State Key Laboratory of Subtropical Silviculture, Zhejiang A&F University, 666 Wusu St, Lin'an District, Hangzhou, Zhejiang 311300, China.
Key Laboratory of Modern Silvicultural Technology of Zhejiang Province, 666 Wusu St, Lin'an District, Hangzhou, Zhejiang 311300, China.
Tree Physiol. 2024 Nov 5;44(11). doi: 10.1093/treephys/tpae124.
Lammas growth of trees means the additional growth of the shoot after the growth cessation and bud set in late summer. In temperate tree species, lammas growth occurs irregularly and is often regarded as abnormal, disturbed growth. In subtropical tree species, however, lammas growth is a prevalent phenomenon, possibly due to the prolonged occurrence of high temperatures in the autumn. The occurrence of lammas growth extends the growing season of trees, but its influence on subsequent dormancy phenomena and bud burst phenology remains largely unexplored. By comparing seedlings showing lammas growth with others not showing it, we carried out an experimental study of how lammas growth affects the bud burst phenology and the underlying dormancy phenomena under both ambient and controlled chilling, forcing and warming conditions in four subtropical tree species: Carya illinoinensis, Cinnamomum japonicum, Phoebe chekiangensis and Torreya grandis. With the exception of C. illinoinensis, lammas growth delayed bud burst in all the species under ambient conditions. In the chilling experiment, the delayed bud burst appeared to be due to higher minimum forcing requirement, higher dormancy depth, and in T. grandis, also due to lower chilling sensitivity in the lammas-growth seedlings than in the non-lammas-growth ones. However, a spring warming experiment showed that the sensitivity of bud burst to spring temperatures was higher in the lammas-growth seedlings than in the non-lammas-growth ones. Because of this, the difference between the two phenotypes in the timing of bud burst vanished with increasing warming. Our findings elucidate the significant impact of lammas growth on the dormancy dynamics of subtropical tree species, highlighting the necessity to better understand how the physiological phenomena causing lammas growth change the trees' subsequent environmental responses under changing climatic conditions.
树木的“Lammas 生长”是指夏末生长停止和芽形成后，新梢的额外生长。在温带树种中，“Lammas 生长”不规则地发生，通常被视为异常的、受干扰的生长。然而，在亚热带树种中，“Lammas 生长”是一种普遍现象，可能是由于秋季高温持续时间较长。“Lammas 生长”的发生延长了树木的生长季节，但它对随后的休眠现象和芽爆发物候的影响在很大程度上仍未得到探索。通过比较表现出“Lammas 生长”的幼苗与其他未表现出“Lammas 生长”的幼苗，我们在四个亚热带树种中进行了一项实验研究，即在环境和控制冷却、强迫和变暖条件下，“Lammas 生长”如何影响芽爆发物候和潜在休眠现象：薄壳山核桃、肉桂、浙江楠和罗汉松。除了薄壳山核桃，在环境条件下，所有树种的“Lammas 生长”都延迟了芽的爆发。在冷却实验中，延迟的芽爆发似乎是由于更高的最小强迫需求、更高的休眠深度，以及在罗汉松中，也由于“Lammas 生长”幼苗比“非 Lammas 生长”幼苗的冷却敏感性更低。然而，春季变暖实验表明，“Lammas 生长”幼苗对春季温度的芽爆发敏感性高于“非 Lammas 生长”幼苗。由于这个原因，两种表型之间在芽爆发时间上的差异随着变暖的增加而消失。我们的发现阐明了“Lammas 生长”对亚热带树种休眠动态的显著影响，强调了需要更好地理解导致“Lammas 生长”的生理现象如何在气候变化条件下改变树木随后的环境反应。
