Initial Growth of Large, Outplanted, Container-Grown Rooted Cuttings of Sugi (Cryptomeria japonica) with Leaf Removal Treatment for Alleviating Transplant Shock and Stem Incline

Abstract

We examined the effectiveness of partial leaf removal for alleviating transplant shock and reducing the risk of stem tilting in large-rooted cuttings of container-grown sugi (Cryptomeria japonica) with high shoot:root ratios. Different intensities of leaf removal (0%, 25%, 50% and 75%) were applied to large sugi rooted cuttings immediately after outplanting, and the stomatal conductance (gs), growth, and degree of stem incline (DSI) during the first growing season were compared to short-rooted cuttings. The 75% removal treatment was associated with high gs values (ca. 1.7–3.0 times of the other treatments) in the early stage of plantation establishment indicating the alleviation of water stress; however, this advantage disappeared within three months after planting. The stems with lower defoliation rates (i.e., 0% and 25%) tended to have large DSI values (about twice those of the 50% and 75% treatments) at an early stage of plantation establishment; however, this effect had almost disappeared within three months. The change in the DSI values and the height-to-diameter ratio (H/D) demonstrated that stem tilting was closely related to a high stem slenderness. The results of the present study showed that the effect of leaf removal on the alleviation of transplant shock and stem tilting was limited. Conversely, both stem elongation and diameter growth tended to be delayed at higher defoliation rates (27%–38% declines in elongation rate and 69%–30% declines in diameter growth compared to the 0% leaf removal treatment, respectively) due to the loss of photosynthetic organs. The large initial H/D also decreased the elongation rate immediately after planting. We consider that it would be better to reduce the initial H/D at the production of the cuttings before outplanting, rather than reducing the risk of stem tilting by leaf removal at the time of outplanting.