Alternative Title緑肥施用土壌の根域および根圏における微生物特性に関する研究
Note (General)Rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth, HV) are cover crops, plants commonly applied in crop production with multifunction. One of the functions is supplying inorganic nitrogen (N) for subsequent plants. Inorganic N supply is abundant during the decomposition phase of cover crop residues which occurs within a month of incorporation. However, utilization of this inorganic N by subsequent plants during this period is not performed well. In bulk soil, bacteria and fungi play roles in the inorganic N supply from cover crop residues. However, their roles during the decomposition period are barely known. During interaction with the subsequent plant, microorganisms inhabiting the plant rhizosphere soils can assist in N utilization (N uptake, Nup) affecting plant yield. Plant–microbe interactions in the subsequent plant rhizosphere soil during cover crop decomposition is still not well understood. Therefore, to understand the effects of cover crops on horticultural systems, this study was carried out (1) to clarify N availability and its utilization by the subsequent plant, (2) to identify microorganisms contributing to N availability in the bulk soil, and (3) to evaluate plant–microbe interactions in the rhizosphere soil of subsequent plant cultivated during the decomposition periods of cover crop residues. The research, which included field and pot experiments, was conducted for two years (i.e., 2017 and 2018). Treatments were soil without any cover crops (control) and soils with rye, HV, and mixed (rye+HV) cover crops. In the fields, two ammonium sulfate application rates (i.e., 0 and 2.5 g N m−2 in 2017 and 0 and 6 g N m−2 in 2018) were applied to compare the effects of cover crops and synthetic N fertilizer. The effects of cover crops were clarified in the pot. Red leaf lettuce (Lactuca sativa L. var. crispa cv. Red fire), the subsequent plant, was transplanted 5 days after incorporation (DAI) of cover crops and harvested at a mature stage in the field and at the mid growth and mature stages in the pot to evaluate lettuce Nup and yield. Bulk and rhizosphere soils were collected during the experiments (i.e., 5–38 DAI in 2017 and 3–31 DAI in 2018). The bulk soils were analyzed for soil inorganic N (i.e., NO3—N+NH4+-N), activity of β-glucosidase enzyme (BG), and carbon-based soil microbial biomass (SMB). Bulk and rhizosphere soils from the potswere subjected to DNA-based molecular analysis to quantify and identify bacteria and fungi. Influenced microbial taxa, whose relative abundance was affected by cover crops, were selected; and their relative abundance was correlated with values of BG activity and SMB or lettuce Nup and yield. Results of N availability as concentration of soil inorganic N was as follows HV > rye+HV > rye = control. This clarifies the common effects of cover crops on N supply. In the fields, HV-0N and rye+HV-0N promoted lettuce yield and Nup over control-0N. Conversely, lettuce performances in rye depended on 2.5N or 6N fertilizer addition. This indicates that HV and rye+HV, but not rye, could alternate application of synthetic N fertilizer. However, in the pots, HV effect was initial soil carbon dependent, resulting in a suppression and promotion of lettuce performances in 2017 and 2018, respectively, at the plant mid growth stage. Specific analysis to rhizosphere soils showed that plant–microbe interactions had significant negative correlations between bacterial influenced taxa and Nup and yield in HV in 2017. On the contrary, vigorous lettuce growth in HV in 2018 showed that the roots recruited more beneficial microorganisms that positively direct and indirect effected on Nup and yield promotion. In bulk soils, bacterial and fungal DNA was relatively higher in cover crop-treatments than control within 5–10 DAI, concomitant with active N mineralization periods, up to 15 DAI, of cover crops. Further, microorganisms in bulk soil sequentially promoted BG activity and SMB during the decomposition period, implying BG activity and SMB as indicators of microbial roles in N availability. Specifically, family Parachlamydiaceae and unidentified bacteria of class SAR202 were correlated with BG activity and SMB positivelyin HV and rye+HV or negatively in rye. This indicates that each cover crop enhances specific microbial roles relating to Navailability. This study demonstrated the technique to maximize utilization of N supplied from cover crops during the residual decomposition periods. The technique can be adapted in cover crop-horticulture rotation systems. Furthermore, microbial pathways of N supply and N utilization were molecularly revealed. In cover cropping system, thus, cover crops can be selected based on the N benefit and microbial feature.
(主査) 教授 星野 洋一郎, 教授 森川 正章, 教授 山田 敏彦（大学院国際食資源学院）, 教授 荒木 肇（新潟食料農業大学）, 准教授 内田 義崇（農学研究院）, 助教 平田 聡之
環境科学院（生物圏科学専攻）
Collection (particular)国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
Date Accepted (W3CDTF)2023-05-05T22:12:33+09:00
Data Provider (Database)国立国会図書館 : 国立国会図書館デジタルコレクション