木榄幼苗对淹水胁迫的生长和生理反应

在搭建于广西英罗湾红树林外裸滩的试验平台上设置8个海面高程组,研究全日潮海区潮汐淹水胁迫对木榄(Bruguiera gymnorrhiza)幼苗的生长和生理影响.幼苗立地基质平面的海面高程为320～390 cm,相邻高程组相差10 cm,幼苗培养时间为1 a.结果表明:小高程和大高程处理均促进木榄幼苗茎高度的增长,中等高程则起抑制作用;中等高程组幼苗茎节数稍少;叶数、叶面积与叶保存率均随淹水程度加大而急剧下降;小高程生境对叶片叶绿素含量的促进作用较微弱,而大高程生境更有利于叶绿素含量上升;但较长时间的淹水胁迫使叶绿素a/b比值反而较高;小高程处理均促使叶片和根系中超氧物歧化酶(SOD)和过氧化物酶(POD)酶活性增强,同一高程组的木榄幼苗根系中超氧物歧化酶和过氧化物酶酶活性均高于叶片的数倍;较大高程生境更有利于木榄幼苗生物量累积,尤其是叶生物量,同时随着淹水程度的加大,新生器官中生物量分配比例由叶向茎转移;所有高程组均有一些幼苗死亡,海面高程越小幼苗存活率越低,由73.6%下降到35.0%.综合考虑,建议北部湾海区木榄胚轴造林的宜林临界线高程不低于当地平均海面以上21 cm.

Growth and physiological responses of Bruguiera gymnorrhiza seedlings to waterlogging stress

From September 2004 to September 2005, the effects of waterlogging on the seedlings growth and physiological characteristics of Bruguiera gymnorrhiza were studied in the diurnal tide region of Yingluo Bay in Guangxi. Eight tidal flat altitude (TFA) treatments were installed, with the surface plane of seedlings substrates ranged from 320 to 390 cm and a 10 cm difference between each other. The growth characteristics and some physiological parameters of the seedlings were measured, and the results showed that both the lower and the higher TFA treatments promoted the longitudinal development of stem significantly, while moderate TFA treatments did not. The seedlings in moderate TFA treatments had fewer knots on the stems. The leaf number, leaf area and leaf conservation rate presented congruously a rapid decline as the TFA fell. A slight promotion to the chlorophyll contents was found in lower TFA habitats, while a stronger promotion occurred in the higher ones. The Chl-a /Chl-b ratio in lower TFA treatments was higher than that under higher TFAs, while the SOD and POD activities in leaves and roots were both promoted significantly in lower TFAs. At the same TFA, the activities of SOD and POD in roots were several times higher than those in leaves. Higher TFA habitats were more beneficial to the biomass accumulation of the seedlings, especially for their leaves. The biomass partition tended to transfer from leaf to stem with increasing degree of waterlogging stress. Seedlings death occurred in all treatments, but the survival rate decreased from 73.6% to 35.0% as the TFA lowered. It was suggested that the critical tidal level for B. gymnorrhiza in terms of forestation with hypocotyls directly in Beibu Gulf region was 21 cm higher than the altitude of local mean sea level.