Environmental effects on community productivity of aquatic macrophytes are mediated by species and functional composition

Abstract

Environmental variations are rapidly altering plant species and functional composition, which may have consequent influences on ecosystem functioning. We measured species and functional diversity of macrophyte community as well as environmental variables in 1,008 plots in 24 freshwater lakes across Yunnan-Guizhou plateau and Yangtze River in south China. We used generalized multilevel path models to test how the environmental effects on macrophytes productivity directly and indirectly through changes in species and functional diversity. We found distinct species and functional responses to the four groups of environmental variables:water quality, heterogeneity, climate, and topography. Macrophyte communities tended to be high richness and dominated by species with high-stem dry mass content and long flowering duration at eutrophic, heterogeneous, high altitude, or deepwater habitats.Submersed and annual species with high-specific leaf area dominated in heterogeneous and high altitude conditions, whereas species with high shoot and leaf dry mass content as well as thin stem and lamina dominated in heterogeneous and lowaltitude conditions. Functional dispersion (FDis) decreased in heterogeneous and high-altitude habitats and increased at deepwater. These changes in functional composition have subsequently significant influences on community productivity, involving the opposite pathways of positive effects of community-weighted mean (CWM) traits and negative effects of FDis, ultimately contributing to the observed invariable macrophytes productivity along the tested environmental gradients. Our results provide strong evidences that both species and functional composition mediate the cascading effects of environments on macrophytes productivity. K E Y W O R D Scommunity-weighted mean, functional diversity, functional traits, macrophytes, productivity

Local habitat is a strong determinant of spatial and temporal patterns of macrophyte diversity and composition in boreal lakes

“…Consistent with earlier studies our analyses revealed significant relationships between macrophyte species and trait assemblages and lake productivity (e.g. Alahuhta et al., 2018; Fu et al., 2019; Johnson et al., 2014; Viana et al., 2014). Shifts in macrophyte assemblages and biodiversity loss are often inversely related to an increase in phytoplankton, epiphytes and filamentous algae (Sand‐Jensen & Borum, 1991; Sand‐Jensen et al., 2008), that is, factors limiting incident light and nutrient availability, with highly productive lakes frequently characterised by only a few highly competitive tolerant species (Sayer et al., 1999).…”

“…Although macrophyte‐based indices are primarily used for assessing eutrophication (Kolada et al., 2014; Penning, Dudley et al., 2008; Penning, Mjelde et al., 2008), other environmental pressures have been assessed such as water regulation and drawdown (Mjelde et al., 2013; Rørslett, 1991), catchment ditching (Ecke, 2009), acidification (Baastrup‐Spohr et al., 2017; Crowder, 1991), heavy metals (Bonanno & Giudice, 2010; Crowder, 1991) and biological invasions (Strayer, 2010). Macrophyte assemblages have been shown to correlate strongly with variables related to productivity (Alahuhta et al., 2018; Fu et al., 2019), ecosystem size and depth (Lacoul & Freedman, 2006; Middelboe & Markager, 1997; Rørslett, 1991), light conditions (Jeppesen et al., 2000) and alkalinity (Vestergaard & Sand‐Jensen, 2000) as well as other biological assemblages (Johnson & Hering, 2010; Kelly et al., 2016). A prerequisite of developing biological response metrics is understanding not only species’ responses to disturbance but also responses to the natural environmental gradients underpinning patterns in biodiversity.…”