School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, 06511, USA.
Department of Biology, Memorial University of Newfoundland, St John's, Newfoundland, A1B 3X9, Canada.
Ecology. 2019 May;100(5):e02674. doi: 10.1002/ecy.2674. Epub 2019 Mar 29.
Numerous biotic mechanisms can control ecosystem nutrient cycling, but their full incorporation into ecological models or experimental designs can result in inordinate complexity. Including organismal nutrient limitation in models of highly dimensional systems (i.e., those with many nutrient pools/species) presents a critical challenge. We evaluate the importance of explicitly considering microbial and animal nutrient limitation to predict ecosystem nitrogen cycling across plant-based and detritus-based food chains. We investigate how eight factorial scenarios of microbial, herbivore, and microbi-detritivore (i.e., omnivores consuming microbes and detritus) nitrogen or carbon limitation alter the stocks and flows of nitrogen in an ecosystem model. We used a combination of partial derivatives of model equilibrium solutions and numerical simulations using randomly drawn parameter sets to explore the impact of each nutrient limitation scenario on nutrient stocks and flows. We show that switching microbes, herbivores, or microbi-detritivores from nitrogen to carbon limitation consistently altered the ecosystem response to changes in inorganic nitrogen supply, plant C:N ratio, and microbial C:N ratio. Organism nutrient limitation changed ecosystem nitrogen flows by altering the feedbacks between the abiotic and biotic pools. For example, microbi-detritivore nutrient limitation determined whether the microbial response to changes in inorganic nitrogen supply and C:N ratios was dependent on the size of detrital carbon or detrital nitrogen pool. Such correlated responses among biotic and abiotic pools set up a network of predictable changes in ecosystem properties sensitive to organism nutrient limitation. Scenarios with microbial limitation were generally sufficient to capture the suite of ecosystem responses to increasing inorganic nitrogen supply, while scenarios with animal limitation added new behavior whenever C:N ratios changed. We make the case for explicitly considering both microbial and animal nutrient limitation when predicting the flow and distribution of nitrogen across green and brown food chains.
众多生物机制可以控制生态系统养分循环，但将它们完全纳入生态模型或实验设计可能会导致过度复杂。在高度维数系统（即具有许多养分库/物种的系统）的模型中纳入生物体养分限制是一个关键挑战。我们评估了明确考虑微生物和动物养分限制以预测基于植物和碎屑的食物链中生态系统氮循环的重要性。我们研究了微生物、食草动物和微生物-碎屑食者（即同时消耗微生物和碎屑的杂食动物）的氮或碳限制的八种组合情景如何改变生态系统模型中氮的存量和流量。我们使用模型平衡解的偏导数和使用随机抽取的参数集进行数值模拟的组合来探索每种养分限制情景对养分存量和流量的影响。我们表明，将微生物、食草动物或微生物-碎屑食者从氮限制切换为碳限制会一致改变生态系统对无机氮供应、植物 C:N 比和微生物 C:N 比变化的反应。生物体养分限制通过改变生物和非生物库之间的反馈来改变生态系统氮流动。例如，微生物-碎屑食者养分限制决定了微生物对无机氮供应和 C:N 比变化的反应是否取决于碎屑碳或碎屑氮库的大小。生物和非生物库之间的这种相关响应建立了一个生态系统属性的可预测变化网络，这些属性对生物体养分限制敏感。具有微生物限制的情景通常足以捕捉到生态系统对增加无机氮供应的一系列反应，而具有动物限制的情景则在 C:N 比变化时增加了新的行为。我们提出了在预测绿链和褐链中氮的流动和分布时，明确考虑微生物和动物养分限制的理由。
