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 CO2 fertilization. However, phosphorus (P) limitations on vegetation photosynthesis and productivity could significantly reduce the CO2 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 CO2 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 CO2 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 CO2 fertilization effect resulting from P limitation in tropical forests.

中文翻译：

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耦合生物地球化学模型对热带森林 CO2 施肥效应的磷限制


热带森林储存了世界陆地碳 （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 CO2 施肥，整个 21 世纪热带森林的生产力得到了提高。然而，磷 （P） 对植被光合作用和生产力的限制可能会显著降低 CO2 施肥效应。在这里，我们使用了碳-氮-磷耦合模型（动态土地生态系统模型;DLEM-CNP） 具有异质性最大羧化速率，以研究 P 限制如何影响 1860-2018 年期间热带森林的 C 通量。我们的模型结果表明，包含 P 过程增强了模拟生态系统生产力的模型性能。我们进一步比较了 DLEM-CNP、DLEM-CN 和 DLEM-C 的模拟，结果表明，相对于仅 CN 和仅 C 模型，包含 P 过程将 CO2 施肥对总初级生产力 （GPP） 和 NEP 的影响分别降低了 25% 和 45%，以及生态系统净生产 （NEP） 分别降低了 28% 和 41%。从 1860 年代到 2010 年代，DLEM-CNP 估计，在热带森林中，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%，NEP 每单位面积增加了 121%。此外，DLEM-CNP 的因子实验表明，由于 1860 年代至 2010 年代的森林砍伐，受益于 CO2 施肥效应的增强型 NPP 已被抵消了 135%。我们的研究强调了 P 限制对 C 循环的重要性以及热带森林 P 限制导致 CO2 施肥效应的减弱。