FACE环境下不同秸秆与氮肥管理对稻田土壤硝化和反硝化菌的影响

Effect of Different Levels of Straw-Returning-Back-to-Field and N Fertilization on Nitrifiers and Denitrifiers of Paddy Soils in FACE (Free-Air Carbon Dioxide Enrichment)

利用位于江都市小记镇的中国稻-麦轮作FACE平台，采用最大可能（MPN）法，在2004年水稻生长季研究了不同施肥情况（施常规N量UN和低N量LN）、不同秸秆还田情况（秸秆全还田HR和秸秆不还田NR）下，土壤中硝化和反硝化细菌数量在FACE条件下随时间的变化。结果表明，FACE条件下，土壤硝化菌数普遍在抽穗期或乳熟期达到最大值，而对照土壤的硝化菌数普遍到成熟期才达到最大值，并且显著高于FACE处理的相应值（P〈0．05）。在HR条件下，LN和UN小区FACE处理的土壤硝化细菌数量较对照减少6％-10％。FACE条件LN小区的反硝化菌数在成熟期达到最大值，而对照处理则在乳熟期达到最大值，并显著高于FACE处理（P〈0．05）；而UN小区的反硝化菌数二者均在抽穗期达到最大值。在LN小区HR和NR情况下。FACE处理土壤反硝化细菌数量分别低于对照处理的相应值8％和13％。在HR情况下，土壤反硝化潜势FACE处理显著低于对照。在LN和UN小区，FACE处理土壤的反硝化作用潜势分别是对照的83．7％和95．4％。

Elevated atmospheric CO2concentration may alter nitrifiers and denitrifiers population which play a pivotal role in N turnover of paddy soil. A free-air CO2 enrichment （FACE） experiment was conducted in paddy fields under two N fertilization levels （Normal N-250 kg/ hm^2 and Low N-150 kg/hm^2） and two levels of straw- returning-back-to-field （HR, NR） during rice-growing season in 2004 at Jiangdu of Jiangsu province to evaluate changes of nitrifiers and denitrifiers population by the-most-probable-number （MPN） method. Results showed that elevated atmospheric CO2 concentration stimulated nitrifiers population to reach maximum at jointing or ripening stages, while ambient at booting stage and significantly higher than that of FACE. LN and UN treatments reduced nitrifiers population by 6% - 10% in HR condition. Denitrifiers population of LN treatments from FACE plots reached maximum at booting stage, while ambient at ripening stage and significantly higher than that of FACE. But denitrifers population of UN plots reached maximum at jointing stage. LN treatments reduced denitrifiers population by 8% - 13% in HR and NR conditions. FACE significantly reduced denitrification potential （DP） in straw-returning-back-to-field treatments, and DP （denitrification potential） of LN and UN treatments from FACE plots were only 83.7% and 95.4% of those of ambient.