on root fresh weights, and no significant interaction effects between salinity and NAs on shoot (P < 0.79) and root (P < 0.77) fresh weights. Stomatal conductance was significantly reduced by NaCl (P < 0.01) and NAs (P < 0.01) treatments (Figure 1a). There was a significant (P < 0.01) interaction effect between NaCl and NAs on gs . Addition of NAs to plants treated with NaCl reduced mean gs values by 33% compared with plants treated with NaCl treatment alone. Both NaCl (P < 0.01) and NAs (P < 0.01) significantly inhibited Kr (Figure 1b). A significant (P < 0.01) interaction effect between NaCl and NAs was observed for Kr . Mean Kr of plants treated with NaCl alone was reduced by 73%, while Kr of NAs-treated plants was 75% lower compared with control plants. When NAs were added to NaCl treatment, plants showed almost 90% reduction in Kr compared with control plants. When applied individually, NaCl (P < 0.01) and NAs (P < 0.04) significantly reduced root respiration rates, but the interaction effect between NaCl and NAs was not significant (P < 0.5) (Figure 2a). Respiration rates were significantly lower in both the NaCl-treated plants (0.61 mmol O2 root system−1 min−1 ) and in NAs-treated plants (0.76 mmol O2 root system−1 min−1 ) compared with control plants (1.33 mmol O2 root system−1 min−1 ).
187
Figure 3. Effects of NAs on Na+ concentrations in (a) shoots and (b) roots of NaCl-treated jack pine seedlings. Each data point represents mean (n = 6) ± SE.
Figure 2. Effects of NAs on (a) root respiration, (b) needle electrolyte and (c) root electrolye leakage of NaCl-treated jack pine seedlings. Each data point represents mean (n = 6) ± SE.
Needle electrolyte leakage significantly increased in response to NaCl (P < 0.01) and NAs (P < 0.03) treatments, but their interaction effect was not significant (P < 0.13) (Figure 2b). Needle electrolyte leakage from plants treated with NaCl was 51% higher, while NAs-treated plants had a 23% increase compared with the control plants. Results of the ANOVA showed that neither NaCl nor NAs treatments significantly affected root electrolyte leakage (Figure 2c). Relative to the controls, shoot Na+ concentrations were higher in all NaCl-treated plants, but this effect was greater in plants treated with NaCl, compared to plants treated with both NaCl and NAs (Figure 3a). The addition of NAs resulted in a significant (P < 0.01) reduction of shoot Na+ concentrations by almost 40%. Sodium concentrations of roots in NaCl-treated plants and in NaCl + NAs-treated plants were similar (Figure 3b). As for Na+ , plants treated with only NaCl had higher shoot Cl− concentrations than those treated
with NaCl + NAs (Figure 4a). Shoots contained about 40% less Cl− when plants were grown under the combined NAs + NaCl treatments, compared with NaCl alone. Root Cl− concentrations were not significantly altered by NAs (P < 0.88) (Figure 4b). Concentrations of most of the analyzed tissue elements and ions were similar in control and treated plants and are not presented here. In the NaCl-treated plants, the root K+ (P < 0.03) and Mg2+ (P < 0.01) concentrations were significantly lower than those in the control plants, while the shoot concentrations were unaffected. Root SO2− 4 concentrations increased significantly (P < 0.04) in plants treated with NAs, but not in the NaCl treatments (data not shown). Mean root SO2− 4 concentration in NAs-treated plants was 2.63 mg g−1 DW compared with 1.67 mg g−1 DW measured in NaCl-treated plants. Results of short, 1-h exposure of jack pine to NaCl and NAs treatments showed that Na+ and Cl− concentrations in the xylem sap were higher in NaCltreated plants compared with the control plants, with Cl− concentrations several fold higher than those of Na+ . Mean Cl− concentrations in the xylem sap were 1.54 mg g−1 while Na+ concentrations were 0.91 mg g−1 in both NaCl-treated plants. The presence of NAs did not appear to alter the concentrations of
188
Figure 4. Effects of NAs on Cl− concentrations in (a) shoots and (b) roots of NaCl-treated jack pine seedlings. Each data point represents mean (n = 6) ± SE.
either the Na+ or Cl− in the xylem sap. Mean osmotic potential values of −0.302 MPa were measured in the xylem sap of plants treated with NaCl, compared with −0.453 MPa in NaCl + NAs-treated plants. Mean NAs concentrations in the xylem sap were approximately 28.60 ± 4.71 mg l−1 in NAs-treated plants, compared with 84.11 ± 16.56 mg l−1 in NAs + NaCl treatments.
