Characterization of water stress during cold storage and establishment for Acer platanoides and Crataegus phaenopyrum

This study examined the affects of desiccation during and after cold storage on the physiology, growth, and marketability of bare-root Acer platanoides (Norway maple), Crataegus phaenopyrum (Washington hawthorn) and Prunus x yedoensis (Yoshino cherry). Histological examination of Acer and Crataegus stems was also conducted. Maple and cherry trees were transplanted into pine bark-filled containers and subjected to mist or non-mist treatments. Xylem water potential increased (became less negative) for misted maple and cherry trees. Water potential increased for non-misted maple and decreased for non-misted cherry trees. Maple and hawthorn seedlings were subjected to cold storage durations of 2, 4, 6, 8, 10, and 12 weeks and storage treatments: whole plant covered, shoots exposed, roots exposed and whole plant exposed. Shoot (Ψ_s) and root (Ψ_r) water potentials for all treatments and both species decreased during storage. For maple, (Ψ_s) and (Ψ_r) of the exposed shoot treatment were the same as the whole plant covered treatment. In contrast, hawthorn (Ψ_s) and (Ψ_r) of the exposed shoot treatment were lower (more negative) than for the whole plant covered treatment. Root hydraulic conductivity was the same for both species and decreased with increased storage duration and for treatments with exposed roots. For the root covered treatments, maple root growth potential (RGP) increased while hawthorn RGP decreased with increased cold storage duration. RGP for both species remained low throughout storage for treatments exposing roots. Days to bud break for Acer and Crataegus seedlings decreased with increased storage time for the whole plant covered treatments but increased for both species when stored with exposed roots. Maple marketability, percent of trees with ≤ 10% shoot dieback, for root covered treatments was high for most storage durations. Hawthorn marketability was generally low except for the whole plant covered treatment during the first six weeks of storage. There was a high positive correlation between RGP and marketability for both maple and hawthorn. Histological examination revealed that Acer stems had a highly suberized periderm, and a uniform cuticle with few disruptions. Periderm suberization of Crataegus stems was variable and extensive peridermal cracking was evident. Cuticle wax decreased with increasing distance from the stem apex for both species. Collectively, results indicated that hawthorn stems had more pathways for water loss than maple shoots. While protection of roots of all bare-root stock is important, desiccation sensitive species such as Washington hawthorn require both root and shoot protection during storage and at transplanting to minimize water loss.