Chemical and air pruning of roots influence post-transplant root traits of the critically endangered Serianthes nelsonii

Container production of Serianthes nelsonii Merr. plants for out-planting within the endemic range is a major component of the plan to recover the critically endangered tree species. We exploited the ability to prune roots with copper or with strategically placed air holes in container walls to determine if root quantity or quality would increase in comparison to traditional container design. Following 23 days of growth after transplanting, new root length and root dry weight did not differ among the container types. However, most roots from the control and copper-treated containers developed from the bottom of the root system, and direction of root growth was primarily geotropic. In contrast, the air-pruning containers produced plants with plagiotropic root growth near the soil surface. Root growth was positioned with 58% in the top two-thirds of a rhizotron window for the air-pruning, 29% for the copper-pruning, and 16% for the control containers. Our results indicate that direction but not length or dry weight of post-transplant root growth was changed by use of air-pruning containers. For a critically endangered tree like Serianthes nelsonii, the improved root morphology afforded by containers that use air-pruning of roots in the nursery may improve tree stability following transplanting.