Study On The Basic Physiology Of Salt Tolerance In Kosteletzkya Virginica (L.) Presl

1. Salt-tolerance threshold of K. virginicaSeedlings of K. virginica were treated with Hoagland solution containing 0(CK), 10, 20, 30, 40, 50, 60, 70 and 80mmol/L NaCl respectively. The results showed under 40 mmol/L NaCl, the dry weight, fresh weight, Pn, Fv/Fm andφPSâ…¡of K. virginica were all the biggest. However, Compared with CK, Fv/Fm was no significantly affected, while the others were different (P<0.05). This showed the optimum salt- resistance threshold of K. virginica is 40 mmol/L NaCl.2. Effect of iso-osmotic water and salt stress on the growth of K. virginicaThe growth of K. virginica was lowered under the treatment of NaCl and isotonic PEG. The water content and succulent degree of seedlings will be increased under the treatment of 100 mmol/L NaCl (P>0.05), but the water content and succulent degree of plants were obviously decreased under the treatment of 200 mmol/L NaCl and all concentrations of PEG (P<0.05). Furthermore, The Na⁺ contents of plants were increased under NaCl treatments, while the K⁺ contents were decreased. However, both of Na⁺ and K⁺ contents decreased significantly under the treatments of PEG. In addition, along with the concentration increase of NaCl and PEG, the osmotic adjustive ability of K. virginica also increased, but the degree of NaCl treatments was higher than that of PEG. Simultaneity, the plasma membrane permeability, net photosynthetic rate (Pn), stomatal conductance (Gs) and photochemical efficiency (Fv/Fm) all decreased under the treatments, but the effect of isotonic PEG was more serious than NaCl. The results indicated that K. virginica was much more adapted to salt stress, rather than to osmotic stress. In addition, we can conclude stomatal factor was the main reson for Pn under the 100mmol/L NaCl treatment, but the non-stomatal factor dominated under the 200 mmol/L NaCl and both PEG treatments.3. Effect of NaCl on the growth and physiology of K. virginicaUnder the treatment of 100 to 300mmol/L NaCl, the fresh weight and dry weight of K. virginica decreased with the increase of NaCl concentrations However, compared with control, the growth indexes of K. virginica decreased slightly under the treatment of 100 mmol/L NaCl (P>0.05), and then decreased significantly as the increase of NaCl concentration (above 200 mmol/L NaCl). Water contents and succulent degree decreased with the increase of NaCl concentration. These indicateed that low concentrations of NaCl only has slightly effect on K. virginica; and salt-dilution does not seem to be the way of salt adaption in K. virginica. Under the treatments of CK and 100 mmol/L NaCl, the daily change of photosynthesis curves displayed two-apices. In the morning and the evening, Pn, Gs were low, but Ci was high; in the other time of the day, Gs and Ci simultaneously decreased when Pn decreased. The daily change of photosynthesis curves displayed single-apice under the treatments of 200 and 300 mmol/L NaCl. We can see Gs and Ci are decreased when Pn increased. So we can conclude stomata factors mainly led to the decrease of Pn under low NaCl treatments, and non-stomata factors prevailed under high NaCl treatments. In the morning and evening, low Pn was results of insufficient illumination, low temperature and low active of correlative enzymes. On the contrary, abundance illumination and higher temperature were easy to lead photoinhibition or the inactivition of PSâ…¡, which can explain the midday depression of photosynthesis siesta of K. virginica under the treatments of CK and 100 mmol/L NaCl. There is no midday depression under the treatments of 200 and 300 mmol/L NaCl, which may be the result of cross-adaption, i.e. K. virginica strengthen its ability to adapt insufficient illumination and high temperature in the course of adaptation to salt-stress.NR activities of shoots and roots showed greatly difference under NaCl treatments. With the increase of NaCl concentration, NR activities rose at first, subsequently fall in shoots; however NR activities gradually fall in roots. Compares with CK, NR activities were prominently different under salt treatments (P<0.05). In addition, the directions of NO3- contents were contrary to NR activities in leaves, but which were coincident to NR activities in roots. These results predicated some probable conclusions that NO3- mainly deoxidized in roots under CK treatments while it did in leaves under the salt-treatments.The total length, surface area, total volume and top tips of roots of K. virginica decreased with the increase of NaCl concentration. The reductive capability of TTC got to the max under the treatments of 100mmol/L NaCl, and then gradually decreased with the increase of NaCl concentration. So we concluded that K. virginica needed more energies to meet growth under lower salt-treatments, in addition, the growth and metabolism greatly decreased under 300 mmol/L NaCl treatments.4. Salt-exclusion characteristic of K. virginicaUnder NaCl treatments, the contents of inorganic ions (Na⁺,K⁺,Ca²⁺,Cl^-,NO₃^-) in the roots,caudexes,stalks,leafstalks and leaves were mensurated and analyzed for their variational trends as well as their distribution in the different organs. Moreover, the dynamic changes of Na⁺ and K⁺ and their transportations to the shoots were analyzed. The data suggested that exclusion of Na⁺ was the main method of salt-adaptation. The roots-stalks-leafstalks system was responds for the storage and exclusion of Na⁺. Through this way less Na⁺ were transported to leaves, which can maintain normal function of leaves. And this has largerer capability under higher NaCl treatments.5. Osmotic potential and osmotic adjustment capabilities of K. virginicaIn the roots and leaves, the contents of inorganic ions (Na⁺,K⁺,Ca²⁺,Cl^-,NO₃^-) as well as soluble organic substances (Pro,FAA,SS,OA) in the leaves and roots were determined. Furthermore, we also calculated and analyzed the role of inorganic ions and soluble organic substances played in osmotic potential. The results showed K. virginica could tolerate salinity by osmotic adjustment, and inorganic ions were dominant osmotic regulators.