Study In Photosynthetic And Stress Ecophysiology Of Leymus Chinensis Along The Salinity-alkalinity Gradients On The Songnen Grassland In Northeastern China

L. chinensis is perennial, rhizome plant that has strongly adaptability and widely ecological plasticity. It can be adaptive to different menaces come from bad habitat conditions. It can also be widely grown in multi agrotype. It can be grown as dominant species, inferior species and co-existing species. Because grow for a long time in bad environment, it has obvious changes in physiological and biochemical process. Hence it can adapt to different menaces come from bad environment. The study of photosynthetic and anti-ecological physiology of L. chinensis has significant meaning. It reveals L. chinensis's ecological adaptive. Besides the study also plays an important role in native pasture and the construction of artificial grassland.Songnen grassland is one of the main districts in which Chinese saline-alkali soil concentrates. It is also an inner flow area. It is influenced by the changes of middle small and micro geographic features and the typical soil-forming conditions. So it has unique process of modern salt accumulate and it also has abundance of minerals in ground water. Extensive distribution of the saline-alkali soil has influenced the growth and distribution of the area vegetation type. In the past 20 years, various factors, especially human over-utilization of the grassland, resulted in desertification.During the retrogressive succession of L. chinesis in Songnen grassland, pH and conductance in grassland soil increase gradually, which means the degree of soil alkalization and salinization becomes higher. The character of L. chinensis community has changed obviously. For example the population density, height and biomass become lower gradually. In different saline alkali grassland, the changes in photosynthetic characteristic of I. chinensis are also obvious. The study of photosynthetic characteristic of L. chinensis in retrogression grassland indicates: during the retrogression, the leaves of L. chinensis has changed significantly in net photosynthetic rate, transpiration rate, stomata conductance, ratio of sub-stomatal to atmospheric CO₂ concentration and water use efficiency of L. chinensis leaves have changed significantly. Especially after 1:00 pm, the difference becomes clear. The net photosynthetic rate, transpiration rate, stomata conductance, ratio of sub-stomatal to atmospheric CO₂ concentration and water use efficiency increase in the early period. But after reaching a certain degree, as the retrogression become worse, the rates decrease gradually. The analysis of photosynthetic pigment in L. chinesis reveals that with the retrogression of the grassland, chlorophyll and the total amount of photosynthetic pigment in L. chinesis tend to become less gradually. By contrast, the total annual amount of chlorophyll a/b and carotenoid increase first and then decrease gradually. During different periods of retrogression, plasticity total sugar, saccharise, laevulose all tend to accumulate. This phenomenon especially exists clear in L. chinesis leaves and rhizome which grow in the area where retrogression is worse. At the mean time the trend also exists in the content of plasticity protein in L. chinesis. The data also shows that the net photosynthetic rate, transpiration rate, stomata conductance, ratio of sub-stomatal to atmospheric CO₂ concentration, water use efficiency, chlorophyll, plasticity total sugar, sacch-arise. laevulose and plasticity protein have the intimate relationship with the form of L. chinesis community.Experiments show that during the retrogressive succession of the L. chinensis grassland. The antioxidant enzyme activity, proline, inorganic ion, organic acid and other accumulating the matter of penetrate adjustment and the content of plasticity protein in the L. chinensis plants have changed greatly during physiological and biochemical process.The density, height and biomass of the L. chinensis population decline for the degenerated succession of the L. chinensis grassland and salinization of the grassland soil. However, the antioxidant enzyme activity of the L. chinensis leaves increases distinctly; especially the activity of CAT increases not only during the whole period of the growth of L. chinensis but also year by year. Though declines in annual average, the activity of POD increases at the earlier stage and the later stage of the growth of L. chinensis. Though complicated, the activity of SOD shows a trend of increasing after first declining as the grassland degradation. The change of seasonal proline content and the annual average in L. chinensis leaves and rhizome quite resemble. As the aggravation of the grassland salinization, proline content shows a trend of declining after increasing, especially the specific change of proline content in the rhizome of L. chinensis. This shows that the accumulation of proline increases the osmotic adjustment ability of the L. chinensis plants living in nature in low salinization. The change of proline metabolism shows the physiological mechanism of the L. chinensis in