Although freshwater systems comprise a small portion of land surface, they play a pivotal role in landscape carbon (C) cycling. Carbon processing by heterotrophic bacteria is critical, contributing to ecosystem production and dissolved organic carbon (DOC) processing. Riverine bacterial C metabolism is related to a diversity of factors, including (1) physiochemical conditions and inorganic nutrient concentrations and (2) DOC quality and quantity; however, the relative importance of these factors in influencing C metabolism across arid fluvial networks remains equivocal. This study examined C metabolism by heterotrophic bacterioplankton in the Rio Grande drainage, an arid river network in Texas, USA. We examined spatial variation in physicochemical and inorganic nutrient conditions, bacterial C metabolism, and DOC lability across the drainage and assessed whether variation in bacterial C metabolism was more related to physicochemical–inorganic nutrient conditions or DOC quantity and lability. Across the drainage, hydrology and landscape position influenced physicochemical conditions, bacterial abundance, phytoplankton biomass, and bacterial C metabolism and the proportion of variation in bacterial C metabolism explained by physicochemical/inorganic nutrient and DOC quality–quantity gradients was approximately equal. Bacterial abundance and production were associated with greater NH₄⁺ and DOC concentrations and phytoplankton biomass, whereas bacterial respiration and growth efficiency were driven by DOC color and suspended particulate concentrations. Results indicate that aspects of bacterial C metabolism are influenced by different environmental factors related to autochthonous and allochthonous inputs to riverine systems, which has implications for C transformation, sequestration, and transport to the ocean.

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理化和碳量-质量梯度同样会影响干旱河道中细菌的碳代谢

尽管淡水系统仅占陆地表面的一小部分，但它们在景观碳（C）循环中起着关键作用。异养细菌的碳加工至关重要，有助于生态系统生产和溶解性有机碳（DOC）加工。河流细菌碳代谢与多种因素有关，包括（1）理化条件和无机养分浓度以及（2）DOC的质量和数量；然而，这些因素在影响整个干旱河流网络中碳代谢的相对重要性仍然不明确。这项研究通过美国得克萨斯州的干旱河网里约格兰德河中的异养浮游细菌检查了碳代谢。我们研究了物理化学和无机营养条件，细菌C代谢，和DOC在整个排水系统中的不稳定性，并评估细菌C代谢的变化是否与理化-无机营养状况或DOC的数量和不稳定性更相关。在整个排水系统中，水文和地形位置对理化条件，细菌丰度，浮游植物生物量和细菌C代谢的影响均很大，而理化/无机养分和DOC质量-量梯度所解释的细菌C代谢变化的比例大致相等。细菌丰度和生产与NH含量升高有关 浮游植物的生物量，细菌C代谢以及细菌C代谢变化的比例由理化/无机养分和DOC质量-数量梯度所解释。细菌丰度和生产与NH含量升高有关 浮游植物的生物量，细菌C代谢以及细菌C代谢变化的比例（由理化/无机养分和DOC质量-质量梯度所解释）大致相等。细菌丰度和生产与NH含量升高有关₄ ⁺和DOC浓度以及浮游植物生物量，而细菌的呼吸和生长效率则受DOC颜色和悬浮颗粒浓度的驱动。结果表明，细菌碳代谢的各个方面受到与河流系统的本地和异源输入有关的不同环境因素的影响，这对碳的转化，螯合和向海洋的运输具有影响。