亚热带土壤氮素反硝化气态产物研究

亚热带可变电荷土壤化学性质与温带地区恒电荷土壤有诸多不同特点,使得反硝化具有一些与温带土壤不同的特性,进一步深入研究亚热带土壤反硝化气体产物的组成比例、主要影响因素和机理,将有助于加深对亚热带环境条件下土壤N循环的理解和认识,以及为正确评价亚热带土壤反硝化环境效应提高科学依据。因此,就亚热带土壤厌氧培养条件下反硝化的气态产物问题进行了探讨。土样采自江西典型亚热带红壤地区,在加入K15NO3（10 atom%15N,加入N量为200 mg·kg-1）条件下进行了7 d 30℃、密闭、淹水、充N2的严格厌氧培养试验。试验结果表明：随培养时间推移,15N回收率逐渐下降,土壤总残留的15NO3-质量分数和回收率之间存在显著正相关关系（p〈0.001）,表明反硝化作用越弱的土样回收率越高。总气态氮损失率的估计值和实测值都随培养时间延长呈上升趋势,两者之间存在显著正相关性（p〈0.001）。根据稳定性同位素15N示踪试验结果初步估计,厌氧培养7 d内反硝化作用产生的气态产物中N2O占总气态氮损失的17.1%,N2占8.7%,估计NO可能是主要的反硝化产物之一。以未能回收的氮计算,NO约占总气态氮损失的67.5%~78.6%,平均为74.1%。反硝化气态产物中NO和N2O总量占总气态氮损失的91.3%。NO、N2O和N2分别占总施入氮量的18.6%、4.4%、2.0%。因此,亚热带土壤氮素反硝化过程中主要气态产物可能为NO和N2O,而非对环境无害的N2。

Nitrogenous gas products of denitrification in subtropical soils

Denitrification characteristics in subtropical variable charge soils may be different from other soils in temperate zone with constant charge due to their unique soil chemical properties. The identification of composition, ratios, influencing factors, and mechanism of nitrogenous gas products of denitrification in the area is crucial to understand soil nitrogen （N） cycle under subtropical conditions, and provide scientific basis for proper assessment of environmental effect of denitrification in subtropical soil. The objective was to study the gas products of denitrification in subtropical soils under anoxic incubation condition by applying stable isotope 15N tracer technique. Soil samples were collected from Jiangxi province, a typical subtropical red soil region in China. A 7-day anaerobic incubation was conducted under N2 gas in the headspace, at 30 ℃ after treatment with 200 mg 15NO3--N kg-1 soil （10 atom%15N）. The results showed that the recovery rate of 15N was reduced with increased incubation time. The soil 15NO3--N content remained at the end of the incubation was significantly positively correlated with the 15N recovery rate （p〈0.001）, indicating that the weaker the soil denitrification the higher the 15N recovery rate. Both the estimated and measured ratios for the total gaseous nitrogen loss increased during the incubation, presenting a significant positive relationship between them （p〈0.001）. It was estimated preliminarily by the 15N tracer results that N2O and N2 accounted for proximately 17.1%and 8.7%of the total N gas produced during the 7 days anaerobic incubation, respectively. Nitric oxide （NO） would probably be the main N gas product of denitrification, accounting for about 67.5%-78.6% of the total N gas products with the mean value of 74.1%, by the estimation of the 15N unrecoverable. The ratio of NO and N2O to the total N gas loss produced by denitrification was 91.3%. The percentage of NO, N2O and N2 to the N added were 18.6%, 4.4%and 2.0%, respectively. The result