氮添加对樟子松人工林氮转化及相关功能基因丰度的影响

土壤氮(N)的有效性是影响土壤微生物群落结构以及土壤氮循环的重要因子。为探索N添加对樟子松人工林氮素转化及N功能基因(NFGs)表达的影响及其作用机制,该文以塞罕坝千层板林场的樟子松人工林为研究对象,进行了2年的氮添加处理,设置4个不同氮添加水平0、1、5、10 g N·m^-2·a^-1,分别记作N0、N1、N5、N10,采用功能基因微阵GeoChip 5.0系统及室内土壤培养法,探讨了土壤NFGs对氮添加的反应及其对氮转化过程的影响。结果表明:(1)与N0相比,中低N添加处理(N1、N5)促进了氨化(ureC、nirA、nrfA)、硝化(amoA)和反硝化(norB)相关基因的相对丰度,高N处理(N10)则抑制了所有NFGs的表达。(2)相关分析表明,N1、N5的促进作用与土壤有机碳(SOC)、硝态氮(NO₃^--N)和微生物生物量碳(MBC)显著相关,N10处理显著降低了所有氮转化过程NFGs的相对丰度,这种负面影响与溶解性有机碳(DOC)、MBC含量的减少有关。(3)与氮转化基因丰度规律趋势相似,N1和N5处理显著增加了净N硝化、净N矿化以及N₂O的排放速率,但N10促进作用不明显,表明氮添加对氮转化的促进作用存在阈值。(4)多元回归分析进一步表明,amoA-AOB和MBC是影响净N硝化的关键因素,ureC、nirK和MBC是影响净氮矿化的关键因素,narG、nirS是影响N₂O排放的关键因素。综上,N添加可提高促进樟子松人工林的氮转化及提高部分特定酶功能基因的相对丰度,但氮添加水平存在阈值,当施用10 g N·m^-2·a^-1时,氮转化受到抑制,添加5 g N·m^-2·a^-1是促进樟子松人工林土壤N转化的较佳水平。

Effects of nitrogen addition on nitrogen transformation and related functional gene abundance in Pinus sylvestris var. mongolica plantation

Soil nitrogen(N)effectiveness is an important factor affecting soil microbial community structure and soil N cycling. In order to explore the effect of N addition on nitrogen transformation and N functional gene(NFGs)expression in Pinus sylvestris plantation and its mechanis, in this study, the Pinus sylvestris var. mongolica plantation in the Saihanba Melaleuca Forest Farm were added four different N levels of 0, 1, 5, 10 g N·m^-2·a^-1 for two years, which were designated with N0, N1, N5 and N10, and with the GeoChip 5.0 functional gene microarray system and the greenhouse soil culture method, the response of soil NFGs to N addition and its influence on N transformation processes were discussed. The results were as follows:(1)The N1 and N5 treatments significantly affected the ammonification(ureC, nirA, nrfA), nitrification(amoA)and denitrification(norB)and compared with the N0 treatment, N10 treatment reduced the expression of all NFGs.(2)Correlation analysis showed that the above promotion was significantly associated with soil organic carbon(SOC), nitrate nitrogen(NO₃^--N)and microbial biomass carbon(MBC), and N10 treatment significantly reduced the relative abundance of NFGs for all N transformation processes, and this negative effect was associated with a reduction in dissolved organic carbon(DOC)and MBC content.(3)Similar to the trend of nitrogen transformation gene abundance, N1 and N5 treatments significantly increased net N nitrification, net N mineralization and N₂O emission rate, but the promotion of N10 was not significantly, which indicated that there was a threshold for the promotion of nitrogen conversion by nitrogen addition.(4)Furthermore, multiple regression analysis further showed that amoA-AOB and MBC were key factors affecting net N nitrification, ureC, nirK and MBC were key factors affecting net N mineralization, and narG and nirS were key factors affecting N₂O emissions. In conclusion, N addition can improve the promotion of N transformation and increase the relative abundance of some specific enzyme functional genes in Pinus sylvestris var. mongolica plantation, but there is a threshold value for N addition level, when 10 g N·m^-2·a^-1 is applied, N transformation is inhibited, and 5 g N·m^-2·a^-1 is a better level to promote soil N transformation in Pinus sylvestris var. mongolica plantation.