Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA.
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, USA.
Ecol Appl. 2022 Jun;32(4):e2530. doi: 10.1002/eap.2530. Epub 2022 Mar 25.
Models of terrestrial system dynamics often include nitrogen (N) cycles to better represent N limitations on terrestrial carbon (C) uptake, but simulating the fate of N in ecosystems has proven challenging. Here, key soil N fluxes and flux ratios from the Community Land Model version 5.0 (CLM5.0) are compared with an extensive set of observations from the Hubbard Brook Forest Long-Term Ecological Research site in New Hampshire. Simulated fluxes include microbial immobilization and plant uptake, which compete with nitrification and denitrification, respectively, for available soil ammonium (NH ) and nitrate (NO ). In its default configuration, CLM5.0 predicts that both plant uptake and immobilization are strongly dominated by NH over NO , and that the model ratio of nitrification:denitrification is ~1:1. In contrast, Hubbard Brook observations suggest that NO plays a more significant role in plant uptake and that nitrification could exceed denitrification by an order of magnitude. Modifications to the standard CLM5.0 at Hubbard Brook indicate that a simultaneous increase in the competitiveness of nitrifying microbes for NH and reduction in the competitiveness of denitrifying bacteria for NO are needed to bring soil N flux ratios into better agreement with observations. Such adjustments, combined with evaluation against observations, may help to improve confidence in present and future simulations of N limitation on the C cycle, although C fluxes, such as gross primary productivity and net primary productivity, are less sensitive to the model modifications than soil N fluxes.
陆地系统动力学模型通常包括氮（N）循环，以更好地表示陆地碳（C）吸收对 N 的限制，但证明模拟生态系统中 N 的命运具有挑战性。在这里，比较了社区土地模型版本 5.0（CLM5.0）的关键土壤 N 通量和通量比与新罕布什尔州哈伯德布鲁克森林长期生态研究站的大量观测结果。模拟通量包括微生物固定和植物吸收，它们分别与硝化和反硝化竞争可用的土壤铵（NH ）和硝酸盐（NO ）。在其默认配置中，CLM5.0 预测植物吸收和固定均主要由 NH 主导，而硝化：反硝化的模型比约为 1:1。相比之下，哈伯德布鲁克观测表明，NO 在植物吸收中发挥了更重要的作用，硝化作用可能超过反硝化作用一个数量级。在哈伯德布鲁克对标准 CLM5.0 的修改表明，需要同时提高硝化微生物对 NH 的竞争力和降低反硝化细菌对 NO 的竞争力，以使土壤 N 通量比与观测结果更好地吻合。这种调整，结合对观测结果的评估，可能有助于提高对当前和未来 C 循环 N 限制模拟的信心，尽管 C 通量（如总初级生产力和净初级生产力）比土壤 N 通量对模型修改的敏感度较低。
