10:45 AM - 12:15 PM
[MIS09-P08] Effects of drying treatments in density fractionation using organic soil in the alpine zone of the volcano
Keywords:Soil organic matter, Alpine zone, peat
Soil organic matter is the largest carbon reservoir in terrestrial ecosystems and plays a crucial role in the global carbon cycle. Recent studies have shown that soil organic matter in mineral soils is protected from microbial degradation by mineral materials through chemical interaction and physical protection. The density fractionation method using sodium polytungstate is a commonly used to assess organic matter-mineral interactions. This method utilizes the difference in density between organic matter and mineral materials; the density of organic matter in soil is generally lower than 1.6 g cm-3, and that of mineral material is generally higher than 1.6 g cm-3. In the alpine zone of the volcano with heavy snow in Northeast Japan, organic soils contain a high amount of active Al and Fe. In these soils, organic matter-mineral interactions also impact the dynamics of soil organic matter. There is some problem with using the density fraction method in such soils, for example, homogenization of samples and control of moisture content. However, no studies investigate the pretreatment method. While air-dried soil is often used for density fractionation in mineral soils, it can lead to artificial aggregation in organic soils with high organic matter, moisture, and active Al and Fe contents. However, drying treatment is necessary for long-term storage of soil sample. In this study, we evaluated the effect of drying methods in the density fractionation method using organic soils with high active Al and Fe contents.
We use soil samples in Kawarajuku of Mt.Chokai, located at an elevation of 1,600 m. The samples were 7.5-11.5 cm (K1) of Pinus pumila and Sasa kurilensis, 5-12 cm (K2) of Sasa kurilensis and 7.5-11.5 cm (K3) of Poaceae. The samples were selected because the dense root mats in the horizons upper than sample horizons are not suitable to evaluate organic matter-mineral interactions. After collection, the wet soils were sieved at 8 mm and some of the samples were air-dried or freeze-dried. Organic carbon and total nitrogen contents were determined for bulk samples of freeze-dried samples that were finely ground. For density fractionation, each of wet , air-dried, and freeze-dried samples was fractionated into three fractions using sodium polytungstate: < 1.6 g cm-3 (LF), 1.6-1.8 g cm-3 (MF), and > 1.8 g cm-3 (HF). Each fraction was freeze dried, weighed, and observed by scanning electron microscopy (SEM).
The carbon content of each sample was K1: 330 g kg-1, K2: 209 g kg-1 and K3: 357 g kg-1 with C/N ratios between 14-18. The mass of each fraction was similar for the wet and freeze-dried samples but differed significantly for the air-dried samples. The mass of LF in each fraction was about 20 % for the wet and freeze-dried samples, but about 10 % for the air-dried sample. Mass of MF in wet and freeze-dried sample was about 60 %, which is significantly lower than 85 % in air-dried sample. By contrast, the mass of HF was higher in the wet and freeze-dried samples than in the air-dried samples, about 20 % and 5 %, respectively. SEM images of each fraction in the wet and freeze-dried samples showed coarse roots and decomposed plant residues in LF, aggregates composed of fine roots, decomposed plant residues and mineral particles in MF, and mineral particles and mineral rich aggregate in HF. The aggregates in MF of the air-dried samples were bigger than in other treatments suggesting that the aggregates were artificially formed by air-drying. The results suggest that freeze-drying is a more suitable drying treatment than air-drying for the density fractionation method using organic soils with high active Al and Fe contents. The presentation will also include the results of K2 and K3 fractionation and discuss the effect of drying treatment.
We use soil samples in Kawarajuku of Mt.Chokai, located at an elevation of 1,600 m. The samples were 7.5-11.5 cm (K1) of Pinus pumila and Sasa kurilensis, 5-12 cm (K2) of Sasa kurilensis and 7.5-11.5 cm (K3) of Poaceae. The samples were selected because the dense root mats in the horizons upper than sample horizons are not suitable to evaluate organic matter-mineral interactions. After collection, the wet soils were sieved at 8 mm and some of the samples were air-dried or freeze-dried. Organic carbon and total nitrogen contents were determined for bulk samples of freeze-dried samples that were finely ground. For density fractionation, each of wet , air-dried, and freeze-dried samples was fractionated into three fractions using sodium polytungstate: < 1.6 g cm-3 (LF), 1.6-1.8 g cm-3 (MF), and > 1.8 g cm-3 (HF). Each fraction was freeze dried, weighed, and observed by scanning electron microscopy (SEM).
The carbon content of each sample was K1: 330 g kg-1, K2: 209 g kg-1 and K3: 357 g kg-1 with C/N ratios between 14-18. The mass of each fraction was similar for the wet and freeze-dried samples but differed significantly for the air-dried samples. The mass of LF in each fraction was about 20 % for the wet and freeze-dried samples, but about 10 % for the air-dried sample. Mass of MF in wet and freeze-dried sample was about 60 %, which is significantly lower than 85 % in air-dried sample. By contrast, the mass of HF was higher in the wet and freeze-dried samples than in the air-dried samples, about 20 % and 5 %, respectively. SEM images of each fraction in the wet and freeze-dried samples showed coarse roots and decomposed plant residues in LF, aggregates composed of fine roots, decomposed plant residues and mineral particles in MF, and mineral particles and mineral rich aggregate in HF. The aggregates in MF of the air-dried samples were bigger than in other treatments suggesting that the aggregates were artificially formed by air-drying. The results suggest that freeze-drying is a more suitable drying treatment than air-drying for the density fractionation method using organic soils with high active Al and Fe contents. The presentation will also include the results of K2 and K3 fractionation and discuss the effect of drying treatment.