Discussion After four weeks of NaCl treatments, there was a significant reduction in shoot fresh weight, but root fresh weight was not affected. In spite of apparent lack of the effect on root growth, NaCl + NAs-treated plants showed extensive root necrosis and absence of fine white root tips after four weeks of treatments. These responses suggest that the growth of roots could be reduced by longer-term treatments. Shoot visible injuries in NaCl + NAs-treated seedlings included needle chlorosis and some needle tip necrosis, however, some yellowing of needles was also observed in control plants. These injury symptoms are commonly associated with high pH through its effects on nutrient uptake (Islam et al., 1980; Noggle and Fritz, 1983). A relatively high pH of the treatment and con-
trol solutions that were used in the present study likely contributed to the injury symptoms observed in both treated and untreated seedlings. It is also plausible that the lack of significant differences in root growth between control plants and treated plants could be due to the growth inhibition by high pH before the effects of NaCl and NAs could be observed. The pH selected for these treatments was representative of the reclamation areas that are affected by the oil sands tailings. Under these conditions, NAs remain soluble and available for root uptake. Contrary to the original hypothesis of this study, the results showed that the shoots of plants treated with NAs had lower Na+ and Cl− concentrations, when compared with plants treated with NaCl alone (Figures 3, 4). This response could be in part due to the inhibitory effects of NAs on transpiration and root hydraulic conductance, since a reduction in water flow rates could affect the rates of salt uptake. Stomatal conductance (gs ) was reduced in plants treated with NAs by 80% compared with the control plants. In treatments where the NAs were combined with NaCl, gs was further reduced. A similar pattern of reduction was observed for root hydraulic conductance (Kr ). The two processes are often linked in plants exposed to different environmental stresses (Wan and Zwiazek, 1999; Apostol and Zwiazek, 2003; Siemens and Zwiazek, 2003), although the exact signalling mechanism between roots and shoots remains unknown. The surfactant properties of naphthenic acids could partly explain the reduction in root water uptake (Kamaluddin and Zwiazek, 2002) through the action on water channel activity. Kamaluddin and Zwiazek (2002) also showed that reduced activity of water channels was reflected by a decline in root respiration. However, we did not observe significant synergistic effects between NaCl and NAs treatments on root respiration after 4 weeks of treatment. It is possible that significant interaction effects between NaCl and NAs on root respiration may have occurred before the first measurements. Horowitz and Givelberg (1979) showed that surface-active compounds are capable of binding to cell membranes and denaturation of membrane proteins. The inhibition of root hydraulic conductance in NAs-treated plants could be due to direct effects of NAs on water channel proteins. However, the denaturation of root membrane proteins by NAs was not detected by the electrolyte leakage test. In the present study, we measured relatively high root electrolyte leakage values. These high values may have been due to some root necrosis that commonly
189 develops in hydroponically grown plants as they age. In our previous studies (Apostol and Zwiazek, 2003), using a similar test, we have found the mean root electrolyte leakage of a seven-month-old hydroponicallygrown jack pine seedlings to be about 40%. The results of the present study may also suggest that the effects of NaCl on root respiration dominated the interactive effects of NaCl and NAs, and the high variability of seedling responses, as demonstrated by large standard errors, produced statistically insignificant results (Figure 2a). We offer the same explanation for the insignificant interaction effect between NaCl and NAs treatments on needle electrolyte leakage. Since naphthenic acids have surfactant properties, they may alter root nutrient uptake (Parr and Norman, 1965; Kamaluddin and Zwiazek, 2002). However, we did not see many changes in the composition of essential elements in the treated tissue. Therefore, the interference with nutrient uptake may be more important as a longer-term effect and cannot explain the physiological responses reported in the present study. In the present study, the higher concentrations of Cl− compared with Na+ in the xylem sap reflect greater delivery of Cl− to the shoots, and subsequently a higher shoot accumulation of Cl− , compared with Na+ , was observed after the 4-week exposure to NaCl (Figures 3, 4). This suggests that roots of jack pine had lower capacity to store Cl− than Na+ . At high external Cl− concentrations, and relatively low cytoplasmic concentrations, it is possible for the membrane potential to be less negative than the Cl− equilibrium potential, leading to passive Cl− uptake into roots (Tyerman and Skerrett, 1999). The low (more negative) value of osmotic potential observed in the xylem sap of plants exposed to both NaCl and NAs treatments paralleled the accumulation of K+ . The mean K+ concentrations in the xylem sap of NaCl-treated plants were 0.17 mg g−1 and 0.20 mg g−1 for NAs-treated plants compared with 0.7 mg g−1 for the control seedlings. To date, there have been no reliable methods developed to measure NAs concentrations in plant tissues. This is largely due to the interference from other tissue organic compounds in the NAs analysis. Therefore, the analysis of NAs in the xylem sap offers an alternative method of estimating NAs uptake by plants and their transport to shoots. Due to the complexity involved in the sample collection for the analyses of naphthenic acids, we tested only two samples from each treatment. In both samples, NaCl drastically increased NAs uptake by plants. However, the mechanisms of this response remain to be determined.
