Abstract Bamboo, as a pioneer vegetation, often forms forests on bare lands after catastrophic landslides. Compared to evergreen forest soil, bamboo forest soil is much more labile, with a higher percentage of microbially derived organic carbon (OC), lower molecular weight, and lower humic acid content. We hypothesised that different terrigenous organic matter (tOM) sources with varying lability and phosphorus (P) availability select for bacterioplankton with distinct metabolic pathways. We incubated natural bacterioplankton assemblages with tOM leached from bamboo forest soil (BOM) and evergreen forest soil (EOM) and compared these to a lake water control. To test if microbial metabolism would be limited by OC or P availability of each tOM treatment, we used acetate as an extra labile OC source and phosphate as an inorganic P source. Bacterial metabolism was measured by analysing respiration via O2 consumption and production via tritiated thymidine (TdR) assimilation. Bacterioplankton metabolism is limited by the availability of P in BOM substrates. When using BOM, bacteria had higher enzymatic activities for phosphatase. The nutrients required for bacterial biomass seemed to be derived from organic matter. Under BOM treatment, bacterial production (BP) (0.92 ± 0.13 μg C L−1 hr−1) and cell specific TdR assimilation rates (0.015 ± 0.002 10–18 M TdR cell−1 hr−1) were low. Adding P enhanced BP (BOM+P 1.52 ± 0.31 and BOM+C+P 2.25 ± 0.37 μg C L−1 hr−1) while acetate addition had no significant effect on BOM treatment. This indicated that the bacteria switched to using added inorganic P to respire a P‐limited BOM substrate, which increased total BP and abundance, resulting in even more active respiration and lower growth efficiency. We also found higher activities for chitin‐degrading enzyme β‐N‐acetylglucosaminidase, which is associated with N mining from aminosaccharides. Microbes using EOM, however, did not change metabolic strategies with additional acetate or/and inorganic P. This is due to higher concentrations of organic P in EOM substrates and the presence of inorganic N in the EOM leachates an alternative nutrient source. Bacteria produced β‐glucosidase and leucyl‐aminopeptidase in order to utilise the humic substances, which sustained greater bacterial abundance, higher BP (2.64 ± 0.39 μg C L−1 hr−1), and lower cell‐specific respiration. This yielded a much higher bacterial growth efficiency (15 ± 9.2%) than the lake water control. Our study demonstrated the aquatic metabolic discrepancy between tOM of different forest types. Bacterioplankton in BOM and EOM exhibit distinct metabolic responses. Bacterial metabolic strategy when using BOM implied that the supposedly stabilised biomass OM might be efficiently used by aquatic bacterioplankton. As the labile and nutrient‐deficient BOM is more susceptible to the influence of additional nutrients, fertiliser residues in bamboo forest catchments might have a stronger effect on aquatic bacterial metabolic pathways. Thus, it is important to take tOM differences into consideration when building models to estimate soil carbon turnover rates along a terrestrial–aquatic continuum.

中文翻译：

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陆源有机底物和额外磷对浮游细菌代谢和外酶化学计量的影响


摘要 竹子作为先锋植被，经常在灾难性山体滑坡后在裸露的土地上形成森林。与常绿森林土壤相比，竹林土壤更加不稳定，微生物来源的有机碳（OC）百分比较高，分子量较低，腐殖酸含量较低。我们假设不同的陆源有机物（tOM）来源具有不同的不稳定性和磷（P）可用性，选择具有不同代谢途径的浮游细菌。我们用从竹林土壤 (BOM) 和常绿森林土壤 (EOM) 浸出的 tOM 培养天然浮游细菌组合，并将其与湖水对照进行比较。为了测试微生物代谢是否会受到每种 tOM 处理的 OC 或 P 可用性的限制，我们使用乙酸盐作为额外不稳定的 OC 源，使用磷酸盐作为无机 P 源。通过分析氧气消耗的呼吸作用和氚化胸苷 (TdR) 同化的产生来测量细菌代谢。浮游细菌的代谢受到 BOM 底物中磷的可用性的限制。当使用BOM时，细菌对磷酸酶具有较高的酶活性。细菌生物量所需的营养物质似乎来自有机物。在 BOM 处理下，细菌产量 (BP) (0.92 ± 0.13 μg CL−1 hr−1) 和细胞特异性 TdR ​​同化率 (0.015 ± 0.002 10–18 M TdR ​​cell−1 hr−1) 较低。添加 P 增强 BP（BOM+P 1.52 ± 0.31 和 BOM+C+P 2.25 ± 0.37 μg CL−1 hr−1），而添加醋酸盐对 BOM 处理没有显着影响。这表明细菌转而使用​​添加的无机磷来呼吸磷受限的 BOM 底物，这增加了总 BP 和丰度，导致呼吸更加活跃，生长效率更低。 我们还发现几丁质降解酶 β-N-乙酰氨基葡萄糖苷酶具有较高的活性，这与从氨基酸中开采氮有关。然而，使用 EOM 的微生物并没有改变添加乙酸盐或/和无机磷的代谢策略。这是由于 EOM 基质中有机磷浓度较高，并且 EOM 中无机氮的存在渗滤出了替代营养源。细菌产生β-葡萄糖苷酶和亮氨酰-氨基肽酶以利用腐殖质，从而维持更大的细菌丰度、更高的血压（2.64 ± 0.39 μg CL−1 hr−1）和更低的细胞特异性呼吸。这产生了比湖水对照高得多的细菌生长效率（15±9.2%）。我们的研究证明了不同森林类型的 tOM 之间的水生代谢差异。 BOM 和 EOM 中的浮游细菌表现出不同的代谢反应。使用 BOM 时的细菌代谢策略表明，所谓的稳定生物量 OM 可能被水生浮游细菌有效利用。由于不稳定且缺乏养分的 BOM 更容易受到额外养分的影响，竹林流域中的肥料残留可能对水生细菌代谢途径产生更强的影响。因此，在建立模型来估计沿陆地-水生连续体的土壤碳周转率时，考虑到 tOM 差异非常重要。