Snow and snowpack controls on deep-soil carbon storage in northern forest soils

土壤是世界上最大的碳(C)储存库之一，其碳含量是大气的2-3倍。大部分碳存在于深层土壤层（30厘米深）中，研究很少，随着时间的推移，这些土壤层通常被认为是稳定的。然而，最近的研究表明，由于土地管理或植物生产力的变化，储存在土壤深层的C可能以二氧化碳（CO2）的形式流失到大气中。在这个研究项目中，研究人员将测试一个新的假设，即北方森林中深层土壤中碳的储存是由融化的积雪通过土壤剖面输送碳而增强的。如果这是真的，那么积雪量的减少可能代表了对全球气候变化的一种正反馈机制，通过减少土壤深层的碳储存并增加大气中的碳储存。他们的假设是基于美国大湖地区湖泊效应降雪梯度中冬季积雪深度和深层土壤C储存之间的强烈正相关关系。研究人员将使用两种互补的方法来验证他们的假设。首先，他们将在上五大湖地区的三个自然发生的湖泊效应降雪梯度中检查土壤C的分布和化学成分。其次，他们将对土壤中溶解碳的通量进行密集测量，以响应自然发生的年降雪量变化，以及实验施加的除雪和增雪处理。支持他们假设的证据包括：1)降雪量大的深层土层C浓度较高，化学特征表明其来自地表植物凋落物；2)降雪量小的深层土层C浓度较低，化学特征表明其来自根系或微生物代谢；3)实验操作积雪深度导致地表植物凋落物向深层土层C的运输和滞留变化可预测。该项目将促进对气候控制土壤C循环过程的基本理解，并为土壤成因理论做出贡献。了解积雪对土壤C动态影响的性质和潜在机制尤为重要，因为随着气候变暖和冬季降雪减少，降雪量、地面积雪持续时间和积雪厚度都是气候的组成部分，在未来几十年可能受到很大影响。

Soils are one of the largest reservoirs for carbon (C) worldwide, holding 2-3 times as much C as the atmosphere. Much of this C resides in poorly-studied deep soil horizons (30 cm in depth), that have generally been viewed as stable over time. However, recent research has shown that C stored in deep soil horizons can be lost as carbon dioxide (CO2) to the atmosphere due to changes in land management or plant productivity. In this research project investigators will test a new hypothesis that deep soil C storage in northern forests is enhanced by the transport of C through the soil profile by melting snowpacks. If true, declining snowpacks may represent a positive feedback mechanism to global climate change, by reducing C storage in deep soil horizons and adding to atmospheric C stores. Their hypothesis is based on strong positive relationships between winter snowpack depth and deep-soil C storage across lake-effect snowfall gradients in the Great Lakes Region, USA. Investigators will test their hypothesis using two complimentary approaches. First, they will examine the distribution and chemical composition of soil C across three naturally-occurring, lake-effect snowfall gradients in the Upper Great Lakes region. Second, they will conduct intensive measurements of fluxes of dissolved C through soil in response to naturally-occurring annual variation in snowfall, as well as experimentally-imposed snow removal and snow augmentation treatments. Evidence that would support their hypothesis includes: 1) Deep soil horizons in high snowfall areas have higher concentrations of C with chemical signatures indicating that it is derived from surface plant litter, 2) Deep soil horizons from low-snow areas have low C concentrations with chemical signatures indicating that it is derived from roots or microbial metabolism, and 3) Experimental manipulation of snowpack depth results in predictable changes in the transport and retention of C from surface plant litter to deep soil horizons.This project will advance fundamental understanding of climatic controls over soil C cycling processes, as well as contributing to soil genesis theory. Understanding the nature and underlying mechanisms of snowpack effects on soil C dynamics is particularly important, given that snowfall amounts, duration of snow on the ground, and snowpack thickness are all components of climate that are likely to be greatly impacted in the next few decades, as climate warms and winters become less snowy.