Host-mediated effects on the reproductive phenological asynchrony of a generalist mistletoe in China

一种泛性桑寄生植物繁殖物候异步性的寄主介导效应

Host-mediated effects on hemiparasitic mistletoes were hypothesized to contribute to mistletoes reproductive phenological asynchrony,thus providing a longer period of food supply to its mutualistic pollinators and dispersers.However,studies with empirical data interrogating this hypothesis are lacking.Weekly monitoring of flowering and fruiting patterns on a generalist mistletoe Dendrophthoe pentandra(Loranthaceae)was conducted for two consecutive years in tropical Xishuangbanna,Southwest China.We examined whether flowering and fruiting patterns were seasonal,quantified the degree of stagger within D.pentandra populations and determined the factors influencing the first flowering date(FFD)of D.pentandra.Furthermore,the effect of change in the number of host species on reproductive phenological asynchrony of mistletoe was examined.We found that(i)both flowering and fruiting exhibited unimodal peaks in the two consecutive years of the study;(ii)the FFD was significantly influenced by crown area of mistletoe and light,such that clump with larger crown and more light exposure had an earlier FFD and longer flowering and fruiting durations;(iii)different host species had a significant impact on the phenology of mistletoes.However,contrary to our hypothesis,the number of host species did not significantly change the asynchrony of reproductive phenology of mistletoe.Therefore,these results suggest that alternative hypotheses are needed to interpret the ecological significance of the number of host species and phenological asynchrony of generalist mistletoes.

寄主介导效应被认为会导致半寄生性的桑寄生植物的繁殖物候异步性,并由此为与桑寄生植物互惠共生的传粉者和种子散布者提供更长时间的食物资源供应,但目前关于此方面的研究还缺乏相关的实证数据。本研究以广泛分布于中国西南西双版纳地区的一种泛性桑寄生科植物五蕊寄生(Dendrophthoe pentandra)为材料,每周监测其开花、结果物候,检测了其开花和结果物候是否呈季节性格局,量化了五蕊寄生繁殖物候的异步程度,并检测了影响该植物始花期早晚的因素。最后,本研究还检验了五蕊寄生繁殖物候的异步性随寄主种类数量变化的效应。研究结果表明:(i)在连续两年的物候观测中五蕊寄生的花期和果期都呈单峰分布格局;(ii)始花期显著受到植物大小和光照强度的影响,即冠幅越大和受光程度越高的植物个体有更早的始花期和更长的花期和果期;(iii)不同的寄主种类对五蕊寄生的繁殖物候有显著的影响,但与假设相反的是,随着寄主种类数量的增加,五蕊寄生繁殖物候的异步性没有显著提高。这项研究表明,在解释泛性桑寄生植物的繁殖物候异步性及寄主种类的数量对其影响的生态学意义还需进行更深入的探究。