Widespread spring warming and an earlier start of the growing season (SOS) compensated for spring vegetation productivity, simultaneously resulting in reduced retention of accessible nutrition and water resources in subsequent seasons. In this case, however, it is unknown whether the increased summer growth induced by earlier SOS will be sustained. Here, we analyzed the legacy effects of SOS on summer growth under historical and future scenarios, through combining remote sensing products, flux tower observations and model simulations. We observed that the background climate (summer temperature and summer precipitation) modulated the response of summer growth to SOS. In the past two decades, the advance of SOS promoted summer growth in most areas of the northern ecosystems, except for dry and hot regions. Moreover, the effects of SOS on plant growth reversed within the summer months, which may be related to the continued deterioration of moisture conditions. Models predicted a general shift from a negative to a positive correlation between SOS and summer growth under future warming and regionally uneven precipitation. In particular, under SSP370 and SSP585 scenarios, areas of positive correlation will exceed that of negative correlation by the end of the century. These results indicated the stimulation of summer growth by SOS advance may shift to inhibition in more regions in the future. Our findings highlighted the limited enhancement of plant carbon sink by altered spring phenology under future climate change.

中文翻译：

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在未来情景下，早春绿化对北方生态系统夏季生长的效益下降

春季普遍变暖和生长季节（SOS）提前开始补偿了春季植被生产力，同时导致后续季节可获取营养和水资源的保留减少。然而，在这种情况下，尚不清楚早期 SOS 引起的夏季生长增加是否会持续。在这里，我们通过结合遥感产品、通量塔观测和模型模拟，分析了历史和未来情景下SOS对夏季生长的遗留影响。我们观察到背景气候（夏季气温和夏季降水）调节了夏季生长对 SOS 的响应。过去二十年来，SOS的推进促进了北方生态系统除干热地区外大部分地区的夏季生长。此外，SOS对植物生长的影响在夏季出现逆转，这可能与水分条件的持续恶化有关。模型预测，在未来变暖和区域降水不均的情况下，SOS 与夏季生长之间的总体关系将从负相关转变为正相关。特别是，在SSP370和SSP585情景下，到本世纪末，正相关的面积将超过负相关的面积。这些结果表明，未来更多地区SOS提前对夏季生长的刺激可能会转变为抑制。我们的研究结果强调了未来气候变化下春季物候变化对植物碳汇的增强有限。