EFFECTS OF ENVIRONMENTAL GRADIENTS ON PLANT-HERBIVORE SYSTEMS OF WOODY PLANTS BELONGING TO THE FAGACEAE FAMILY

植物的诱导防御，即草食后酚类物质的增加和氮的减少，是各种植物普遍存在的现象。研究了环境因子对壳斗科四种植物组成防御和诱导防御的影响。我们检验了一个假设，即叶食性昆虫的海拔依赖性爆发是由与海拔相关的环境曲线相关的叶子特性引起的。研究结果表明，叶片质量可能是点状丝虫病发生地点依赖性爆发的原因之一：在爆发地点，高质量的食物促进了该昆虫的种群增长。当非疫区的山毛榉树遭受严重落叶时，叶片质量恶化，这减缓了斑点针叶虫种群的增长。相反，在暴发地区，在大量落叶之后的一年中，质量会提高，这可能会促进人口增长和暴发。因此，养分循环、叶片质量和昆虫种群生长之间可能存在正反馈过程。草食施肥效应是导致疫情区土壤氮有效性较高的一个直接因素。实验结果表明，防御性化合物的数量受叶片碳-养分平衡的控制。碳氮平衡是生物量分配和化学防御的重要因素。然而，落叶对植物体内碳氮平衡的影响在不同物种之间是不同的，这可能导致不同物种在食草反应中存在差异。

Induced defense of plants, increase in fenolics and decrease in nitrogen following herbivory, is a widely recognized phenomenon in various plants. Influence of environmental clines on constitutive and induced defense of four species of Fagaceae species were studied. We tested a hypothesis that altitudinal-dependent outbreaks of the folivorous insects were caused by foliage properties in relation to environment clines along with altitude. Our results suggest that the foliage quality is one of the possible causes of site-dependent outbreaks of S. punctatella: During an increasing period, high quality food at outbreak sites promotes population growth of this insect. When beech trees suffer heavy defoliation in the non-outbreak areas, foliage quality deteriorates, which slows down S. punctatella population growth. In contrast, in outbreak areas, quality increases in the year following heavy defoliation, and this may promote population growth and outbreaks. A positive feedback process thus may operate among nutrient cycling, foliage quality and insect population growth. A fertilizing effect from herbivory was a proximate factor causing higher soil nitrogen availability in the outbreak area. Results of our experiment suggested that the amount of defensive compounds was controlled by the carbon-nutrient balance at a leaf level. The C/N balance is an important factor for biomass allocation and chemical defense. However, the effect of defoliation on the C/N balance in a plant is variable between species, probably leading to a species variability in herbivory responses.