Songnen grassland which makes the plant adopts the salinization and drought. The result of the inorganic ions measurement to L. chinensis shows that the inorganic cations in the leaves and rhizome of L. chinensis, especially K⁺ and Ca²⁺,changes distinctly during the process of degraded succession. The contents of Na⁺ and K⁺ in leaves are consistent with the present research, but the content of K⁺ in rhizome increases. We also analyze the SA and ST in L. chinensis living in nature state for the first time. It shows that the L. chinensis plant can adjust its physiological metabolism well by absorbing K⁺ while refusing Na⁺ as well as by transporting K⁺ in the process of monitoring the transporting of Na⁺. This specific process of metabolism can help the L. chinensis in adopting the salinization in Songnen grassland. In the process of degraded succession, the anion in L. chinensis leaves and rhizome shows a tendency of accumulation, which can strength its osmotic adjustment ability as well as balance the cation and anion in the plant and relief the harm bringing by the accumulation of Na⁺.By measuring the contents of organic acid in L. chinensis in different salinizated grassland, we found that the content of tartaric acid, malic acid, oxalic acid, succinic acid and citric acid in the leaves and rhizome of L. chinensis shows a tendency of accumulation in July and August. In mild salinization grassland, L. chinensis mainly accumulates tartaric acid and citric acid; while in moderate and severe salinization grassland, it mainly accumulates succinic acid. The accumulation of some organic acid can relief the stress of salinizated soil of Songnen grassland on L. chinensis and enhance its ability against poor environment. But in different periods and different plants, the content of organic acid is different. Further study needs to be done.Experiments show that the L. chinensis plants can enhance its antioxidant enzyme activity and osmotic adjustment ability and relief the harm of Na⁺ by adjusting its physiological metabolism. And by changing the composition of soluble protein, it adapts to the stress of salinized soil in Songnen grassland. Therefore, it can grow normally as well as spread its population in arid and semiarid salinized grassland.We first use saline-alkali soil in Songnen grassland as water solution to do micro-model under the stress of saline-alkali. The result reveals the same thing. Under a certain stress, young seedling grows well, and its height, weight is higher than with no saline-alkali soil. While under high degree of saline-alkali, its height and weight decrease. Plasticity total sugar, plasticity protein and the content of chlorophyll in young seedling has the same changes while under a certain degree of saline-alkali stress. All these indicate that as the forming community in Songnen saline-alkali grassland, L. chinensis has high adaptability to salt-alkali. Besides, it can grow well than with no salt-alkali soil. Plasticity total sugar, plasticity protein, chlorophyll a/b, carotenoid in rhizome accumulate differently while under saline-alkali stress. This has the same metabolism with L. chinensis which grow in natural retrogression grassland. This further proves that L. chinensis has the ability to adapt and anti saline-alkali.Through the analysis of activation of the Anti-oxidase, accumulating the matter of penetrate adjustment and the content of plasticity protein in young seedling shows that under saline-alkali stress become strengthen, 3 kinds of activation of the Anti-oxidase and proline in leaves have accumulated significantly. All of them are almost the same with the L. chinesis's metabolism in natural condition. Further analysis proves that proline plays an important role in resisting bad habitat, especially under saline-alkali stress. The result is the same in the content of inorganic ion. Young seedlings' rhizome can resist absorbing Na⁺. But it absorbs K⁺ actively and transports it. Under a certain density saline-alkali stress, young seeding can specific property absorbing and accumulating anion. The content of calcium, hydroxysuccinic acid, succinic acid and citric acid in young seedlings all has different levels of accumulation. All these increase the capacity of penetrate adjustment and release the saline-alkali stress to young seedlings. This is also proved that L. chinesis is adaptive to the bad habitat and the salt-alkali stress.There is a little difference between experience young seedlings club and experiment in outdoor habitat. For example, in experience club the activity of POD and SOD tend to increase till reaching the maximum level of saline-alkali. Proline mainly accumulates in caudex and leave. Sand is used as medium and complete nutrient solution is used to irritate it daily. All these conditions are helpful for the growth of young seedling, so it can grow fully. At the same time, when young seedlings grow well, they are put into saline-alkali for only a short time. Through this, young seedlings are easier to give stress reaction and bring a different result. It also reminds us that it is important to combine micro-model and the experiment in outdoor habitat together.