Effects Of Salinity Stress On Ion Balance And Rhizosphere Ph Change Of Pea(Pisum Sativum L.)Seedlings

Soil salinization is one of the major abiotic stresses affecting crop growth and productivity which limits the sustainable development of agriculture. Secondary salinization has also become more increasingly serious, especially in arid and semi-arid regions. To cope with the problem, the amelioration and improvement of soil salinity have been researched as a popular topic.In the context of the study, Based on a calcareous salt-affected soil in the irrigated region in Northwest China, the present study compared the rhizosphere pH change potential of salt-sensitive three varieties of pea (Pisum sativum L.) and salt tolerate malting barley (Hordeum vulgare var. vulgare) using a solution culture assay, in the meanwhile, mixed salt solutions were prepared which were treated with Na+or Cl-by using a combination of different Na salts and Cl salts, respectively.The main results were as followed:1. Under salinity stress the shoot dry biomass decreased in comparison with contrast, and the shoot dry biomass was reduced by19%-35%under Na salt stress, but the root biomass and root/shoot ratio increased significantly under NaCl and Cl salt stress (P<0.05). In addition, root length was stimulated to increase under NaCl and Cl salt stress. But Na salt stress inhibited the growth of the seedlings seriously, and the water content of pea seedlings decreased obviously, Yinwan NO.11fell18.5%(P<0.05).2. Root length, root surface area and root volume reduced under Na salt stress. However, plants under C1salt and NaCl treatments showed a decreasing of root length in parallel with a decreasing in root surface area. The root/shoot ratio decreased under salinity stress. Both high Na+and high Cl" reduced growth of peas but plants were more sensitive to Na+than to Cl-.High salinity stress reduced shoot growth more than root growth, The growth under salinity stress was in order of Yinwan NO.3> Yinwan NO.1>Yinwan NO.11. This study demonstrated that the importance of Na+toxicity as a cause of reductions in growth and yield under salinity stress.3. Large genotypic variation was found for ion concentrations, selective absorption (AS) and selective transportion(AT) for Na+, K+, and accumulation of compatible solutes under salinity stress. The average shoot Na+concentration in both varieties significantly increased under NaCl and Na salt stresses. On the contrary, K+content decreased (P<0.05). K+, Ca2+, Mg2+contents of seedlings under Cl salt treatments were longer than that of the control group (P<0.05). Cl-concentration decreased under Na salt stress. High Na+competitively interfered with K+, Ca2+and Mg2+nutrition, and induces their deficiencies. The ability of K+, Ca2+and Mg2+transporting from root to shoot was inhibited under NaCl and Na salt treatment. Furthermore, the addition of K+and, to a lesser extent, Ca2+alleviated the toxic effects of Na. Thus, Ca2+is essential but may also be intoxicating or ameliorative.4. K+/Na+, Ca2+/Na+, Mg2+/Na+and (K++Ca2++Mg2+)/Na+ratio decreased significantly under Na salt and NaCl treatments, on the contrary, those indexs increased as compared with the control group. K+had become a priority under salinity stress during the ion transportation and separation process which was significant for keeping ion homeostasis which results in a depression of growth.5. The key adaptive tolerance mechanism of peas and malting barley to salt stress can be attributed to the high selective absorption and transportation of K+, and K+/Na+thereby maintaining the normal growth of shoots.6. Root-induced pH changes in the rhizosphere significantly modified the root environment and the mobility of mineral, whereas the imbalance of cation/anion uptake by plants is a major contributor to the rhizosphere pH change. When peas and malting barley grown under normal conditions, which accumulated of excess K+, and consequently took up more cations than anions, protons are released from the root to the environment maintain electrical neutrality; these protons are then released into the rhizosphere contributing to its acidification. Conversely, under Na salt treatment, plants supplied with NO3-as their source of N will release OH" or HCO3-into the rhizosphere thereby increasing the pHleading to the rhizosphere alkalinization. Under NaCl treatment, when anion uptake into the cells exceeds cation uptake, the excess negative charge is balanced by the release of OH-/HCO3-leading to the rhizosphere alkalinization. Under Cl salt stress, rhizosphere alkalinization of peas and malting barley because of absorbing too much Cl-.7. The calculated H+release determined on the basis of the pH change. Under normal growth conditions, the amount of protons into solution varied between2-3500umol H+/m-h for the different genotypes. In general the rhizosphere alkalinization, pea>malting barley. Under NaCl treatment, the degree of rhizosphere alkalinization in order of Yinwan NO.11>Yinwan NO.3>Yinwan NO.1. The results also showed that there were significant genotype and species differences between cation/anion balance and rhizosphere pH change.8. For rhizosphere pH change, it doesn’t necessarily mean that cation-anion balance theoretical approach was better than chromogenic in situ.