The amplitude of the diurnal temperature (ADT) has been decreasing under climate change, with substantial anticipated effects on alpine grassland carbon budgets. Here, we quantified the temporal response of the growing seasonal CO₂ fluxes to ADT over alpine shrubland on Qinghai‐Tibetan Plateau (QTP) from 2003 to 2016. At a daily scale, net ecosystem exchange (NEE) and gross primary production (GPP) quadratically responded to ADT with optimum values of 15.4 and 13.4°C, respectively. Ecosystem respiration (RES) negatively linearly correlated with ADT. Partial correlation, and classification and regression trees (CART) analysis, both showed that the maximal (MaxTa) or minimal air temperature (MinTa), rather than ADT, played much more important role in daily variations of CO₂ fluxes. At a monthly scale, GPP and NEE were both positively and negatively controlled by MaxTa while RES was negatively determined by MinTa, respectively. Monthly ADT exerted a negligible influence on monthly CO₂ fluxes. At an annual scale, only MaxTa played a significant role in variations of GPP and RES. NEE did not significantly respond to ADT, MaxTa or MinTa. The little direct correlations between NEE and ADT at daily, monthly or annual scales contradicts a previous hypothesis that a larger ADT would enhance carbon sequestration capacity over alpine ecosystems. Given the positive impact of MaxTa on GPP and MinTa on RES, our study would suggest that a decreasing ADT could indirectly stimulate more carbon loss and weaken the carbon sequestration capacity of alpine shrublands under the scenario of further increases in MinTa over QTP.

中文翻译：

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日温振幅对青藏高原高山湿地灌木丛中生长的季节性CO2通量的直接影响很小

在气候变化下，昼夜温度（ADT）的幅度一直在下降，这对高寒草原的碳收支有很大的预期影响。在这里，我们量化了2003年至2016年青藏高原（QTP）上高寒灌木丛上日益增长的季节性CO ₂通量对ADT的时间响应。在日常规模上，净生态系统交换（NEE）和初级总产值（GPP）分别对ADT进行二次响应，最佳值分别为15.4和13.4°C。生态系统呼吸（RES）与ADT呈线性负相关。偏相关以及分类树和回归树（CART）分析均显示，最高（MaxTa）或最低气温（MinTa）而非ADT在CO _2的每日变化中起着重要的作用通量。在每月范围内，GPP和NEE分别由MaxTa负控制，而RES由MinTa负控制。每日ADT对每月CO _2的影响可忽略不计通量。在年度规模上，只有MaxTa在GPP和RES的变体中发挥了重要作用。NEE对ADT，MaxTa或MinTa没有明显反应。在日，月或年尺度上，NEE和ADT之间几乎没有直接的相关性，这与先前的假设相反，即较大的ADT会增强高山生态系统的固碳能力。鉴于MaxTa对GPP的积极影响以及MinTa对RES的积极影响，我们的研究表明，在MinTa超过QTP进一步增加的情况下，降低的ADT可以间接刺激更多的碳损失并削弱高山灌丛的固碳能力。