Ecosystem functional responses such as soil CO₂ emissions are constrained by microclimate, available carbon (C) substrates and their effects upon microbial activity. In tropical forests, phosphorus (P) is often considered as a limiting factor for plant growth, but it is still not clear whether P constrains microbial CO₂ emissions from soils. In this study, we incubated seven tropical forest soils from Brazil and Puerto Rico with different nutrient addition treatments (no addition, Control; C, nitrogen (N) or P addition only; and combined C, N and P addition (CNP)). Cumulative soil CO₂ emissions were fit with a Gompertz model to estimate potential maximum cumulative soil CO₂ emission (C _m) and the rate of change of soil C decomposition (k). Quantitative polymerase chain reaction (qPCR) was conducted to quantify microbial biomass as bacteria and fungi. Results showed that P addition alone or in combination with C and N enhanced C _m, whereas N addition usually reduced C _m, and neither N nor P affected microbial biomass. Additions of CNP enhanced k, increased microbial abundances and altered fungal to bacterial ratios towards higher fungal abundance. Additions of CNP, however, tended to reduce C _m for most soils when compared to C additions alone, suggesting that microbial growth associated with nutrient additions may have occurred at the expense of C decomposition. Overall, this study demonstrates that soil CO₂ emission is more limited by P than N in tropical forest soils and those effects were stronger in soils low in P.

中文翻译：

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磷而不是氮会增加热带森林土壤中的二氧化碳排放量：一项来自实验室孵化研究的证据

生态系统的功能响应（例如土壤CO ₂排放）受小气候，可利用的碳（C）基质及其对微生物活性的影响所限制。在热带森林中，磷（P）通常被认为是植物生长的限制因素，但目前尚不清楚P是否会限制土壤中微生物的CO ₂排放。在这项研究中，我们将巴西和波多黎各的7种热带雨林土壤进行了不同的营养添加处理（不添加，不添加；仅添加碳，氮（N）或磷；并添加碳，氮和磷（CNP））。用Gompertz模型拟合累积的土壤CO ₂排放量，以估算潜在的最大累积土壤CO ₂排放量（C _m ）和土壤C分解的变化率（k）。进行定量聚合酶链反应（qPCR）以量化微生物生物量，如细菌和真菌。结果表明，单独添加P或与C和N组合添加P均会提高C _m，而添加N通常会降低C _m，而N和P均不会影响微生物生物量。CNP的添加增强了k，增加了微生物的丰度，并改变了真菌与细菌的比例，从而提高了真菌的丰度。然而，CNP的添加倾向于降低C _m 对于大多数土壤而言，与单独添加碳相比，表明与营养添加相关的微生物生长可能是以碳分解为代价的。总体而言，这项研究表明，热带森林土壤中P的土壤CO ₂排放受N的限制要大于N，而P较低的土壤的影响更强。