球形棕囊藻同化吸收硝酸盐的氮氧稳定同位素分馏研究

NITROGEN AND OXYGEN STABLE ISOTOPIC FRACTIONATION OF NITRATE ASSIMILATION BY PHAEOCYSTIS GLOBOSE

球形棕囊藻(Phaeocystis globosa)赤潮是一种全球范围的生态灾害,而硝酸盐稳定同位素技术是研究海洋富营养化与赤潮暴发机制的前沿技术。为将该技术应用于球形棕囊藻赤潮暴发机制方面的研究,首先需了解其同化吸收硝酸盐的稳定同位素分馏特征。为此开展了球形棕囊藻室内培养实验,获取培养过程中氮、磷、硅等营养盐的浓度及硝酸盐氮、氧稳定同位素(δ^(15)N-NO_(3)^(-)、δ^(18)O-NO_(3)^(-))等参数的变化特征,计算球形棕囊藻同化吸收硝酸盐的稳定同位素分馏系数。结果显示,NO_(3)^(-)和PO4_(3)^(-)浓度随培养时间均呈现先明显下降后稳定的特征,同时伴随直径2~3 mm的囊体出现并生长至2~3 cm。NH4+浓度先后两次出现升高,推测可能是受到有机氮矿化过程的补充所致。随NO_(3)^(-)浓度降低,δ^(15)N和δ^(18)O的值分别在第13天和第7天达到相对峰值。经计算,球形棕囊藻同化吸收硝酸盐过程δ^(15)N和δ^(18)O分馏系数分别为3.32‰±0.38‰和3.12‰±0.59‰,而前者的分馏系数呈逐渐降低的特点,原因可能是随球形棕囊藻生长,发生酶还原的NO_(3)^(-)较参与跨膜运输的NO_(3)^(-)比例逐渐升高。研究首次给出了球形棕囊藻同化吸收硝酸盐过程的氮、氧稳定同位素分馏系数及其变化特征,补充了海洋微藻同位素分馏数据库,为稳定同位素技术研究球形棕囊藻赤潮暴发的营养机制提供了重要的基础数据。

The red tide caused by Phaeocystis globosa is a worldwide ecological disaster.And the nitrate stable isotopes are the advanced technique in studying the marine eutrophication and the mechanism of red tide bloom.For applying this technique in understanding the mechanism of P.globosa red tide bloom,the isotopic fractionation in nitrate assimilation should be obtained primarily.This study conducted the P.globosa culture in lab,from which the temporal variations of nutrients concentrations and nitrogen and oxygen isotopes in nitrate were analyzed.Results show that the concentrations of NO_(3)^(-)and PO4_(3)^(-)were reduced significantly and then stabilized with time.Meanwhile,P.globosa colonies in diameter of 2~3 mm were observed,and later they grew up to 2~3 cm.The concentration of NH4+was doubled during the culture period due to organic nitrogen mineralization.With nitrate decreasing,δ^(15)N-NO_(3)^(-)andδ^(18)O-NO_(3)^(-)were increased gradually and reached relatively high values on Day 13 and Day 7,respectively.The δ^(15)N andδ^(18)O fractionations of nitrate assimilation by P.globosa were calculated to be 3.32‰±0.38‰ and 3.12‰±0.59‰,respectively,of which δ^(15)N fractionation was reduced gradually.With the growth of P.globosa, the ratio of nitrate participated in the enzyme reduction to the nitrate involved in transmembrane transport was decreased gradually.This study reported nitrogen and oxygen isotopic fractionations of nitrate assimilation by P.globosa for the first time,filled the blank in isotopic fractionation pool of marine microalgae,and provided a basis for the application of nitrate stable isotope technique in studying the nutritional mechanism of P.globosa red tide.