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[HTT18-06] Using Sr isotopes to estimate the depths of the soils that supply base cations for plants.
Keywords:Sr isotopes, Base cations, Plants, Soils
The geographic distribution of 87Sr/86Sr ratios has potential in determining the provenance of agricultural products. However, if volcanic ash is present as a tephra layer in soils, vertical distribution of 87Sr/86Sr ratios in soils may not be uniform and 87Sr/86Sr ratios of plants may depend on rooting depth. Conversely, 87Sr/86Sr of above-ground parts of the plants may indicate the depth of the roots taking up Sr and other base cations (Ca, Mg, Na, K etc.). Using this idea, we tried to estimate rooting depth of Koshiabura (Eleutherococcus sciadophylloides : a deciduous tree belonging to the Araliaceae family), a popular edible wild plant, in a forest in Iitate village where Adatara volcanic ash is present as a tephra layer in granitic soils.
The leaves of Koshiabura were sampled, rinsed with water, dried, pulverized, and digested using nitric acid. The soils were sampled 50 cm away from the investigated Koshiabura trees. Organic soils within frames (700 cm2 in area) were sampled by hand. Fresh litter layers were removed and fermentation layers and humus layers (FH layers) were collected. Mineral soils were sampled using core samplers (13 cm2 in area, 50 cm in depth), and divided into the increments according to the depth of 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, and 30-50 cm. The soils were passed through 2-mm sieve, and plant roots were removed by hand. The sieved soils were air-dried and extracted with 1 M ammonium acetate. Base cation concentrations in the solutions of leaf digests and soil extracts were determined using ICP-AES and ICP-MS. The 87Sr/86Sr ratios of the leaf-digests and soil-extracts were analyzed using a thermal ionization mass spectrometer (Triton; Thermo Fisher Scientific, Waltham, MA, USA) at the Research Institute for Humanity and Nature (Kyoto, Japan) after Sr purification using Sr spec resin. The roots were rinsed with water, ground, and subjected to DNA extraction. To identify rate of Koshiabura root in each core sample, both matK and rbcL region were amplified with PCR, and the PCR products were sequenced with high throughput sequencer (Miseq, Illumina, San Diego, CA, USA). Rate of Koshiabura sequences were calculated with dividing number of Koshiabura sequences by that of total plants. Finally, estimation of Koshiabura root weight in each core sample was calculated by multiplying rate of Koshiabura by total root weight.
The 87Sr/86Sr ratios of soil extracts were the lowest in 30-50 cm depth, and increased toward surface soils, which may reflect the presence of more Adatara volcanic ash in 30-50 cm depth. The 87Sr/86Sr ratios of leaf digests were closest to those of soil extracts from FH layers and 0-5 cm depth, which suggests that Koshiabura is taking up base cations from shallow soil layers. DNA analysis of roots also indicated that amount of the roots of Koshiabura is the highest in 0-5 cm depth of mineral soils, which supports the validity of the estimation of the rooting depth using 87Sr/86Sr ratios.
The leaves of Koshiabura were sampled, rinsed with water, dried, pulverized, and digested using nitric acid. The soils were sampled 50 cm away from the investigated Koshiabura trees. Organic soils within frames (700 cm2 in area) were sampled by hand. Fresh litter layers were removed and fermentation layers and humus layers (FH layers) were collected. Mineral soils were sampled using core samplers (13 cm2 in area, 50 cm in depth), and divided into the increments according to the depth of 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, and 30-50 cm. The soils were passed through 2-mm sieve, and plant roots were removed by hand. The sieved soils were air-dried and extracted with 1 M ammonium acetate. Base cation concentrations in the solutions of leaf digests and soil extracts were determined using ICP-AES and ICP-MS. The 87Sr/86Sr ratios of the leaf-digests and soil-extracts were analyzed using a thermal ionization mass spectrometer (Triton; Thermo Fisher Scientific, Waltham, MA, USA) at the Research Institute for Humanity and Nature (Kyoto, Japan) after Sr purification using Sr spec resin. The roots were rinsed with water, ground, and subjected to DNA extraction. To identify rate of Koshiabura root in each core sample, both matK and rbcL region were amplified with PCR, and the PCR products were sequenced with high throughput sequencer (Miseq, Illumina, San Diego, CA, USA). Rate of Koshiabura sequences were calculated with dividing number of Koshiabura sequences by that of total plants. Finally, estimation of Koshiabura root weight in each core sample was calculated by multiplying rate of Koshiabura by total root weight.
The 87Sr/86Sr ratios of soil extracts were the lowest in 30-50 cm depth, and increased toward surface soils, which may reflect the presence of more Adatara volcanic ash in 30-50 cm depth. The 87Sr/86Sr ratios of leaf digests were closest to those of soil extracts from FH layers and 0-5 cm depth, which suggests that Koshiabura is taking up base cations from shallow soil layers. DNA analysis of roots also indicated that amount of the roots of Koshiabura is the highest in 0-5 cm depth of mineral soils, which supports the validity of the estimation of the rooting depth using 87Sr/86Sr ratios.