Characteristic Of Element Sulphur Oxidation In The Rhizosphere Of Rice And Its Ecological Significance

Sulfur is one of the essential elements for plant growth. Human activity has greatlyperturbed the sulfur cycle through anthropogenic emission from fossil fuel burning (coaland oil) and fertilization, and which results in spatial variability of sulfur in soil-plantsystem. The excessive sulfur was observed in paddy at acid rain area, but the paddy sulfurdeficiency also occurs in some area of China. Elemental sulfur (S⁰) is often used as afertilizer to meet the sulfur demand of crops. It has high concentration and cheap price. TheS⁰ must be oxidized to SO^2-₄ by soil microorganism, before it becomes plant available. Therhizosphere is a key zone with respect to the mechanisms of soil nutrient dynamics.Physico-chemical processes at the soil-root interface differ considerably from those in thenon-rhizosphere soil. In the recent years, paddy soil has greatly been contaminated byarensic. The chronic As poisoning by drinking tube-well water and the consumption ofAs-contaminated food is a disaster on a human health scale. It has a practical significanceby decreasing As concentration of rice. In the present study, characteristic of elementalsulfur oxidization in the rhizosphere of rice (Oryza sativa) and its significance on nutrientsbio-availability was studied in a soil culture experiment using a rhizobox technique, andeffect of elemental sulfur supply on formation of iron manganese plaque of rice (Oryzasativa) root surface and its impact on arsenic uptake by rice seedlings were alsoinvestigated in a soil-sand combination culture experiment using a rhizobox technique. Themain results were as following:1. Significant differences of elemental sulfur oxidization between the rhizosphere of rice and non-rhizosphere were determined in dependence on water management and soil type. Elemental sulfur oxidation rates in rhizosphere and non-rhizosphere of rice were lower at water-logged (1cm water depth) than aerobic condition (80%WHC). On the paddy soil originated from lime rock, oxidation rate of elemental sulfur in rhizosphere of rice was greater than non-rhizosphere at water-logged (1cm water depth) and aerobic condition (80%WHC). However, the difference was not observed on the paddy soil originated from granite.2. Effects of elemental sulfur supply on the bio-availability at water-logged (1cm water depth) and aerobic condition(80%WHC) of nitrogen, phosphorus, sulfur, iron, manganese, and root morphology of rice and its biomass depended on soil type, watermanagement. Generally, elemental sulfur supply increased rice uptake on nitrogen, phosphorus, sulfur, iron, manganese, and resulted in increment of the root length, root volume, dry root weight and biomass.3. Effects of arsenic and sulfur supply on rice dry weight exhibited an obvious interaction. Supply of As 20mg/kg combined with S0 30mg/kg resulted in decrement of rice root, shoot dry weight. But rice root, shoot dry weight showed to have a increasing tendency when supply of As 20mg/kg combined with S0 120 mg/kg. Supply of S0 120mg/kg resulted in decrement of rice root, shoot dry weight relative to without sulfur added, but the difference was not observed when application of S0 30mg/kg.4. Supply of As 20mg/kg significantly increased contents of As in rice tissues. Concentration of As in tissue of rice grown at As 20mg/kg was 11-83 times of those of rice grown without As supply.5. Arsenic was mainly distributed at the roots of rice regardless of sulfur supply, and the arsenic combined with iron plaque accounted for 90% of As in roots.6. Supply of S0 30mg/kg, 120mg/kg decreased concentrations of arsenic at rice shoot by 14.4% and 26.7% respectively; and 0.9% and 13.2% respectively for rice root; and 7.5%,28.7% respectively for root without iron plaque relative to without sulfur supply.7. Concentrations of iron, manganese in iron plaque of rice root surface were obviously greater at sulfur supply than without sulfur supply, implying that sulfur can induce formation of iron plaque of rice root surface. Supply of S0 120mg/kg increased iron concentration with arsenic supply, but it w...