To identify factors driving soil respiration (Rsoil) in a tropical C4-dominated perennial managed grassland ecosystem exposed to elevated carbon (C) dioxide concentration ([CO2]) and temperature. The perennial grass Panicum maximum was grown at 600 μmol CO2 mol−1 and + 2 °C above ambient temperatures for one full growing cycle (from grazing to regrowth for about ~30–45 days) using a free-air CO2 and infrared warming system. Plant growth and CO2 fluxes were measured during the growing cycle. Both high [CO2] and warming increased canopy photosynthesis but warming alone increased biomass by 53% and Rsoil by 26%. There was a strong diel effect on Rsoil, which was 16% greater at noon than at 18:00 h. Rsoil had low sensitivity to soil temperature (Q10 ~ 1) regardless of the CO2 treatment. In this tropical managed pasture, diel variation in photosynthesis strongly affected Rsoil, suggesting that Rsoil may be more limited by substrate availability than abiotic factors such as temperature. Predicted changes in climate for the region will likely affect the C dynamics of C4-dominated tropical pastures. Although, the short-term experiment may limit the extrapolations of our findings, the highly controlled settings of the experiment highlighted the role of canopy photosynthesis on Rsoil respiration in tropical C4-pastures.

中文翻译：

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植物昼夜循环驱动暴露于高二氧化碳和变暖的以 C4 为主的热带管理草地土壤呼吸的变化

确定暴露于二氧化碳 (C) 浓度 ([CO2]) 和温度升高的热带 C4 主导的多年生管理草地生态系统中驱动土壤呼吸 (Rsoil) 的因素。在一个完整的生长周期（从放牧到再生长约 30-45 天），使用自由空气 CO2 和红外加热系统，多年生草 Panicum 最大值在 60​​0 μmol CO2 mol−1 和 + 2 °C 环境温度下生长. 在生长周期中测量植物生长和 CO2 通量。高 [CO2] 和变暖都增加了冠层光合作用，但仅变暖就使生物量增加了 53%，Rsoil 增加了 26%。对 Rsoil 有强烈的日粮效应，中午比 18:00 大 16%。无论 CO2 处理如何，Rsoil 对土壤温度 (Q10 ~ 1) 的敏感性都较低。在这个热带管理的牧场上，光合作用的日夜变化强烈影响 Rsoil，这表明 Rsoil 可能比非生物因素（如温度）更受底物可用性的限制。该地区预测的气候变化可能会影响以 C4 为主的热带牧场的 C 动态。尽管短期实验可能会限制我们的研究结果的外推，但实验的高度控制设置突出了冠层光合作用对热带 C4 牧场中 Rsoil 呼吸的作用。