Effects of vegetation restoration on soil aggregate microstructure quantified with synchrotron-based micro-computed tomography

Abstract

Vegetation restoration is expected to improve soil microstructure and therefore enhance soil stability and reduce soil erosion. The objective of this study was to evaluate the effect of long-term vegetation restoration on the modification of aggregate microstructure with synchrotron-based high resolution X-ray micro-computed tomography (SR-μCT). Triplicate aggregates (5-mm diameter) from (a) severely eroded bare land (BL) and (b) two decades of vegetation restoration land (RL) from Ultisol, Southern China, were collected and scanned with 9μm voxel-resolution at SSRF (Shanghai Synchrotron Radiation Facility). ImageJ software and multifractal theory were used to analyze and quantify aggregate pore structure. Aggregate water stability, mechanical stability, and basic soil properties were also evaluated. Results showed that aggregate water stability and SOM content significantly increased in the RL treatment, while aggregate mechanical stability showed an inverse trend. The microstructure of aggregates had evolved from a very dense massive microstructure to a more porous hierarchical microstructure after two decades of vegetation restoration. Porosity, macro-porosity, fraction of elongated pores, and specific surface area were significantly higher in the RL aggregates as compared to the BL aggregates. Multifractal scaling was observed for the pore structure of the studied aggregates. Generalized dimensions (Dq) were significantly higher in the RL treatment as compared to BL treatment, indicating improved pore system after vegetation restoration. This improved microstructure of RL aggregates was attributed to the increased SOM that prompted soil aggregation. This study showed the positive effects of vegetation restoration on soil microstructure and water stability, which was beneficial to the reduction of soil erosion and to the improvement of soil quality in this region.