海草土壤种子库:特征、影响因素、研究方法及其在受损海草场恢复中的作用

Characteristics,influence factors,research methods of seagrass seed bank and its significance in seagrass bed recovery

海草的土壤种子库具有巨大的时空异质性,不同种类密度差别可达5个数量级,同一种植被的土壤种子库,在不同环境、不同阶段亦相差甚大。种子具有休眠现象的海草可形成持久种子库(种子寿命≥1 a),例如喜盐草属(Halophila)、针叶草属(Syringodium)、川蔓草属(Ruppia)和丝粉草属(Cymodocea),或短暂种子库(种子寿命<1 a),例如鳗草属(Zostera)和虾形草属(Phyllospadix)。种子没有休眠现象,例如海菖蒲属(Enhalus)和泰来草属(Thalassia),或具有胎生现象的海草,例如全楔草属(Thalassodendron)和根枝草属(Amphibolis),则不形成土壤种子库。植被特性、环境条件、动物行为等影响海草的土壤种子库。海草土壤种子库密度的研究方法可分为直接计数法和幼苗萌发法两种,采用何种方法取决于种子的大小以及破除休眠的可控性。土壤种子库尤其是持久种子库是一年生海草场或受到较大干扰海草场恢复的关键。我国绝大部分的海草场面临巨大的人为威胁,且不少海草场由一年生海草组成,因此,保护好这些海草场的土壤种子库至关重要。

The seed bank of seagrasses shows highly temporal and spatial heterogeneity and the variability can be as high as five orders of magnitude among seagrass species,ranging from 10^(0) to 10^(5).The soil seed bank of same seagrass species is also highly variable across habitats and seasons.Only those seagrass species with dormant seeds can form persistent seed bank(seed longevity≥1 a)such as Halophila,Syringodium,Ruppia and Cymodocea,or transient seed bank(seed longevity<1 a)such as Zostera and Phyllospadix;while those seagrasses without distinct seed-dormancy(Enhalus and Thalassia),and viviparous seagrasses(Thalassodendron and Amphibolis)can not form soil seed bank.Vegetation characteristics,environmental conditions and marine animal behaviors,etc.,can affect the seagrass seed bank.Two general methods,direct counting method and germination method(enumeration of germinated seedlings)are applied for estimating the size of the seed bank.The choice of method depends upon seed size and the ease with which dormancy can be broken.Maintaining the existing soil seed bank,especially the persistent seed bank,is crucial for the recovery of disturbed seagrasses,especially for those annual forms.Since most of seagrass meadows in China face intensive anthropogenic threats and many of them are composed of annual seagrasses,it is pivotal to conserve their seed bank for the recovery of these disturbed meadows.