Department of Entomology, University of Wisconsin, Madison, WI 53706, USA.
J Chem Ecol. 2010 Jan;36(1):2-21. doi: 10.1007/s10886-009-9731-4.
Prominent among the many factors now affecting the sustainability of forest ecosystems are anthropogenically-generated carbon dioxide (CO2) and ozone (O3). CO2 is the substrate for photosynthesis and thus can accelerate tree growth, whereas O3 is a highly reactive oxygen species and interferes with basic physiological functions. This review summarizes the impacts of CO2 and O3 on tree chemical composition and highlights the consequences thereof for trophic interactions and ecosystem dynamics. CO2 and O3 influence phytochemical composition by altering substrate availability and biochemical/physiological processes such as photosynthesis and defense signaling pathways. Growth of trees under enriched CO2 generally leads to an increase in the C/N ratio, due to a decline in foliar nitrogen and concomitant increases in carbohydrates and phenolics. Terpenoid levels generally are not affected by atmospheric CO2 concentration. O3 triggers up-regulation of antioxidant defense pathways, leading to the production of simple phenolics and flavonoids (more so in angiosperms than gymnosperms). Tannins levels generally are unaffected, while terpenoids exhibit variable responses. In combination, CO2 and O3 exert both additive and interactive effects on tree chemical composition. CO2-and O3-mediated changes in plant chemistry influence host selection, individual performance (development, growth, reproduction), and population densities of herbivores (primarily phytophagous insects) and soil invertebrates. These changes can effect shifts in the amount and temporal pattern of forest canopy damage and organic substrate deposition. Decomposition rates of leaf litter produced under elevated CO2 and O3 may or may not be altered, and can respond to both the independent and interactive effects of the pollutants. Overall, however, CO2 and O3 effects on decomposition will be influenced more by their impacts on the quantity, rather than quality, of litter produced. A prominent theme to emerge from this and related reviews is that the effects of elevated CO2 and O3 on plant chemistry and ecological interactions are highly context- and species-specific, thus frustrating attempts to identify general, global patterns. Many of the interactions that govern above- and below-ground community and ecosystem processes are chemically mediated, ultimately influencing terrestrial carbon sequestration and feeding back to influence atmospheric composition. Thus, the discipline of chemical ecology is fundamentally important for elucidating the impacts of humans on the health and sustainability of forest ecosystems. Future research should seek to increase the diversity of natural products, species, and biomes studied; incorporate long-term, multi-factor experiments; and employ a comprehensive “genes to ecosystems” perspective that couples genetic/genomic tools with the approaches of evolutionary and ecosystem ecology.
在影响森林生态系统可持续性的诸多因素中，人为产生的二氧化碳（CO2）和臭氧（O3）尤为突出。CO2 是光合作用的底物，因此可以加速树木生长，而 O3 是一种高反应性的含氧物质，会干扰基本的生理功能。本综述总结了 CO2 和 O3 对树木化学成分的影响，并强调了这些影响对营养相互作用和生态系统动态的后果。CO2 和 O3 通过改变底物可用性和生化/生理过程（如光合作用和防御信号通路）来影响植物化学组成。在富含 CO2 的条件下，树木的生长通常会导致 C/N 比的增加，这是由于叶片氮的减少和碳水化合物和酚类物质的增加所致。萜类化合物的水平一般不受大气 CO2 浓度的影响。O3 会引发抗氧化防御途径的上调，导致简单酚类和类黄酮的产生（在被子植物中比裸子植物更为明显）。单宁水平一般不受影响，而萜类化合物则表现出不同的反应。总之，CO2 和 O3 对树木化学成分的影响既有累加效应，也有交互效应。CO2 和 O3 介导的植物化学变化会影响宿主选择、个体表现（发育、生长、繁殖）以及食草动物（主要是植食性昆虫）和土壤无脊椎动物的种群密度。这些变化会影响树冠受损的数量和时间模式以及有机基质的沉积。在 CO2 和 O3 升高的条件下产生的凋落物的分解速率可能会发生变化，也可能不会发生变化，并且可以对污染物的独立和交互作用做出反应。然而，总的来说，CO2 和 O3 对分解的影响将更多地受到它们对产生的凋落物数量而非质量的影响。从本综述和相关综述中出现的一个突出主题是，升高的 CO2 和 O3 对植物化学和生态相互作用的影响具有高度的情境特异性和物种特异性，因此阻碍了识别普遍的、全球的模式的尝试。控制地上和地下群落和生态系统过程的许多相互作用都是通过化学物质介导的，最终会影响陆地碳封存，并反馈到大气成分的影响。因此，化学生态学学科对于阐明人类对森林生态系统健康和可持续性的影响至关重要。未来的研究应努力增加所研究的天然产物、物种和生物群落的多样性；纳入长期、多因素实验；并采用综合的“从基因到生态系统”的观点，将遗传/基因组工具与进化和生态系统生态学的方法相结合。
