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[MIS22-P08] Can climate change stimulate organic matter decomposition in the volcanic ash soils under the two types of forest ecosystems?
Keywords:volcanic ash soil, organic matter decomposition, soil microorganisms, Stable isotope tracer, Temperature sensitivity, Moisture sensitivity
Introduction
Andisols developed from volcanic ash accumulate a large amount of soil organic matter due to high carbon storage capacity. However, Andisol can play both carbon sink or source, depending on environmental conditions and land management. It has been pointed out that the higher temperature associated with recent climate change may increase the organic matter decomposition activity by soil microorganisms and decrease soil carbon storage. On the other hand, even in forests in Japan under humid climate, annual non-precipitation days are recently increasing. This drier condition may suppress organic matter decomposition by soil microorganisms and increase carbon storage. It has been reported that the temperature and moisture sensitivities of soil microorganisms can change depending on the chemical properties of the organic matter, the microbial community structure, and the physicochemical properties of the soil. If the mechanism of microbial responses to temperature and moisture variations can be elucidated, it may be possible to manage Andisols under forest ecosystems as a carbon sink. Therefore, we compared (1) the temperature and moisture sensitivities of the organic matter decomposition rate by microorganisms and (2) the response of organic matter decomposition enzyme activity of soil microorganisms to moisture fluctuations in Andisols from different forests.
Materials & Methods
Two types of forest surface soils used in the experiments were sampled from Nikko, Tochigi Prefecture, and experimental forest of Takayama Field Station belonging to the River Basin Research Center of Gifu University, Japan. In (1), we conducted soil incubation experiments with 13C15N-labeled litter (Quercus serrata/Quercus glauca) addition under different temperature and moisture conditions. The temperature conditions were 20°C (optimum) and 35°C (high), and the moisture conditions were 60% of the maximum water holding capacity (WHC) and 20% dry condition. After adding 13C15N-labeled litter to the soil, the soil was incubated in an incubator. Head space gas were taken over time during the incubation period, and the total CO2 emission was quantified by GC-TCD, and its carbon stable isotope ratio (atom%) was quantified by GC-MS. In (2), we examined metabolic functions of soil microorganisms to the moisture condition using BIOLOG EcoPlate. After applying soil suspension to the EcoPlate and incubating them, the EcoPlate was read absorbance values of each well including substrates (31 types) such as monosaccharides, organic acids, and amino acids with a microplate reader (Ninomiya, 2017). The average well-color development values (AWCD) were calculated.
Results & Discussion
(1) In both test plots, total evolved CO2 amounts increased exponentially with the passage of time. The evolved amounts of total CO2 and 13CO2 were higher in Takayama soil throughout the incubation, suggesting that the organic matter decomposition rate in Takayama soil was faster than that in Nikko soil. Comparing decomposition rates, those in Nikko soil tended to be more sensitive to moisture, while those in Takayama soil tended to be more sensitive to temperature. It was considered that the temperature and moisture sensitivities of the decomposition rate varies depending on the types of forest and Andisol. (2) The AWCD values tended to be higher in Takayama soil, and it was inferred that the average decomposition activity was more active than that of Nikko soil. Comparing the average absorbance of each substrate under each moisture condition, the value of Takayama soil was significantly higher under moderate moisture conditions and that of Nikko soil under dry conditions (p < 0.05). Focusing on 31 metabolic substrates, the coloring pattern tended to be similar between the moisture conditions in Nikko soil, but the tendency differed depending on moisture conditions in Takayama soil, and substrates that were actively metabolized even under dry conditions. This suggests that the microbial communities in Nikko soil and Takayama soil can be different. Based on these two points, it is possible that the response of organic matter decomposition activity to temperature and moisture changes varies depending on the types of forest or Andisol due to differences in the microbial communities.
Andisols developed from volcanic ash accumulate a large amount of soil organic matter due to high carbon storage capacity. However, Andisol can play both carbon sink or source, depending on environmental conditions and land management. It has been pointed out that the higher temperature associated with recent climate change may increase the organic matter decomposition activity by soil microorganisms and decrease soil carbon storage. On the other hand, even in forests in Japan under humid climate, annual non-precipitation days are recently increasing. This drier condition may suppress organic matter decomposition by soil microorganisms and increase carbon storage. It has been reported that the temperature and moisture sensitivities of soil microorganisms can change depending on the chemical properties of the organic matter, the microbial community structure, and the physicochemical properties of the soil. If the mechanism of microbial responses to temperature and moisture variations can be elucidated, it may be possible to manage Andisols under forest ecosystems as a carbon sink. Therefore, we compared (1) the temperature and moisture sensitivities of the organic matter decomposition rate by microorganisms and (2) the response of organic matter decomposition enzyme activity of soil microorganisms to moisture fluctuations in Andisols from different forests.
Materials & Methods
Two types of forest surface soils used in the experiments were sampled from Nikko, Tochigi Prefecture, and experimental forest of Takayama Field Station belonging to the River Basin Research Center of Gifu University, Japan. In (1), we conducted soil incubation experiments with 13C15N-labeled litter (Quercus serrata/Quercus glauca) addition under different temperature and moisture conditions. The temperature conditions were 20°C (optimum) and 35°C (high), and the moisture conditions were 60% of the maximum water holding capacity (WHC) and 20% dry condition. After adding 13C15N-labeled litter to the soil, the soil was incubated in an incubator. Head space gas were taken over time during the incubation period, and the total CO2 emission was quantified by GC-TCD, and its carbon stable isotope ratio (atom%) was quantified by GC-MS. In (2), we examined metabolic functions of soil microorganisms to the moisture condition using BIOLOG EcoPlate. After applying soil suspension to the EcoPlate and incubating them, the EcoPlate was read absorbance values of each well including substrates (31 types) such as monosaccharides, organic acids, and amino acids with a microplate reader (Ninomiya, 2017). The average well-color development values (AWCD) were calculated.
Results & Discussion
(1) In both test plots, total evolved CO2 amounts increased exponentially with the passage of time. The evolved amounts of total CO2 and 13CO2 were higher in Takayama soil throughout the incubation, suggesting that the organic matter decomposition rate in Takayama soil was faster than that in Nikko soil. Comparing decomposition rates, those in Nikko soil tended to be more sensitive to moisture, while those in Takayama soil tended to be more sensitive to temperature. It was considered that the temperature and moisture sensitivities of the decomposition rate varies depending on the types of forest and Andisol. (2) The AWCD values tended to be higher in Takayama soil, and it was inferred that the average decomposition activity was more active than that of Nikko soil. Comparing the average absorbance of each substrate under each moisture condition, the value of Takayama soil was significantly higher under moderate moisture conditions and that of Nikko soil under dry conditions (p < 0.05). Focusing on 31 metabolic substrates, the coloring pattern tended to be similar between the moisture conditions in Nikko soil, but the tendency differed depending on moisture conditions in Takayama soil, and substrates that were actively metabolized even under dry conditions. This suggests that the microbial communities in Nikko soil and Takayama soil can be different. Based on these two points, it is possible that the response of organic matter decomposition activity to temperature and moisture changes varies depending on the types of forest or Andisol due to differences in the microbial communities.