长期缺素施肥及石灰石膏施用对江西鹰潭红壤反硝化微生物功能基因丰度的影响

Long-term effects of imbalanced fertilization with lime and gypsum additions on denitrifying functional genes of an Ultisol at Yingtan,Jiangxi,China

反硝化功能基因丰度是决定温室气体氧化亚氮(N_(2)O)排放潜力的重要生物因素。反硝化功能基因主要包括产生N_(2)O的关键基因nirK和nirS,以及将N_(2)O还原成氮气的基因nosZⅠ和nosZⅡ。本研究利用实时荧光定量PCR,研究了32年缺施氮(N)、磷(P)或钾(K)肥,以及施用石灰、石膏处理下江西鹰潭红壤反硝化功能基因的丰度,分析了其关键影响因素。结果表明:与平衡施肥的NPK处理相比,缺施P肥显著降低了nirK、nirS、nosZⅠ和nosZⅡ基因丰度;缺施N肥显著降低了nirK、nosZⅠ和nosZⅡ丰度,对nirS丰度无显著影响;缺施K肥则对反硝化功能基因丰度无显著影响。逐步回归和随机森林分析表明,土壤pH值是影响旱地红壤nosZⅠ和nosZⅡ基因丰度的关键环境因子。施用石灰或石灰+石膏提高了土壤pH值,进而显著提高了nosZⅡ基因丰度和nosZⅡ/nosZⅠ比值,增幅分别为151%~233%和127%~155%。旱地红壤施用石灰或石灰+石膏更有利于nosZⅡ型N_(2)O还原菌生长,可能提高nosZⅡ在N_(2)O还原中的相对重要性。缺施P肥对红壤反硝化功能基因丰度的负面影响最大,而施用石灰或石灰+石膏可以提高nosZⅡ丰度和nosZⅡ/nosZⅠ比值,有利于降低红壤N_(2)O排放潜力。

The abundance of denitrifying functional genes plays a key role in driving the soil nitrous oxide(N_(2)O)emission potential.Nitrite reductase genes(nirK and nirS)and nitrous oxide reductase genes(nosZⅠand nosZⅡ)are the dominant denitrifying funtional genes.Ⅰn this study,real-time quantitative PCR was conducted to evaluate the effects of 32-year imbalanced fertilization and lime and gypsum additions on the abundances of nirK,nirS,nosZⅠand nosZⅡgenes in an Ultisol at Yingtan,Jiangxi Province.We further explored the underlying driving factors.The results showed that,compared with the balanced fertilization treatment,fertilization without phosphorus(P)signifi-cantly decreased the abundances of nirK,nirS,nosZⅠand nosZⅡgenes.Fertilization without nitrogen(N)significantly reduced the abundances of nirK,nosZⅠand nosZⅡ,but did not affect the abundance of nirS.Fertilization without potassium(K)did not affect the abundances of all denitri-fying functional genes.Results of stepwise regression analysis and random forest analysis showed that soil pH was a key environmental factor affecting the abundances of nosZⅠand nosZⅡ.The application of lime or lime+gypsum significantly increased soil pH,which subsequently increased the abundances of nosZⅡand nosZⅡ/nosZⅠby 150%-231%and 127%-155%,respectively.Our results suggested that application of lime or lime+gypsum favored nosZⅡmore than nosZⅠin upland Ultisols,which might enhance the relative importance of nosZⅡin N_(2)O reduction.Overall,fertilization without P would reduce denitrifying gene abundances,while the application of lime or lime+gypsum enriched nosZⅡand increased ratio of nosZⅡ/nosZⅠ,which might be beneficial for reducing N_(2)O emission potential in the Ultisols.