Collaborative Research LTREB: Soil warming and forest ecosystem feedbacks to the climate system

土壤在土壤有机质(SOM)中储存的碳至少是大气或植被的三倍。土壤有机质对气温升高的响应是生态系统与气候相互作用的一个重要方面。如果温度升高导致土壤碳转移到大气中，其结果将是对气候系统的自我强化(正)反馈，变暖导致更多的变暖。尽管这种反馈具有潜在的重要性，但目前对影响SOM温度敏感性的机制尚不完全了解。该项目将继续在哈佛森林进行一项长期的土壤变暖实验，该实验目前已进入第三个十年。这些实验使用加热电缆来加热东部一片成熟森林中的土壤。到目前为止，这个实验的结果已经显示了SOM随着时间的推移对温度的动态响应。该项目将继续研究和监测土壤对变暖的长期反应，以促进对温度如何在十年时间尺度上控制土壤有机质分解的科学理解。这一结果将改善用于预测未来气候的地球系统模型中土壤过程的表示。在哈佛森林落叶林地正在进行的田间变暖实验，在8年、11年和23年的三个重复地点，使环境土壤温度高出5摄氏度，现在对应于最长运行实验中的三个不同阶段的二氧化碳排放。在第一个十年中，土壤呼吸对气候变暖的响应是增加的，随后没有响应，最后在最后的8年中，土壤呼吸又出现了一个较高的时期。三个变暖实验的时间序列提供了一个独特的机会来理解土壤温度上升如何随时间影响土壤生物地球化学、植物-土壤相互作用和微生物群落组成。这项研究有三个主要部分：1)继续进行碳、氮储量和通量的核心测量；2)结合生物地球化学和微生物群落变化的关键指标测量短期温度控制；3)有针对性的过程水平测量，以加强对土壤对长期变暖的反应的机械理解。该项目将测量碳和氮的同位素组成，有机质的化学组成，以及沿时间序列的微生物群落组成。土壤变暖实验将继续作为一个开放式设施，供全国学生和研究人员研究变暖对生态系统过程的长期影响。

Soils store at least three times more carbon in soil organic matter (SOM) than either the atmosphere or vegetation. The response of SOM to increasing temperature is an important aspect of the interactions between ecosystems and climate. If increasing temperatures cause soil carbon to be transferred to the atmosphere, the result would be a self-reinforcing (positive) feedback to the climate system, with warming leading to more warming. Despite the potential importance of this feedback, there is currently an incomplete understanding of the mechanisms that affect the temperature sensitivity of SOM. This project will continue a long running soil warming experiment at Harvard Forest which is currently in its third decade. The experiments use heated cables to warm the soil in a mature eastern forest. To date, the results of this experiment have shown dynamic responses of SOM to temperature over time. This project will continue to study and monitor long-term soil responses to warming to advance the scientific understanding of how temperature controls decomposition of SOM on a decadal time scale. The results will improve the representation of soil processes in the Earth system models that are used to project future climate.Ongoing field warming experiments in the deciduous forest stands at Harvard Forest have imposed 5oC above ambient soil temperatures at three replicated sites for 8, 11 and 23 years, which now correspond to three distinct phases of CO2 emissions in the longest running experiment. There was an initial increase in soil respiration in response to warming in the first decade, followed by no response, and finally another period of higher soil respiration in the heated plots in the last 8 years. The chronosequence of the three warming experiments offers a unique opportunity to understand how increasing soil temperatures affect soil biogeochemistry, plant-soil interactions, and microbial community composition over time. The research has three major components: 1) continuation of core measurements of carbon and nitrogen stocks and fluxes; 2) short-term temperature manipulations combined with measurements of key indicators of biogeochemical and microbial community changes; and 3) targeted process-level measurements that enhance a mechanistic understanding of soil responses to long-term warming. The project will measure the isotopic composition of carbon and nitrogen, the chemical composition of SOM, and microbial community composition along the chronosequence. The soil warming experiments will continue to operate as an open facility for students and researchers nationwide to study the long-term effects of warming on ecosystem processes.