Cunningham Saul A, Pullen Kimberi R, Colloff Matthew J
CSIRO Entomology, Box 1700, Canberra, ACT, 2601, Australia.
Oecologia. 2009 Jan;158(4):633-40. doi: 10.1007/s00442-008-1170-3. Epub 2008 Oct 25.
Ecohydrological models consider the relationship between tree size and structure (especially leaf area index) and water use but generally treat herbivory as a source of unwanted noise in the data. Little is known of how insect damage to leaves influences whole-plant water use in trees. Water use is driven by environmental demand and the total leaf area through which transpiration can occur, but the effects of insects are expected to be complex. Different kinds of insects could have different effects; for example, chewing insects reduce leaf area, whereas sucking and tissue mining insects reduce leaf function without reducing area. Further, plants respond to herbivory in a range of ways, such as by altering leaf production or abscising leaves. We examined the effect of insects on Eucalyptus blakelyi in a woodland near Canberra, Australia, using sap flow velocity as a measure of whole-plant water use. We applied insecticide to 16 trees matched to an untreated control group. After 6 months, we examined the effects on sap flow velocity and crown condition. There was a general increase in sap flow velocity as trees produced leaves over the growing season, but the increase in sap flow for trees without insecticide protection was half that of the protected trees (increase: 4.4 vs. 9.0 cm/h, respectively). This dramatic effect on sap flow was consistent with effects on crown condition. Unprotected trees had 20% less leaf mass per unit stem in the crown. In addition, unprotected trees had a 20% greater loss of leaf functional area from necrosis. It should be noted that these effects were detected in a year in which there was not an outbreak of the psyllids (Homoptera) that commonly cause severe leaf damage to this tree species. It is predicted that the effect in a psyllid outbreak year would be even more substantial. This result underscores the significant impact that insect herbivores can have on an ecological process of significance to the ecosystem, namely, the movement of water from the soil to the atmosphere.
生态水文模型考虑了树木大小与结构（尤其是叶面积指数）和水分利用之间的关系，但通常将食草作用视为数据中不必要的噪声来源。对于昆虫对树叶的损害如何影响树木全株的水分利用，人们知之甚少。水分利用受环境需求和可发生蒸腾作用的总叶面积驱动，但昆虫的影响预计很复杂。不同种类的昆虫可能有不同的影响；例如，咀嚼式昆虫会减少叶面积，而吸食式和组织取食式昆虫会降低叶片功能但不减少面积。此外，植物会以多种方式对食草作用做出反应，比如改变叶片产量或落叶。我们在澳大利亚堪培拉附近的一片林地中，以液流速度作为全株水分利用的指标，研究了昆虫对布莱克利桉的影响。我们对16棵树施用了杀虫剂，并与未处理的对照组进行匹配。6个月后，我们研究了对液流速度和树冠状况的影响。随着树木在生长季节长出叶子，液流速度总体上有所增加，但未受杀虫剂保护的树木液流速度的增加量仅为受保护树木的一半（增加量分别为4.4厘米/小时和9.0厘米/小时）。这种对液流的显著影响与对树冠状况的影响一致。未受保护的树木树冠中每单位树干的叶质量减少了20%。此外，未受保护的树木因坏死而损失的叶片功能面积增加了20%。需要注意的是，这些影响是在没有木虱（同翅目）爆发的一年中检测到的，木虱通常会对该树种造成严重的叶片损害。据预测，在木虱爆发的年份，影响会更加显著。这一结果强调了食草昆虫对生态系统中一个重要生态过程，即水从土壤到大气的移动，可能产生的重大影响。
