5:15 PM - 6:45 PM
[HTT16-P11] A bomb-carbon dating approach to compare trophic structure of soil microarthropods between two types of forest
Keywords:Radiocarbon Isotope Ratio (Δ14C), Bomb-carbon Dating, Relationship between Biodiversity and Ecosystem Functioning, Food Web Analysis
For the elucidation of soil food web structure, which are highly complex due to the multiple energy and material sources comprising the webs, isotope measurements, typically of Carbon and Nitrogen isotopes have been applied in many studies to untangle the complex structures of them. Based on the simplified and the bipartite view, relative importance of the living and fresh sources in contrast to the dead and old sources is a hot topic in the soil food web studies for decades. Therefore, measurements of the “age” of C using bomb C dating by Δ14C values should provide novel insights in the soil food web studies. Fujii et al. (2021) first applied the multi-isotope approach with the soil mesofauna, primarily Collembola, and showed a significant proportion of mesofauna species depended their foods on fresh C fraction, such as C from rhizosphere. However, results obtained from the previous study was limited to a case in a Japanese cypress stand. In case casting spotlight on root-derived fresh C deposition, the dominant tree has some important difference with the other tree species. Particularly, Japanese cypress forms AM symbiosis, while substantial proportion of tree species that can become dominant form ECM symbiosis. Therefore, to test if the difference of dominant tree species and associated differences of rhizosphere environment affect dependencies of soil microarthropods on fresh C, we compared mesofauna δ13C, δ15N, Δ14C values between two types of forest and microarthropods of different microhabitat preference.
Sampling was conducted at a Japanese cypress (Chamaecyparis obtusa) stand and a jolcham oak (Quercus serrata) stand in Kamigamo Experimental Station in 2022. To extract microarthropods from soil using Tullgren apparatus, organic layer (litter and humus) and surface soil was clipped and brought to the laboratory. To avoid elution of tissues from collected microarthropods, animal samples were extracted to the cold water (less than 5 ℃), instead of ethanol. Additional samplings were conducted by hand to collect the larger arthropods, such as cockroaches, silverfishes, and spiders. Owing to the tiny body of soil microarthropods of interest (typically ranging from less than 1 µg to tens of µg) compared to the C amount used for 14C natural abundance measurements, C amount used for 14C measurements were reduced to 0.5 mg by modification of the sample preparation (graphitization) method.
After the primary measurements of Δ14C and in case analytical precision (σ) were by far worse than the other measurements, or in case AMS-based δ13C values were highly different with IRMS-based δ13C values, we repeated the sample preparation for 14C measurements and Δ14C were measured again. The result so far indicated that the measurements in the Japanese cypress stand showed the similar pattern with the previous study and the absolute 14C concentration was decreased as expected, due to the time elapsed since the previous study and decreases in the bomb-carbon signal of 14C. In both forests Δ14C of some species were close to, and in case of the cypress stand even less than the value of sympatric litter, which indicate the species assimilate similarly aged C compared to the litter. More importantly, humus dwellers; species which inhabit in decomposed soil organic layer and their microhabitat were apparently comprised of aged C compared to C of fresh litter, were present in the species with Δ14C value close the Δ14C of sympatric litter. Based on the result, our preliminary result indicated importance of the fresh C for soil microarthropods irrespective of the dominant tree species. In the presentation, we are going to update Δ14C data with re-analyzed results and further discuss how did the difference of dominant tree, and C cycle in consequence, affect Δ14C values of microarthropod species and how did the species specific traits affected to the response of Δ14C values.
Sampling was conducted at a Japanese cypress (Chamaecyparis obtusa) stand and a jolcham oak (Quercus serrata) stand in Kamigamo Experimental Station in 2022. To extract microarthropods from soil using Tullgren apparatus, organic layer (litter and humus) and surface soil was clipped and brought to the laboratory. To avoid elution of tissues from collected microarthropods, animal samples were extracted to the cold water (less than 5 ℃), instead of ethanol. Additional samplings were conducted by hand to collect the larger arthropods, such as cockroaches, silverfishes, and spiders. Owing to the tiny body of soil microarthropods of interest (typically ranging from less than 1 µg to tens of µg) compared to the C amount used for 14C natural abundance measurements, C amount used for 14C measurements were reduced to 0.5 mg by modification of the sample preparation (graphitization) method.
After the primary measurements of Δ14C and in case analytical precision (σ) were by far worse than the other measurements, or in case AMS-based δ13C values were highly different with IRMS-based δ13C values, we repeated the sample preparation for 14C measurements and Δ14C were measured again. The result so far indicated that the measurements in the Japanese cypress stand showed the similar pattern with the previous study and the absolute 14C concentration was decreased as expected, due to the time elapsed since the previous study and decreases in the bomb-carbon signal of 14C. In both forests Δ14C of some species were close to, and in case of the cypress stand even less than the value of sympatric litter, which indicate the species assimilate similarly aged C compared to the litter. More importantly, humus dwellers; species which inhabit in decomposed soil organic layer and their microhabitat were apparently comprised of aged C compared to C of fresh litter, were present in the species with Δ14C value close the Δ14C of sympatric litter. Based on the result, our preliminary result indicated importance of the fresh C for soil microarthropods irrespective of the dominant tree species. In the presentation, we are going to update Δ14C data with re-analyzed results and further discuss how did the difference of dominant tree, and C cycle in consequence, affect Δ14C values of microarthropod species and how did the species specific traits affected to the response of Δ14C values.