Characteristics of the elemental stoichiometry of submerged macrophytes and their relationships with environments in Honghu Lake (China)

Ecological stoichiometry is the study of the balance of energy and elements in ecological interactions. We investigate 18 representative sampling sites in Honghu Lake (China) here to compare the elemental stoichiometry of submerged macrophytes and the corresponding environments in different parts of a large lake. We hypothesized that differences in elemental concentrations of water and sediments between the western and eastern parts of Honghu Lake can cause significant differences in the elemental stoichiometry of submerged macrophytes between the western and eastern parts. At the species level, significant differences in tissue C, C:N and C:P ratios of Potamogeton pectinatus and Myriophyllum spicatum are found between the western and eastern parts of Honghu Lake. Significant differences in the tissue N of P. pectinatus are found between the two parts of the lake, whereas no significant difference in tissue P of submerged macrophyte species is found between the two parts. A markedly higher tissue C and C:P is found in the western part of the lake compared with that in the eastern part. Pearson correlation analysis showed the significantly positive correlation between tissue C:P and sediment N (r = 0.76, p < 0.01), as well tissue N:P and sediment N (r = 0.86, p < 0.01), which suggest that sediment N is closely related with the elemental stoichiometry of submerged macrophytes in Honghu Lake. In addition, the submerged macrophytes had significant effects on sediment N and sediment N:P at the whole-lake level. Based on these results, we successfully tested our hypothesis, and conclude that the elemental stoichiometry of submerged macrophytes can vary spatially within lakes, which is probably the result of differences in sediment N availability.