不同水分条件下坚韧胶衣固氮活性对冻融的响应

坚韧胶衣Collema tenax是干旱和半干旱生态系统中生物土壤结皮的重要组分,其固氮作用对生态系统氮素循环具有重要影响。该地衣生长于温度和水分条件变化剧烈的土壤表面,但在我国北方其固氮活性对冻融的响应尚不清楚。采用乙炔还原法研究了坚韧胶衣固氮活性在不同水分条件下(湿冻组:地衣体含水量200%干重;干冻组:地衣体含水量20%干重)和4次冻融处理之间的差异。坚韧胶衣固氮活性为2,371.0-8,701.8nmolC2H4/m2·h,湿冻组固氮活性低于干冻组,对照组固氮活性最高,湿冻组和干冻组的固氮活性(对照的百分比)均与冻融次数呈显著的线性负相关关系(干冻组:R2=0.916,p0.001;湿冻组:R2=0.965,p0.001),但湿冻组的斜率绝对值(25.05)明显高于干冻组斜率绝对值(7.60)。结果表明低温对坚韧胶衣固氮活性具有显著抑制作用,干燥条件下坚韧胶衣固氮活性对于低温胁迫的敏感性比地衣体湿润条件下更低,这种较低的敏感性可能是该地衣对我国北方干燥和冷热变化剧烈的气候特点的生理适应策略。

Nitrogen fixation response of Collema tenax to freezing-thawing under different thallus water conditions

Collema tenax is an important component of biological soil crusts in arid and semiarid ecosystems where its nitrogen fixation is important in ecosystem N cycling. This lichen occurs in surface soil with sharp temperature and water fluctuations, but its N fixation response to freezing-thawing in northern China is yet unknown. Differences in N-fixing activity of C. tenax among four freezing-thawing events under two thallus water conditions (wet-freezing: thallus water content > 200% dry weight; dry-freezing: thallus water content<20% dry weight) were measured using acetylene reduction assay. N-fixing activity ranged between 2,371.0-8,701.8nmol C_2H_4/m~2.h and followed the decreasing order of control > dry-freezing > wet-freezing. N-fLxing activity (% of the control) of both dry-freezing and wet-freezing shows significant negative linear relationship with freezing-thawing times (R~2=0.916for dry-freezing and R~2 = 0.965 for wet-freezing, all at p<0.001). The absolute value of slope of wet-freezing (25.05) is much higher than that of dry-freezing (7.06). These results show a higher sensitivity of N fixation of C. tenax to freezing in wet than in dry condition. The lower sensitivity to low temperature in N-fixing activity for dry thallus of C. tenax is likely a physiological adaptation strategy to climate of northern China that characterized by prolonged drought and sharp temperature fluctuations.