Trade-offs in plant responses to herbivory influence trophic routes of production in a freshwater wetland

Abstract

Responses of aquatic macrophytes to leaf herbivory may differ from those documented for terrestrial plants, in part, because the potential to maximize growth following herbivory may be limited by the stress of being rooted in flooded, anaerobic sediments. Herbivory on aquatic macrophytes may have ecosystem consequences by altering the allocation of nutrients and production of biomass within individual plants and changing the quality and quantity of aboveground biomass available to consumers or decomposers. To test the effects of leaf herbivory on plant growth and production, herbivory of a dominant macrophyte, Nymphaea odorata, by chrysomelid beetles and crambid moths was controlled during a 2-year field experiment. Plants exposed to herbivory maintained, or tended to increase, biomass and aboveground net primary production relative to controls, which resulted in 1.5 times more aboveground primary production entering the detrital pathway of the wetland. In a complementary greenhouse experiment, the effects of simulated leaf herbivory on total plant responses, including biomass and nutrient allocation, were investigated. Plants in the greenhouse responded to moderate herbivory by maintaining aboveground biomass relative to controls, but this response occurred at the expense of belowground growth. Results of these studies suggest that N. odorata may tolerate moderate levels of herbivory by reallocating biomass and resources aboveground, which in turn influences the quantity, quality and fate of organic matter available to herbivores and decomposers.

Recent advances in wetland degradation research

“…(1) 生物学机理 在湿地退化过程中,人为活动主要通过改变原生湿地植物种间关系 [35] 、导致外来种入侵 [78] 、减少动物和 土壤微生物种类和数量 [38] 、改变生态系统营养结构 [79] 等方式导致湿地生态系统退化。 其中外来种的他感作 用在当前研究中受到较多关注。 Gopal [80] 曾归纳水生生物群落中的几种主要的作用机制,指出他感作用、种 间竞争是其中最重要的两种机制( 图 1) 。 在滨海湿地生态系统,入侵植物互花米草( Spartina alterniflora) 能够 分泌他感物质影响其他植物生长,从而改变群落结构、功能,导致湿地退化 [81鄄82] 。 Jarchow [83] 的研究表明北美 的外来种狭叶香蒲( Typha angustifolia) 也具有强烈的他感作用,降低本地种 Bolboschoenus fluviatilis ( 块茎藨草 属一种) 的叶长、根、茎和总生物量。 目前已发现在湿地生态系统中他感作用广泛存在。 图 1摇 水生生物群落主要相互作用的概念图 [80] 摇 Fig. 1摇 Conceptual diagram of major interactions in aquatic communities [80] 摇 摇 A: 他感作用;C: 竞争作用;H: 食草作用…”