Tracking carbon (C) flow through ecosystems requires quantification of myriad biophysical processes, including its routing through microbial and metazoan food webs. Yet, detailed organic matter budgets are rarely combined with simultaneous measurement of C flows supporting microbial and animal production. Here, we synthesize concurrent data sets on organic matter, microbes, and macroinvertebrates from two forest stream ecosystems, one of which was subject to experimental nitrogen (N) and phosphorus (P) enrichment. Our synthesis provides new insights into C flow through forest stream ecosystems. Over three years, the reference stream showed a striking balance of inputs and outputs, with a mean surplus of only 7 g C m-2 y-1 (~1% of annual inputs) presumably stored in sediments as fine particulate organic matter (FPOM). In contrast, N and P enrichment over two years resulted in severe deficits of C (-576 g C m-2 y-1 or ~170% of annual inputs), a shortfall presumably met by stored C. Our data set provides an ecosystem-based estimate of the fate of forest litter C at ambient nutrient concentrations: 6.2% was leached as dissolved organic C, 40.6% and 8.5% flowed to litter-associated fungi and bacteria, respectively, 7.5% was consumed by macroinvertebrates, 1.8% was exported as coarse particles, while the remainder (35.4%) was presumably fragmented by biophysical processes. Our calculations also allowed an estimate of inputs into the heterogeneous FPOM pool, which is otherwise difficult to obtain. At naturally low nutrient concentrations, 50.7% was derived from fragmented litter, 39.1% from microbial biomass (mostly fungal), and 10.2% from macroinvertebrate egesta. Nutrient addition drove large changes in C fluxes in the experimental stream, especially in flows of leaf litter to fungi (×1.7 pre-treatment) and macroinvertebrates (×2.7), and of FPOM to hydrologic export (×2.6). Our results underscore the key roles of both microbes and metazoans in controlling C flow through detritus-based ecosystems, as well as how release from persistent nutrient limitation may perturb steady-state conditions of C inputs vs. outputs. Our analysis also suggests areas for future research, including assessing the relative importance of stored vs. recycled C in fueling detrital food webs subject to altered nutrient regimes and other global-change drivers.

中文翻译：

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结合碳流经参考和实验丰富的河流生态系统中的碎屑、微生物和动物

跟踪生态系统中的碳 (C) 流需要对无数生物物理过程进行量化，包括其通过微生物和后生动物食物网的路径。然而，详细的有机物质预算很少与支持微生物和动物生产的 C 流量的同步测量相结合。在这里，我们合成了来自两个森林溪流生态系统的有机物质、微生物和大型无脊椎动物的并发数据集，其中之一受到实验性氮 (N) 和磷 (P) 富集的影响。我们的合成为森林溪流生态系统中的 C 流提供了新的见解。三年多来，参考流显示出输入和输出的惊人平衡，平均盈余仅为 7 g C m-2 y-1（约占年度输入的 1%），可能作为细颗粒有机物 (FPOM) 储存在沉积物中）。相比之下，两年多的 N 和 P 富集导致 C 严重不足（-576 g C m-2 y-1 或每年输入的约 170%），这一不足可能由存储的 C 满足。我们的数据集提供了基于生态系统的估计环境养分浓度下森林凋落物 C 的命运：6.2% 作为溶解的有机 C 浸出，40.6% 和 8.5% 分别流入与凋落物相关的真菌和细菌，7.5% 被大型无脊椎动物消耗，1.8% 作为粗粒出口颗粒，而其余的 (35.4%) 可能是由生物物理过程破碎的。我们的计算还允许估计异构 FPOM 池的输入，否则很难获得。在天然低营养浓度下，50.7% 来自碎片垃圾，39.1% 来自微生物生物量（主要是真菌），10.2% 来自大型无脊椎动物 egesta。养分添加驱动了实验流中 C 通量的巨大变化，特别是在落叶流向真菌（×1.7 预处理）和大型无脊椎动物（×2.7）以及 FPOM 流向水文输出（×2.6）中。我们的结果强调了微生物和后生动物在控制碳流通过基于碎屑的生态系统中的关键作用，以及持续营养限制的释放如何扰乱碳输入与输出的稳态条件。我们的分析还提出了未来研究的领域，包括评估储存碳与回收碳在为受营养体系改变和其他全球变化驱动因素影响的碎屑食物网提供燃料方面的相对重要性。和 FPOM 到水文输出 (×2.6)。我们的结果强调了微生物和后生动物在控制碳流通过基于碎屑的生态系统中的关键作用，以及持续营养限制的释放如何扰乱碳输入与输出的稳态条件。我们的分析还提出了未来研究的领域，包括评估储存碳与回收碳在为受营养体系改变和其他全球变化驱动因素影响的碎屑食物网提供燃料方面的相对重要性。和 FPOM 到水文输出 (×2.6)。我们的结果强调了微生物和后生动物在控制碳流通过基于碎屑的生态系统中的关键作用，以及持续营养限制的释放如何扰乱碳输入与输出的稳态条件。我们的分析还提出了未来研究的领域，包括评估储存碳与回收碳在为受营养体系改变和其他全球变化驱动因素影响的碎屑食物网提供燃料方面的相对重要性。