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[MIS09-05] Initial Soil Aggregation Process in the Terrestrial Surface Layer of the Ancient Earth
Keywords:Soil Aggregates, Biological Activity, Water Holding Capacity
Most of the soils on the earth today have both permeability and water retention properties due to their aggregate structure, which supports many forms of life. This is thought to have been largely due to the appearance of vascular plants on land after the Silurian period, which accelerated weathering and accumulated organic matter in cooperation with the plants themselves and microorganisms. However, for vascular plants to shoot roots and live on the land, the soil must have had a certain amount of water storage and aeration, and the plant roots and the microorganisms that coexist with the plants must have been able to breathe adequately in the soil. In other words, some soil structure may have been formed before vascular plants arrived on land. In the first experiment, we investigated the microbial aggregates formation in an unweathered soil under bio-crusts in an ancient terrestrial surface layer, based on the microbial activity and the amount of aggregates formation when nutrient-rich organic matter was added from the surface layer (Experiment 1). In the second experiment, the effects of organic matter and clay content on microbial aggregate formation were examined assuming the surface layer weathered and the clay content increased (Experiment 2).
The results of Experiment1 showed that as the amount of organic matter added increased, the FDA activity and MWD of the soil samples increased, indicating that microbial activity caused the formation of aggregates. However, the aggregates formed at that time were called macro-aggregates, which did not contribute to water retention. Therefore, vascular plants did not appear to be able to land at this, because the microbes metabolized the organic matter added from the bio-crusts to form the aggregates, but did not exhibit water retention properties.
The results of experiment2 showed that when the weathering processed and the clay content increased, the water holding capacity increased with 5 % clay content. Although the overall permeability decreased with 5 % clay, the aggregates with 1 % organic matter showed relatively high permeability. The results suggest that the formation of organic matter-mediated aggregates in the presence of 5% clay results not only in the formation of macro-aggregates but also in the formation of micro-aggregates that contribute to water retention, suggesting that the initial aggregates are formed and then transformed into stable aggregates.
The results of Experiment1 showed that as the amount of organic matter added increased, the FDA activity and MWD of the soil samples increased, indicating that microbial activity caused the formation of aggregates. However, the aggregates formed at that time were called macro-aggregates, which did not contribute to water retention. Therefore, vascular plants did not appear to be able to land at this, because the microbes metabolized the organic matter added from the bio-crusts to form the aggregates, but did not exhibit water retention properties.
The results of experiment2 showed that when the weathering processed and the clay content increased, the water holding capacity increased with 5 % clay content. Although the overall permeability decreased with 5 % clay, the aggregates with 1 % organic matter showed relatively high permeability. The results suggest that the formation of organic matter-mediated aggregates in the presence of 5% clay results not only in the formation of macro-aggregates but also in the formation of micro-aggregates that contribute to water retention, suggesting that the initial aggregates are formed and then transformed into stable aggregates.