Nitrification and denitrification in subalpine coniferous forests of different restoration stages in western Sichuan, China

Nitrification is the biological conversion of organic or inorganic nitrogen compounds from a reduced to a more oxidized state. Denitrification is generally referred to as the microbial reduction of nitrate to nitrite and further gaseous forms of nitric oxide, nitrous oxide and molecular nitrogen. They are functionally interconnected processes in the soil nitrogen cycle that are involved in the control of long-term nitrogen losses in ecosystems through nitrate leaching and gaseous N losses. In order to better understand how nitrification and denitrification change during the process of ecosystem restoration and how they are affected by various controlling factors, gross nitrification rates and denitrification rates were determined using the barometric process separation (BaPS) technique in subalpine coniferous forests of different restoration stages. The results showed that forest restoration stage had no significant effects on gross nitrification rates or denitrification rates (One-way ANOVA (analysis of variance), p < 0.05). There was no significant difference in the temperature coefficient (Q ₁₀) for gross nitrification rate among all the forest sites (One-way ANOVA, p < 0.05). Gross nitrification rates were positively correlated with water content (p < 0.05), but not with soil pH, organic matter, total nitrogen, or C/N ratios. Denitrification rates in all the forest soils were low and not closely correlated with water content, soil pH, organic matter, or total nitrogen. Nevertheless, we found that C/N ratios obviously affected denitrification rates (p < 0.05). Results from this research suggest that gross nitrification is more responsible for the nitrogen loss from soils compared with denitrification. Translated from Journal of Plant Ecology, 2006, 30(1): 90–96 [译自: 植物生态学报]     

Nitrification activity in tropical rain forest soils of the Coastal Lowlands and Atherton Tablelands,Queensland, Australia

Intact soil cores from a montane tropical rain forest site in the Atherton Tablelands (Kauri Creek) and from a lowland tropical rain forest site in the Coastal Lowlands (Bellenden Ker), Queensland, Australia were investigated during different hygric seasons for the magnitude of gross nitrification rates using the Barometric Process Separation technique (BaPS). Pronounced seasonal variations of gross nitrification rates were found at both sites with highest values during the transition period between dry and wet season (montane site: 24.0 mg N (kg SDW)^—1 d^—1; lowland site: 13.1 mg N (kg SDW)^—1 d^—1) and significantly lower rates of gross nitrification during the dry and wet season. Rates of gross nitrification were always higher at the montane site than at the lowland site, but the opposite was found for N₂O emissions. The results indicated that the high losses of N₂O at the lowland tropical rain forest site may be contributed largely by high denitrification activity due to its wetter and warmer climate as compared to the dryer and colder climate at the montane tropical rain forest site. This conclusion was supported by analysis of cell numbers of microbes involved in N‐cycling. Higher numbers of denitrifiers were present at the lowland site, whereas higher numbers of nitrifiers were found at the montane site.     

荒漠绿洲带膜下滴灌土壤硝化-反硝化和呼吸作用的研究

采用气压过程分离(BaPS)方法研究了覆膜和裸地(CK)土壤在常规施肥和不施肥条件下的硝化-反硝化速率和呼吸速率,目的是探讨膜下滴灌土壤硝化-反硝化作用及呼吸作用的规律.结果表明:覆膜与裸地土壤在两种施肥水平下的硝化-反硝化速率及呼吸速率都有明显的季节变化;覆膜与裸地两种不同栽培措施的硝化-反硝化速率、呼吸速率差异极显著,在相同栽培措施下,不同施肥处理间的硝化-反硝化、呼吸速率也达极显著水平;硝化-反硝化速率、呼吸速率在不同栽培措施和不同施肥水平下大小排列为:覆膜＞裸地,常规施肥＞不施肥.可见,农业栽培措施和不同施肥水平对土壤硝化-反硝化及呼吸作用都有一定的影响.     

基于BaPS技术的橡胶林土壤呼吸研究

阐明橡胶林生态系统土壤呼吸作用及影响因素,对制定橡胶林土壤管理措施、培育土壤有机碳库和评估区域碳收支平衡具有重要意义。本文采用气压分离技术(Ba PS)研究了橡胶林砖红壤的土壤呼吸速率对温度、水分及碳氮源的响应。结果表明,随着土壤温度(10~30℃)的升高,土壤呼吸速率先增加后下降;土壤孔隙度水(WFPS)为35%~60%时,土壤呼吸速率与其呈显著正相关关系(R~2=0.448,p<0.05)。WFPS为60%~90%,二者呈极显著负相关关系(R~2=0.923,p<0.01);与不施氮相比,低量硝态氮的添加(0.5、2.0、4.0 g/m~2)显著促进了土壤呼吸速率(p<0.05),高量铵态氮的添加(10.0~40.0 g/m~2)则显著抑制了土壤呼吸速率(p<0.05)。土壤呼吸速率与硝态氮、铵态氮(4.0~40.0 g/m~2)均呈显著负相关关系(R~2=0.282,p<0.05;R~2=0.345,p<0.05);与不施碳相比,添加碳(1.0~40.0 g/m~2)激发了土壤呼吸速率(p<0.05),二者呈极显著正相关关系(R~2=0.307,p<0.01)。      

间作群体内土壤呼吸和硝化-反硝化作用研究

通过田间试验,采用气压分离过程法(BaPS)测定了2个氮肥处理下,玉米/大豆间作群体的土壤呼吸速率、硝化速率和反硝化速率。结果表明,施氮处理根区根系生物量高于不施氮处理,而非根系生物量差异较小。施氮处理下,根区土壤呼吸速率约为不施氮处理的1.1倍,非根区土壤呼吸差异较小。施氮处理下,玉米和大豆条带土壤硝化速率分别约为不施氮处理的1.71倍和1.82倍。施氮和不施氮处理下,间作条带根区硝化速率均高于非根区。反硝化作用不是试验区玉米/大豆间作系统氮肥损失的主要途径。因此,该区加强水肥管理以控制硝化-反硝化作用,有利于减少间作系统的氮流失和提高氮肥利用效率。     

基于BaPS系统的棉花土壤硝化和反硝化作用分析

介绍了气压过程分离法(BaPS法)用于土壤碳氮循环测定的基本原理、优点及测定方法。应用BaPS法测定了棉花田不同水、肥处理土壤的硝化-反硝化作用。试验结果表明:在相同的灌溉水平下,随着施氮量的增加,土壤总硝化速率与反硝化速率总体上均呈现加强的趋势;在相同的施肥水平下,随着灌溉水平的增大,土壤总硝化速率总体上呈下降趋势,而反硝化速率则呈先下降后上升的变化趋势。     

基于BaPS系统的南疆膜下滴灌土壤硝化-反硝化

为了解膜下滴灌土壤硝化、反硝化作用的变化规律,应用气压过程分离(Barometric process separation,BaPS)方法,研究了施氮肥、有机肥与氮肥配施和不施肥3种不同施肥处理的土壤硝化、反硝化速率在覆膜与裸地条件下的动态变化。结果显示,不同处理下土壤硝化、反硝化作用随着玉米生育期的推移有明显的变化。相同栽培措施不同施肥处理间土壤硝化、反硝化速率差异均达极显著水平,且大小顺序为氮+有机肥配施处理施氮肥处理不施肥处理(对照);相同施肥处理不同栽培措施间土壤硝化、反硝化速率大小顺序均为覆膜处理裸地处理。