花蜜微生物及其生态功能研究进展

花蜜是虫媒植物提供给传粉者最有效的报酬,对花蜜特征介导的植物-传粉者相互关系的研究已成为当今传粉生物学研究中最活跃的领域之一。开花植物分泌的原始花蜜是无菌的,不过一些微生物可经由空气传播至花蜜或(和)通过与传粉者的喙接触而聚集于花蜜中,并利用花蜜中的营养物质进行快速繁殖。花蜜的高渗透压环境导致花蜜中微生物(酵母菌,细菌)的物种多样性相对较低。此外,某些生物(传粉者组成,微生物间的竞争)与非生物因素(渗透压,糖组成,次生代谢物质,抗菌化合物,可利用氮源,温度,pH)也可影响花蜜中微生物群落的形成。花蜜中微生物的代谢活动能够改变花蜜物理(温度,粘度)与化学(pH,H_2O_2含量,糖组成和浓度,氨基酸组分和浓度,以及气味)特性,进而影响传粉者的访花行为与植物的繁殖适合度。因而,对花蜜中微生物及其生态功能的研究近年来颇受传粉生物学家的关注。在总结已发表研究成果的基础上,提出今后的研究有必要结合分子生物学与化学分析技术,以进一步揭示影响花蜜中微生物群落的潜在因素的作用机制,同时对花蜜微生物改变花蜜的物理、化学特性及植物-传粉者之间相互作用的可能原因进行更详尽的阐释,特别是对花蜜微生物在生态系统中所发挥的生态功能进行进一步的研究与认识。

Nectar-dwelling microorganisms and their ecological functions

Floral nectar,a sweet, aqueous secretion that consists mainly of sugars and to a lesser extent amino acids, is an effective reward that entomophilous plants could provide for their pollinators. Plant-pollinator relationships mediated by nectar characteristics have been recently studied in pollination biology. Floral nectar is initially sterile, but some yeasts and bacterial species survive in floral nectar when they have been dispersed into nectar via air or by flower-visiting insects such as pollinators. The identification of microorganisms in floral nectar from broad-scale surveys has shown that nectar yeasts are widespread and occur in a wide range of habitats. No such surveys are currently available for bacteria, but limited studies suggest that bacteria may also be widespread in nectar. However, high sugar content and consequentially low water activity that characterize the nectar of many plant species limit the number of microbial species that are capable of surviving and proliferating in the harsh environment of nectar, leading to species-poor communities with one or a few culturable species per nectar sample. Other factors affecting nectar-dwelling microorganism communities are nitrogen availability, pH, sugar composition, temperature and the presence of secondary or antimicrobial compounds. The presence of yeasts and bacteria in nectar decreased sugar concentrations and altered sugar ratios. Besides, the metabolic activity of nectar-dwelling microorganisms affected other floral attractive traits, including temperature, scent and amino acid content. In some cases, changes in physical and chemical properties of nectar affected on pollinator behavior and as a result on plant reproductive success. Therefore, nectar-dwelling microorganisms and their ecological functions are of great interests among pollination biologists. In the future, molecular and chemical analysis technologies should be combined to further reveal the mechanisms of potential factors that might affect the shaping of nectar-dwelling microorganism community, to fully elucidate the possible mechanisms that nectar-dwelling microorganisms alter nectar physico-chemical characteristics and the plant-pollinator relationships, and to further understand the ecological roles that nectar-dwelling microorganisms might play in different ecosystems.