Elucidation of gas diffusion and transport mechanisms in mangroves adapted to high salinity and anaerobic soil conditions

为了有效地进行红树林造林，了解人工林幼苗在环境因素影响下的生长特征是非常重要的。一些红树林物种的幼苗具有发育良好的下胚轴。幼苗的下胚轴在其生长早期起着重要的作用。本研究以6 ~ 12月龄的裸木和茎柱根hora幼苗为研究材料，研究了抑制下胚轴气体交换对下胚轴氧浓度和根叶电导的影响。植物受到四种处理。每个处理有3-5个重复植株。其中一组保持生长条件作为对照。在其他三种处理中，下胚轴要么在表面涂上硅腻子，屏蔽阳光，要么同时涂上腻子并屏蔽阳光。下胚轴和根的氧浓度分别为19.2%和12.7%。施腻子后根部氧浓度降至3.1%，施腻子加屏蔽后降至2.5%。在光合光子密度为500 ~ 1500□mol m^<-2> s^<-1>的对照条件下，裸子叶导度为0.59 cm s^<-1>。涂腻子、屏蔽、涂腻子和屏蔽后，电导率分别降至0.16 cm s^<-1>、0.46 cm s^<-1>和0.12 cm s^<-1>。涂腻子对下胚轴、根部氧浓度和叶片电导率的降低比屏蔽更显著。在相同的处理条件下，柱花草表现出与裸子根相似的趋势。因此，长时间浸没和遮蔽下胚轴可能会抑制叶片中的气体交换。

In order to carry out afforestation of mangroves efficiently, it is important to understand the growth characteristics of young seedlings as affected by environmental elements at plantation sites. Young seedlings of some mangrove species have well developed hypocotyls. The hypocotyls of the seedlings would have important role for their growth in an early growth stage. In the present study, we examined the effect of inhibition of gas exchange in the hypocotyls on oxygen concentrations in the hypocotyls and the roots and leaf conductance, using 6-12 months old seedlings of Bruguiera gymnorrhiza and Rhizophora stylosa. Plants were subjected to four treatments. There were 3-5 replicate plants per treatment. One group remained in the growing conditions as a control. In the other three treatments, the hypocotyls were either applied by silicon putty on the surfaces, shielded from sunlight or both applied putty and shielded. The oxygen concentrations were 19.2% and 12.7% in the hypocotyls and the roots, respectively, of B.gymnorrhiza. Oxygen concentration in the roots decreased to 3.1% with applying putty, and to 2.5% with applying putty and shielding. The leaf conductance of B.gymnorrhiza was 0.59 cm s^<-1> in the control at photosynthetic photon flux density of 500 to 1500 □mol m^<-2> s^<-1>. The conductance decreased to 0.16 cm s^<-1>, 0.46 cm s^<-1>, and 0.12 cm s^<-1> with applying putty, shielding, and applying putty and shielding, respectively. Decreases of oxygen concentrations in the hypocotyls and the roots and the leaf conductance were more remarkable with applying putty than that with shielding. R.stylosa showed the similar tendency to B.gymnorrhiza as affected by the same treatment. Therefore, extended submergence and shielding of the hypocotyls may inhibit gas exchange in leaves.