Widespread global greening driven by CO2 fertilization implies a denser canopy structure, and more leaves could be used to collect light from the atmosphere for plant photosynthesis. Whether this increase in leaf quantity could enhance the capacity of vegetation to convert absorbed light to photosynthate remains unclear. In this study, we investigate the spatial-temporal variations of canopy light-use efficiency (LUE), an indicator of leaf photosynthesis capacity, with FLUXNET recordings of 540 site-years and seven satellite-derived proxies. We find that flux tower measurements identify an increasing trend of LUE, and the temporal variations of cross-site LUE are mainly caused by nitrogen fertilization (18.09 %), temperature (17.06 %), and CO2 fertilization (16.59 %). Globally, satellite-derived datasets also show widespread increasing LUE over the past two decades, most attributed to the nitrogen deposition and CO2 fertilization effects, especially in evergreen broadleaf forests. Future projections of terrestrial LUE by CMIP6 Earth system models further suggest an overall increasing trend of LUE to the end of the 21st century. Our findings highlight the importance of vegetation physiology such as LUE in understanding of enhancement on terrestrial plant photosynthesis and carbon sink under climate change.

中文翻译：

---

观察到陆地总初级生产力的光利用效率提高


二氧化碳施肥驱动的全球广泛绿化意味着更密集的树冠结构，可以使用更多的叶子从大气中收集光进行植物光合作用。这种叶子数量的增加是否能增强植被将吸收光转化为光合产物的能力尚不清楚。在这项研究中，我们研究了冠层光利用效率 （LUE） 的时空变化，LUE 是叶片光合作用能力的指标，FLUXNET 记录为 540 个站点年和 7 个卫星衍生的代理。我们发现磁通塔测量确定了 LUE 的增加趋势，跨站点 LUE 的时间变化主要由氮肥 （18.09 %）、温度 （17.06 %） 和 CO2 施肥 （16.59 %） 引起。在全球范围内，卫星衍生的数据集还显示，在过去二十年中，LUE 普遍增加，这主要归因于氮沉积和 CO2 施肥效应，尤其是在常绿阔叶林中。CMIP6 地球系统模式对地面 LUE 的未来预测进一步表明，到 21 世纪末，LUE 总体呈增长趋势。我们的研究结果强调了植被生理学（如 LUE）在理解气候变化下增强陆生植物光合作用和碳汇方面的重要性。