里塘河亚洲苦草分布特点及光照因子影响分析

Distribution properties and effects of light intensity on Vallisneria natans in Litang River

2012年对上海市临港新城里塘河水体状况和亚洲苦草（Vallisneria natans）分布特点进行了调查,并研究了不同光照强度对亚洲苦草生长及光合放氧速率的影响。调查结果表明,里塘河透明度为80~100 cm,苦草生物量按生长在水深20~30 cm、30~60 cm、60~90 cm、90~120 cm 4个范围计算,随水深增加先增大后减小,其中60~90 cm水深范围内亚洲苦草生物量最大。苦草密度与水深成负相关,而平均叶长与水深呈正相关,河道近岸苦草密集,中间最深处无水草生存。室内进一步研究表明,平均每株生物量、分蘖数、平均根长、光合放氧速率均随着光照强度降低而降低（P〈0.01）,10μmol/（m^2·s）为临界光照强度,这时亚洲苦草生物量开始出现负增长,其光合放氧速率为10.52μmol/（g·h）,仅为80μmol/（m^2·s）光照强度组的22.79%。该研究表明河道苦草分布深度与透明度深度相一致,进一步揭示了低光条件下苦草群落难以繁殖扩散的原因。

Water quality and distribution of Vallisneria natans in the Litang River in Shanghai were investigated in 2012. We also studied the effects of different light intensity on the growth and photosynthetic oxygen evolution rate of V. natans. Results showed that the transparency of Litang River was 80-100 cm,and when the water depth increases,the V. natans biomass firstly increased and then decreased,and the turning point is at the depth of 60-90 cm in the four experiment groups,which showed the largest biomass. The density of V. natans was negatively correlated with the depth of water while the average leaf length of V. natans was positively correlated. Investigation showed that plenty of V. natans was found in offshore area of the river,but no V. natans was found in the center of the river. Experiment in lab circumstances showed that plant biomass,tiller number,average root length and photosynthetic oxygen evolution rate of V. natans were all reduced with the decrease of the light intensity（ P〈0. 01）. The critical light intensity of V. natans was 10μmol /（ m^2·s）,and at that point,the photosynthetic oxygen evolution rate was 10. 52 μmol/（ g·h）,and the V. natans biomass started to decrease. This study showed that the V. natans distribution at different depth in Litang River was consistent with transparency. This study further revealed the reason why V. natans communities were difficult to reproduce and spread in low light conditions.