Anderson Thomas R, Hessen Dag O, Elser James J, Urabe Jotaro
Southampton Oceanography Centre, University of Southampton, Waterfront Campus, Southampton SO14 3ZH, United Kingdom.
Am Nat. 2005 Jan;165(1):1-15. doi: 10.1086/426598. Epub 2004 Nov 19.
Animals encountering nutritionally imbalanced foods should release elements in excess of requirements in order to maintain overall homeostasis. Quantifying these excesses and predicting their fate is, however, problematic. A new model of the stoichiometry of consumers is formulated that incorporates the separate terms in the metabolic budget, namely, assimilation of ingested substrates and associated costs, protein turnover, other basal costs, such as osmoregulation, and the use of remaining substrates for production. The model indicates that release of excess C and nonlimiting nutrients may often be a significant fraction of the total metabolic budget of animals consuming the nutrient-deficient forages that are common in terrestrial and aquatic systems. The cost of maintenance, in terms of not just C but also N and P, is considerable, such that food quality is important even when intake is low. Many generalist consumers experience short-term and unpredictable fluctuations in their diets. Comparison of model output with data for one such consumer, Daphnia, indicates that mechanisms operating postabsorption in the gut are likely the primary means of regulating excess C, N, and P in these organisms, notably respiration decoupled from biochemical or mechanical work and excretion of carbon and nutrients. This stoichiometrically regulated release may often be in organic rather than inorganic form, with important consequences for the balance of autotrophic and heterotrophic processes in ecosystems.
遇到营养不均衡食物的动物应释放超出需求的元素，以维持整体内稳态。然而，量化这些过量元素并预测它们的去向存在问题。本文构建了一个新的消费者化学计量模型，该模型纳入了代谢预算中的不同项，即摄入底物的同化作用及相关成本、蛋白质周转、其他基础成本（如渗透调节）以及将剩余底物用于生产。该模型表明，对于摄食陆地和水生系统中常见的营养缺乏草料的动物而言，过量碳和非限制性营养素的释放量可能常常占其总代谢预算的很大一部分。维持生存的成本，不仅涉及碳，还包括氮和磷，相当可观，以至于即便摄入量很低，食物质量依然很重要。许多泛食性消费者的饮食会经历短期且不可预测的波动。将该模型的输出结果与一种此类消费者（水蚤）的数据进行比较表明，肠道吸收后起作用的机制可能是调节这些生物体内过量碳、氮和磷的主要方式，尤其是与生化或机械功解耦的呼吸作用以及碳和营养物质的排泄。这种化学计量调节的释放形式通常可能是有机的而非无机的，这对生态系统中自养和异养过程的平衡具有重要影响。
