臭氧污染对杨树叶片化学组成及昆虫食叶量的影响

Insect-mediated biomass loss is one of the significant impact factors of forest carbon sequestration potential, which could be influenced by several environmental changes. Anthropogenic O3 emissions have become an important environmental problem in China, and is affecting the performance of forest pests. However, how tropospheric O3 may affect insect consumption through changing phytochemistry in plant tissue is still unknown. Here we intend to assess the effect of elevated O3 on insect leaf consumption in poplar and its underlying mechanism at open top chambers and free air O3 concentration enrichment (O3-FACE) facility. This project aims to determine the linear/nonlinear relationship between poplar leaf quality and elevated O3 by establishing the dose relationship between poplar foliage phytochemistry and O3 concentrations; to clarify the indirect effect mechanism of elevated O3 on the performance of poplar defoliators by analyzing the relationships among O3-mediated poplar phytochemistry changes, the insect feeding behaviors and their leaf consumption; and to reveal the impacts of tropospheric O3 pollution on the total consumption of poplar defoliator community and its potential mechanism by investigating the degree of insect damage to foliage in the poplar plantation base on the results of the former two studies. The results of this research could provide a theoretical basis for understanding the impact of tropospheric O3 pollution on the carbon sequestration capacity of forest ecosystems, and provide scientific guidance when designing the forest protection and management frameworks in northern China under global changes scenario.

昆虫取食导致的生物量损失是影响森林固碳能力的重要因素，其取食行为会受环境变化的影响。人类活动引起的大气O3浓度增加已成为中国面临的重要环境问题，正在改变森林害虫的行为。然而，O3将如何通过改变植物化学组成来影响昆虫的取食量尚不明确。本研究拟以杨树为研究对象，利用开顶箱和开放式O3熏蒸平台(O3-FACE)，探究O3增加对昆虫食叶量的影响规律及机制。通过建立叶片化学组成与O3浓度的剂量关系，明确杨树叶片品质与O3浓度变化的线性/非线性关系；通过分析O3导致的叶片化学组成变化、昆虫取食行为及其食叶量之间的关系，阐明O3对杨树害虫取食的间接影响机制；并在此基础上对野外杨树人工林叶片虫食强度进行调查，以揭示大气O3污染对杨树食叶昆虫群落取食量的影响规律及其潜在机制。研究成果为理解O3污染对森林固碳能力的影响提供理论基础，并为全球变化下我国北方森林保护和管理措施的制定提供科学参考。

昆虫取食导致的生物量损失是影响森林固碳能力的重要因素，其取食行为会受环境变化的影响。人类活动引起的大气O3浓度增加已成为中国面临的重要环境问题，正在改变森林害虫的行为。然而，O3将如何通过改变植物化学组成来影响昆虫的取食量尚不明确。本项目以杨树为研究对象，利用开顶箱(OTCs)和开放式O3熏蒸平台(O3-FACE)，调查了杨树叶片化学组成对O3浓度升高的响应规律，分析了O3导致的叶片化学组成变化及美国白蛾（Hyphantria cunea）食叶量之间的关系，并对杨树人工林冠层虫食强度进行了为期3年的调查。研究结果表明：O3熏蒸（环境浓度+40ppb）可显著增加杨树氮、可溶性糖、木质素浓度，降低淀粉浓度，改变杨树叶片的化学组成；土壤水分亏缺会减轻O3对杨树碳水化合物以及木质素浓度的影响。杨树酚类化合物对O3剂量升高的响应呈非线性响应模式，表现为先上升后下降的双相响应曲线；该现象主要出现在强抗氧化能力的酚类化合物（如缩合单宁）中。美国白蛾饲养实验结果表明O3熏蒸后的杨树会缩短幼虫发育历期，降低食物转化效率，并增加总叶消耗量；这些结果表明O3升高将导致杨树叶片品质下降，进而促使昆虫进行补偿性取食。综上所述，本研究表明大气O3浓度升高可能会通过改变植物叶片化学组成影响食叶昆虫的行为和取食量。本研究还发现在O3污染对植物化学成分的影响会因其他伴生环境因素以及O3浓度的变化而改变。忽视O3污染-其他环境胁迫的交互作用以及O3的剂量效应，可能会导致错误估计O3污染的生态效应，不利于大气污染环境下森林保护和管理措施的制定与完善。