Microbial activity and temperature change affect growth of vesicular pores

Abstract

Vesicular pores are observed in many different soil-forming environments. They can also be re-created in the lab through exposure to cyclic wetting and drying. However, little is known about the physical, chemical, and biological mechanisms involved in vesicular pore formation. This study was conducted to test the hypotheses that 1) microbial activity and 2) thermal expansion are important drivers of vesicular pore growth. These hypotheses were tested through laboratory experiments employing treatments to manipulate the biota (i.e., sterile, non-sterile, and glucose-amended treatments) and temperature change (i.e., wetting at 7 °C, 23 °C, and 40 °C before drying at 40 °C). The growth of vesicular pores, as well as vughs and planar voids, was compared among the treatments using bulk densities measured by three-dimensional laser scanning and pore analysis by computed tomography. Pore growth was found to be significantly greater in sterile soils compared to non-sterile and glucose-amended soils. Comparison among the temperature treatments showed the greatest pore growth in the samples that experienced the greatest temperature change between wetting and drying (7 °C to 40 °C). These results support the thermal expansion hypothesis of vesicular pore development, but contradict the microbial activity hypothesis.