In conclusion, the results of the present work have demonstrated that the responses of jack pine to NaCl are altered by the presence of NAs. We suggest that the mechanisms of NAs action in NaCl-treated jack pine are linked to water transport, and that the reduction of water uptake and plant water flow may be partly responsible for the reduction in Na+ and Cl− concentrations in the shoots. Therefore, the responses of plants to these factors and their successful growth in oil sands reclamation sites may be also strongly affected by soil moisture conditions.
Acknowledgements We gratefully acknowledge funding in the form of research grants from the Environmental Science and Technology Alliance Canada and the Natural Sciences and Engineering Research Council of Canada to JJZ and a research assistantship to KGA from the Faculty of Graduate Studies and Research, University of Alberta. We thank Betty Fung of Syncrude Canada Ltd. for help in naphthenic acids analyses, Akiko Ichikawa of University of Alberta for help in tissue ion analyses, and the analytical support from the Analytical Group of Syncrude Canada’s Research Centre.
References Apostol K G and Zwiazek J J 2003 Hypoxia affects root sodium and chloride concentrations and alters water conductance in salttreated jack pine (Pinus banksiana) seedlings. Trees 17, 251– 257. Apostol K G, Zwiazek J J and MacKinnon M D 2002 NaCl and Na2 SO4 alter responses of jack pine (Pinus banksiana) seedlings to boron. Plant Soil 240, 321–329. Aizazeh H, Gunse B and Steudle E 1992 Effects of NaCl and CaCl2 on water transport across root cells of maize (Zea mays L.) seedlings. Plant Physiol. 99, 866–894. Bolanos J A and Longstretch D J 1984 Salinity effects on water potential components and bulk elastic modulus of Alternanthera philoxeroides (Mart.) Griseb. Plant Physiol. 75, 281–284. Brient J A, Wessner P J and Doly M N 1995 Naphthenic acids. In Encyclopedia of Chemical Technology. Ed. J I Kroschwitz. Fourth Edition. pp. 1017–1029. John Wiley and Sons, Inc., CONRAD 1998. Naphthenic acids background report. CEATAG Report, June 1998 Alberta Department of Energy, Edmonton, Alberta. Evlagon D, Ravina I and Neumann P M 1992 Effects of salinity stress and calcium on hydraulic conductivity and growth in maize seedlings roots. J. Plant Nutr. 15, 795–803. Fan T P 1991 Characterization of naphthenic acids in petroleum by fast atom bombardment mass spectrometry. Energy Fuels 5, 371– 375.
