麦田根际土壤反硝化作用对O_3熏气和太阳辐射减弱的响应

为研究臭氧浓度升高和太阳辐射减弱复合背景下,麦田土壤反硝化作用及N2O排放的变化,采用开顶箱(OTC)法和遮光网技术,设置3个臭氧浓度梯度及3个辐射减弱梯度,连续4a对小麦生长季麦田土壤进行臭氧浓度增加太阳辐射减弱以及它们的复合作用的试验。采用MPN(最大或然数)法测定反硝细菌的数量,用气相色谱法测定反硝化强度。结果显示反硝化细菌数量和反硝化强度受小麦生长发育的影响,在小麦成熟期收割后土壤反硝化细菌数量和反硝化强度增加得特别明显。O3连续作用3个生长季后,以及太阳辐射减弱处理,土壤反硝化菌和反硝化强度显著升高,N2O排放量显著增加。减弱的太阳辐射与增加的O3复合作用,在小麦的每个生育期均显著促进了反硝化菌数量增加和反硝化强度增强,促进率显著高于O3和遮荫的单独作用。结果说明,O3浓度增加以及太阳辐射减弱对土壤反硝化菌和反硝化强度均有一定的促进作用,减弱的太阳辐射与高浓度的O3两因素之间存在协作关系,太阳辐射减弱有利O3的吸收,增加O3伤害,促进反硝化过程。

Soil denitrification responses of wheat rhizosphere against ozone fumigation and reduction of solar irradiance

To determine the changes in soil denitrification and N₂O emission from crop rhizosphere under ozone (O₃) stress and the declined solar irradiance, ozone treatments in OTCs (open top chambers) and solar irradiance manipulate in shading nets were used. The effect of increased atmospheric surface O₃ level and declined solar irradiance with their combination contents on soil denitrification in rhizosphere of winter wheat (Triticum aestivum)was thus investigated, during the growing/development (G/D) periods including reviving, jointing, booting, heading, filing and mature stages. And four experiments were performed during a four years experiment by testing once in each year,using six OTCs or six shaded chambers, and OTCs combine with shading net in each, respectively. The results showed that each OTC was equivalent, but two were fed with air while the other four with ozone at different concentration, of which two chambers were 100 nL/L and the other two were 150 nL/L. Shaded chambers were found to be equivalent either, they were all shading but with uent flow, solar irradiance was found to be reduced by 20%,40%,60%, respectively, when tests in each chamber were repeated twice. The unshaded treatment was found to be contrasts. Complex-action of O₃ and declined solar irradiance were tested by shading net over OTCs, where winter wheat was grown to all life stage in shading net and combine chambers. From reviving to mature stages, the plants were treated for 8 h (8:00-16:00) in every sunny day with different dose of O₃, respectively in OTCs of shading chambers covered with net all life stage. Soil amount of denitrifying bacteria and denitrifying capacity were measured, with each treatment assayed thrice. Data were initially compared by analyzing the variance and differences between means using the Duncans Multiple Range Tests. Values of P < 0.05 was set to indicate significance. Quite similar results were obtained during four years'' experiments, suggesting that when a G/D stage is progressing, soil denitrifying bacteria remains at similarity level. Untill mature stage that is postharvest, it rises up sharply. Without enhanced O₃ or lower solar irradiance condition, soil denitrifying capacity were found to decline firstly but consequently increased. Under O₃ stress, denitrifying capacity gradually increased. After ozone fumigated continuously during three growing season it increased significantly, compared to the control, but the soil N₂O emission risk was heighten at the same time. O₃ combine with the shading treatments'' soil denitrifying bacteria and capacity were found to be induced in every growing/development (G/D) periods of winter wheat, while the promoting rate were higher than O₃ or shading separate role. The results indicated that the enhanced O₃ and lower solar irradiance can improve soil denitrifying process, with cooperative relations. Lower solar is irradiant to the benefit of O₃ absorb, to O₃ damages increase and to facilitate denitrifying process.