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

Abstract

Dynamics in non-structural carbohydrate (NSC) pools may underlie observed drought legacies in tree growth. We assessed how aridity influences the dynamics of different-aged NSC pools in tree sapwood at two sites with differing climate conditions (‘wet’ vs. ‘dry’) that also experienced widespread regional drought five years earlier. We used an incubation method to measure radiocarbon (Δ14C) in CO2 respired from Populus tremuloides (aspen) tree rings to evaluate NSC storage and mixing patterns, coupled with measurements of NSC (soluble sugars, starch) concentrations and respired δ13C-CO2. At a wet site, CO2 respired from rings formed during 1962–1967 was only ~ 11 years old, suggesting deep sapwood mixing of NSCs as starch. At a dry site, total NSC was about one-third of wet site totals, maximum ages in deep rings were lower, and ages more rapidly increased in shallow rings then plateaued. These results suggest historically shallower mixing and/or relatively higher consumption of NSCs under dry conditions. Both sites, however, had similar aged NSC (<1 yr) in the most recent six rings, indicative of deep radial mixing following relatively wet conditions during the sampling year. We suggest significant differences in NSC mixing among sites are driven by moisture stress, where aridity reduces NSC reserves and restricts the depth of radial mixing. However, dynamic climate conditions in the southwestern US resulted in more complex radial patterns of sapwood NSC age than previously described. We suggest a novel conceptual framework to understand how moisture variability might influence the dynamics of NSC mixing in the sapwood.

Anatomical distribution of starch in the stemwood influences carbon dynamics and suggests storage‐growth trade‐offs in some tropical trees

“…Wood is always in contact with the secondary phloem, the main tissue transporting NSC from leaves to roots and in itself an important NSC storage tissue (Rosell et al, 2021). There is constant mixing of NSC between the secondary phloem and adjacent wood tissue, allowing trees to store some portion of NSC for years or even decades (Furze et al, 2018;Peltier et al, 2023).…”