Characteristics of amino acids during the process of algae-originated particles decomposition in Lake Taihu

Abstract

在实验条件下研究了高浓度蓝藻堆积后水体中的藻源性颗粒物中氨基酸的分解速率、分解量和氨基酸态氮形态的变化情况.在自然光照组中，颗粒态氨基酸（PAA）的浓度从实验前的0.46 mmol/L降至实验后的0.30 mmol/L；而在无光分解组中PAA从0.44 mmol/L降至0.06 mmol/L.两种处理下PAA的降解速率常数分别为0.03916和0.17424 d^-1.溶解态氨基酸（DAA）在分解过程中浓度比较低，随时间的变化表现出先增大后减小的趋势，在两种不同的处理下，最大值分别为10.94和7.94 μmol/L，21 d后减小到与实验开始时持平，甚至低于初始值.实验初期，PAA所占比例高达74%~80%，但迅速被分解转化为DAA和铵态氮（NH₄⁺-N），随着实验的进行NH₄⁺-N又逐渐转化为硝态氮，其中无光分解组中的分解更为彻底，而自然光照组中PAA分解量小于无光分解组.实验结果表明，氨基酸作为水体中浮游植物的潜在氮源，可以被分解为水华过程中藻类所需的NH₄⁺-N，对水华的维持具有一定的促进作用.;The characteristics of decomposition rate and quantity of amino acids, as well as the change of nitrogen forms, were explored during the process of decomposition of high-density cyanobacterial particles in this study. The results showed that the initial concentrations of particulate amino acids (PAA) were 0.46 mmol/L in natural light group and 0.44 mmol/L in the aphotic group. At the end of the experiment, the PAA was much stable with a concentration of 0.30 mmol/L in natural light group, while decreased dramatically to 0.06 mmol/L in the aphotic group. The degradation rate constants were 0.03916 and 0.17424 d^-1, respectively. The concentration of dissolved amino acids (DAA) was much lower in comparison to PAA in the process of decomposition. In detail, the DAA increased gradually and peaked at 10.94 and 7.94 μmol/L for the two groups, respectively, and then declined to around the initial value in the end of the 21st day. At the beginning of the experiment, PAA accounted for 74%-80% of the total amino acids, then PAA was transformed to DAA and ammonia (NH₄⁺-N) quickly, and finally the NH₄⁺-N was transformed gradually to NO₃^--N by nitrification. Compared with the natural light group, the decomposition of particles in aphotic group was more complete. Algal photosynthesis inhibited the decomposition of cyanobacterial particles in the natural group. Our results demonstrated that amino acids are potential nitrogen sources of phytoplankton and could be demineralized to NH₄⁺-N to support phytoplankton growth during cyanobacterial blooms. Therefore, the decomposition of high-density algal particles plays a key role in the maintenance of cyanobacterial blooms.