Key message

Severe insect defoliation induced non-lignified tracheids and thin-walled latewood tracheids in the defoliation year in Larix kaempferi. These anomalous tracheids had heterogenous lignin deposition of S₂ layer.

Abstract

Severe insect defoliation induces the formation of light ring consisted of thin-walled latewood tracheids in larch trees, which would affect wood quality. However, the identity of the secondary wall layers affected by insect defoliation remains unclear. The aim of this study is to clarify the effects of insect defoliation on the formation of secondary cell walls of tracheids in Larix kaempferi with focus on the defoliation timing. We observed by light microscopy and transmission electron microscopy (TEM) the secondary cell walls of tracheids produced in a defoliation year in L. kaempferi trees on which needles were attacked in July (gypsy moth, GM samples) or August (larch sawfly, LS samples). Light microscopy observations revealed that GM samples produced non-lignified tracheids in the transition zone between earlywood and latewood, as well as thin-walled latewood tracheids, and non-lignified tracheids were observed near the cambial zone in LS samples following defoliation for two consecutive years. TEM observations revealed that the tracheids in both samples had anomalous layers in secondary walls such as thin S₂ layers with heterogeneous lignin deposition. The production of non-lignified tracheids corresponded to defoliation date in both samples, unlike changes in the layer composition of anomalous tracheids. Our study suggests that changes in wood structure depend on the date of insect defoliation and that insect defoliation affects the formation of secondary cell walls of tracheids, presumably in response to inadequate photosynthate supply as a result of defoliation.

中文翻译：

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不同时期的严重昆虫脱叶影响落叶松次生木质部气管中细胞壁的形成

关键信息

在落叶松落叶年，严重的昆虫脱叶诱导了非木质化的气管和薄壁的胶木气管。这些异常气管中的木质素沉积在S ₂层。

抽象

严重的昆虫脱叶会在落叶松树中形成由薄壁紫檀气管组成的轻环，这会影响木材质量。但是，受昆虫落叶影响的次生壁层的身份仍然不清楚。这项研究的目的是阐明昆虫落叶对落叶松（Larix kaempferi）的气管次级细胞壁形成的影响，重点是落叶时间。我们通过光学显微镜和透射电子显微镜（TEM）观察了L. kaempfer在落叶期产生的气管的次生细胞壁。在7月（吉普赛蛾，GM样品）或8月（落叶松锯虫，LS样品）上被针刺过的树木。光学显微镜观察显示，GM样品在早材和晚材之间的过渡带中产生了非木质化的气管，以及薄壁的晚材气管中，并且在连续两年脱叶之后，在LS样品的冈比亚区附近观察到了未木质化的气管。 。TEM观察表明，两个样品中的气管都在次生壁中有异常层，如薄S ₂木质素沉积不均的有机层。在两个样品中，非木质化气管的产生都对应于落叶的日期，这与异常气管的层组成的变化不同。我们的研究表明，木材结构的变化取决于昆虫脱叶的日期，并且昆虫脱叶会影响气管次级细胞壁的形成，大概是由于脱叶导致光合产物供应不足所致。