Carbon–mineral interactions along an earthworm invasion gradient at a Sugar Maple Forest in Northern Minnesota

Carbon–mineral interactions along an earthworm invasion gradient at a Sugar Maple Forest in Northern Minnesota

The interactions of organic matter and minerals contribute to the capacity of soils to store C. Such interactions may be controlled by the processes that determine the availability of organic matter and minerals, and their physical contacts. One of these processes is bioturbation, and earthworms are the best known organisms that physically mix soils. Earthworms are not native species to areas previously glaciated, and the introduction of earthworms to these regions has been associated with often dramatic changes in soil structure and geochemical cycles. The authors are studying C mineral interaction along an approximately 200m long earthworm invasion transect in a hardwood forest in northern Minnesota. This transect extends from the soils where earthworms are absent to soils that have been invaded by earthworms for nearly 30–40years. Pre-invaded soils have an approximately 5cm thick litter layer, thin (∼5cm) A horizon, silt rich E horizon, and clay-rich Bt horizons. The A and E horizons formed from aeolian deposits, while the clay-rich Bt horizons probably developed from underlying glacial till. With the advent of earthworm invasion, the litter layer disappears and the A horizons thicken at the expense of the O and E horizons. In addition, organic C contents in the A horizons significantly increase with the arrival of earthworms. Simultaneously, measured mineral specific surface areas suggest that minerals’ capacities to complex the organic matter appear to be greater in soils with active earthworm populations. Based on the data from two end member soils along the transect, mineral specific surface areas in the A and E horizons are larger in the earthworm invaded soil than in the pre-invasion soil. Additionally, within<5 a of earthworm invasions, A horizon materials are turned from single grain to a strong medium granular structure. While A horizon organic matter content and organic C-mineral complexation increase after earthworm invasion, they are also more vigorously mixed. This growing data set, when ultimately combined with ongoing measurements of (1) the population dynamics of earthworms along the invasion transect, (2) C-mineral association (via surface adsorption and physical collusion in mineral aggregates) and (3) dissolved organic C will show how and how much soil capacity to store C is affected by burrowing organisms, which are often the keystone species of given ecosystems.

有机物和矿物质的相互作用有助于土壤储存碳的能力。这种相互作用可能受决定有机物和矿物质的可利用性以及它们物理接触的过程所控制。其中一个过程是生物扰动，蚯蚓是最广为人知的对土壤进行物理混合的生物。蚯蚓不是先前被冰川覆盖地区的本地物种，将蚯蚓引入这些地区往往与土壤结构和地球化学循环的剧烈变化有关。作者们正在明尼苏达州北部一片阔叶林中沿着一条约200米长的蚯蚓入侵样带研究碳 - 矿物质相互作用。这条样带从没有蚯蚓的土壤延伸到被蚯蚓入侵了近30 - 40年的土壤。入侵前的土壤有一层约5厘米厚的枯枝落叶层、较薄（约5厘米）的A层、富含粉砂的E层以及富含黏土的Bt层。A层和E层由风积物形成，而富含黏土的Bt层可能由下伏的冰碛物发育而来。随着蚯蚓入侵，枯枝落叶层消失，A层变厚，代价是O层和E层变薄。此外，随着蚯蚓的到来，A层中的有机碳含量显著增加。同时，测量的矿物质比表面积表明，在有活跃蚯蚓种群的土壤中，矿物质与有机物络合的能力似乎更强。根据样带上两种端元土壤的数据，A层和E层的矿物质比表面积在被蚯蚓入侵的土壤中比入侵前的土壤中更大。此外，在蚯蚓入侵不到5年的时间里，A层物质从单粒结构转变为强中粒结构。虽然蚯蚓入侵后A层有机物含量和有机碳 - 矿物质络合增加，但它们也被更剧烈地混合。这个不断增长的数据集，最终与以下正在进行的测量相结合：（1）沿着入侵样带的蚯蚓种群动态，（2）碳 - 矿物质结合（通过表面吸附和矿物质团聚体中的物理碰撞）以及（3）溶解有机碳，将展示挖掘生物如何以及在多大程度上影响土壤储存碳的能力，挖掘生物往往是特定生态系统的关键物种。