Williams R S, Lincoln D E, Thomas R B
Department of Biological Sciences, University of South Carolina, 29208, Columbia, SC, USA.
Botany Department, Duke University, 27706, Durham, NC, USA.
Oecologia. 1994 Jun;98(1):64-71. doi: 10.1007/BF00326091.
Seedlings of loblolly pine Pinus taeda (L.), were grown in open-topped field chambers under three CO regimes: ambient, 150 μl l CO above ambient, and 300 μl l CO above ambient. A fourth, non-chambered ambient treatment was included to assess chamber effects. Needles were used in 96 h feeding trials to determine the performance of young, second instar larvae of loblolly pine's principal leaf herbivore, red-headed pine sawfly, Neodiprion lecontei (Fitch). The relative consumption rate of larvae significantly increased on plants grown under elevated CO, and needles grown in the highest CO regime were consumed 21% more rapidly than needles grown in ambient CO. Both the significant decline in leaf nitrogen content and the substantial increase in leaf starch content contributed to a significant increase in the starch:nitrogen ratio in plants grown in elevated CO. Insect consumption rate was negatively related to leaf nitrogen content and positively related to the starch:nitrogen ratio. Of the four volatile leaf monoterpenes measured, only β-pinene exhibited a significant CO effect and declined in plants grown in elevated CO. Although consumption changed, the relative growth rates of larvae were not different among CO treatments. Despite lower nitrogen consumption rates by larvae feeding on the plants grown in elevated CO, nitrogen accumulation rates were the same for all treatments due to a significant increase in nitrogen utilization efficiency. The ability of this insect to respond at an early, potentially susceptible larval stage to poorer food quality and declining levels of a leaf monoterpene suggest that changes in needle quality within pines in future elevated-CO atmospheres may not especially affect young insects and that tree-feeding sawflies may respond in a manner similar to herb-feeding lepidopterans.
火炬松（Pinus taeda L.）幼苗在开放式田间试验箱中，于三种二氧化碳浓度条件下生长：环境浓度、比环境浓度高150 μl l二氧化碳、比环境浓度高300 μl l二氧化碳。设置了第四个非试验箱环境处理，以评估试验箱的影响。在96小时的取食试验中，使用针叶来测定火炬松主要食叶害虫红头松叶蜂（Neodiprion lecontei (Fitch)）二龄幼虫的生长情况。在二氧化碳浓度升高条件下生长的植株上，幼虫的相对取食率显著增加，在最高二氧化碳浓度条件下生长的针叶，其被取食的速度比在环境二氧化碳浓度下生长的针叶快21%。叶片氮含量显著下降以及叶片淀粉含量大幅增加，共同导致了在二氧化碳浓度升高条件下生长的植株中淀粉:氮比值显著升高。昆虫取食率与叶片氮含量呈负相关，与淀粉:氮比值呈正相关。在所测定的四种挥发性叶片单萜中，只有β-蒎烯表现出显著的二氧化碳效应，且在二氧化碳浓度升高条件下生长的植株中含量下降。尽管取食量发生了变化，但各二氧化碳处理间幼虫的相对生长率并无差异。尽管取食二氧化碳浓度升高条件下生长植株的幼虫氮消耗量较低，但由于氮利用效率显著提高，所有处理的氮积累率相同。这种昆虫在幼虫早期、可能易受影响的阶段对较差食物质量和叶片单萜含量下降做出反应的能力表明，在未来二氧化碳浓度升高的大气环境中，松树针叶质量的变化可能不会特别影响幼龄昆虫，而且以树为食的叶蜂可能会以与以草本植物为食的鳞翅目昆虫类似的方式做出反应。
