We previously reported the species-specific annual ring formation characteristics of three conifers (slash pine (Pinus elliottii), hinoki (Japanese cypress, Chamaecyparis obtusa) and sugi (Japanese cedar, Cryptomeria japonica)) grown in the same stand over 2 years. We found that the species-specific annual ring formation characteristics affected the inherent difference in wood density among these conifers (slash pine > hinoki > sugi). Plant hormones in cambial-region tissues were believed to affect annual ring formation. However, seasonal variation of the amounts of plant hormones in cambial-region tissues had only been examined in a few tree species. In this study, as the first step to elucidating the role of plant hormones in annual ring formation in conifers, we report the seasonal variations of the auxin (indole acetic acid, IAA) and gibberellin A4 (GA4) levels in cambial-region tissues and their effects on annual ring formation in three conifers (slash pine, hinoki, and sugi) with inherently different wood densities. Sugi (small wood density) had significantly higher levels of IAA and formed more tracheids in the early season than in the late season, although slash pine (large wood density) had higher levels of IAA and formed significantly more tracheids in the late season than in the early season. Hinoki (intermediate wood density) had constant IAA levels and formed a constant number of tracheids throughout the season. There were significant positive correlations between the levels of IAA in cambial-region tissues and the number of tracheids formed during late season in the two conifer species. A close relationship was observed between the seasonal ratio of the IAA levels (late/early season) and wood density. No consistent trend in the change in the level of IAA during the transition from earlywood to latewood formation was recognized among the three conifers. The IAA levels in slash pines were significantly higher than those in sugi and hinoki. The GA4 levels had no significant effect on number of tracheids formed in the three conifers. These results suggest that the species-specific seasonal variation patterns of the IAA levels might lead to the inherent differences in wood density among these three conifers through species-specific characteristics in the formation of annual rings.

中文翻译：

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三种具有固有木材密度的针叶树（松、扁柏和柳杉）形成层区组织中生长素和赤霉素A4水平的季节性变化

我们之前报道了在同一林分上生长超过 2 年的三种针叶树（红松（Pinus elliottii）、桧木（日本柏，Chamaecyparis obtusa）和杉木（日本雪松，Cryptomeria japonica））的物种特异性年轮形成特征。我们发现特定物种的年轮形成特征影响了这些针叶树（阔叶松>丝柏>杉）木材密度的内在差异。形成层区域组织中的植物激素被认为会影响年轮的形成。然而，仅在少数树种中检查了形成层区域组织中植物激素量的季节性变化。在这项研究中，作为阐明植物激素在针叶树年轮形成中作用的第一步，我们报告了生长素（吲哚乙酸、IAA) 和赤霉素 A4 (GA4) 在形成层区域组织中的水平及其对具有固有不同木材密度的三种针叶树（阔叶松、丝柏和杉木）年轮形成的影响。Sugi（木材密度小）的 IAA 水平显着高于季末，并在早季形成了更多的管胞，尽管阔叶松（大木密度）的 IAA 水平更高，并且在晚季形成的管胞明显多于季末。赛季初。桧木（中等木材密度）在整个季节具有恒定的 IAA 水平并形成恒定数量的管胞。两种针叶树种形成层区组织中IAA水平与晚季形成的管胞数呈显着正相关。观察到 IAA 水平（晚/早季）的季节性比率与木材密度之间存在密切关系。在三种针叶树中，在从早材到晚材形成的过渡过程中，IAA 水平的变化没有一致的趋势。斜线松的 IAA 水平明显高于杉木和丝柏。GA4 水平对三种针叶树中形成的管胞数量没有显着影响。这些结果表明，IAA 水平的物种特异性季节性变化模式可能通过年轮形成中的物种特异性特征导致这三种针叶树之间木材密度的内在差异。在三种针叶树中，在从早材到晚材形成的过渡过程中，IAA 水平的变化没有一致的趋势。斜线松的 IAA 水平明显高于杉木和丝柏。GA4 水平对三种针叶树中形成的管胞数量没有显着影响。这些结果表明，IAA 水平的物种特异性季节性变化模式可能通过年轮形成中的物种特异性特征导致这三种针叶树之间木材密度的内在差异。在三种针叶树中，在从早材到晚材形成的过渡过程中，IAA 水平的变化没有一致的趋势。斜线松的 IAA 水平明显高于杉木和丝柏。GA4 水平对三种针叶树中形成的管胞数量没有显着影响。这些结果表明，IAA 水平的物种特异性季节性变化模式可能通过年轮形成中的物种特异性特征导致这三种针叶树之间木材密度的内在差异。