Table_2_Response of Background Herbivory in Mature Birch Trees to Global Warming.XLSX

Given the time scale based on the duration of exposure to global warming, natural climate-gradient studies and experimental manipulations have detected long-term (decades to centuries) and short-term (years to decades) ecological responses to global warming. Combination of these two complementary approaches within a single study may enable prediction of the likely responses of ecological processes to global warming. To understand how global warming affects plant–herbivore interactions within a canopy of Erman’s birch, we combined an elevational gradient study and a warming experiment involving mature birch trees in which the soil and tree branches were warmed separately. In the elevational gradient study, herbivory by chewing insects and plant growth increased as elevation decreased, and the concentrations of condensed tannins and total phenolics in the leaves decreased. In the warming experiment, soil warming alone increased herbivory, and the addition of branch warming amplified the effect on herbivory. Soil warming alone decreased the tannin concentration, and the addition of branch warming led to a further reduction. The variation in herbivory was best explained by the tannin content of leaves. Our experimental results demonstrate that the decreased tannin content of leaves due to a combination of soil and branch warming was an important driver of increased herbivory in the canopy of the mature birch trees. The similar tendencies in the short- and long-term responses imply that global warming is likely to increase background herbivory in mature birch trees by decreasing the tannin content of leaves in the canopy.

基于全球变暖暴露时长构建的时间尺度框架下，自然气候梯度研究与野外操控实验均已观测到全球变暖引发的长期（数十年至数百年）与短期（数年至数十年）生态响应。将这两种互补研究方法整合至同一项工作中，或可实现对生态过程响应全球变暖的潜在趋势预测。为明确全球变暖如何影响耳曼桦（Erman’s birch）冠层内的植物-植食者互作，本研究整合了海拔梯度研究与野外增温实验：实验对象为成熟桦树，分别对其土壤与树枝实施独立增温处理。在海拔梯度研究中，随着海拔降低，咀嚼式昆虫的植食危害与植物生长速率均有所提升，而叶片中缩合单宁与总酚类物质的浓度则呈下降趋势。在增温实验中，仅土壤增温即可提升植食危害程度，而额外添加树枝增温则会进一步放大该效应；仅土壤增温即可降低叶片单宁浓度，辅以树枝增温则会使单宁浓度进一步下降。叶片单宁含量可最佳解释植食危害程度的变异情况。本实验结果表明，土壤与树枝联合增温导致的叶片单宁含量降低，是成熟桦树冠层植食危害加剧的重要驱动因素。短期与长期响应呈现的相似趋势表明，全球变暖或可通过降低成熟桦树冠层叶片的单宁含量，提升其背景植食危害水平。