Effect Of Saline-alkali Stress On Growth And Physiologyof Amorpha Fruticosa

The plants are usually stressed by various and different environmental factors under natural environment; and among these, saline-alkali stress is one of the most common environmental stresses. Salinization of soil is the primary reason leading to saline-alkali stresses, which causes serious damages and losses for agricultural production and environment. For this purpose, it is very useful and important to study deeply on salinity tolerance of plants, which can improve and utilize salty soils and make the most use of plant resources. In this study, stimulating typical neutral salt Na Cl and alkalic salt Na2CO3 as salt stress and alkali stress in saline-alkali soils, a perennial shrub Amorpha fruticosa is used as the experimental materials. The experiment is conducted to study the effects of seed germination, seedling growth and physiology of Amorpha fruticosa L. under saline-alkali stresses, and the growth change of Amorpha under natural saline-alkali soil habitat. The main findings and results were as follows:(1) Amorpha seeds have strong tolerance to saline-alkali stresses. Within 200 m M of Na Cl critical concentration, germination rate of Amorpha was not very significant; when Na2CO3 critical concentration was at 40 m M, germination rate was decreased significantly(P<0.05), but the higher 80% seed germination rate was still kept. Contrastively, the growth of Amorpha radicle and plumule were effected very significantly by salt stress and alkali stress(P<0.05), the degree of alkali stress effect much greater than that of salt stress. However, salt stress with low concentration(<100m M) would stimulate the growth of radicle. Therefore, in practical process of production, when Amorpha seeds were soaked with appropriate concentration of saline solution, they would increase the growth of radicle and the effect of planting.(2) Under saline-alkali stresses, the radicle of Amorpha relatively had low intake degree of Na+; and Na+ and Cl- contents of radicle and plumule remained relative level at lower stress(100m M Na Cl, 20 m M Na2CO3). The radicle had different degrees for Na+ and Cl- ion absorption. Under the environments with same Na+ and Cl- contents, Cl- content with osmotic regulation effects in radicle and plumule of Amorpha is 18 times of Na+ content with toxic effect. If K+ content, free Mg2+ content and Na+/K+ in radicle and plumule remained relatively stable, it was beneficial to adapt to saline-alkali stresses; and instead, the contents of K+, free Mg2+, NO3-, H2PO4- and SO42- changed and responded differently under saline-alkali stresses. Under saline-alkali stresses, soluble sugar and organic acid are the main osmotic adjustment substances. Under alkali stress, organic acid responded more greatly than under salt stress; while total free amino acid had played no role on adjusting saline-alkali stresses. Tartaric acid was the main component of eight organic acids; under salt and alkali stresses, each component of eight organic acids accumulated differently. Under salt stress, tartaric acid accumulated substantially; while under alkali stress, the accumulation of citric acid, malic acid, acetic acid, oxalic acid, formic acid, and lactic acid were significantly increased(P<0.05). For sixteen free amino acids, under salt stress arginine and alanine and threonine are response solutes; instead, under alkali stress, glutamic acid and threonine are response solutes. Therefore, the stress effect level of seed germination are high p H > osmotic stress > ion stress.(3) Amorpha pericarp contains large amount of lipids, which has significant influence on seed germination. Under salt stress, after removing pericarp, germination rate and germinability and germination index were increased significantly(P<0.05); and seed germination time was shortened remarkably(P<0.05). That could accelerate seedling establishment, reduce stress time in germination process, change from heterotrophism to autotrophy ahead of time, and accumulate more anions and organic solutes for adaptation of salt stress. Hence, if Amorpha would plant in neutral salt soil, it could be sowed after removing pericarp, which increased significantly the effect of planting. Contrastively, under alkalic stress, owing to the effect of high Na+ absorption and high p H, the growth of Amorpha was inhibited, so that removing the pericarp was not suitable for sowing seeds. Different germination conditions had significant effect on experimental results; and the length and biomass of radicle and plumule through cultivation in sand were higher than that through paper culture method(P<0.05). Sand cultivation method can keep the concentration of treatment liquid well, which is useful to strengthen seedlings and to reduce the disturbance of other mineral elements. Hence, when conducted the experiment of seed germination under saline-alkali stresses, especially focusing on plants with well-developed roots, it is advisable to take sand cultivation method.(4) Low absorption of harmful ions, compartmenting more noxious ions into stems and primary petioles, and changing soluble sugar content in nutritive organs are main response strategies of Amorpha seedlings to adapt to saline-alkali stresses. Salt and alkali stresses had different effects on root growth, stem growth, compound leaf growth of Amorpha seedlings; appropriate concentration of salt stress and alkali stress with(100m M) could stimulate root growth. Under salt and alkali stresses, the biomass distribution rules are: biomass distribution of above- and under- ground is prior to that of root growth; biomass distribution of above ground is prior to that of leaflet growth. Under salt and alkali stresses, seedlings photosynthetic capacity would lower; but appropriate concentration of salt stress(50m M) could stimulate the synthesis of photosynthetic pigment; and under alkali stress, chlorophyll content was decreased significantly(P<0.05). Root had low Na+ absorption, and compartment large Na+ content into stems and primary petioles, in order to keep the stable Na+ contents of root and leaflet. In various plant organs, the contents of K+, free Ca2+ and Mg2+ changed differently under saline-alkali stresses; but under salt stress, the contents of K+ and Ca2+ and Mg2+ in leaflets had no significant change or remained in a relatively stable level, which is beneficial to maintain natural physiological functions of leaflet. Besides large accumulation of Cl- under salt stress, the response of anions was little significant or not obvious under saline-alkali stresses. Root and leaflet can accumulate large amounts of soluble sugar under saline-alkali stresses; and the accumulation of root soluble sugar was greater under alkali stress. Distribution rules of soluble sugar in various nutritive organs had changed: under control, root < stem < primary petioles < leaf; under saline-alkali stresses, stem < root < primary petioles < leaflet.(5) In Songnen grassland, Amorpha was proved to have certain saline-alkaline tolerance ability under natural saline-alkaline soil environment. The growth conditions were better in soil p H 8.65 and conductivity 87 u S/cm under saline-alkaline environments. Strong root system with nodules also effectively improved physical and chemical properties and structures of saline-alkali soils. Therefore, Amorpha can be used as main shrub tree species of afforestation to be planted in some areas with lower degree of salinization and alkalization in Songnen grassland.(6) Compared the effects of salt stress with alkali stress on seed germination and seedlings growth, under salt stress, the length of radicle and plumule were bigger than seedling root length and plant length, while seedling biomass accumulation was bigger than that of radicle and plumule; instead, under alkali stress, radicle length and biomass were larger than that of seedlings, while plumule length and biomass were less than that of seedling leaf. The seedling root intake of Na+ was much lower than that of radices; K+ content was very stable; and Na+/K+ contents in radicle and plumule were significantly higher than that of seedlings. Compared with seedling growth, the contents of Na+, K+ and Na+/K+ are the main sensitive elements to seed germination under saline-alkali stresses. Consequently, under saline-alkali stresses, free Mg2+ accumulation and norganic anions accumulation were the differences between seed germination and seedling responses of Amorpha; while soluble sugar accumulation are their similarities.