Adaptive Responses Of Medicago Sativa To The Stress Of Mixed Salt-alkali

Soil salinization is one world wide environmental problem. Too much salt in soil willrestrain the normal growth of most of plants, especially to the moderate salt resistantMedicago sativa. The inconsistency among grasslands salinization and alkalization,desertification and development of Animal husbandry is more and more prominent. Therefore,it has significant economic value to study the responses of M. sativa to salinized and alkalizedstress as the vastest planted forage in artificial pasture, also explore and breed new specieswhich is resistant to salt and alkali.In order to study the real stress effects of mixed salt-alkali existing in soil to plants andthe relationship of salinized stress and alkalized stress, we carried out this study, which basedon the simulation of the natural salt-alkalied soil in lab, and studied the responses of M. sativato mixed salt-alkali stress.In nature environment, salt-alkalied soil contains complex salts, for example, in west ofJilin province, salt-alkalied soil contains not only neutral salts such as NaCl, Na2SO4, etc., butalso alkali salts such as NaHCO3, Na2CO3, etc. Furthermore, different composition andquantum of salts can result in different salinized and alkalized properties in different regions,or even in the same region.According to the statement above, this study chose two neutral salt NaCl and Na2SO4,two alkali salt NaHCO3 and Na2CO3, and arranged 6 groups (A-F) according to differentalkali to salt ratio and concentration. According salt-tolerance threshold of M. sativa, weselected five gradients of salt in each group, and the total salt concentration of mixedsalt-alkali stress was from 24 mmol/L to 120 mmol/L, as to pH from 7.03-10.32, in total 30different alkali-salt conditions were simulated. We used this mixed salt-alkali stress on seedsand five-week old seedlings of M. sativa, and measured the morphological and physiologicalproperties after stress. The results showed that:(1) M. sativa seedlings showed some law on the physiological responses of to mixedsalt-alkali stress. Proline concentration was increased as the pH increased. The effects of saltconcentration and treatments (pH) gradient to praline concentration of M. sativa seedlingswere significant, and there was significant interrelated influence between them. Relativepermeability of plasma membrane was significant contrasting to CK, and relativepermeability of plasma membrane stopped increase when salt concentration was 96mmol/L.Relative permeability of plasma membrane increased with the pH increase, there weresignificant differences among different groups. Chlorophyll concentration was decreased withthe pH and salt concentration increased. Chlorophyll concentration was higher than the CKwhen salt concentration was lower than 96mmol/L, but lower than the CK when pH wassignificantly higher than 10.0. The effects of salt concentration and treatments, and thesynergetic effect between them to total chlorophyll concentration were significant. Therestrain of pH to root vigor was increased with the pH increase, especially when pH washigher than 9.0. As salt concentration increased, the damage of pH to root cells became severe,there was significant synergistic action between them.(2)Seedlings survival rate was 100% when pH was below 8.30, and 0% when pH was above9.69. There was very significant difference among different salt concentration and pH, andsignificant synergistic action between them. Above and below ground biomass weredecreased as salt concentration increase. The effects of salt concentration, pH gradient and thealternant action between them to above ground biomass of M. sativa seedlings were verysignificant. The effects of salt concentration and pH gradient below ground biomass weresignificant. The effects were very significant of salt concentration and pH to fresh radicelweight of seeds, and there was significant alternant action between them.(3)The effect of salt concentration to M. sativa seeds was significant, but the different pHhad no significant effect to the germination of seeds. Germination potential was decrease asthe pH increase. The effect of salt concentration was significant to germination potential, butno significant different among groups.(4)There was significant effect of salt concentration and pH to fresh embryo weight and dryembryo weight of Medicago sativa seeds, and there was significant alternant action betweenthem(p<0.05).(5)In the process of mixed salt-alkali stress, there were synergetic effects of salt and alkaliconcentration to plant morphological and physiological properties, in another word, thealternant action between high salt concentration and high alkali concentration damagedseedlings much more severe than single salt or alkali. Furthermore, as the intensity ofsalt-alkali stress increased, the synergetic effects were also increase prominently.From above, the morphological and physiological properties of M. sativa under mixedsalt-alkali stress showed that, low concentration of salt and alkali could promote growth of M.sativa. So M. sativa could adapt well to low salt and alkali environment. But highconcentration of salt and alkali restrained growth of M. sativa. Through increasingconcentration of proline, could increase alfafa's resistance to salt and alkali. Therefore, weconcluded that it was possible to plant M. sativa in moderate salt-alkalized fields.