Responses of growth and Chlorophyll photosynthetic fluorescence characteristics of Navicula cryptocephala to different nitrogen in Danjiangkou Reservoir

ZHENG Chuankun; LIU Xiaozhen; LI Weiguo; HE Yuxiao; ZHAO Tongqian

doi:10.13984/j.cnki.cn37-1141.2025.01.010

Abstract：A strain of benthic algae was isolated from the sediment samples collected in Danjiangkou Reservoir using dilution separation and small droplet separation methods.Based on morphological ob-servation and homologous analysis of 18S rDNA,LSU rDNA and rbcL sequences,the strain of diatom SG0529 obtained from Danjiangkou Reservoir was identified as Navicula cryptocephala.Using sodium nitrate,ammonium chloride and urea as nitrogen sources,the change characteristics of the growth and chlorophyll fluorescence parameters(Fv/Fm,a,Ik,ETRmax)of N.cryptocephala under different nitrogen conditions were analyzed.The results showed that the strain of N.cryptocephala grew nor-mally in sodium nitrate,ammonium chloride and urea medium,but the responses to different nitrogen forms were quite different.In sodium nitrate and urea medium,the specific growth rate and the cell density of N.cryptocephala increased with increment of nitrogen concentration.Under ammonium chloride culture condition,the growth rate of N.cryptocephala increased firstly and then reduced as nitrogen concentration increased in culture medium.With the increase of sodium nitrate and urea con-centration,the photosynthesis performance of N.cryptocephala increased,and the high concentration of ammonium chloride condition inhibited its photosynthesis reaction,indicating that increasing the concentration of nitrogen within a certain range is beneficial to the growth of N.cryptocephala,im-proving its photochemical reaction,and high concentration of ammonium nitrogen inhibited its growth and photosynthesis reaction.Compared with ammonia and urea,nitrate was more able to promote the growth of N.cryptocephala.Under the condition of nitro nitrogen culture,the maximum cell density and growth rate of N.cryptocephala are optimal.In addition,N.cryptocephala improved the rate of PSⅡ electron transfer,accelerate the use of light energy,to provide energy for the absorption of ni-trate.Moreover,N.cryptocephala improved α value to increase the utilization efficiency of light ener-gy in response to nitrogen deficiency with the consumption of nitrogen for resisting adverse conditions.Our findings provided not only an experimental basis for the molecular identification of N.cryptoceph-ala in fresh water,but also basic data for water quality protection and ecosystem management in Dan-jiangkou Reservoir.