Soil macronutrient availability is one of the abiotic controls that alters the exchange of greenhouse gases (GHGs) between the soil and the atmosphere in tropical forests. However, evidence on the macronutrient regulation of soil GHG fluxes from central African tropical forests is still lacking, limiting our understanding of how these biomes could respond to potential future increases in nitrogen (N) and phosphorus (P) deposition. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes from a Ugandan tropical forest reserve in the context of increasing N and P deposition. Therefore, a large-scale nutrient manipulation experiment (NME), based on 40 m×40 m plots with different nutrient addition treatments (N, P, N + P, and control), was established in the Budongo Central Forest Reserve. Soil carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes were measured monthly, using permanently installed static chambers, for 14 months. Total soil CO₂ fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and nitrates were measured in parallel to GHG fluxes. N addition (N and N + P) resulted in significantly higher N₂O fluxes in the transitory phase (0–28 d after fertilization; p<0.01) because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands, leaving the excess to be nitrified or denitrified. Prolonged N fertilization, however, did not elicit a significant response in background (measured more than 28 d after fertilization) N₂O fluxes. P fertilization marginally and significantly increased transitory (p=0.05) and background (p=0.01) CH₄ consumption, probably because it enhanced methanotrophic activity. The addition of N and P (N + P) resulted in larger CO₂ fluxes in the transitory phase (p=0.01), suggesting a possible co-limitation of both N and P on soil respiration. Heterotrophic (microbial) CO₂ effluxes were significantly higher than the autotrophic (root) CO₂ effluxes (p<0.01) across all treatment plots, with microbes contributing about two-thirds of the total soil CO₂ effluxes. However, neither heterotrophic nor autotrophic respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by increases in N and P availability over these biomes.

中文翻译：

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养分限制调节来自热带森林的土壤温室气体通量：来自乌干达生态系统规模养分操纵实验的证据

土壤常量营养素的有效性是改变热带森林土壤和大气之间温室气体 (GHG) 交换的非生物控制之一。然而，仍然缺乏关于中非热带森林土壤温室气体通量的常量营养素调节的证据，这限制了我们对这些生物群落如何应对未来氮 (N) 和磷 (P) 沉积的潜在增加的理解。本研究的目的是在氮和磷沉积增加的情况下，解开土壤养分对乌干达热带森林保护区土壤温室气体通量的调节作用。因此，基于40 m×40 m地块，不同养分添加处理（N、P、N  + P 和控制），在 Budongo 中央森林保护区建立。土壤二氧化碳 ( CO ₂ )、甲烷 ( CH ₄ ) 和一氧化二氮 ( N ₂ O ) 通量每月使用永久安装的静态室进行测量，持续 14 个月。通过根沟处理，总土壤CO ₂通量被划分为自养和异养组分。此外，土壤温度、土壤含水量和硝酸盐的测量与温室气体通量平行。N添加（N和N  +  P）导致过渡阶段（施肥后0-28天；p）显着更高的N ₂ O通量<0.01 ) 因为施氮可能增加土壤 N 超过微生物固定和植物营养需求，留下多余的氮进行硝化或反硝化。然而，延长施氮时间并没有引起背景（施肥后 28 天以上）N ₂ O通量的显着响应。P 施肥略微且显着地增加了瞬时 ( p =0.05 ) 和背景 ( p =0.01 ) CH ₄消耗，可能是因为它增强了甲烷氧化活性。N 和 P (N  +  P) 的添加导致过渡相中更大的CO ₂通量 ( p=0.01 )，表明 N 和 P 对土壤呼吸可能存在共同限制。在所有处理地块中，异养（微生物）CO ₂流出显着高于自养（根）CO ₂流出（p <0.01），微生物占土壤CO ₂流出总量的大约三分之二。然而，处理之间的异养呼吸和自养呼吸都没有显着差异。这项研究的结果表明，热带森林对全球土壤温室气体预算的反馈可能会因这些生物群落中 N 和 P 可用性的增加而发生不成比例的改变。