The impacts of submergence duration and salinity on the germination and growth process of Aegiceras corniculatum radicles

Tide level and salinity are crucial environmental factors that significantly impact the growth and development of Aegiceras corniculatum seedlings and to a certain extent, determine if their embryos could land successfully and develop into seedling rapidly. In this paper, the process of A. corniculatum embryos developing to seedings was observed by the indoor controlled experiments, during which, the effects of salinity, submergence duration, as well as the interaction between salinity and submergence duration on the germination and growth of radicles were discussed. The results showed that: (1) the embryos of the A. corniculatum were unable to sprout in the treatment group that the embryos were soaked completely for 24 h/d in a simulated lower low tidal level of flooded environment. For the treatment group that the embryos were soaked completely for 6 h/d and the radicles soaked for 18 h/d in a simulated low to medium tidal level of flooded environment, the highest mean rooting rates and the longest radicle of the embryos were produced. In the treatment group that the base of embryos were soaked in a simulated higher high tide flooded environment, the rooting rates and mean rooting rates of embryos were the lowest, accompanied by the least quantities of radicles. However, in the treatment group where the vermiculites were shallowly inserted into the bottom, which simulated a scene that the base of embryo was immersed within the tidal environment, it was found that the radicle germination was the slowest with the highest rooting rates, and the radicles were the shortest, along with the largest quantities. (2) In the salinity environment of 0, the radicles were the longest after a 11 days cultivation. In the salinity environment of 10, highest levels in both the length and quantities of radicles were observed in the first 13 days of embryo culture. In contrast, the rooting rate and the mean rooting rate of the embryos, as well as the length and quantity of radicle were significantly smaller in the salinity environment of 20, which indicated the germination and growth of radicle were inhibited in such salinity environment. (3) The interaction between submergence duration and salinity had a significant impact on the growth of the radicles of A. corniculatum. If both the submergence duration and salinity were within the tolerance ranges of the radicles of A. corniculatum, its embryos could still sprout normally under the stresses of different combination of submergence duration and salinity. Hence, the optimal way to artificially cultivatethe A. corniculatum seedlings, was that the embryo was completely soaked for 6 h/d and the radicle was soaked for 18 h/d in the salinity environment of 10. The study can provide some theoretical basis for the artificial cultivation and protection of A. corniculatum seedlings in the intertidal zone.