Data from: Forest defoliator pests alter carbon and nitrogen cycles

Climate change may foster pest epidemics in forests, and thereby the fluxes of elements that are indicators of ecosystem functioning. We examined compounds of carbon (C) and nitrogen (N) in insect faeces, leaf litter, throughfall and analysed the soils of deciduous oak forests (Quercus petraea L.) that were heavily infested by the leaf herbivores winter moth (Operophtera brumata L.) and mottled umber (Erannis defoliaria L.). In infested forests, total net canopy-to-soil fluxes of C and N deriving from insect faeces, leaf litter and throughfall were 30- and 18-fold higher compared with uninfested oak forests, with 4333 kg C ha−1 and 319 kg N ha−1, respectively, during a pest outbreak over 3 years. In infested forests, C and N levels in soil solutions were enhanced and C/N ratios in humus layers were reduced indicating an extended canopy-to-soil element pathway compared with the non-infested forests. In a microcosm incubation experiment, soil treatments with insect faeces showed 16-fold higher fluxes of carbon dioxide and 10-fold higher fluxes of dissolved organic carbon compared with soil treatments without added insect faeces (control). Thus, the deposition of high rates of nitrogen and rapidly decomposable carbon compounds in the course of forest pest epidemics appears to stimulate soil microbial activity (i.e. heterotrophic respiration), and therefore, may represent an important mechanism by which climate change can initiate a carbon cycle feedback.

气候变化或加剧森林有害生物暴发，进而改变作为生态系统功能指示因子的元素通量。本研究针对受食叶害虫冬尺蛾（Operophtera brumata L.）和褐尺蛾（Erannis defoliaria L.）重度侵染的落叶栎林（Quercus petraea L.），对昆虫粪便、地表凋落物（leaf litter）、穿透雨（throughfall）中的碳（C）、氮（N）组分进行了检测，并对林分土壤开展了分析。在暴发虫害的林分中，源自昆虫粪便、地表凋落物与穿透雨的碳、氮冠层至土壤净总通量，较未侵染栎林分别提升30倍与18倍；在为期3年的虫害暴发期内，其碳通量与氮通量分别达4333 kg C·ha⁻¹和319 kg N·ha⁻¹。与未侵染林分相比，虫害林分的土壤溶液碳、氮浓度显著升高，腐殖质层碳氮比降低，表明其冠层至土壤的元素迁移路径得以扩展。在微宇宙培养试验（microcosm incubation experiment）中，添加昆虫粪便的土壤处理组，其二氧化碳通量与溶解性有机碳（dissolved organic carbon）通量分别较未添加粪便的对照组高16倍与10倍。综上，森林虫害暴发期大量氮与易分解碳组分的沉降，可刺激土壤微生物活动（即异养呼吸（heterotrophic respiration）），这或为气候变化引发碳循环反馈（carbon cycle feedback）的重要机制之一。