华南地区菜地N2O排放及其对生物质炭陈化过程的响应机制

Biochar has been advocated as an emerging strategy for mitigating nitrous oxide (N2O) while enrich the soil carbon pool in agricultural ecosystem. Although the structure of biochar has been regarded to be stability, the aging process of biochar related to the physicochemical properties exists as the time goes on, and then influences the potential and function of carbon sequestration. High water and fertilizer input from vegetable fields lead to a large amount of N2O emissions. South China has high temperature, frequent rainfall and farming practices, and it is not clear about the influences and the driving factors about the timing effects of N2O emissions induced by the aging process of biochar amended into the agricultural soil in South China. Thus, a study incorporated with the field observation and incubation simulation by using the the static chamber-gas chromatographic techniques and 15N tracing technique-pool dilution methods will be carried out to investigate: ① the dynamic effects of biochar aging process on characteristics N2O emission and related driving factors; ② the portions of different N2O production processes and N2O product ratios and the key N2O emission pathway. Scientific issues would be settled in this study including: qualify the N2O production process, emission characteristics and driving factors and clarify the response mechanism of N2O emissions biochar aging process to provide a scientific basis and data support for a reasonable assessment N2O emissions risks from intensive vegetable fields and the potential N2O reduction effect of biochar in intensive vegetable fields in South China.

生物质炭田间施用是丰富土壤碳库和减缓农田土壤N2O排放的有效措施。生物质炭结构稳定，但其理化特性会因时间推移而发生陈化现象，进而影响其实际固碳减排的潜力和功能。菜地高的水肥投入导致N2O大量排放。我国华南地区高温、多雨且农事操作频繁，生物质炭施用到华南菜地土壤中的陈化过程及时间效应对N2O排放的影响及主要驱动因子尚不清楚。本研究通过田间原位观测及室内模拟研究，采用静态暗箱和15N同位素标记等方法，旨在探究：①生物质炭陈化过程对华南菜地周年N2O排放及其驱动因素的影响；②定量研究生物质炭陈化过程对菜地N2O排放源及关键排放过程的影响。拟解决的科学问题：定量研究华南地区菜地N2O排放特征和驱动因素，阐明华南地区菜地土壤N2O排放以及其驱动因素对生物质炭陈化作用的动态响应机制，为合理评估华南地区集约化菜地N2O排放风险以及生物质炭对华南地区集约化菜地N2O的潜在减排效果提供科学依据和数据支撑。

摘要：生物质炭在农田生态系统中的施用被认为是减缓温室气体排放以及实现低碳农业的重要途径，然而目前为止对于生物质炭在不同土壤中的固碳减排效果以及机理还有待于进一步的研究。因此，本研究基于两年的华南菜地种植田间试验，在集约化蔬菜种植过程中设置不同生物质炭施用量（0、10、20、30和40吨/公顷），动态监测土壤温室气体排放、土壤理化性质以及土壤微生物群落结构，以探究在本生态系统中的最优生物质炭施用量。结果表明：生物质炭的施用显著增加了14-59%的CH4排放量，但是显著降低了40-66%的N2O排放量。此外，与不施用生物质炭的处理相比，生物质炭的施用显著降低了4-31%的土壤磷脂脂肪酸（PLFA）含量以及12-39%的真菌/细菌比例，并且显著降低了革兰氏阳性细菌、真菌、细菌和丛枝菌根真菌含量。生物质炭的施用还显著降低了蔬菜种植过程中的综合温室效应，通过随机森林分析表明其最主要的影响因子为土壤pH、土壤真菌PLFA和土壤有机质。另外，生物质炭的施用量与减排能力呈现出非线性关系，在本试验中20吨/公顷生物质炭被认为是最优的处理因为综合温室效应最低。另外通过把土壤N2O排放与土壤水分温度耦合我们发现，生物质炭在土壤温度超过20摄氏度时减排效果明显，且土壤反硝化过程是控制N2O减排效果的最主要因素。因此我们设置室内培养实验探究不同温度条件下生物质炭陈化对华南菜地土壤反硝化过程的影响。结果表明：温度升高显著增加了菜地土壤N2O和N2的排放量，显著提高了土壤pH 和土壤NH4+含量，显著降低了DOC含量和NO3-含量，但是并未显著影响反硝化过程的关键酶基因丰度；生物质炭（FB）显著降低了菜地土壤N2O排放15.7%-16.1%，并且显著影响了反硝化总脱氮量（N2O+N2）。此外，田间陈化生物质炭（FAB）处理则能显著增加土壤中nirK和nosZ-II基因丰度(p<0.05)。研究结果表明生物质炭施用量、土壤温度条件以及土壤类型均能显著影响其减排效果与田间应用前景，结论能够为助力我国“碳中和”和华南地区低碳农业的实现提供理论支撑。