温度对浒苔降解过程中溶解有机物释放及其组成的影响

Release Dynamics and Composition of Dissolved Organic Matter from the Macroalgae Ulva prolifera under Different Temperature Regimes

2007~2019年浒苔(Ulva prolifera)绿潮在我国南黄海连续13年大规模暴发,每年上百万吨浒苔来不及打捞而沉降至海底。在浒苔绿潮消亡期,大量来不及打捞的浒苔藻体在微生物降解作用下释放丰富的碳、氮等生源要素。本研究探讨了温度对浒苔降解向水体释放溶解有机物(主要包括溶解有机碳和溶解有机氮)及其组成的影响。结果显示,不同温度(15℃、20℃和25℃)对0~7 d浒苔降解过程中溶解有机碳(DOC)的释放有显著影响(P<0.05):20℃条件下,DOC浓度显著高于15℃和25℃条件下,而7~30 d不同温度下水体的DOC浓度没有显著差异(P>0.05)。对于溶解有机氮(DON)而言,温度对0~7 d浒苔释放DON的影响不显著(P>0.05),而7~30 d不同温度下,DON浓度呈现显著差异。其中,25℃条件下,DON浓度显著低于15℃和20℃(P<0.05),这主要是由于在实验中后期,微生物将浒苔释放的DON部分转化为无机氮形式,而25℃条件下,微生物丰度较高,进而导致较多的DON发生转化。另外,利用三维荧光光谱—平行因子分析技术(EEMs-PARAFAC)对浒苔降解过程中荧光溶解有机物(FDOM)的组成和荧光特性进行探究,共鉴别出3个荧光组分:类色氨酸组分(C1和C2)和类腐殖质组分(C3)。不同温度下,3个组分的相对含量表明,温度对FDOM的组成并没有显著影响(P>0.05),而对C2和C3组分的荧光强度具有显著影响(P<0.05),这可能由不同温度下微生物的分解速率不同所导致。

Large green tides of Ulva prolifera had become an annual event from 2007 to 2019 in the southern Yellow Sea and millions of tons of U.prolifera which were not salvaged settled to the bottom every year,releasing a large amount of biogenic elements such as C and N through degradation by microorganisms.This study discusses the effect of different temperature regimes on the release and the composition of dissolved organic matter(DOM)during the decomposition of U.prolifera.The results indicated that temperature significantly influenced the release of dissolved organic carbon(DOC)during 0~7 days(P<0.05):the DOC concentration at 20℃was significantly higher than that at 15℃and 25℃.There was no significant difference in DOC concentration at different temperatures from day 7 to day 30(P>0.05).For dissolved organic nitrogen(DON),temperature did not significantly affect the release of DON during the first 7 days(P>0.05).There were significant differences in DON concentration at different temperatures after 7 days(P<0.05):the concentration of DON was significantly lower at higher temperature(i.e.25℃).The reason for this was that some organic nitrogen was converted to inorganic forms of nitrogen by microorganism during day 7 to day 30 and a higher microorganism abundance at 25℃led to the transformation of more DON.The composition and fluorescence characteristics of fluorescent dissolved organic matter(FDOM)were evaluated by an excitation-emission matrix combined with parallel factor analysis(EEMs-PARAFAC).Three distinct dissolved organic matter fluorescent components(i.e.C1,C2,and C3)were identified using parallel factor analysis.C1,C2,and C3 were considered as tryptophan-like substances(also called protein-like substances),tryptophan-like substances and humic-like substances,respectively.The results showed that temperature had no significant impact on the composition of FDOM through comparing the relative content of three fluorescent components at different temperatures(P>0.05).While the fluorescence intensities of C2 and C3 were larger with the higher temperature(i.e.25℃).Temperature affecting the fluorescence intensity markedly(P<0.05)may be caused by quicker microorganism decomposition rate under the higher temperature.