Edwards P J, Wratten S D, Parker E A
Department of Biology, The University, Building 62, S09 3TU, Southampton, UK.
Oecologia. 1992 Aug;91(2):266-272. doi: 10.1007/BF00317795.
This paper investigates the hypothesis that a rapidly induced phytochemical response to grazing damage, such as that seen in tomato, serves to deflect insect herbivores away from leaves soon after damaging them (the grazing dispersal hypothesis). As a result, grazing damage is more dispersed than it otherwise would be, and young leaves, which may be of particular importance to a plant in competition for light, are not damaged excessively. In the first experiment, artificial removal of c. 15% of leaf area led to a significant reduction in plant performance compared with undamaged controls, but only when the plants were grown together in competition for light. The second experiment demonstrated that the distribution of grazing damage within the plant was an important factor in the outcome of competition; in those plants in which grazing was applied to the lower leaves there was no effect of damage upon performance compared with undamaged controls, whereas grazing to the upper leaves significantly reduced plant performance. A third experiment provided some insight into how this interaction between damage and competition comes about. It was shown that damage to leaves led to a rapid drop in the rate of extension growth of the main shoot, especially when the upper leaves were damaged, and normal rates of growth were not resumed for at least 3 days. It is argued that in a rapidly growing canopy, such an effect may mean that a damaged plant loses its position in the height hierarchy. The final experiment showed that previous damage to plants can affect the distribution of subsequent grazing by larvae of Spodoptera littoralis, apparently through a wound-induced reduction in leaf palatability. Plants which had been artificially damaged 48 h previously were grazed significantly less than controls, and the avoidance effect was greatest in the young leaves. These results are consistent with the grazing dispersal hypothesis, and suggest that rapid wound-induced responses may be of greatest significance in species characteristic of fertile environments where competition for light is particularly intense.
植物对放牧损伤会迅速产生植物化学响应，就像在番茄中观察到的那样，这种响应会在昆虫食草动物损伤叶片后不久，使其离开叶片（放牧扩散假说）。结果，放牧损伤比原本的情况更分散，而幼叶对植物在争夺光照方面可能尤为重要，不会受到过度损伤。在第一个实验中，与未受损的对照组相比，人工去除约15%的叶面积会导致植物生长显著降低，但这仅在植物共同生长以争夺光照时才会出现。第二个实验表明，植物内部放牧损伤的分布是竞争结果的一个重要因素；在那些对下部叶片进行放牧的植物中，与未受损的对照组相比，损伤对生长没有影响，而对上叶进行放牧则显著降低了植物生长。第三个实验对损伤与竞争之间的这种相互作用是如何产生的提供了一些见解。结果表明，叶片损伤会导致主茎伸长生长速率迅速下降，尤其是上部叶片受损时，至少3天内无法恢复正常生长速率。有人认为，在快速生长的树冠中，这种效应可能意味着受损植物在高度层次结构中失去其位置。最后一个实验表明，先前对植物的损伤会影响随后斜纹夜蛾幼虫的放牧分布，显然是通过伤口诱导叶片适口性降低来实现的。48小时前曾被人工损伤的植物被放牧的程度明显低于对照组，并且这种回避效应在幼叶中最为明显。这些结果与放牧扩散假说一致，并表明快速的伤口诱导反应在光照竞争特别激烈的肥沃环境中的物种中可能具有最大的意义。
