Abstract
In order to examine a possible uptake of protein-like organic nitrogen in a soil by tea plants (Camellia sinensis L.) and 6 vegetables species (cucumber (Cucumis sativus L.), chingensai (Brassica campestris L.), leaf lettuce (Lactuca sativa L.), broccoli (Brassica oleracea L. var. italica), spinach (Spinacia oleracea L.) and maize (Zea mays L.)), HPSEC analysis of the xylem saps collected from these 7 plants was conducted. One series of these 7 plant species were grown on a pot filled with soil supplemented with organic matter, while another series of 7 plant species were grown on solution culture or vermiculite-filled pot with chemical fertilizer only. Our findings were as follows : The concentration of mineral nitrogen found in the xylem saps collected from the 6 vegetables in plots with chemical fertilizer were higher than in plots with organic matter. This result showed that the uptake of mineral nitrogen in a soil of these 6 vegetables in plots with chemical fertilizer were higher than in plots with organic matter. Substances with the same molecular weight as protein-like organic nitrogen (estimated molecular weight 4000-5000 Da) extracted with water and potassium chloride in soils were detected from the xylem saps of the 6 vegetables and the tea plants by HPSEC analysis. Interestingly, the HPSEC peak height of same substances of protein-like organic nitrogen from the xylem saps of 6 vegetables and the tea plant (cv. Saemidori) were higher in plots with organic matter than in plots with chemical fertilizer. Moreover, the same HPSEC peak of substances of protein-like organic nitrogen in the xylem saps collected from the tea plants (cv. Yabukita and Yutakamidori) in the general manuring practice, which were cultivated in the tea plantation managed at Chiran region in Kagoshima Japan, were also detected. These results indicated that there was a possibility of a direct uptake of protein-like organic nitrogen in a soil not only by vegetables but also by tea plants in addition to mineral nitrogen in a soil.
