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

下个世纪，随着气候的变化，美国东北部的森林可能会经历积雪深度和持续时间的减少。由于积雪使土壤免受冰点以下气温的影响，积雪的消失将增加冬季冻融事件的频率。过去的研究表明，土壤冻结增加了氮素从森林土壤向附近水道和大气的移动，但这些模式的原因尚不清楚，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，以及对下游氮素损失的影响。该项目还将产生许多社会效益。首先，了解土壤、植物和气候之间的联系将改善对温带森林对气候变化反应的预测，这是更好地理解生物圈和不断变化的气候之间的反馈的关键信息。此外，本研究将为多个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、独立研究经验和一系列领域和实验室方法的培训。来自城市校园波士顿大学的本科生将有一个难得的机会到哈佛森林长期生态研究遗址进行实地考察，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生微生物学课程，并用于培训本科生在这一种植领域的当前方法。过去的研究表明，积雪减少增加了冬季土壤冻结的强度，这可能会通过淋溶和向大气中的气体损失增加生态系统氮的损失。由于土壤细菌和真菌群落的丰度和多样性对土壤氮素循环有显著影响，微生物群落结构的持续变化可能解释了冬季土壤冻结对森林土壤氮素流失的积极影响。该项目将确定冬季土壤冻结是否对土壤微生物产生负面影响，以及这些影响是直接的，是通过破坏土壤结构和诱导生理应激而产生的，还是通过对植物根部的影响而间接产生的。这项研究将在哈伯德布鲁克实验森林的两个冬季气候野外实验中，将过去对土壤氮素循环的测量与使用存档土壤的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被用来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.