Examining the protection of organic carbon in mineral soils of managed landscapes

最近大气中二氧化碳浓度的变化与人类活动有关，人类活动加速了碳从全球长期储存库以二氧化碳的形式进入大气，从而加剧了地球变暖。土壤是最大的活跃循环陆地碳库之一，其碳含量是大气或活植被的三倍。土地利用的变化，如将森林转为农业用地和森林的反复采伐，可能导致以有机物形式储存在土壤中的碳被释放到大气中。这可能对整体土壤健康和肥力产生额外的影响。土壤中储存的大部分碳都储存在矿质土壤中，其中有一半在20厘米以下。长期以来，人们一直认为矿物土壤中的碳具有复杂的化学结构，使微生物群落难以分解。然而，最近的研究表明，土壤中保存的大部分较老的碳实际上很容易分解，但由于与土壤矿物质的相互作用而不被分解。这些相互作用可能导致有机物质在矿物表面的松散吸附，或者有机物质与矿物结合成新的稳定的、复杂程度不同的化合物。在条件随时间不变的土壤中，这种形式的碳可以相当稳定，并在土壤中保留数百至数千年。然而，当土壤条件被诸如陆地表面扰动和气候变化等因素改变时，保护土壤有机质的机制可能被逆转，使其能够被分解并返回大气。当受到由土地利用和/或气候变化引起的物理和化学环境变化的影响时，与矿物有关的碳是如何释放出来的，目前所知甚少。同样，当这些干扰停止时，关于土壤恢复这些碳储量的潜力的信息也很少。该提案概述了一项研究计划，旨在调查加拿大东部典型土壤中不同强度和复杂性的矿物相关碳库中碳是如何分配的。将检查不同年龄的森林，并将其与当地农业土壤进行比较，以确定这些土壤碳库的大小和可变性。将从现有储存的档案中收集土壤，并在实地取样。实验将使这些土壤的一个子集经受土壤温度的长期升高，并测量这些土壤中的碳及其化学成分是如何变化的。目标是了解这种受保护的碳对土壤条件变化的敏感性，并能够预测这种碳对土壤条件变化的反应。它还寻求确定可以用作监测矿物土壤中土壤有机质变化的标准指数的重要测量方法。

Recent changes in atmospheric carbon dioxide concentrations are linked to human activities that accelerate the movement of carbon from long-term global reservoirs into the atmosphere as carbon dioxide, contributing to planetary warming. Soils represent one of the largest actively cycling terrestrial carbon reservoirs, and hold three times as much carbon as the atmosphere or living vegetation. Changes in land use such as conversion of forests to agricultural land and repeated harvesting of forests can cause carbon stored in soils as organic matter to be released to the atmosphere. This can have additional consequences for overall soil health and fertility. The bulk of carbon stored in soils is held within the mineral soil, up to half of it below 20cm depth. It was long assumed that carbon held within the mineral soil had a complex chemical structure that made it difficult for microbial communities to decompose. Recent studies, however, show that much of the older carbon held in soils is actually readily decomposable, but is protected from decomposition by interactions with soil minerals. These interactions may result in the loose adsorption of organic matter to mineral surfaces, or the combining of organic matter with minerals in new stable compounds of varying complexity. In soils where conditions are unaltered over time, this form of carbon can be quite stable, and remain in soils for hundreds to thousands of years. However, when soil conditions are altered by factors such as land surface disturbance and changes in climate, the mechanisms that protect soil organic matter can be reversed, making it available to be decomposed and returned it to the atmosphere. Little is known about how carbon associated with minerals is released when subjected to an altered physical and chemical environment arising from changes in land use and/or climate. Likewise, there is little information about the potential of soils to recover these carbon stores when these disturbances cease. This proposal outlines a research plan to investigate how carbon is partitioned within a range of mineral-associated carbon pools of varying strength and complexity in soils typical of Eastern Canada. Forests of varying ages will be examined, and compared to local agricultural soils to determine the size and variability of these soil carbon pools. Soils will be collected from existing stored archives and sampled in the field. Experiments will subject a subset of these soils to long term increases in soil temperature, and measure how the carbon held in these pools and its chemical composition changes. The goals are to understand how susceptible this protected carbon is to changes in soil conditions, and to be able to make predictions about how this carbon will respond to altered soil conditions. It also seeks to identify important measurements that can be used as standard indices for monitoring changes in soil organic matter within mineral soils.