190 Grieve A M and Walker R R 1983 Uptake and distribution of chloride, sodium and potassium ions in salt-treated Citrus plants. Aust. J. Agric. Res. 34, 133–143. Hatch L F and Matar S 1977 From hydrocarbons to petrochemicals. Hydrocarbon Processing 56, 165–173. Holowenko F M, MacKinnon M D and Fedorak P M 2002 Characterization of naphthenic acids in oil sands wastewaters by gas chromatography-mass spectrometry. Water Res. 36, 2843–2855. Horowitz M and Assia G 1979 Toxic effects of surfactants applied to plant roots. Pestic Sci. 10, 547–557. Howat D R 2000 Acceptable salinity, sodicity and pH values for boreal forest reclamation. Alberta Environment, Environmental Sciences Division, Edmonton Alberta. Report # ESD/LM/00-2. 191 pp. Islam A K M S, Edwards D G and Asher C J 1980 pH optima for crop growth. Results of a flowing solution culture experiment with six species. Plant Soil 54, 339–357. Jivraj M N, MacKinnon M and Fung B 1996 Naphthenic acids extraction and quantitative analyses with FT-IR Spectroscopy. Syncrude Canada Ltd. Research Report. Sept. 1996 Syncrude Canada Ltd., Fort McMurray, AB. 12 pp. Kamaluddin M and Zwiazek J J 2002 Naphthenic acids inhibit root water transport, gas exchange and leaf growth in aspen (Populus tremuloides) seedlings. Tree Physiol. 22, 1265–1270. Kuiper P J C 1968 Lipids in grape roots in relation to chloride transport. Plant Physiol. 43, 1367–1371. Lauter D J and Munns R 1987 Salt sensitivity of chickpea during vegetative growth and at different humidities. Aust. J. Plant Physiol. 14, 171–180. MacKinnon M D and Boerger H 1986 Description of two treatments for detoxifying oil sands tailings pond water. Water Pollut. Res. J. Can. 21, 496–512. MacKinnon M D, Matthews J G, Shaw W H and Cuddy R G 2001 Water quality issues associated with composite tailings (CT) technology for managing oil sands tailings. Int. J. Surf. Mining Reclam. Environ. 15, 235–256. Mansour M M F 1997 Cell permeability under salt stress. In Strategies for Improving Salt Tolerance in Higher Plants. Eds. P K Jaiwal, R P Singh, A Gulati. pp. 87–110. Science Publishers, Inc. Morales-Izquierdo A 1999 Analysis of naphthenic acids in oil sands wastewater samples by electro spray ionization mass spectrometry (ESIMS). Edmonton, Alberta, Syncrude Canada Contract Report (E0736-26): 197 pp.
Munns R and Termaat A 1986 Whole-plant response to salinity. Aust. J. Plant Physiol. 13, 143–190. Noggle G R and Fritz G J 1983 Introductory plant physiology, Second edition. Prentice-Hall, Englewood Cliffs, N.J. Parr J F and Norman A G 1965 Consideration in the use of surfactants in plant systems: a review. Bot. Gazette 126, 86–96. Renault S, Lait C, Zwiazek J J and MacKinnon M 1998 Effect of high salinity tailings waters produced from gypsum treatment of oil sands tailings on plants of the boreal forest. Environ. Pollut. 102, 177–178. Renault S, Paton E, Nilsson G, Zwiazek J J and MacKinnon M 1999 Responses of boreal plants to high salinity oil sands tailings. J. Environ. Qual. 28, 1957–1962. Richards J E 1993 Chemical characterization of plant tissue. In Soil Sampling and Methods of Analysis. Ed. M R Carter. pp. 115– 139. Canadian Society of Soil Scientists, Lewis Publishers, Boca Raton. Salim M 1989 Effects of salinity and relative humidity on growth and ionic relations of plants. New Phytol. 113, 13–20. Schramm L L, Stasiuk E N and MacKinnon M 2000 Surfactants in Athabasca oil sands slurry conditioning flotation recovery and tailings processes. In Surfactants: Fundamentals and Applications in the Petroleum Industry. Ed. LL Schramm. pp. 365–430. Cambridge University Press, Cambridge, UK. Siemens J A and Zwiazek J J 2003 Effects of water deficit stress and recovery on the root water relations of trembling aspen (Populus tremuloides) seedlings. Plant Sci. 165, 113–120. Singer M and Munns D 1996 Soils: an introduction, Third Edition. Prentice Hall, Upper Saddle River, New Jersey. 480 p. Tyree M T, Patino S, Bennink J and Alexander J 1995 Dynamic measurements of root hydraulic conductance using a highpressure flowmeter in the laboratory and field. J. Exp. Bot. 46, 83–94. van Overbeek J and Blondeau R 1954 Mode of action of phytotoxic oils. Weeds 3, 55–65. Wan X and Zwiazek J J 1999 Mercuric chloride effects on root water transport in aspen (Populus tremuloides) seedlings. Plant Physiol. 121, 936–946. Yeo A R, Kramer D, Lauchli A and Gullasch J 1977 Ion distribution in salt stressed matured Zea mays roots in relation to ultrastructure and retention of sodium. J. Exp. Bot. 28, 17–29.
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