Tropical forests are the largest contributors to global emissions of carbon dioxide (CO₂) to the atmosphere via soil respiration (R_s). As such, identifying the main controls on R_s in tropical forests is essential for accurately projecting the consequences of ongoing and future global environmental changes to the global C cycle. We measured hourly R_s in a secondary tropical moist forest in Puerto Rico over a 3‐year period to (a) quantify the magnitude of R_s and (b) identify the role of climatic, substrate, and nutrient controls on the seasonality of R_s. Across 3 years of measurements, mean R_s was 7.16 ± 0.02 μmol CO₂ m^‐2 s^‐1 (or 2,710 g C m^‐2 year^‐1) and showed significant seasonal variation. Despite small month‐to‐month variation in temperature (~4°C), we found significant positive relationships between daily and monthly R_s with both air and soil temperature, highlighting the importance of temperature as a driver of R_s even in warm ecosystems, such as tropical forests. We also found a significant parabolic relationship between mean daily volumetric soil moisture and mean daily R_s, with an optimal moisture value of 0.34 m³ m^‐3. Given the relatively consistent climate at this site, the large range in mean monthly R_s (~7 μmol CO₂ m^‐2 s^‐1) was surprising and suggests that even small changes in climate can have large implications for ecosystem respiration. The strong positive relationship of R_s with temperature at monthly timescales particularly stands out, as moisture is usually considered a stronger control of R_s in tropical forests that already experience warm temperatures year‐round. Moreover, our results revealed the strong seasonality of R_s in tropical moist forests, which given its high magnitude, can represent a significant contribution to the seasonal patterns of atmospheric (CO₂) globally.

中文翻译：

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波多黎各次热带湿润森林土壤呼吸的季节性大变化

热带森林是通过土壤呼吸（R _s）向大气中排放二氧化碳（CO ₂）的全球最大来源。因此，确定热带森林中R _s的主要控制措施对于准确预测正在进行的和未来的全球环境变化对全球C循环的影响至关重要。我们在3年内测量了波多黎各次热带湿润森林中的每小时R _s，以（a）量化R _s的大小，（b）确定气候，基质和养分控制对R的季节性的作用_s。在3年的测量中，平均R _s是7.16±0.02μmolCO ₂ m ^‐2  s ^-1（或2,710 g C m ‐ ² 年^-1），并显示出明显的季节性变化。尽管每个月的温度变化很小（约4°C），但我们发现每日和每月的R _s与空气和土壤温度之间都存在显着的正相关关系，这突出说明了即使在温暖的生态系统中，温度也是R _s的驱动因素的重要性，例如热带森林。我们还发现土壤平均日体积水分与日平均R _s之间存在明显的抛物线关系，最佳水分值为0.34 m ³ m ^-3。鉴于该地点的气候相对稳定，令人惊讶的是平均每月R _s（〜7μmolCO ₂ m ^-2  s ^-1）很大，这表明即使是很小的气候变化也会对生态系统呼吸产生重大影响。在每个月的时间尺度上，R _s与温度之间的强正相关性尤其突出，因为通常认为水分已被全年常温的热带森林更有效地控制了R _s。此外，我们的结果表明R _s的季节性很强在热带潮湿的森林中，由于其高强度，它可以代表全球大气（CO ₂）季节性模式的重大贡献。