Impacts of soil structural heterogeneity on biogeochemical processes across scales

Abstract

Understanding soil carbon dynamics is necessary to ensure long term soil health and improved understanding of soil-atmosphere interaction. Soil scientists are tasked with understanding how shifts in climate, a soil forming factor, will affect soil carbon stocks so that management decisions and predictions can be better informed. This is of significant interest and importance as shifts in weather patterns are already occurring. These shifts in climate alter soil structure in timescales as short as years, adding a new layer of complexity to understanding soil structure. To achieve the goal of better management and prediction, first, soil structure must be understood as a stationary arrangement. Second, the evolution of soil structure must be understood under varying conditions, however the latter remains a frontier. Finally, once sufficient evidence is gathered, the new information must be incorporated into mechanistic models, which implement a holistic framework. ☐ This dissertation explores the aforementioned experimentally and with in-depth literature reviews. Model experimental systems were created to mimic macropore and preferential flow effects on oxygen dynamics and the spatial distribution phosphatase and β-glucosidase activity after glucose addition. Results show that oxygen consumption and enzyme activity are greatest along macropore linings. This information along with preexisting literature was used to create a conceptual model relating pore size, flow, and carbon processing. In addition, this dissertation outlines how hydrologic connectivity of soil pore networks controls biogeochemical processes across scales. Furthermore, while connectivity and pore size are perhaps the most important factors in controlling biogeochemical processes, it has been found that either are rarely incorporated into current models. Therefore, a conclusion that connectivity and pore size distribution should be further evaluated and considered as model parameters for representing carbon turnover and storage can be made.