Moisture stress limits radial mixing of non-structural carbohydrates in sapwood of trembling aspen.

This article investigates how aridity influences the dynamics of non-structural carbohydrate (NSC) pools—comprising soluble sugars and starch—in the sapwood of quaking aspen (Populus tremuloides Michx.) at two climatically contrasting sites in the southwestern USA, one wetter and one drier, both affected by a regional drought five years prior. Using radiocarbon (Δ14C) dating of CO2 respired from tree rings, alongside measurements of NSC concentrations and stable carbon isotopes (δ13C), the study found that trees at the dry site stored significantly less total NSC—about one-third of wet-site amounts—and exhibited shallower radial mixing of NSCs, with younger NSC ages in deep sapwood compared to the wet site. These patterns suggest that moisture stress restricts the depth of NSC mixing and may increase reliance on older carbohydrate reserves, with inter-annual climate variability influencing NSC dynamics. The authors propose a conceptual framework linking aridity and climate variability to NSC storage, mixing, and utilization, highlighting implications for tree drought resilience and carbon cycling.