Karban Richard
Department of Entomology, One Shields Avenue, University of California, Davis, CA 95616, USA.
Oecologia. 2007 Aug;153(1):81-8. doi: 10.1007/s00442-007-0709-z. Epub 2007 Mar 21.
Deciduous leaf fall is thought to be an adaptation that allows plants living in seasonal environments to reduce water loss and damage during unfavorable periods while increasing photosynthetic rates during favorable periods. Observations of natural variation in leaf shedding suggest that deciduous leaf fall may also allow plants to reduce herbivory. I tested this hypothesis by experimentally manipulating leaf retention for Quercus lobata and observing natural rates of herbivory. Quercus lobata is primarily deciduous although individuals show considerable natural variation in leaf retention. Oak saplings with no leaves through winter experienced reduced attack by cynipid gall makers the following spring. This pattern was consistent with the positive correlation between natural leaf persistence and gall numbers. These cynipids do not overwinter on the leaves that trees retain through winter, although they appear to use persistent leaves as oviposition cues. If these results are general for woody plants in continental temperate habitats, they suggest that an important and unrecognized consequence of deciduous leaf shedding may be a reduction in herbivore damage, and that this effect should be included in models of deciduous and evergreen behavior.
落叶被认为是一种适应性特征，它使生活在季节性环境中的植物能够在不利时期减少水分流失和损害，同时在有利时期提高光合速率。对落叶自然变异的观察表明，落叶还可能使植物减少食草动物的侵害。我通过对加州白栎的叶片保留情况进行实验操作，并观察自然食草率，来验证这一假设。加州白栎主要是落叶植物，尽管个体在叶片保留方面表现出相当大的自然变异。整个冬季没有叶片的橡树幼苗在次年春天受到瘿蜂侵害的情况减少。这种模式与自然叶片留存率和瘿蜂数量之间的正相关关系一致。这些瘿蜂不会在树木整个冬季保留的叶片上过冬，尽管它们似乎将留存的叶片用作产卵线索。如果这些结果对于大陆温带栖息地的木本植物具有普遍性，那么它们表明落叶的一个重要且未被认识到的后果可能是食草动物损害的减少，并且这种影响应纳入落叶和常绿植物行为模型中。
