生物炭连续施用对农田土壤氮转化微生物及N2O排放的影响

【目的】研究连续添加生物炭6年后对农田土壤氮转化相关微生物功能基因的影响,揭示生物炭影响作物产量和N₂O排放的微生物学机制,并为生物炭的推广使用提供理论依据。【方法】通过在潮土农田设置0（BC0,对照)、2.25（BCL,低量）、6.75（BCM,中量）和11.25 t·hm^-2（BCH,高量）4个秸秆生物炭量处理的田间定位试验,采用田间观测、化学分析、荧光定量PCR（qPCR）技术,系统研究施用生物炭对氧化亚氮（N₂O）排放、氨单加氧酶（amoA）、亚硝酸还原酶（nirK、nirS）、氧化亚氮还原酶（nosZ）基因丰度及夏玉米产量的影响。【结果】与对照BC0处理相比,施用生物炭可显著提高夏玉米籽粒产量,且BCM处理籽粒产量达到最大值10 811 kg·hm^-2,显著降低夏玉米生育期N₂O累积排放量,并以BCM处理减少N₂O排放效果最优。研究还发现,在夏玉米多个生育时期,与对照比较,生物炭施用可以显著提高耕层土壤无机氮储量和土壤含水量。此外,随着生物炭施用量增加,土壤氨氧化古菌（AOA）基因拷贝数在夏玉米大喇叭口期和成熟期均表现为先上升后下降趋势,且两个时期均以BCM处理最高,而氨氧化细菌（AOB）基因拷贝数在夏玉米大喇叭口期和成熟期分别为BCH处理和BCM处理最高。与对照相比,中、高量生物炭施用（BCM、BCH处理）可显著提高夏玉米大喇叭口期和成熟期土壤反硝化作用功能相关基因（nirK、nirS、nosZ）拷贝数。相关性分析表明,夏玉米成熟期土壤N₂O排放通量与土壤硝态氮、土壤含水量、AOA、AOB、nirK、nirS、nosZ呈显著负相关关系。【结论】施用生物炭通过增加土壤微生物氮转化功能基因丰度进而降低土壤N₂O排放,通过增加土壤耕层无机氮储量和土壤水分含量进而提高作物产量,并以中等用量（6.75 t·hm^-2）施用效果最优。

Effects of Successive Biochar Addition to Soil on Nitrogen Functional Microorganisms and Nitrous Oxide Emission

【Objective】In recent years, the biochar has been widely concerned due to its some positive roles in soil improvement, agricultural production, and carbon sequestration and emission reduction. The purpose of this experiment was to reveal the microbiological mechanism of biochar on crop yield and nitrous oxide (N₂O) emission and to provide a theoretical basis for extending application of biochar in agriculture.【Method】A fixed field experiment with successive straw-based biochar amended at 0 (BC0, CK), 2.25 (BCL, low rate), 6.75 (BCM, medium rate), and 11.25 t·hm^-2(BCH, high rate) was carried out in the typical farmland with fluvo-aquic soil in Huanghuai area of China. Effect of successive biochar addition after six year on nitrous oxide (N₂O) emission, nitrogen (N) functional genes and grain yield of summer maize were studied by field observation, chemical analysis and real-time quantitative polymerase chain reaction (qPCR) in laboratory.【Result】Compared to BC0, biochar application significantly increased grain yield of summer maize with the maximum value (10 811 kg·hm^-2) under BCM treatment, and also significantly reduced N₂O emissions with the better performance for BCM during summer maize season. Compared with BC0, biochar application could significantly improve inorganic nitrogen storage and moisture content in topsoil. In addition, following biochar application rate, the soil AOA gene abundance increased first and then decreased with the highest gene copy number in BCM treatment at the bellmouth stage and maturity stage of summer maize, while the higher AOB gene abundance under BCH and BCM treatment presented respectively at the bellmouth stage and maturity stage of summer maize. Similar to nitrification function related genes (AOA and AOB), compared with BC0, the medium and high-rate biochar application (BCM, BCH) also significantly increased the copy number of denitrification function related genes (nirK, nirS, nosZ) at the bellmouth stage and maturity stage of summer maize. Correlation analysis indicated that the significantly negative correlation was found between N₂O emissions, NO₃^-, moisture content (MO) and the expression of the AOA, AOB, nirK, nirS, and nosZ genes in topsoil at maturity of summer maize.【Conclusion】Successive biochar addition could reduce N₂O emission by increasing the gene abundance of soil N transformation, and increase crop yield by improving inorganic nitrogen storage and moisture content in topsoil. Overall, the treatment with 6.75 t·hm^-2 biochar led to the best comprehensive performance in the study region.