Kaitaniemi Pekka, Ruohomäki Kai, Ossipov Vladimir, Haukioja Erkki, Pihlaja Kalevi
Section of Ecology, Department of Biology, and Kevo Subarctic Research Institute, University of Turku, FIN-20014 Turku, Finland e-mail:
Laboratory of Physical Chemistry, Department of Chemistry, FIN-20014 Turku, Finland, , , , , , FI.
Oecologia. 1998 Aug;116(1-2):182-190. doi: 10.1007/s004420050578.
In birch, Betula pubescens, herbivore-induced delayed induced resistance (DIR) of defoliated trees may cause a strong reduction in the potential fecundity of a geometrid folivore Epirrita autumnata. In this study, we examined the biochemical basis of DIR in birch leaves during a natural outbreak of E. autumnata. A set of experimental trees was defoliated at four sites by wild larvae in the peak year of the outbreak, whereas control trees were protected from defoliation by spraying with an insecticide. The biochemical composition of leaves was analysed in the following year and, although the DIR response was weak during this outbreak, causing less than a 20% reduction in the potential fecundity of E. autumnata, some consistent relationships between defoliation, biochemistry and pupal mass of E. autumnata suggested a general biochemical basis for the defoliation-induced responses in birch leaves. Total concentrations of nitrogen, sugars and acetone-insoluble residue (e.g. cell wall polysaccharides, cell-wall-bound phenolics, protein, starch, lignin and hemicellulose) were consistently lower, and total concentrations of phenolics, especially of gallotannins and soluble proanthocyanidins, were higher in the leaves of trees defoliated in the previous year than in those protected from defoliation. The capacity of tannins to precipitate proteins correlated with contents of gallotannins, and was highest in defoliated trees. The pupal mass of E. autumnata showed a strong, positive correlation with concentrations of nitrogen and sugars, and a negative correlation with the acetone-insoluble residue and gallotannins in foliage. Correlations with other measured biochemical traits were weak. The correlation coefficients between biochemical traits and pupal mass consistently had similar signs for both defoliated and insecticide-sprayed trees, suggesting that variation in leaf quality due to defoliation in the previous year was based on similar biochemical traits as variation for other reasons. We suggest that DIR is associated with reduced growth activity of leaves, and may be seen as a delay in the biochemical maturation of leaves in defoliated trees. This explains the high concentration of gallotannins in defoliated trees, a characteristic feature of young leaves. However, the lower content of nitrogen and the higher content of soluble proanthocyanidins in defoliated trees are traits usually characterising mature, not young, leaves, indicating defoliation-induced changes in chemistry in addition to modified leaf age. Our results emphasise the importance of understanding the natural changes in chemistry during leaf maturation when interpreting defoliation-induced changes in leaf biochemistry.
在欧洲白桦（Betula pubescens）中，食叶害虫诱导的落叶树延迟诱导抗性（DIR）可能会导致尺蛾科食叶害虫Epirrita autumnata的潜在繁殖力大幅下降。在本研究中，我们调查了在Epirrita autumnata自然爆发期间白桦叶中DIR的生化基础。在爆发高峰期，一组实验树在四个地点被野生幼虫落叶，而对照树通过喷洒杀虫剂来防止落叶。次年分析了树叶的生化组成，尽管在这次爆发期间DIR反应较弱，导致Epirrita autumnata的潜在繁殖力下降不到20%，但落叶、生化特性与Epirrita autumnata蛹质量之间的一些一致关系表明，白桦叶中落叶诱导反应存在一般生化基础。前一年落叶的树的叶子中，氮、糖和丙酮不溶性残渣（如细胞壁多糖、细胞壁结合酚类、蛋白质、淀粉、木质素和半纤维素）的总浓度始终较低，而酚类，尤其是没食子单宁和可溶性原花青素的总浓度较高。单宁沉淀蛋白质的能力与没食子单宁含量相关，且在落叶树中最高。Epirrita autumnata的蛹质量与氮和糖的浓度呈强正相关，与树叶中丙酮不溶性残渣和没食子单宁呈负相关。与其他测量的生化特性的相关性较弱。落叶树和喷洒杀虫剂的树的生化特性与蛹质量之间的相关系数始终具有相似的符号，这表明前一年落叶导致的叶片质量变化与其他原因导致的变化基于相似的生化特性。我们认为DIR与叶片生长活性降低有关，可能被视为落叶树叶片生化成熟的延迟。这解释了落叶树中没食子单宁的高浓度，这是幼叶的一个特征。然而，落叶树中较低的氮含量和较高的可溶性原花青素含量通常是成熟叶而非幼叶的特征，这表明除了叶龄改变外，落叶还诱导了化学变化。我们的结果强调了在解释落叶诱导的叶片生化变化时，理解叶片成熟过程中自然化学变化的重要性。
