Disentangling microbial dynamics in the mesopelagic zone is crucial due to its role in processing sinking photic production, affecting carbon export to the deep ocean. The relative importance of photic zone processes versus local biogeochemical conditions in mesopelagic microbial dynamics, especially seasonal dynamics, is largely unknown. We employed rRNA gene transcript-based high-throughput sequencing on 189 samples collected from both the photic and mesopelagic zones, along with seasonal observations, to understand the South China Sea’s protistan-bacterial microbiota diversity, drivers, and mechanisms. Mesopelagic communities displayed unexpectedly greater seasonal but less vertical dynamics than photic counterparts. Temperature, dissolved oxygen, nutrients, and bacterial abundance drove mesopelagic communities vertically. Photic zone processes (using net community production and mixed layer depth as proxies) of past seasons, coinciding with strong monsoon periods, shaped seasonal fluctuations in mesopelagic communities, indicating a time-lag effect. Furthermore, certain microbes were identified as indicators for beta diversity by depth and season. This investigation deepens our understanding of how and why mesopelagic communities vary with season and depth. Recognizing the time-lagged effect of photic zone processes on mesopelagic communities is crucial for understanding the current and future configurations of the ocean microbiome, especially in the context of climate change and its effect on carbon export and ocean storage.

中文翻译：

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破解深海动态密码：南海中层带活性原生细菌微生物组的意外季节性模式


解开中层区域的微生物动态至关重要，因为它在处理下沉的光产生中发挥着重要作用，影响着向深海的碳输出。在中层微生物动力学，特别是季节动力学中，光带过程与局部生物地球化学条件的相对重要性在很大程度上是未知的。我们对从光带和中层带收集的 189 个样本进行了基于 rRNA 基因转录本的高通量测序，并进行了季节性观测，以了解南海原生细菌微生物群的多样性、驱动因素和机制。与透光群落相比，中层群落表现出出乎意料的更大的季节性动态，但垂直动态较少。温度、溶解氧、营养物质和细菌丰度垂直驱动中层群落。过去季节的光带过程（使用净群落生产和混合层深度作为代理）与强季风期相一致，形成了中层群落的季节性波动，表明存在时滞效应。此外，某些微生物被确定为按深度和季节划分的β多样性指标。这项调查加深了我们对中层群落如何以及为何随季节和深度变化的理解。认识光带过程对中层群落的时滞效应对于了解海洋微生物组当前和未来的配置至关重要，特别是在气候变化及其对碳输出和海洋储存的影响的背景下。