Vertical patterns of leaf physiology and biofilm characteristics for submerged macrophytes in a shallow subtropical lake

Abstract

Little is known about vertical patterns of leaf characteristics for submerged macrophytes in freshwater ecosystems. Here, after sampling Ceratophyllum demersum and Hydrilla verticillata in deep (3.8m) and shallow areas (1.0m) in a shallow subtropical lake, we cut the individuals into segments along the vertical direction, and measured leaf biofilm and physiology characteristics. In the deep area, leaf pigment concentrations showed declining trends with an increasing water depth, but the enzymatic specific activity of peroxidase (POD-ESA) was precisely the opposite. Moreover, the amount of attached biofilm matter and epiphyte biomass were greatest on leaves of upper middle segments, and lowest on bottom segments. In the shallow area, bottom leaves of C. demersum had more attached biofilm matter and epiphyte biomass, but the opposite was true for H. verticillata. Additionally, leaf chlorophyll-a concentration was higher on the bottom segments for H. verticillata, and C. demersum had a higher POD-ESA in bottom leaves. Our analysis found that vertical pattern of leaf physiology was closely related to light intensity, and biofilms played an auxiliary role. Our study highlighted vertical patterns of leaf biofilm and physiology for submerged macrophytes, and suggested that such patterns are generally species-specific, especially in shallow areas.