FIGURE 5.

Declining tree carbon uptake promotes carbon starvation. Sitka spruce (Picea Sitchensis) trees exposed to seawater inundation exhibit strong declines in (a) photosynthetic capacity (the slope of photosynthesis versus internal CO₂ concentration), (b) the fraction of their crowns that are foliated, and (c) starch concentrations in the foliage, branches, stems and roots. Combined, the decline in both photosynthetic capacity and in crown leaf area result in a significant decline in starch concentrations, which is the primary storage pool of carbon. As trees approach death the starch concentrations reach zero, which is rarely seen except for in studies that force carbon starvation (Quirk et al., 2013; Sevanto et al., 2014; Weber et al., 2018). Data used to create these figures are from Li et al. (2021) and Zhang, McDowell, et al. (2021).