Tropical forests store more than half of the world's terrestrial carbon (C) pool and account for one-third of global net primary productivity (NPP). Many terrestrial biosphere models (TBMs) estimate increased productivity in tropical forests throughout the 21st century due to CO fertilization. However, phosphorus (P) limitations on vegetation photosynthesis and productivity could significantly reduce the CO fertilization effect. Here, we used a carbon-nitrogen-phosphorus coupled model (Dynamic Land Ecosystem Model; DLEM-CNP) with heterogeneous maximum carboxylation rates to examine how P limitation has affected C fluxes in tropical forests during 1860–2018. Our model results showed that the inclusion of the P processes enhanced model performance in simulating ecosystem productivity. We further compared the simulations from DLEM-CNP, DLEM-CN, and DLEM-C and the results showed that the inclusion of P processes reduced the CO fertilization effect on gross primary production (GPP) by 25% and 45%, and net ecosystem production (NEP) by 28% and 41%, respectively, relative to CN-only and C-only models. From the 1860s to the 2010s, the DLEM-CNP estimated that in tropical forests GPP increased by 17%, plant respiration (Ra) increased by 18%, ecosystem respiration (Rh) increased by 13%, NEP increased by 121% per unit area, respectively. Additionally, factorial experiments with DLEM-CNP showed that the enhanced NPP benefiting from the CO fertilization effect had been offset by 135% due to deforestation from the 1860s to the 2010s. Our study highlights the importance of P limitation on the C cycle and the weakened CO fertilization effect resulting from P limitation in tropical forests.

中文翻译：

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通过耦合生物地球化学模型了解热带森林中磷的限制对二氧化碳施肥的影响


热带森林储存着世界陆地碳（C）库的一半以上，占全球净初级生产力（NPP）的三分之一。许多陆地生物圈模型 (TBM) 估计，由于二氧化碳施肥，整个 21 世纪热带森林的生产力有所提高。然而，磷（P）对植被光合作用和生产力的限制会显着降低二氧化碳施肥效果。在这里，我们使用具有异质最大羧化率的碳-氮-磷耦合模型（动态土地生态系统模型；DLEM-CNP）来研究P限制如何影响1860年至2018年期间热带森林的C通量。我们的模型结果表明，包含 P 过程增强了模型在模拟生态系统生产力方面的性能。我们进一步比较了 DLEM-CNP、DLEM-CN 和 DLEM-C 的模拟，结果表明，加入 P 过程使 CO 施肥对总初级生产 (GPP) 的影响降低了 25% 和 45%，净生态系统相对于纯 CN 和纯 C 型号，产量 (NEP) 分别提高了 28% 和 41%。从1860年代到2010年代，DLEM-CNP估计热带森林的GPP增加了17%，植物呼吸（Ra）增加了18%，生态系统呼吸（Rh）增加了13%，单位面积NEP增加了121% ， 分别。此外，DLEM-CNP 的析因实验表明，由于 1860 年代至 2010 年代的森林砍伐，受益于 CO 施肥效应的 NPP 增强被抵消了 135%。我们的研究强调了磷限制对碳循环的重要性以及热带森林中磷限制导致的二氧化碳施肥效果减弱。