丛枝菌根真菌对褐土玉米氮素吸收和土壤N2O排放的影响

探究不同氮肥水平下丛枝菌根(AM)真菌对褐土玉米土壤N₂O排放和氮转化功能基因的影响,为阐明AM真菌在褐土N₂O排放中的作用和效应提供理论依据。设置氮肥用量(NⅠ:105 mg/kg;NⅡ:210 mg/kg)、AM真菌(M0:不接种AM真菌;M1:接种根内根孢囊霉(Rhizophagus intraradices);M2:接种摩西斗管囊霉(Funneliformis mosseae);M3:接种Rhizophagus intraradices + Funneliformis mosseae等比例混合)双因素盆栽试验。测定植株地上部全氮含量、土壤铵态氮、硝态氮含量和N₂O排放量,采用实时荧光定量聚合酶链式反应(PCR)法分析土壤硝化功能基因(amoA-AOA和amoA-AOB)和反硝化功能基因(nirS、nirK和nosZ)的丰度。结果表明,两种施氮水平下,接种AM真菌均可显著降低土壤N₂O排放通量和累积排放量,不同AM真菌处理下N₂O累积排放量表现为:M0>M2>M1>M3。相同AM真菌处理的土壤N₂O排放通量和累积排放量在NⅡ施氮水平高于NⅠ施氮水平;相同AM真菌处理的玉米菌根侵染率在NⅡ施氮水平低于NⅠ施氮水平。与M0相比,NⅠ条件下M1、M2和M3处理土壤铵态氮含量分别降低24.5%、20.8%和45.3%,硝态氮含量分别降低19.7%、14.9%和30.2%,植株地上部全氮含量分别增加16.3%、35.2%和59.6%;与M0相比,NⅡ条件下M1、M2和M3处理土壤铵态氮含量分别降低20.9%、24.8%和40.0%,硝态氮含量分别降低36.3%、25.6%和45.2%,植株地上部全氮含量分别增加33.2%、43.9%和95.4%。两种施氮水平下,AM真菌可显著降低土壤硝化功能基因(amoA-AOA和amoA-AOB)丰度,增加反硝化功能基因(nirS、nirK和nosZ)丰度。AM真菌与N₂O排放通量呈极显著负相关。本盆栽试验条件下,接种AM真菌均可增强两种氮肥用量玉米植株氮素吸收能力,调节硝化、反硝化相关功能基因的丰度,减少土壤N₂O气体的排放,且两种AM真菌混合处理的N₂O减排效应强于单一AM真菌接种。

Effects of arbuscular mycorrhizal fungi on nitrogen uptake of maize and soil N2O emissions in cinnamon soil

The aim of this study was to explore the influences of arbuscular mycorrhizal (AM) fungi on N₂O emissions and nitrogen-transforming functional genes in maize-growing cinnamon soil under different nitrogen fertilizer rates, so as to provide the theoretical basis for clarifying the mechanism of AM fungi on N₂O emissions in cinnamon soil. Two factorial pot experiments were established as follows: nitrogen fertilizer application rates (NⅠ: 105 mg/kg; NⅡ: 210 mg/kg) and AM fungi treatments (M0: no AM fungi inoculation; M1: Rhizophagus intraradices; M2: Funneliformis mosseae; M3: Rhizophagus intraradices + Funneliformis mosseae). Soil ammonium nitrogen, nitrate nitrogen, maize total nitrogen content, and soil N₂O flux were measured. The abundance of soil nitrification functional genes (amoA-AOA and amoA-AOB) and denitrification functional genes (nirS, nirK and nosZ) were determined by using real-time fluorescence quota PCR. The results showed that all AM fungi treatments significantly reduced soil N₂O emission fluxes and emission accumulations. The effect of AM fungi in reducing soil N₂O emission accumulation was ranked as follows: M0>M2 >M1>M3. Soil N₂O emission fluxes and emission accumulation of the same AM fungi treatment were higher at NⅡ input than at NⅠ input. AM fungi colonization of the same AM fungi treatment was lower at NⅡ input than at NⅠ input. Compared with M0 treatment, soil ammonium nitrogen content with M1, M2, and M3 treatments under the conditions of NⅠ input reduced by 24.5%, 20.8%, and 45.3%, by 19.7%, 14.9%, and 30.2% for nitrate nitrogen content, and increased by 16.3%, 35.2%, and 59.6% for aboveground total nitrogen content, respectively. However, under the conditions of NⅡ input, soil ammonium nitrogen content with M1, M2, and M3 treatments reduced by 20.9%, 24.8%, and 40.0%, by 36.3%, 25.6%, and 45.2% for nitrate nitrogen content, and increased by 33.2%, 43.9%, and 95.4% for aboveground total nitrogen content, respectively. Under both nitrogen fertilizer input rates, the AM fungi significantly reduced the abundance of nitrification functional genes (amoA-AOA and amoA-AOB) and increased the abundance of denitrification functional genes (nirS, nirK and nosZ). AM fungi was significantly negatively correlated with the soil N₂O emission fluxes. Under the conditions of the present pot experiment, our study concluded that AM fungi could improve nitrogen absorption capacity of maize plants with two nitrogen fertilizer application rates, regulate nitrification and denitrification functional genes abundance and reduce N₂O emission. The N₂O emission reduction effect of two AM fungi mixed treatment was stronger than the single AM fungi inoculation.