东部云杉芽虫的落叶是加拿大北方和半北方森林中最重要的自然干扰之一,其年度影响面积超过了火灾和收获的总和,其影响预计会增加频率,严重程度,以及未来气候情景下的范围。决定采取积极的管理策略,控制疫情,最大限度地减少更广泛的经济,生态,社会影响变得越来越重要。这些策略在抑制落叶的程度上有所不同,但是对落叶的下游后果知之甚少,因此,管理的影响。鉴于上游水流及其微生物对森林景观中河流净生产力的不成比例的作用,我们调查了云杉芽虫落叶对上游生境和微生物组结构和功能的影响,以指导管理决策。在加斯佩西半岛的云杉芽虫爆发期间,我们通过实验操纵了12个流域的落叶梯度,魁北克,加拿大。从2019年5月到2021年10月,河流栖息地(流量,溶解有机物[DOM],水化学,和营养素),藻类生物量,和水温进行了评估。通过在每个分水岭的一条河流中孵育六个叶包五个星期(8月中旬至9月下旬)来检查细菌和真菌生物膜群落。使用16S和ITSrRNA基因的代谢编码确定了微生物群落结构,并使用胞外酶测定法检查群落功能,凋落叶分解率,和分类功能分配。我们发现,累积落叶与增加的流速和温度相关,和更多的芳香DOM(测量为254nm的特定紫外线吸光度),但与营养浓度无关。累积落叶也与改变的微生物群落组成有关,碳水化合物生物合成的增加,减少芳香族化合物的降解,这表明微生物正在转向优先使用简单的碳水化合物,而不是更复杂的芳香化合物。这些结果表明,高水平的落叶可以影响源头水流微生物群落,以改变河流生态系统的生产力和碳循环潜力。强调将更广泛的生态过程纳入云杉芽虫管理决策的重要性。
Defoliation by eastern spruce budworm is one of the most important natural disturbances in Canadian boreal and hemi-boreal forests with annual area affected surpassing that of fire and harvest combined, and its impacts are projected to increase in frequency, severity, and range under future climate scenarios. Deciding on an active management strategy to control outbreaks and minimize broader economic, ecological, and social impacts is becoming increasingly important. These strategies differ in the degree to which defoliation is suppressed, but little is known about the downstream consequences of defoliation and, thus, the implications of management. Given the disproportionate role of headwater streams and their microbiomes on net riverine productivity across forested landscapes, we investigated the effects of defoliation by spruce budworm on headwater stream habitat and microbiome structure and function to inform management decisions. We experimentally manipulated a gradient of defoliation among 12 watersheds during a spruce budworm outbreak in the Gaspésie Peninsula, Québec, Canada. From May through October of 2019-2021, stream habitat (flow rates, dissolved organic matter [DOM], water chemistry, and nutrients), algal biomass, and water temperatures were assessed. Bacterial and fungal biofilm communities were examined by incubating six leaf packs for five weeks (mid-August to late September) in one stream reach per watershed. Microbiome community structure was determined using metabarcoding of 16S and ITS rRNA genes, and community functions were examined using extracellular enzyme assays, leaf litter decomposition rates, and taxonomic functional assignments. We found that cumulative defoliation was correlated with increased streamflow rates and temperatures, and more aromatic DOM (measured as specific ultraviolet absorbance at 254 nm), but was not correlated to nutrient concentrations. Cumulative defoliation was also associated with altered microbial community composition, an increase in carbohydrate biosynthesis, and a reduction in aromatic compound degradation, suggesting that microbes are shifting to the preferential use of simple carbohydrates rather than more complex aromatic compounds. These results demonstrate that high levels of defoliation can affect headwater stream microbiomes to the point of altering stream ecosystem productivity and carbon cycling potential, highlighting the importance of incorporating broader ecological processes into spruce budworm management decisions.