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<p>Periodic impoundment in reservoirs leads to vegetation decay and decomposition, which, in turn, affects nutrient release from sediment. The aim of this study is to investigate the nitrogen and phosphorus release characteristics of <i>Cynodon dactylon</i> (L.) Pers., a dominant plant species in the water-level fluctuation (WLF) zone of one of the world’s largest reservoirs, the Three Gorges Reservoir (TGR), China. A total of 288 live and dead plant samples were subjected to a 120 d submergence experiment at water depths of 0, 3, 6, 10, 20, and 30 m. The dry weights of the plants, as well as the total nitrogen (TN) and total phosphorous (TP) contents of the plant samples, were studied. The water environment and microbial structure and function were also analysed. The findings demonstrated that, in contrast to that of the dead vegetation, the dry weight of the live plants exhibited sustained growth throughout the early submergence period. However, the dead plants experienced continuous dry weight loss. The TN content in the live plants peaked at approximately 30 d (15 d at 30 m water depth) post-submergence, followed by a gradual decline, while significantly higher concentrations (<i>P</i> &lt; 0.05) were maintained than the preflooding levels after 120 d of submergence. However, the dead plants presented a gradual decrease in TN, with significant differences among the various water levels after 120 d. The TP content in the live plants first decreased but then increased, whereas in the dead plants it continuously decreased. Significant differences in TN and TP release were observed between the live and dead plants (<i>P</i> &lt; 0.05). Compared with that of the live plants, the decomposition of the dead plants resulted in significantly greater TN release (4.35 ± 0.59 g kg<sup>−1</sup>). Similarly, the dead plants presented tenfold greater TP release (1.02 ± 0.030 g kg<sup>−1</sup>) than the live plants (0.09 ± 0.063 g kg<sup>−1</sup>). The microbial communities, dominated by <i>Actinobacteria</i> (25.3%) and <i>Proteobacteria</i> (24.1%), were found to significantly influence nutrient release. Water environmental factors such as water depth, light intensity, dissolved oxygen, and specific conductivity affected mainly the nitrogen and phosphorus contents of the live plants. This research provides valuable insights into nutrient dynamics in the WLF zone of the TGR and highlights the differential contributions of live and dead plants to nutrient cycling processes.</p>

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Nitrogen and phosphorus release from a dominant plant in the water-level fluctuation zone of the Three Gorges Reservoir

  • 期刊论文

  • 发表日期：

    2025年7月12日

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  • Ying Liu,
  • Ziyan Lu,
  • Genghua Wu,
  • Defu Liu,
  • Henglin Xiao,
  • Hong Yang,
  • Heyun Wang,
  • Jinhong Feng

摘要

Periodic impoundment in reservoirs leads to vegetation decay and decomposition, which, in turn, affects nutrient release from sediment. The aim of this study is to investigate the nitrogen and phosphorus release characteristics of Cynodon dactylon (L.) Pers., a dominant plant species in the water-level fluctuation (WLF) zone of one of the world’s largest reservoirs, the Three Gorges Reservoir (TGR), China. A total of 288 live and dead plant samples were subjected to a 120 d submergence experiment at water depths of 0, 3, 6, 10, 20, and 30 m. The dry weights of the plants, as well as the total nitrogen (TN) and total phosphorous (TP) contents of the plant samples, were studied. The water environment and microbial structure and function were also analysed. The findings demonstrated that, in contrast to that of the dead vegetation, the dry weight of the live plants exhibited sustained growth throughout the early submergence period. However, the dead plants experienced continuous dry weight loss. The TN content in the live plants peaked at approximately 30 d (15 d at 30 m water depth) post-submergence, followed by a gradual decline, while significantly higher concentrations (P < 0.05) were maintained than the preflooding levels after 120 d of submergence. However, the dead plants presented a gradual decrease in TN, with significant differences among the various water levels after 120 d. The TP content in the live plants first decreased but then increased, whereas in the dead plants it continuously decreased. Significant differences in TN and TP release were observed between the live and dead plants (P < 0.05). Compared with that of the live plants, the decomposition of the dead plants resulted in significantly greater TN release (4.35 ± 0.59 g kg−1). Similarly, the dead plants presented tenfold greater TP release (1.02 ± 0.030 g kg−1) than the live plants (0.09 ± 0.063 g kg−1). The microbial communities, dominated by Actinobacteria (25.3%) and Proteobacteria (24.1%), were found to significantly influence nutrient release. Water environmental factors such as water depth, light intensity, dissolved oxygen, and specific conductivity affected mainly the nitrogen and phosphorus contents of the live plants. This research provides valuable insights into nutrient dynamics in the WLF zone of the TGR and highlights the differential contributions of live and dead plants to nutrient cycling processes.