Storage of carbon reserves in spruce trees is prioritized over growth in the face of carbon limitation

Significance Forest decline due to climate change is increasing worldwide. Accurate forecasting of forest dynamics requires a mechanistic understanding of carbon allocation strategies that can link molecular process regulation to whole-tree responses. However, dedicated transdisciplinary investigations spanning these scales are lacking. Here we used a unique experimental platform to manipulate the whole-tree carbon balance and combine metabolic flux measurements with transcriptional information to reveal tree resource allocation priorities under reduced carbon supply. In contrast to current understanding and model implementations, we show that trees prioritize carbon allocation to storage and mobilization of storage to support respiration rather than growth to ensure immediate and future survival under negative carbon balance that may occur during critical periods of stress.