Ecological Stoichiometry Characteristic of Phytoplankton in Mountain Stream

This research investigated the phytoplankton ecological stoichiometry characteristics and the balance of the relationship between elements in a mountain river in a cold region. The samples of phytoplankton of four seasons were collected in May 2020, August 2020, November 2020, and February 2021 from the Taizicheng River in Chongli, Zhangjiakou City, China. We determined the contents of carbon (C), nitrogen (N), phosphorus (P), sulfur (S), hydrogen (H), and iron (Fe), and analyzed their ecological stoichiometric characteristics and correlation. Our results showed that the contents of C, N, P, S, H, and Fe in phytoplankton were 82.14 ± 32.12 g/kg, 9.22 ± 3.5 g/kg, 1.46 ± 0.55 g/kg, 1.96 ± 0.86 g/kg, 2.36 ± 1.36 g/kg, and 12.64 ± 10.57 g/kg, respectively. Generally, the contents of C, N, and P were relatively stable, while the contents of S, H, and Fe fluctuated greatly, and the coefficient of variation of Fe content was as high as 83.62%. The elemental molar composition of phytoplankton in the Taizicheng River is C156.00N15.41S1.54H51.17Fe5.10P, which showed a significant difference compared with the classical Redfield ratio C106N16P. The high proportion of element C indicated that phytoplankton in the Taizicheng River have a high demand for C and a strong ability to consolidate C. The ratio of N:P was consistent with previous research results. The N:P ratio of phytoplankton in the Taizicheng River was 15.41, suggesting that the growth of phytoplankton in the Taizicheng River was restricted by both N and P. The contents of C, N, and P were positively correlated, while there was no significant correlation among S, H, and Fe. C:P was significantly positively correlated with C:N and N:P, while there were no strong correlations between C:N and C:P, as well as H:S, Fe:S, and H:Fe, indicating that the coupling correlation between phytoplankton elements was different and C, N, and P were highly correlated as important phytoplankton nutrient elements. This study contributes to our understanding of the phytoplankton ecological stoichiometry characteristics and the limiting factors of nutrients in a mountain river and provides a scientific basis for further ecological conservation and management efforts.