不同微生境下齿肋赤藓(Syntrichia caninervis)生理生化特性对不同季节的响应

齿肋赤藓(Syntrichia caninervis)作为典型的耐旱藓类,在古尔班通古特沙漠的藓类结皮中占优势地位。该沙漠的季节气候差异较大,冬季低温湿润,春季干旱,夏季高温且干旱。荒漠藓类植物叶片仅具单层细胞,对外界环境的变化十分敏感。而有关荒漠藓类植物在生理上如何适应这种剧烈环境变化还不得而知。研究测定了生长于两种不同微生境下的齿肋赤藓,经由低温湿润的冬季到干旱的春季再到高温干旱的夏季过程中生理生化变化特征,以探究不同微生境下齿肋赤藓在水热变化剧烈的不同季节的适应机制。研究发现:季节、微生境及二者的交互作用能够显著影响齿肋赤藓的游离脯氨酸、可溶性糖、可溶性蛋白及丙二醛(MDA)含量、过氧化氢酶(CAT)、过氧化物酶(POD)、超氧化物歧化酶(SOD)活性。夏季的高温干旱使齿肋赤藓的脯氨酸、可溶性糖、MDA含量及3种抗氧化酶活性均显著高于冬季及春季,而可溶性蛋白含量却呈相反趋势。干旱的春季齿肋赤藓脯氨酸及可溶性糖显著高于冬季。而在低温湿润的冬季,齿肋赤藓丙二醛含量及过氧化氢酶活性均显著高于春季。表明夏季齿肋赤藓所受胁迫最大,脯氨酸、可溶性糖含量及抗氧化酶活性大幅度提高。同时,在具有积雪覆盖的冬季,两种微生境下的齿肋赤藓生理生化特性无显著差异;而在无积雪覆盖的春夏季节,灌丛的遮阴作用为齿肋赤藓提供了水含量相对较高的良好生活环境,其下齿肋赤藓的渗透调节物质含量和抗氧化酶活性均显著低于裸露地。表明生长在裸露地的齿肋赤藓较活灌丛拥有更强的胁迫耐受性。

The response of Syntrichia caninervis physiological and biochemical characteristics to different microhabitats and seasons

Syntrichia caninervis is a typical drought-tolerant moss found worldwide in various semiarid and arid regions. Biological soil crusts (BSCs) develop well in Gurbantünggüt Desert, and S. caninervis is a dominant species in the moss crusts of this cold desert. Gurbantünggüt Desert is home to stable and abundant snow cover in winter, little rain in spring, and high temperatures and drought in summer. There is a large variation in climatic conditions across seasons in Gurbantünggüt Desert. The leaves of desert moss have only a single layer of cells, and thus are extremely sensitive to the changing environment. However, there have been few studies exploring how desert moss maintains its physiological functions even under such a drastically changeable environment. One of the major goals of this study was to investigate the physiological regulatory mechanisms and relevant antioxidant enzyme activities of S. caninervis in different microhabitats and seasons. Microclimate and soil conditions were continuously monitored in sampling sites starting in November 2013. We measured physiological and biochemical characteristics of S. caninervis, including water content; concentration of proline, soluble sugar, soluble protein, and malondialdehyde (MDA); and activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). The results showed that, in different seasons, microhabitats and their interactions significantly affected the content of proline, soluble sugar, soluble protein, and MDA in shoots of this species, as well as the enzyme activity of CAT, POD, and SOD. Extreme high temperature and drought caused significantly high proline and soluble sugar content and higher CAT, POD, and SOD activity, but soluble protein content was the lowest in summer among the three seasons. The aridity in spring caused significantly higher proline and soluble sugar content than in winter. Moreover, there was higher MDA content and CAT activity in low-temperature winter than in spring. According to correlation analysis, MDA content, and POD, CAT, and SOD activity all had significantly negative correlations with plant water content, whereas all the physiological and biochemical characteristics displayed no significant correlations with plant water content in winter. In spring, all the physiological and biochemical characteristics, except soluble sugar content, had significantly negative correlations with plant water content, whereas proline content and temperature had no significant correlations with the other physiological and biochemical characteristics. Furthermore, during the summer, all the physiological and biochemical characteristics had significantly negative correlations with plant water content and significantly positive correlations with temperature. These findings suggested that the desert moss experienced different types of stress in the three seasons:low-temperature stress in winter, drought stress in spring, and drought and high-temperature stresses in summer. When compared to those growing in other habitats, under shrubs and on open ground, because the snow cover decreased the effects of the shrubs, there was no difference in the characteristics that reflect physiological and biochemical activities between the two microhabitats in winter. Furthermore, shrubs could provide a moister environment for S. caninervis than exposed ground for the duration of desiccation (spring and summer). As a result, the osmoregulation substance contents and antioxidant enzyme activities in the mosses under the shrubs were lower than in those on exposed grounds. This may suggest that S. caninervis growing on exposed ground has a greater tolerance to stress in harsh environmental conditions than those occurring under live shrubs.