Cobb N S, Mopper S, Gehring Catherine A, Caouette Matt, Christensen Kerry M, Whitham Thomas G
Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ86011, USA fax: 602-523-7500, e-mail:
Oecologia. 1997 Feb;109(3):389-397. doi: 10.1007/s004420050098.
Using 6 years of observational and experimental data, we examined the hypothesis that water and nutrient stress increase the susceptibility of pinyon pine (Pinus edulis) to the stem- and cone-boring moth (Dioryctria albovittella). At two geographic levels, a local scale of 550 km and a regional scale of 10,000 km, moth herbivory was strongly correlated with an edaphic stress gradient. At a local scale, from the cinder soils of Sunset Crater to nearby sandy-loam soils, nine of ten soil macro- and micronutrients, and soil water content were lowest in cinder-dominated soils. Herbivore damage was six times greater on trees growing in the most water and nutrient deficient site at Sunset Crater compared to sites with well-developed soils. Percentage silt-clay content of soil, which was highly positively correlated with soil nutrient and soil moisture at a local scale, accounted for 56% of the variation in herbivory at a regional scale among 22 sites. Within and across sites, increased stem resin flow was positively associated with reduced moth attack. On the basis of moth distribution across a stress gradient, we predicted that pinyons growing in highly stressful environments would show increased resistance to herbivores if supplemented with water and/or nutrients. We conducted a 6-year experiment at a high-stress site where individual trees received water only, fertilizer only, and water + fertilizer. Relative to control trees, stem growth and resin flow increased in all three treatments, but only significantly in the water + fertilizer treatment. Although there was no significant difference in herbivore damage among these three treatments, there was an overall reduction in herbivore damage on all treatment trees combined, compared to control trees. This experiment suggests that release from stress leads to increased resistance to insect attack and is consistent with our observational data. While other studies have predicted that short-term stress will result in herbivore outbreaks, our studies extend this prediction to chronically stressed host populations. Finally, while flush-feeders are not predicted to respond positively to stressed host plants, we found a positive association between herbivore attack and stressed pinyon populations.
利用6年的观测和实验数据，我们检验了以下假设：水分和养分胁迫会增加矮松（Pinus edulis）对蛀干和蛀球果蛾（Dioryctria albovittella）的易感性。在两个地理尺度上，一个是550公里的局部尺度，另一个是10000公里的区域尺度，蛾类食草作用与土壤胁迫梯度密切相关。在局部尺度上，从日落火山口的火山灰土壤到附近的砂壤土，在以火山灰为主的土壤中，十种土壤大量和微量养分中的九种以及土壤含水量最低。与土壤发育良好的地点相比，在日落火山口水分和养分最缺乏的地点生长的树木，食草动物造成的损害要大六倍。在局部尺度上与土壤养分和土壤湿度高度正相关的土壤粉砂 - 粘土含量百分比，在区域尺度上的22个地点间占食草作用变化的56%。在各地点内部和不同地点之间，茎干树脂流量增加与蛾类攻击减少呈正相关。基于蛾类在胁迫梯度上的分布，我们预测，在高胁迫环境中生长的矮松，如果补充水分和/或养分，将表现出对食草动物抵抗力的增强。我们在一个高胁迫地点进行了为期6年的实验，对单株树木分别仅浇水、仅施肥以及浇水 + 施肥。相对于对照树木，所有三种处理中茎干生长和树脂流量均增加，但仅在浇水 + 施肥处理中显著增加。虽然这三种处理之间食草动物造成的损害没有显著差异，但与对照树木相比，所有处理树木组合在一起时食草动物造成的损害总体上有所减少。该实验表明，解除胁迫会导致对昆虫攻击的抵抗力增强，这与我们的观测数据一致。虽然其他研究预测短期胁迫会导致食草动物爆发，但我们的研究将这一预测扩展到了长期受胁迫的寄主种群。最后，虽然预计掠食性昆虫不会对受胁迫的寄主植物产生积极反应，但我们发现食草动物攻击与受胁迫的矮松种群之间存在正相关。
