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。这种碳的大部分存在于研究较少的深层土壤中(30厘米深)，通常被认为是随着时间的推移而稳定的。然而，最近的研究表明，由于土地管理或植物生产力的变化，储存在深层土壤中的碳可能会以二氧化碳(CO2)的形式流失到大气中。在这项研究项目中，研究人员将检验一个新的假设，即北部森林深处的土壤碳储存是通过积雪融化通过土壤剖面的碳运输来增强的。如果是真的，积雪减少可能代表着对全球气候变化的一种积极反馈机制，因为它减少了深层土壤中的碳储存，增加了大气中的碳储存。他们的假设是基于美国五大湖地区冬季积雪深度与湖泊效应降雪梯度上深层土壤碳储量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检验他们的假设。首先，他们将研究上五大湖地区三个自然发生的湖泊效应降雪梯度上土壤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，以响应自然降雪的年度变化，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)高降雪区深层土壤中C的浓度较高，化学特征表明它来自地表植物凋落物；2)低雪区深层土壤中的C浓度低，化学特征表明它来自根或微生物代谢；3)实验操作积雪深度导致C从表层植物凋落物向深层土壤的运输和保持发生可预测的变化。本项目将促进对气候控制土壤C循环过程的基本理解，并有助于土壤发生学理论的提出。考虑到降雪量、地面积雪持续时间和积雪厚度都是气候的组成部分，随着气候变暖和冬季变少，了解积雪对土壤C动态的影响的性质和潜在机制尤为重要。

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.