球状棕囊藻的形态结构、生活史及生态意义研究进展

Morphology, life cycle and ecological characteristics of Phaeocystis globosa

球状棕囊藻生活史独特，在两种完全不同的生活状态——游离单细胞和粘液质的囊体之间相互转换。生活史中共出现4种不同类型的单细胞，存在有性和无性两种生殖方式。不同的细胞能够适应不同的环境，占据不同的生态位，有利于棕囊藻细胞的生长。球状棕囊藻的囊体直径最大可达几个厘米，外被坚韧、紧密并且具有弹性，为内部的单细胞提供了一个良好的栖息和保护场所，并且储存着能量可供细胞在营养盐限制条件下继续生长。由于囊体粒径较大，浮游动物难以摄食，并且有效的抵御了细菌和病毒的侵蚀，从而降低了棕囊藻的死亡率。与其它浮游植物相比，球状棕囊藻的竞争策略更加优越，提高了球状棕囊藻在海洋生态系统中的竞争能力。

The transitions between colonies and solitary cells are considered to be responsible for the success of Phaeocystis in marine systems and for the subsequent changes in ecological and biogeochemical properties. Four morphotypes of single cells exist： diploid colonial cells, diploid flagellates, and two types of haploid flagellates. The co-existence of different morphotypes, two ploidy levels related to phase changes, and the ability of both haploid and diploid stages to divide mitotically, support the existence of a haploid-diploid life cycle ofP. globosa. The occurrence of haploid-diploid life cycle is generally considered as an evolutionary adaptation to an environment that is seasonally variable or contains two different niches. The colonies are surrounded by a thin yet mechanically very strong skin. Diameter of colonies may reach 30 mm. The colony skin and big size apparently confer protection against, or at least reduce losses to, smaller zooplankton grazers and perhaps viruses. P. globosa utilizes the colony to offer the refuge from biological attack and to contain the nutrition for the growth of single cells and colonies. The life cycle alternations and the characteristics of the colony permit P. globosa to out-compete other phytoplankton lacking a functionally comparable gelatinous house in marine ecosystem.