Characterization of dry weight and elements contents of biofilms attached on aquatic macrophytes and non-living substrates surface

As one of the most important interfaces in shallow lakes, the submerged macrophyte-water boundary layer plays an important role in structure, function and diversity maintenance and biogeochemical cycling of freshwater ecosystem. The stem and leaf surfaces of submerged macrophytes provide the accessible substrates surface area and available nutrients for periphyton, and therefore forms a special bio-water boundary layer. In this study, dry weight and carbon, nitrogen and phosphorus contents in epiphytic biofilms attached on leaves, stems and roots of aquatic macrophytes (Ceratophyllum demersum and Potamogeton pectinatus) and non-living substrates surface were investigated from four natural lakes for three months. The results showed that: 1) the dry weight of in epiphytic biofilms attached aquatic macrophytes surfaces was 79.36 —283.12 g·kg⁻¹ for Jinhu, 31.72—111.89 g·kg⁻¹ for Tushuguan, 50.07—150.33 g·kg⁻¹ for Nanshan and 51.02—219.61 g·kg⁻¹ for Bainiangzi park, respectively, which was significantly difference at four different sampling sites (P<0.05) and at three sampling times (P<0.05). Plant species and growing stages were the main biotic factors to affect the dry weight in epiphytic biofilms attached on aquatic macrophytes and non-living surface. In addition, the day weight was higher in Ceratophyllum demersum surface than in Potamogeton pectinatus surface, which was related to the differences in the morphology of these two species. The TN average content was 1.49, 4.75, 4.24 and 3.90 g·kg⁻¹; TOC average content was 20.59, 60.00, 48.47 and 97.58 g·kg⁻¹, respectively; TP average content was 0.09, 0.47, 0.42 and 0.49 g·kg⁻¹, respectively, on Jinghu, Tushuguan, Nanshan and Bainiangzi park, respectively. The difference of carbon, nitrogen and phosphorus contents on Potamogeton pectinatus and Ceratophyllum demersum surface might be effect by species differences, whereas, the differences of the same species may be affected by the physical and chemical factors as well as habitats and plant growth stage; The TN contents were higher on plant surface than in non-living substrates surface for Tushuguan, Nanshan and Bainiangzi park, respectively. In addition, no significant difference for TOC content were observed between aquatic plants and non-living substrates in Jinghu Lake, Nanshan and Bainiangzi park (P>0.05) and no significant difference for TP content were observed among four lakes (P>0.05). Compared with aquatic plants, non-living substrates mainly influence the element content and their ratio of the attachments by providing attachment carriers. Therefore, differences in the material, composition and morphology of non-living substrates may be the key factors affecting the content and composition of the attachments.