Study On Physiological Characteristics Of Dominant Mosses Brachythecium Salebrosum In Biological Crusts Of Sand And Loess Hilly Region

The article studied Water Retention,Photosynthetic Pigments content,Diurnal changes of Net Photosynthetic rate and chlorophyll fluorescence parameters\Photosynthesis-light response curves and the effect of desiccation and rehydration process on Net Photosynthetic rate,Respiratory rate,Active Oxygen Metabolism and osmotic adjustment content of dominant mosses Brachythecium salebrosum in biological crusts of sand and loess hilly region. The results showed:1. Brachythecium salebrosum grows under the Juniperus Communis and Prunus davidiana Franch bushes, it has characterision of poikiohydric plants, water content of Brachythecium salebrosum decreased with desiccation. water content of Brachythecium salebrosum decreased rapidly for desiccation 75 min.this moment, it reduce 86.30% than the normal, After the desiccation 75 min, the water content decreased slowly and was steady for desiccation 105 min. as the Rehydration, Brachythecium salebrosum absorbed rapidly. The water content of Brachythecium salebrosum recovered faster and it was normal levels for about the Rehydration 60 min.2. Brachythecium salebrosum have characteristics of shade plant. Chlorophyll a and chlorophyll b ratio is 1.78.the ability of Capturing light is strong under the low light conditions, which Improve the efficiency of using light energy. Light saturation point and light compensation point are low, Light compensation point, saturation point and dark respiration rates were 34.90μmol·m-2·s-1,475.00μmol·m-2·s-1 and 13.18μmol·kg-1 (DW)·s-1.3. Brachythecium salebrosum appeared photoinhibition under high temperature and strong light. Pn,qN,ETR were the same as PAR and temperature were low in the early morning and at dusk. They reached the maximum at noon. In contrast,The Fv/Fm, Fm, Yield and qP are high in early morning and evening, theywere small at strong light and high temperature.4. Bracythecium salebrosum has characteristics of resurredion plant. ETR, Pn, Fv/Fm, Fm, Yield, qP and respiratory rate all became low,when Brachythecium salebrosum desiccat. desiccation not only caused damage of photosynthesis and respiration institutions, but Also affected enzyme activity. Most indicators returned quickly to normal levels as the rehydration.5. Desiccation caused to generate superoxide anion, which brought about damage of Relative cell membrane permeability and led to increase of peroxidation product MDA content.But Brachythecium salebrosum cleared away reactive oxygen free radicals by enzyme defense system and non-enzymatic defense system and defend cells from damage. With the increase of desiccation and stress, SOD, POD, CAT activity of Brachythecium salebrosum increased gradually.However, Superoxide anion content did not increase. It is positive correlation between AsA and free radical generation rate. It is negative correlation between GSH and free radical generation rate.It indicate That AsA and GSH play an important role of the Brachythecium salebrosum scavenging reactive oxygen free radicals in the desiccation process.In contrast, the cell membrane damage of Brachythecium salebrosum was gradually restored during rehydration. SOD activity, CAT activity, POD activity, GSH content and AsA content were the opposite the trend at desiccation. Damage of membrane by reactive oxygen species and redox imbalance has been repaired.6.In the early stage of water stress, soluble sugar and praline was accumulated in Brachythecium salebrosum. The total acid, trehalose, soluble protein, glycerin and K+ occured the accumulation phenomenon in the desiccation process. In Drought stress, Brachythecium salebrosum maintained cellular osmotic balance by accumulation of small molecules and proteins protective agent.Trehalose and proline has a protective function of intracellular reactive substances, which refrained from the stress damage.In the Sensitive and vulnerable Huang Pu River Basin Native vegetation ecological environment of Ordos Plateau, Brachythecium salebrosum be distributed largely unter the shrub forest. The Study of physiological characteristics of Brachythecium salebrosum in water stress, not only helps to understand the physiological mechanism of drought adaptation, but also revealed the ecological adaptability characteristics of Brachythecium,the formation of bryophyte ground layer and maintenance mechanism.