Declined benefit of earlier spring greening on summer growth in northern ecosystems under future scenarios

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.