Kazuto Shima

Change in Uptake, Transport and Accumulation of Ions in Nerium oleander (Rosebay) as Affected by Different Nitrogen Sources and Salinity

BACKGROUND AND AIMS The source of nitrogen plays an important role in salt tolerance of plants. In this study, the effects of NaCl on net uptake, accumulation and transport of ions were investigated in Nerium oleander with ammonium or nitrate as the nitrogen source in order to analyse differences in uptake and cycling of ions within plants. METHODS Plants were grown in a greenhouse in hydroponics under different salt treatments (control vs. 100 mm NaCl) with ammonium or nitrate as the nitrogen source, and changes in ion concentration in plants, xylem sap exuded from roots and stems, and phloem sap were determined. KEY RESULTS Plant weight, leaf area and photosynthetic rate showed a higher salt tolerance of nitrate-fed plants compared with that of ammonium-fed plants. The total amount of Na+ transported in the xylem in roots, accumulated in the shoot and retranslocated in the phloem of ammonium-fed plants under salt treatment was 1.8, 1.9 and 2.7 times more, respectively, than that of nitrate-treated plants. However, the amount of Na+ accumulated in roots in nitrate-fed plants was about 1.5 times higher than that in ammonium-fed plants. Similarly, Cl- transport via the xylem to the shoot and its retranslocation via the phloem (Cl- cycling) were far greater with ammonium treatment than with nitrate treatment under conditions of salinity. The uptake and accumulation of K+ in shoots decreased more due to salinity in ammonium-fed plants compared with nitrate-fed plants. In contrast, K+ cycling in shoots increased due to salinity, with higher rates in the ammonium-treated plants. CONCLUSIONS The faster growth of nitrate-fed plants under conditions of salinity was associated with a lower transport and accumulation of Na+ and Cl- in the shoot, whereas in ammonium-fed plants accumulation and cycling of Na+ and Cl- in shoots probably caused harmful effects and reduced growth of plants.

Composting of Sewage Sludge with a Simple Aeration Method and its Utilization as a Soil Fertilizer

The objective of this study was to examine the feasibility of sewage sludge composting using a simple aeration method. Two consecutive composting trials (run A and run B) using Japanese sludge and woodchips (1:1, v/v) were conducted in cubic boxes (0.45 × 0.45 × 0.45 m3) made by plywood at Okayama University. Air was forced up through small holes perforated on two open-ended parallel PVC pipes (ø 16 mm, 0.25 m apart) laid at the base. The results show that compost temperatures were rapidly increased to the peak points of 47.4 °C (run A) and 74.8 °C (run B) within the first 2–3 days and varied depending on each composting run and vertical locations. The changes in physicochemical properties with particular attention to inorganic nitrogen (NH4–N, NO3–N) and free amino acid nitrogen (FAA-N) indicated that the biodegradation took place by different mineralization pathways during the composting process. The degradation of organic matter into amino acids followed by ammonification was predominant in run B, whereas the nitrification was greater in run A. A pot experiment using the two finished composts and their raw materials was carried out to study their effectiveness as fertilizer to Komatsuna (Brassica rapa var. perviridis). The total plant biomass produced by the composts was similar to chemical fertilizer. The lowering proportions of FAA-N/T-N, NH4–N/NO3–N, and C/N ratios in the composts compared to those in raw materials was found to correlate with the increase in plant biomass.

Effect of the Change of Soil Moisture Content on Nitrogen Mineralization Rate and CO2 Release: Case of a Topsoil from a 9 Years Old Burned Forest

瀬戸内沿岸の花歯岩地帯に位置する山火事後の荒廃林地において表層土を用いた培養試験を行った。その結果, 土壌水分と窒素の無機化速度および炭酸ガス放出速度の間には密接な相関があることが示された。比較的高い含水比で培養した土壌では窒素の無機化速度も高くなっていた。培養初期に乾燥させたのち含水比を最大容水量の70%まで増加させると, 乾燥処理が強いほど初めの3日間に窒素の無機化速度も大きく増加したが, その後減少に転じて, 最終的にはどの処理でも同程度の無機化速度となった。窒素の無機化速度に及ぼす乾燥処理期間の影響は, 培養初期に14日間乾燥させた場合に比べて7日間で顕著に現れた。炭酸ガス放出速度は乾燥処理時の水分に応じて高くなっていた。また, 培養期間中の窒素の無機化速度の低下にともなう炭酸ガス放出速度の増加が認められ, 窒素の無機化にともない有機化速度が増加したことを示唆していた。