Abstract: The nectar compositions and their ecological functions have become one of the most active and promising areas among the recent pollination biology studies. The nectar ecological functions represent the coupled ecological significance of all nectar compounds in the context of plant-pollinator interactions. Currently, the nectar compounds are considered to be a tradeoff consequence of selective pressures on plant evolution in attracting pollinators, deterring nectar robbers and protecting nectar from microbial infestation for enhancing plant reproductive fitness. In this paper, we presented a review of the recent advances in the studies of chemical compounds that have been found in nectar rest on their ecological functions. The ecological functions of nectar sugars, amino acids, proteins, inorganic ions, lipids, phenols, alkaloids, and terpenoids were respectively proposed here. We further summarized the origins of nectar components and their differences among plants and emphasized the importance of nectar chemical characteristics research in the studies of pollinator guilds and pollination syndrome. In addition, for future research, we suggested that 1) molecular and ecological methods should be combined to elucidate the molecular mechanism of nectar production and thus to reveal the ecological adaptation mechanisms underlying the plant regulation on nectar composition and 2) experiments at the scale of the community and high taxonomic levels should be carried out to study nectar constituents combined with functions, to compare the variation of the nectar components for co-flowering species and thus to explore the interactive relationships among plants and their specialist or generalized pollinator groups, and to illustrate the potential mechanism of nectar chemical composition effect on pollination networks in plant community.

Key words: ecological quality,