Abstract: Deep lakes experience alternate oxidation and reduction environment, which mayaffect the biogeochemical processes of nitrogen. Lake sediments generally have a unique reduction environment with complicated biogeochemical processes of nitrogen. In the present study, vertical sediments were collected from a typical plateau deep lake, Baihua Lake, during summer stratification. The concentration of nitrogenous species in pore water, watersoluble, adsorptionsoluble, and particle organic nitrogen (PON) with δ¹⁵NPON in the different depths of sediments were analyzed. The results showed that the concentration of total nitrogen (TN) in the pore water,ranging from 6.9 to 42.8 mg·L^-1, was mainly composed of NH₄⁺-N, ranging from 6.6 to 25.6 mg·L^-1, and dissolved organic nitrogen. The concentrations of nitrate and nitrite were underdetection line, indicating that the nitrate was used by denitrification or the potential dissimilatory reduction. The concentration of adsorptionsoluble NH₄⁺-N was higher than that of watersoluble NH₄⁺-N. The concentration of PON in the sediment ranged from 0.22% to 0.60%. Meanwhile, its variation tendency was well fit to the exponential decay pattern, suggesting that the variation of PON concentration in the sediment may be due to the diagenetic effect and mineralization. The δ¹⁵NPON value above 31 cm depth decreased with depth, ranging from 3.4‰ to 10.0‰ and with an average of 6.4‰. It showed a more decrease tendency above 10 cm depth, which may be caused by the microbial degradation activity and the water exchange between pore water and lake water. The trend of δ¹⁵NPON value below 31 cm depth was opposite to that of the surface, which may be the result of diagenesis at early stage. TN in pore water had higher δ¹⁵N value than did watersoluble and adsorptionsoluble N. TN in watersoluble and adsorptionsoluble N had similar δ¹⁵N value, which was higher than the δ¹⁵NPON. The results suggested that the increases of NH₄⁺-N concentration in pore water may be related to the dissimilatory reduction process.

Key words: dripping, Verticillium wilt control effect, high-throughput sequencing, cotton, biological agent, soil microorganism