Research On Photosynthetic Characteristics And Ion Homeostasis Of Glycine Soja Seedlings Under Saline And Alkaline Stresses

Glycine soja is annual herbaceous legumes, wild relatives of Glycine max, has astrong disease resistance, insect resistance, drought resistance, barren and other stressresistance, and widely distributed in China. The research of photosyntheticcharacteristics, ions homeostasis and mutual restriction relation of G. soja undersaline-alkali stress, not only can reveal physiological mechanism of G. soja to resistsaline and alkaline stresses, but also lay the foundation for the rational development ofsoybean germplasm and breeding soybean saline-alkaline tolerance.Two neutral salts were mixed at a1:1molar ratio of NaCl: Na₂SO₄and appliedto the saline stress group. Similarly, two alkaline salts were mixed at a1:1molar ratioof NaHCO₃to Na₂CO₃and applied to the alkaline stress group. Five differentconcentrations of saline and alkaline stresses were designed to treat the four weeksold G. soja seedlings for five days, and then the growth parameters were determined,including: length of root, shoot height, water contents and relative growth rate;photosynthetic parameters were determined, including: diurnal change ofphotosynthetic parameters, photosynthetic pigments and photosynthetic products; ionscontents and distribution in roots, stems and leaves.The relative growth rates were inhibited of G. soja seedlings under saline andalkaline stresses. The root growth was not affected by the appropriate saline stress, butobviously inhibited by alkaline stress. The shoot height was inhibited by saline stress,but was promoted by the lower concentration of alkaline stress. Water content of rootwas higher than that in shoot of G. soja seedlings under higher saline and alkalinestresses.The results showed that diurnal change of PN, gs, and E exhibited the bimodalcurves in low salinity under both stresses, but it showed a single peak curve in highsalinity. Diurnal average value of PN, gs, E were all decreased under both stresses; thereduction degree under alkaline stress was obviously higher than that under salinestress. Diurnal average value of WUE showed an increasing trend under saline stress,but increased first and then decreased under alkaline stress. The results ofphotosynthetic pigments indicated that total photosynthetic pigments and Chlorophyllwere inhibited under both stresses, although the synthesis of pigment was promotedby lower alkaline stress. Carotenoids of G. soja seedlings were fluctuated in a range under saline stress and its synthesis was promoted in a low concentration of alkalinestress. The chla/chlb ratio of G. soja seedlings maintained at3:1under saline stress,but it was decreased with increasing salinity under alkaline stress and the value ofchla/chlb ratio was2approximately under higher alkaline stress. Although PNofG.soja seedlings was inhibited by saline and alkaline stress, the synthesis ofcarbohydrate was promoted by low concentration of alkaline stress, and solublecarbohydrate, sucrose, fructose were all specific accumulation in stems and leaves,especially under higher alkaline stress.Na+, Cl-and SO₄^2-were increased in roots, leaves and stems of saline stressedseedlings, K+, NO₃-and Ca²⁺were fluctuated in a range. Na+and Cl-in stems andleaves were increased whereas K+, NO₃-and Ca²⁺were also increased under alkalinestress. Na⁺and Cl-percentages in roots, stems and leaves under saline stress or Na⁺and Cl-percentages in roots under alkaline stress were increased, but the increasingdegree of Cl-percentage was much greater than that of Na⁺. Cl-percentages in stemsand leaves of G. soja seedlings were decreased under alkaline stress. With increasingsalinity, Na⁺/K⁺in roots, stems and leaves of G. soja seedlings were all increasedunder both stresses. SA increased under saline stress, and increased first thendecreased under alkaline stress, compare with alkaline stress, selective absorption ofNa+and K+in root of G. soja seedling under saline stress was stronger than that underalkaline stress.