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Báo cáo lâm nghiệp: "Water relation characteristics and photosynthesis of saline-stressed seedlings of non-halophyte species"

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Water relation characteristics and photosynthesis of saline-stressed seedlings of non-halophyte species...

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Nội dung Text: Báo cáo lâm nghiệp: "Water relation characteristics and photosynthesis of saline-stressed seedlings of non-halophyte species"

Water relation characteristics and photosynthesis of saline-stressed seedlings of non-halophyte species T. Suzaki H. Yahata H. Shigenaga Laboratory of Silviculture, Department of Forestry, Faculty of Agriculture, Kyushu University, Fukuoka, Japan artificial seawater) were imposed by daily irriga- Introduction tion of 100 ml for 40 d. Time-course changes in photosynthetic rates were determined using an open gas-exchange system with an infrared gas Most plants show growth retardation at analyzer. The conditions of measurement were low salinity and die in high salinity. The that light intensity was 40 klx, leaf temperature causes are considered to be mainly water was 25°C, and the air flow rate was 1.2 I/min. stress and/or ion excess. Plants may be Pressure-volume curves were constructed at the termination of treatment. After treatment, able to cope with an adverse water rela- sodium, potassium and chloride concentrations tion, if they absorb salts in leaf cells to were determined for leaves, stem, main root adjust osmotically. But, without efficient and fine roots. Sodium and potassium were compartmentation in vacuoles or exclu- estimated by flame photometry. Chloride was sion of excessive salt in osmotic adjust- determined by silver ion titration. ment, which are recognized in halophytes, plants will suffer from ion excess. The objective of the present study was to ex- amine the distribution of salts and its effect Results photosynthesis for non-halophyte on woody species. In addition, the contribu- tion of sodium and chloride to osmotic Time in photosynthetic changes course adjustment is discussed. shown relative values rates were as against 0% treatment. Photosynthesis by O. asiaticus var. aurantiacus decreased progressively as the salinity level in- Materials and Methods creased and time lapsed (Fig. 1 a). In D. racemosum, the lower salinity treatments The seedlings of each species, Osmanthus stimulated photosynthesis on d 10. After asiaticus var. aurantiacus, Distylium racemo- that, while declining substantially above sum, Cinnamomum camphora and Euonymus 20% treatment, it remained high in 10% japonicus were established in 1/5000 a Wagner and 5% treatments (Fig. 1b). In C. cam- pots. Salt treatments (0, 5, 10, 20 and 40%
there were no significant effects In D. racemosum and C. camphora, it phora, 2a). under 10% treatment but gradual de- decreased for lower salt treatments (Fig. creases above 20% (Fig. 1 c). E japo- 2b, c). These reductions were considered nicus showed some decreases for higher to be caused mainly by other solutes and salt treatments, which were less compared not by sodium or chloride. At the higher to the other species (Fig. 1d). concentration, osmotic potential became higher than that of the calculated value. The extent of sodium accumulation in E. japonicus seemed to use sodium and leaves and fine roots showed marked dif- chloride for osmotic adjustment, while, in ferences between O. asiaticus var. auran- this situation, the sodium and chloride tiacus and the other 3 species. In O. asia- concentration in leaves was low (Fig. 2d). ticus var. aurantiacus, sodium concentra- tions in leaves increased as the salt level increased. The other 3 species maintained low concentrations for lower salt treat- Discussion and Conclusion ments, but further treatments caused increases. However, that in fine roots for lower salt treatment increased in the O. asiaticus var. aurantiacus, which accu- order: O. asiaticus var. aurantiacus, E. mulated more sodium and chloride in its japonicus, D. racemosum, and C. cam- leaves, showed conspicuous decreases of phora. Stem and main root concentrations photosynthesis. However, the other spe- tended to increase gradually in all 4 spe- cies, except for the seedlings subjected to cies. On the other hand, the changes of higher salt treatments, did not show sodium concentration per whole plant tis- conspicuous reduction of photosynthesis sues, which indicated the differences in under the low sodium and chloride the amounts of absorption, showed similar concentration in leaves. Therefore, it is increases in all 4 species except for 40% considered that salt tolerance depends upon an ability to avoid the accumulation treatment. of salts in leaves. This ability seems to be The changes in the chloride concentra- attained mainily by sequestering salts in tion were similar to that of sodium. fine roots to alter the distribution. It is There were no clear concentration dif- known that the characteristics of salt distri- ferences among the species for potas- bution differ in species (Grieve and Wal- sium. ker, 1983). Walker (1986) reported that the The relative values of net photosynthetic mechanism to avoid the accumulation of rates on d 32 tended to decrease as the sodium in leaves in trifoliate orange exist- sodium concentration in leaves increased. ed in proximal root and basal stem, which withdraw sodium from the transpiration The changes of sodium and chloride stream. Suberized endoderms located in concentration in leaves and of osmotic fine roots are considered to have selective potential at full turgor are compared (Fig. permeability, which acts as a barrier to the 2). The broken line represents the calcu- flow of soluble salts into xylem. Further lated value of osmotic potential under the study, to determine whether structural dif- assumption that all sodium and chloride ferences in fine roots exist between spe- are sequestered in cells and generate cies, may be required. osmotic potential. O. asiaticus var. auran- As for the primary cause of death of tiacus maintained an almost constant leaves, the possibility that excessive accu- osmotic potential, but increased the poten- mulation of salts in apoplast brings about tial at high concentration in leaves (Fig.
dehydration of cells was discussed References (Munns and Passioura, 1984). If the salt concentration increases outside the living Grieve A.M. & Walker R.R. (1983) Uptake and distribution of chloride, sodium and potassium cells, the value of osmotic potential at full ions in salt-treated citrus plants. Aust. J. Agric. turgor may be estimated experimentally to Res. 34, 133-143 be higher than the true value. Therefore, Munns R. & Passioura J.B. (1984) Effect of pro- the high osmotic potential calculated longed exposure to NaCi on the osmotic pres- above suggests that ion accumulation in sure of leaf xylem sap from intact, transpiring barley plants. Aust. J. Plant Physiol. 11, 497- apoplast occurred. It might be considered 507 that for non-halophytes, absorbing salts in Walker R.R. (1986) Sodium exclusion and leaves does not seem to be useful for potassium-sodium selectivity in salt-treated tri- osmotic adjustment, although it might foliate orange (Poncirus trifoliata) and Cleopatra contribute to some extent but only at low mandarin (Citrus reticulata) plants. Aust. J. concentrations. Plant PhysioL 13, 293-303

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