Abstract：
Human activities have caused an imbalance in the input nitrogen and phosphorus (N/P) in the biosphere. The imbalance of N/P is one of the characteristics of water eutrophication, which is the fundamental factor responsible for the blooms. The effects of the N/P imbalance on diatom and phycospheric bacteria in blooms are poorly understood. In this study, the N/P molar ratio in real water (14:1) and the predicted N/P molar ratio in future water (65:1) were simulated to analyze the response of Cyclotella sp. and phycospheric bacteria to the N/P imbalance. The results showed that the N/P imbalance inhibited the growth of Cyclotella sp., but prolonged diatom bloom duration. The resistance of Cyclotella sp. to the N/P imbalance is related to phycospheric bacteria, and there are dynamic regulatory mechanisms within the phycospheric bacteria community to resist the N/P imbalance: (1) the increase of HNA bacterial density, the decrease of LNA bacterial density, (2) the increase of phycospheric bacterial diversity and eutrophic bacteria abundance, and the change of denitrifying bacteria abundance, (3) the activity of nitrogen and phosphorus metabolism of HNA bacteria enhanced, while that of LNA bacteria decreased. And the gene hosts of nitrogen and phosphorus metabolism were most enriched in Proteobacteria, indicating that Proteobacteria played an important role in maintaining the stability of phycospheric bacteria and was the dominant phylum resistant to the N/P imbalance. This study clarified that the algal-bacteria system was resistant to the N/P imbalance and implied that the N/P imbalance had little effect on the occurrence of diatom bloom events due to the presence of phycospheric bacteria.
摘要：
人类活动导致生物圈中氮和磷（N/P）的输入失衡。氮磷不平衡是水体富营养化的特征之一,这是造成开花的基本因素。N/P失衡对水华中硅藻和藻层细菌的影响知之甚少。在这项研究中,模拟了实际水中的N/P摩尔比（14：1）和未来水中的预测N/P摩尔比（65：1），以分析Cyclotellasp。和菌层细菌的N/P失衡。结果表明，N/P失衡抑制了Cyclotellasp的生长。,但硅藻开花持续时间延长。Cyclotellasp。N/P失衡与菌层细菌有关，菌层细菌群落内部存在动态调节机制以抵抗N/P失衡：（1）HNA细菌密度的增加，LNA细菌密度的降低，(2)藻层细菌多样性和富营养化细菌丰度的增加,以及反硝化细菌丰度的变化，(3)HNA菌氮磷代谢活性加强，而LNA细菌的下降。而氮磷代谢的基因宿主以变形杆菌最为富集,表明变形杆菌在维持菌层细菌的稳定性中起着重要作用，并且是抵抗N/P失衡的优势门。这项研究阐明了藻类细菌系统对N/P失衡具有抗性，并暗示由于存在藻类细菌，N/P失衡对硅藻水华事件的发生几乎没有影响。
