Deep under cover: a pedological perspective on soil carbon

土壤是地球上最大的陆地碳库。仅加拿大土壤就含有全球土壤碳储量的10%以上。由于土壤所含的碳比所有植物和大气的总和还要多，即使土壤碳储量的微小变化也会显著改变全球碳循环。 土壤中的碳储量反映了几种环境因素的影响，从局部尺度的地形（斜坡位置）到区域乃至大陆尺度的母地质物质、气候和植被的相互关联的变化。目前尚不清楚的是，这些自然环境变化如何影响土壤碳的累积途径和持久性。此外，对土壤碳对人为变化的反应，如降雨变化和植物根系生长，还没有广泛的了解。 我的研究计划将集中在加拿大土壤碳的三个关键组成部分：1.底土有机碳：超过一半的土壤碳位于30厘米以下。对于这第一个目标，我将量化净碳平衡在加拿大各地的主要土壤类型，与总体假设，不同的土壤类型的成土过程控制输入途径在深度和底土碳的持久性。在局部尺度上，我将确定总碳储量如何增加，但碳持久性如何随着排水量的减少而减少。2.无机碳：碳酸盐（无机碳）是加拿大西部许多土壤中碳的主要形式。这一重要的土壤碳库在全球气候变化下最终将如何运作尚未确定。我的第二个目标是评估排水和地下植物生产力的变化模式如何改变无机碳对土壤碳平衡的贡献。 3.土壤动物：气候变化和土地利用变化可能引发生物入侵。特别是，非本地蚯蚓不断入侵加拿大土壤，对其碳动态产生深远影响。在这里，我将调查蚯蚓入侵土壤的净碳平衡如何在主要代表性土壤类型之间变化。 土壤作为碳汇还是碳源取决于进入（输入）和离开（输出）土壤的碳之间的净平衡。在许多情况下，测量土壤碳输入和输出之间的净平衡是复杂的，但通过利用稳定碳同位素的自然变化，或通过使用人工标记跟踪碳通量，可以大大改善评估。结合一个健全的土壤学领域的方法和实验室控制条件下的实验应该提供前所未有的深入了解土壤中的碳持久性的过程。总体而言，该研究计划的目标是建立改善预测土壤碳模型所需的基础科学知识，并创建可针对不同土壤类型的有意义和可持续的气候变化适应战略。

Soils are the largest terrestrial carbon storehouse on Earth. Canadian soils alone contain more than 10% of global soil carbon stocks. As soils contain more carbon than all plants and the atmosphere combined, even small changes in soil carbon stocks can significantly alter the global carbon cycle. Carbon storage in soils reflects the influence of several environmental factors, ranging from topography (slope position) at the local scale, to interlinked variations in parent geological material, climate, and vegetation at the regional to continental scale. What remains unclear is how these natural environmental variations impact the accrual pathways and persistence of soil carbon. Further, a broad understanding of soil carbon response to anthropogenic changes, such as altered rain events and plant root growth, does not exist. My research program will focus on three key components of carbon in Canadian soils: 1.Subsoil organic carbon: More than half of total soil carbon is located below 30 cm. For this first objective, I will quantify net carbon balances in key soil types across Canada, with the overarching hypothesis that different pedogenic processes across soil types control both input pathways at depth and subsoil carbon persistence. At the local scale, I will determine how total carbon stocks increase but carbon persistence decreases with decreasing drainage. 2.Inorganic carbon: Carbonates (inorganic carbon) are the dominant form of carbon in many soils from Western Canada. How this important soil carbon pool will eventually fare under global climate change has not been ascertained. My second objective will be to assess how shifting patterns in drainage and below-ground plant productivity alter the contribution of inorganic carbon to soil carbon balances. 3.Soil fauna: Climate change and land-use changes may trigger biological invasions. In particular, the ongoing invasion of non-native earthworms into Canadian soils is having a profound impact on their carbon dynamics. Here I will investigate how the net carbon balance in earthworm-invaded soils varies among key representative soil types. Whether soils act as carbon sinks or sources depends on the net balance between carbon entering (inputs) and leaving (outputs) the soil. In many cases, measuring the net balance between soil carbon inputs and outputs is complex, but assessments can be greatly improved by taking advantage of natural variation in stable carbon isotopes, or by tracking carbon fluxes using artificial labeling. Combining a sound pedological field approach and experiments under controlled-laboratory conditions should provide unprecedented insight into the processes of carbon persistence in soils. Overall, the goal of this research program is to establish the foundational scientific knowledge required to improve predictive soil carbon models, and to create meaningful and sustainable climate change adaptation strategies that can be tailored to different soil types.