长期施氮对土壤氨化细菌和氮矿化作用的影响

Effects of Long-term Nitrogen Application on the Soil Ammonifier and Nitrogen Mineralization

摘要:

氨化作用是微生物将有机氮转化为无机氮的过程，可提升土壤氮素供应状况，不同肥料长期施用情景下土壤有机氮发生显著变化，但其氨化过程尚不清楚。据此，依托沈阳农业大学29年长期定位施肥试验，针对4个不同的施肥处理，包括不施肥（CK）、施用化肥（HCF）、施用减量化肥（LCF）和化肥减量配施有机肥（CMF），3个土壤深度（0～20 cm、20～40 cm和40～60 cm）和3个采样时期（播种前、玉米抽雄期和收获后），采用实时荧光定量PCR（qPCR）方法，研究长期不同施肥处理后玉米生长期不同土层中土壤氨化基因gdh丰度、活性和氮矿化变化规律，揭示施肥、季节、土壤深度及其相互作用对氨化细菌和土壤净氮矿化速率的影响。结果表明：1）相比于土层和施肥处理，采样时期对gdh基因丰度和活性的影响最显著；三个采样时期中，玉米抽雄期土壤gdh基因活性和净氮矿化速率显著高于播种前和收获后（P < 0.05）；2）与不施肥（CK）相比，长期施加化肥（LCF和HCF）显著增加抽雄期土壤氮矿化速率（P < 0.05），CMF则表现出稳定或增加收获后土壤氮矿化速率；3）氨化细菌丰度、活性与土壤净氮矿化速率呈极显著正相关，铵硝比是影响氨化细菌的重要因子（P < 0.01）。综上，施氮与作物吸收改变了土壤铵硝比，引起土壤氨化细菌丰度与活性差异，导致土壤氮矿化速率发生变化。LCF和HCF有利于增加播种前和抽雄期表层土壤氮矿化速率，CMF则有助于稳定收获后土壤氨化细菌活性，促进土壤有机氮的氨化过程。

Abstract:

【Objective】 Ammoniation is the process by which microorganisms convert organic nitrogen into inorganic nitrogen, which can improve soil nitrogen supply. Under different long-term fertilizer application scenarios, soil organic nitrogen undergoes significant changes, which makes comprehension of its ammonification process challenging. 【Method】 This study relied on a 29-year long-term targeted fertilization experiment at Shenyang Agricultural University, targeting four different fertilization treatments, including no fertilization (CK), chemical fertilizer (HCF), chemical fertilizer reduction (LCF), and fertilizer reduction combined with organic fertilizer (CMF), considering three soil depths (0-20 cm, 20-40 cm, and 40-60 cm), and three sampling period (pre-planting, maize tasseling stage and post-harvest). Using the real-time fluorescence quantitative PCR (qPCR) method, the abundance, activity, and nitrogen mineralization changes of soil ammonification gene gdh in different soil layers were studied during maize growth period after long-term different fertilization treatments. Also, the effects of fertilization, season, soil depth, and their interactions on ammonifier and soil net nitrogen mineralization rate were evaluated. 【Result】 The results showed that: 1) Compared with soil layer and fertilization treatment, the sampling period had the most significant impact on the abundance and activity of gdh genes. During the three sampling periods, the soil gdh gene activity and net nitrogen mineralization rate during the maize tasseling stage were significantly higher than pre-planting and post-harvest (P < 0.05) ; 2) Compared with no fertilization (CK), long-term application of chemical fertilizers (LCF and HCF) significantly increased soil nitrogen mineralization rate during the tasseling period (P < 0.05) while reduction of fertilizer combined with organic fertilizer (CMF) showed stable or increased soil nitrogen mineralization rate in post-harvest; 3) The abundance and activity of ammonifiers were significantly positively correlated with soil net nitrogen mineralization rate, and the ammonium nitrate ratio was an important factor affecting ammonifiers (P < 0.01). 【Conclusion】 In summary, nitrogen application, and crop absorption change the soil ammonium nitrate ratio, causing differences in the abundance and activity of soil ammonifiers. This led to changes in soil nitrogen mineralization rate. Long-term application of LCF and HCF is beneficial for increasing the rate of surface soil nitrogen mineralization in pre-planting and tasseling. CMF can help stabilize the activity of soil ammonifiers in post-harvest and promote the ammonification process of soil organic nitrogen.