DISSERTATION RESEARCH: Direct and indirect effects of winter climate change on microbes: implications for nitrogen retention in temperate hardwood forests

随着气候变化，美国东北部的森林在下一个世纪可能会经历积雪深度和持续时间的减少。由于雪使土壤与低于冰点的气温隔绝，积雪的损失将增加冬季冻融事件的频率。过去的研究表明，土壤冻结增加了氮从森林土壤向附近水道和大气的移动，但这些模式的原因还不清楚，特别是土壤微生物的作用。该项目的目标是更深入地了解土壤微生物对这些变化的反应，以及下游氮素损失的后果。该项目还将产生一些社会效益。首先，了解土壤、植物和气候之间的联系将有助于预测温带森林对气候变化的反应，这是更好地了解生物圈和气候变化之间反馈的关键信息。此外，这项研究将为多年级的学生提供新的教育活动。波士顿公立学校系统的高中生将获得宝贵的实践，独立的研究经验和一系列领域和实验室方法的培训。波士顿大学是一个城市校区，来自该校的本科生将有一个难得的机会到哈佛森林长期生态研究基地实地考察，了解冬季气候变化。最后，这项研究产生的数据将被纳入本科微生物学课程，并用于培训本科生在这一日益增长的领域的现有方法。过去的研究表明，积雪减少增加了冬季土壤冻结的强度，这可能会增加生态系统氮流失通过淋溶和气体流失到大气中。 由于土壤细菌和真菌群落的丰富度和多样性对土壤氮循环有显著影响，微生物群落结构的持续变化可能解释冬季土壤冻结对森林土壤氮流失的积极影响。 该项目将确定冬季土壤冻结是否会对土壤微生物产生负面影响，以及这些影响是直接的，通过破坏土壤结构和诱导的生理压力，还是间接的，通过对植物根系的影响。这项研究将在哈伯德布鲁克实验森林的两个冬季气候实地实验中对土壤氮循环的过去测量与使用存档土壤对土壤细菌和真菌的丰度和多样性的新测量相结合。来自自然气候梯度的土壤、微生物和植物样本也将用于确定冬季气候对土壤氮循环、植物-微生物相互作用和微生物群落组成的影响。

Forests in the northeastern United States are likely to experience a reduction in the depth and duration of snow cover during the next century as the climate changes. Because snow insulates soils from below-freezing air temperatures, loss of snow cover will increase the frequency of freeze - thaw events in winter. Past studies show that soil freezing increases movement of nitrogen from forest soils to nearby waterways and the atmosphere, but the causes of these patterns are not well understood, especially the role of soil microbes. The goal of this project is to gain a deeper understanding of the response of soil microbes to these changes, and the consequences for nitrogen loss downstream. This project will also produce a number of societal benefits. First, understanding connections among soils, plants, and climate will improve predictions of the response of temperate forests to climate change, critical information to better understand feedbacks between the biosphere and a changing climate. In addition, this research will provide new educational activities for students at multiple grade levels. High-school students in the Boston public school system will gain valuable hands-on, independent research experience and training in a range of field and laboratory methods. Undergraduate students from Boston University, an urban campus, will have a rare opportunity to take field trips to the Harvard Forest Long-Term Ecological Research site to learn about winter climate change. Finally, data generated by this research will be incorporated into an undergraduate microbiology class and used to train undergraduate students in current methods in this growing field.Past studies have shown that reductions in snow cover increase the intensity of winter soil freezing, which can increase ecosystem nitrogen loss via leaching and gas loss to the atmosphere. Because the abundance and diversity of soil bacterial and fungal communities can have significant effects on soil nitrogen cycling, sustained changes in microbial community structure might explain the positive effect of winter soil freezing on N losses from forest soils. This project will determine whether soil freezing in winter negatively affects soil microbes, and whether these effects are direct, via disruption of soil structure and induced physiological stress, or indirect, through effects on plant roots. This research will pair past measurements of soil nitrogen cycling at two winter climate field experiments at Hubbard Brook Experimental Forest with new measurements of the abundance and diversity of soil bacteria and fungi using archived soils. Soil, microbial and plant samples from a natural climate gradient will also be used to determine the effects of winter climate on soil nitrogen cycling, plant-microbial interactions, and microbial community composition.