中文摘要：

海草凋落叶分解释放是海草床有色溶解有机物（CDOM）的主要来源,且海草凋落叶的分解释放受盐度的影响较为明显。本文以夏季海南新村湾不同区域海水盐度分布为背景,结合湾内盐度变化范围设计了4个盐度水平（0、11、22和33）,研究盐度对不同海草凋落叶分解释放的CDOM光降解的影响。结果表明：各盐度条件下,两种海草源CDOM均发生了明显的光降解,且极低盐度明显加速了海菖蒲源CDOM的光降解速率,延缓了DOC的光降解,但各个盐度对海草凋落叶源CDOM光降解过程中有机物质组分（类蛋白质和类腐殖质）的影响并无明显差异。盐度为0时,海菖蒲凋落叶源溶解性有机氮（DON）的光矿化过程显著加速,26.44%的海菖蒲源DON发生了光矿化,转变为DIN,其中94.32%转变为NH4＋,而极低盐度对泰来草源DON光矿化的影响不明显。因此,极低盐度会影响不同海草种类来源CDOM的光降解,加快海菖蒲源DON光矿化过程,加速海草床CDOM和DON的转化过程。

英文摘要：

Seagrass leaf litter has been proved to be the main source of chromophoric dissolved organic matter（ CDOM） in seagrass beds and CDOM released from seagrass leaf litter is greatly influenced by salinity. According to the salinity range in Xincun Bay,Hainan,China,a salinity gradient（ 0,11,22,33） was set to study the effects of salinity on CDOM released by leaf litter of two types of seagrass（ Enhalus acoroides and Thalassia hemprichii）. The results showed that CDOM was rapidly degraded under ultraviolet-B in four salinity conditions,and significantly higher CDOM and lower DOC photodegradation rates of E. acoroides leaf litter were found under low salinity（ 0） than under the other three salinity levels. However,no significant difference in organic components of CDOM such as protein-like and humic-like substances was found during photodegradation for both seagrass species under these four salinity levels. The photodegradation of dissolved organic nitrogen（ DON） released by E. acoroides was intensely promoted under 0salinity. Especially,26.44% of DON was photo-degraded to dissolved inorganic nitrogen（ DIN）,of which 94.32% was converted to ammonium. However,no obvious effect of extremely low salinity was found on the photodegradation of DON released by T. hemprichii. Therefore,extremely lowsalinity would influence the photodegradation of CDOM and accelerate the conversion rate from DON to DIN released by E. acoroides,which may change carbon and organic nitrogen cycle in seagrass beds.