Microbial Immobilization and Plant Uptake of Different N Forms in Three Forest Types in Shikoku District, Southern Japan     

Yoshiyuki Inagaki  Ayato Kohzu 《Soil Science and Plant Nutrition》2005,51(5):667-670

Soil microbial immobilization and plant uptake of N were evaluated for three forest types in Kochi, Shikoku district. During 196-d laboratory incubation, soil NO₃-N production in the Hinoki cypress forest was negligible for the initial 40 d and then rapidly increased, whereas NO₃-N production was rapid from the beginning in Japanese cedar and deciduous hardwood forests. Microbial immobilization of the labeled ¹⁵N decreased in the order of NH₄-N>glycine-N>NO₃-N. The ¹⁵N immobilization was higher for soil in the Hinoki cypress forest than other two soils. The delayed NO₃-N production in the Hinoki cypress forest was likely related with low availability of NH₄-N due to NH₄-N immobilization and substantial NO₃-N immobilization. In the field experiment, ¹⁵N uptake by roots decreased in the order of NH₄-N>NO₃-N>glycine-N. The absorption of the labeled ¹³C suggested direct uptake of organic N. The preference of N forms by root uptake was not different among forest types. Trees in three forest types can absorb inorganic and organic forms of N, suggesting trees absorb the N form that is the most abundant in the soil.  相似文献   

Development of a new high-throughput and small-size method for measuring sediment oxygen demand in lakes     

Shimotori  Koichi  Yamamoto  Haruki  Imai  Akio  Kohzu  Ayato  Okamoto  Takahiro 《Journal of Soils and Sediments》2021,21(2):1222-1231

Journal of Soils and Sediments - Sediment oxygen demand (SOD) measurement currently requires a long preparation time and bulky experimental equipment, which represent major obstacles to conducting...  相似文献   

Dynamics of C natural abundance in wood decomposing fungi and their ecophysiological implications     

Ayato Kohzu  Toshihiro Miyajima  Takashi Watanabe  Eitaro Wada 《Soil biology & biochemistry》2005,37(9):1598-1607

Factors that affect the δ¹³C values of fungi need to be analyzed for the progress of isotope-based studies of food-chain or organic matter dynamics in soils. To analyze the factors that control δ¹³C values of the fungal body, basidiomycete and ascomycete species were grown on a beechwood substrate (six species) and in glucose medium (nine species), and the δ¹³C value of produced fungal body was compared to that of the carbon source. The ¹³C enrichment (Δδ¹³C) in the fungal aggregates compared to the decomposed wood varied from 1.2 to 6.3‰ among six species. In the glucose substrate experiment, the degree of ¹³C enrichment in the hyphal mat was relatively small and varied from −0.1 to 2.8‰ among nine basidiomycetes species depending on their growth stage. Calculated δ¹³C values of the respired CO₂ were lower than those of the hyphal mat, organic metabolites and the glucose used. The degree of ¹³C enrichment was affected by fungal species, substrate and growth stage. Fungal internal metabolic processes are the plausible mechanism for the observed isotopic discrimination between fungal bodies and substrates. Especially, dark fixation of ambient CO₂ and kinetic isotope fractionation during assimilation and dissimilation reactions could well explain Δδ¹³C dynamics in our experiments. Through the analysis of field Δδ¹³C, we could know undisturbed fungal status about starvation, aeration and type of decomposition.  相似文献   

Nitrogen isotope fractionation during nitrogen transport from ectomycorrhizal fungi,Suillus granulatus,to the host plant,Pinus densiflora     

Ayato Kohzu  Takahiro Tateishi  Akiyoshi Yamada  Keisuke Koba  Eitaro Wada 《Soil Science and Plant Nutrition》2013,59(3):733-739

The ¹⁵N natural abundance in Pinus densiflora Sieb. et Zucco that had been inoculated and not inoculated with ectomycorrhizal fungi (Suillus granulatus (L.:Fr.) O. Kuntze) was compared. The inoculated pine needles showed a lower δ¹⁵N value, while the uninoculated ones showed a higher δ¹⁵N value. Higher δ¹⁵N values in the mycelial mat of the ectomycorrhizal fungi compared to those of the inoculated pine needles were also observed. These facts indicate that nitrogen isotope fractionation occurred during the nitrogen transport from mycorrhizal fungi to the host plants.  相似文献   

Long-term observations of the vertical distributions of mineral elements and phosphorus dynamics in sediments in a shallow eutrophic lake in Japan     

Shimotori  Koichi  Imai  Akio  Kohzu  Ayato  Komatsu  Kazuhiro  Koshikawa  Masami Kanao  Hayashi  Seiji  Watanabe  Mirai 《Journal of Soils and Sediments》2019,19(3):1566-1575

Purpose

To explore the mechanisms in the deposition and release of phosphorus (P) in the sediment of a shallow eutrophic lake using preserved samples, we investigated the vertical and temporal changes in P, manganese (Mn), sulfur (S), iron (Fe), aluminum (Al), calcium (Ca), and magnesium (Mg) in the sediment samples and the phosphate in the sediment pore water samples over a period of 6 years.

Materials and methods

The upper 15 cm of sediment from Lake Kasumigaura in Japan was collected monthly from 2003 to 2008 from the center of the lake. Sediment cores were divided into seven depth segments and were acid-digested for an elemental analysis via inductively coupled plasma atomic emission spectroscopy. Phosphate concentrations of the sediment pore water were determined using the molybdenum blue method. A multiple regression analysis was conducted by setting the P content as the response variable and Mn, S, Fe, Al, Ca, and Mg as explanatory variables.

Results and discussion

The results of the multiple regression analysis demonstrated that P co-precipitates with Fe and Al oxides and accumulates on the sediment surface. The vertical distributions of Mn and S suggest that Mn reduction occurs within the 0–1-cm-depth layer of the sediment and that iron sulfide is actively formed in the 6–10-cm-depth layer of the sediment. These findings imply that the layer in which ferric oxides are reduced to ferrous ions is present near the 1–6-cm-depth layer of the sediment. This layer corresponds to the layer in which the maximum phosphate concentration of the sediment pore water often occurred (the 2–6-cm-depth layer). These results indicate that vertical distributions of mineral elements are useful for assessing P dynamics in sediments.

Conclusions

The lake sediments record the dynamics of P in the sediment. Our analytical approach using long-term observation data demonstrated that the accumulation and release of P associated with a change in the redox state can be assessed based on the vertical distributions of mineral elements in the lake sediments.

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