冻融过程对荒漠区不同微生境下齿肋赤藓渗透调节物含量和抗氧化酶活力的影响

Impacts of freeze-thaw processes on antioxidant activities and osmolyte contents of Syntrichia caninervis under different desert microhabitats

齿肋赤藓(Syntrichia caninervis)作为典型的耐旱藓类,广泛分布于世界干旱和半干旱荒漠地区,是古尔班通古特沙漠生物土壤结皮中的优势藓类植物。该沙漠冬季具有稳定的降雪,初春的积雪融化为植物的生长提供了良好的水热条件。荒漠藓类植物叶片仅具一层细胞,对外界环境的变化十分敏感,有关荒漠藓类植物在冬季和早春地表冻融交替过程中如何适应环境剧烈变化的研究鲜见报道。该研究探讨了生长于3种不同微生境(活灌丛、枯死灌丛和裸露地)下的齿肋赤藓,经由冬季低温冻结到早春融雪复水再到春季中旬自然干燥过程中的生理生化变化特征。结果表明:不同冻融期、微生境及二者的交互作用能够显著影响齿肋赤藓的渗透调节物质(游离脯氨酸、可溶性糖、可溶性蛋白)含量、丙二醛(MDA)含量、抗氧化酶活性(过氧化氢酶(CAT)、过氧化物酶(POD)和超氧化物歧化酶(SOD)活性)。冬季低温冻结期的极端低温和春季中旬的干燥环境使得齿肋赤藓可溶性糖和MDA含量,以及3种抗氧化酶活性均显著高于早春融雪期,可溶性蛋白含量显著低于融雪期。同时,在融雪期灌丛遮阴所形成的"冷岛效应"使得生长于灌丛下的齿肋赤藓植株可溶性糖和MDA含量显著高于枯死灌丛和裸露地。但灌丛的存在也为春季中旬干旱无雨期齿肋赤藓提供了一个相对良好(含水量高)的生活环境,其下齿肋赤藓的渗透调节物含量和抗氧化酶活性均显著低于其他两个生境。在整个冻融过程中裸露地齿肋赤藓的3种抗氧化酶活性均显著高于灌丛下,这可能是由于生活于裸露地的苔藓有更强的耐胁迫特性。

Aims Syntrichia caninervis, a typical drought-tolerant moss species found worldwide in various semiarid and arid regions, is the dominant species of soil crust mosses in the Gurbantinggit Desert, which is a temperate northern desert of Central Asia. It appears able to endure frequent and intensive freeze-thaw cycles in the surface soil and maintain physiological functions active even under extreme low temperatures in winter. However, there have been few studies exploring the adaptive strategies of the species during freeze-thaw processes and interpreting well the phenomena. One of the major goals of this study was to investigate physiological regulatory mecha-nisms of the species when undergoing freezing-thawing periods and relevant antioxidant enzyme activities. Methods A series of microclimate and soil conditions were continuously monitored in the sampling sites starting from November 2013. The samples of the moss were collected during the early spring of 2014 from February to April and from three microhabitats including the sites under live shrub, under dead shrub and on an open ground. The moss samples were quickly treated in the field for keeping freshness and then brought to laboratory for meas-urement and analysis. The traits/characteristics that reflect physiological and biochemical activities were measured for analyzing responses of the species to freeze-thaw processes and for comparing the impacts of different habi-tats, which included water content, concentrations of proline, soluble sugar, soluble protein and malondialdehyde＆amp;nbsp;（MDA）, as well as catalase （CAT）, peroxidase （POD）, superoxide dismutase （SOD） activities Important findings The results showed that, during different freeze-thaw periods, microhabitats and their inter-actions with alternative freeze-thaw processes significantly affect the contents of proline, soluble sugar, soluble protein and MDA in shoots of the species, as well as the enzyme activities of CAT, POD, and SOD. Extreme low temperature and drought caused significantly higher soluble sugar and MDA contents, higher CAT, POD and SOD activities, but lower soluble protein content, in snow covered period （February） and dry period （April） than the snow melting period （March）. The existence of live shrub decreased temperature around the bushes during snow melting because of the effect of shade, causing increased contents of soluble sugar and MDA in moss shoots, when compared to those growing in the habitats under dead shrub and on open ground. However, live shrub could provide a moister environment for S. caninervis than dead shrub and exposed ground for the duration of desicca-tion. As the result, the proline content, soluble sugar content and MDA content of the species under the live shrub canopy were the lowest among the three habitats. Furthermore, the mosses lived on the exposed ground showed the highest antioxidant enzyme activities comparing to those under the dead shrub and living shrub. This may suggest that S. caninervis grown on exposed grounds has developed rather a specific adaptations for a harsher en-vironment condition than that occurred in other two habitats.