对准噶尔荒漠中24种十字花科短命植物的扩散体特征与扩散对策的观测结果表明:种间果实和种子的形态各异,角果开裂与否与其木质化程度有关。木质化程度较高的角果不开裂。其中长角果以果节为扩散单元自体扩散。而短角果有两种扩散单元,以果实为扩散单元的无辅助扩散结构或具翅或绵毛,分别进行自体或风媒扩散;以果序的一段为扩散单元的果实具坚硬呈勾状的喙,通过果序梗断裂或附在动物体表散布,兼具自体扩散和动物体外传播的二重性。木质化程度较低的角果开裂,以种子为单元扩散。其中微尘状种子无辅助扩散结构,在果皮开裂时产生的张力或风力的作用下散布;粘液种子以水媒为主,兼具风媒和动物传播的特点;粘液和翅并存的种子具有风媒和水媒扩散的二重性。果翅等辅助扩散结构有利于长距离散布,绵毛及种皮粘液使果实或种子与地表能更好地粘附,木质化结构及种皮粘液还具有保水和保护作用。从扩散的时��特征看,24种植物在扩散持续时间上有集中扩散和持续扩散两种方式,前者避免了种子干旱失水和被捕食,属逃逸对策;后者形成空气种子库逐批扩散,属保护对策。从空间上,异果芥(Diptychocarpus strictus)果序上、下部果实的开裂方式与时间、种子形态完全不同,导致其扩散时间与距离不同;离子芥(Chorispora tenella)等类群果实不同部位的果节非同步脱落以及爪花芥(Oreoloma sulfureum)果实上、下部木质化程度及开裂方式不同,导致其果节或种子的扩散时间不同。以上这些特征对于它们在荒漠环境中成功地扩散、定居,抵御干旱、逃避捕食,避免同胞种子间的竞争、保障物种延续并扩大种群等,具有重要的生态学意义。

Aims Members of Brassicaceae are one of the most important groups of ephemeral plants in the Junggar Basin and serve many ecological roles in the desert. However, studies on dispersal syndromes of Brassicaceae, especially the ephemerals, are rare. This study addresses the following questions: 1) what are the dispersal unit and the dispersal mode of these species, 2) what are the spatio-temporal patterns of dispersal of these species and 3) how are these characters adaptive to the arid desert environment?

Methods The study was conducted on 24 ephemeral species of Brassicaceae from June to October 2005 and 2006. We observed and recorded 1) morphology of the fruits and seeds, 2) dehiscence mode of the fruit, type of dispersal unit and accessory structures and 3) dispersal mode and its duration in natural habitats.

Important findings The dehiscence mode of fruit depends on degree of lignification. There are three types of dispersal units of the species whose pods cannot dehisce. Species whose dispersal unit is the fruit node are autochorous. Species in which dispersal occurs by the whole fruit have silicula. Some do not have accessory structures to dispersal, and the dispersal mode is autochorous. Others have wings or hairs and disperse by wind. Species whose dispersal unit is a section of the infructescence also have silicula with a hard and hook-like beak that can attach to the coat of animals. Species with pods that dehisce easily only disperse by seeds. Their seeds have three types. One type is tiny without any accessory structures for dispersal, and seeds are dispersed by wind. Seeds in the second type have wings, and their modes of dispersal are diverse, but the main one is hydrochory. Seeds in the third type have wings and mucilage and are dispersed by anemochory and hydrochory. There are two types of dispersal patterns, depending on duration of dispersal. The first type is the short-term dispersal pattern in which all dispersal units on the plant are dispersed from the mother plant mainly in June and July. In the second type, dispersal units are shed from the mother plant from June to October or even the next spring. In this pattern, pods in the upper and lower positions of one infructescence differ in morphology, degree of lignification, kind of dispersal unit, dispersal time and dispersal mode.