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，重要的是要了解幼苗生长特性的影响，在种植园地点的环境因素。有些红树林的幼苗具有发育良好的下胚轴。幼苗的下胚轴在生长早期对幼苗的生长起着重要的作用。在本研究中，我们研究了抑制下胚轴中的气体交换对下胚轴中的氧浓度以及根和叶的电导率的影响，使用6-12个月龄的木榄和红海榄幼苗。对植物进行四次处理。每个处理有3-5个重复植物。一组保持在生长条件下作为对照。在其他三种处理中，下胚轴或者在表面上施加硅腻子，遮蔽阳光，或者既施加腻子又遮蔽。下胚轴和根中的氧浓度分别为19.2%和12.7%，B. gymnorrhiza。根中氧浓度在涂腻子时下降到3.1%，在涂腻子和屏蔽时下降到2.5%。在<-1>500 ~ 1500 □mol·m ~（-1）·s ~（-1）的光量子通量密度下，对照组B.gymnorrhiza的叶片电导率为0.59 cm·<-2>s ~（-1）<-1>。施加腻子、屏蔽以及施加腻子和屏蔽时，电导率分别降至0.16 cm s^<-1>、0.46 cm s^<-1>和0.12 cm s^<-1>。下胚轴和根的氧浓度和叶电导的下降，涂腻子比屏蔽更显着。在相同的处理条件下，红海榄表现出与B.gymnorrhiza相似的趋势。因此，延长淹没和屏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.