冻融交替对河岸缓冲带土壤无机氮和土壤微生物量氮的影响

Effect of freezing-thawing on soil dissolved inorganic nitrogen and soil microbial biomass nitrogen in riparian zone

辽宁东部山区土壤冻融交替强度和频次变化是土壤氮循环的重要影响因素,冻融温差和冻融循环次数影响微生物数量和群落的变化,进而影响土壤氮素生物地球化学循环。以大伙房实验林场小流域的河岸缓冲带生态系统为研究对象,通过分析冻融交替对河岸缓冲带土壤无机氮和土壤微生物量氮的影响,阐明非生长季土壤无机氮含量变化机制,为评估小流域氮素流失风险提供依据。研究结果表明,随着冻融循环次数的增加,土壤无机氮含量呈增加趋势;不同温差的冻融循环对土壤无机氮影响不同,冻融条件为-5℃/+5℃和-20℃/+5℃时土壤无机氮含量分别为34.9±0.9 mg·kg-1和37.2±0.8 mg·kg-1,是处理前的1.21和1.41倍;冻融温差和冻融循环次数对土壤NH+4-N含量有极显著影响(P<0.01),土壤冻融后土壤NH+4-N含量是+5℃处理的4—10倍;土壤NO-3-N含量和土壤微生物量氮含量对冻融循环的响应显著(P<0.01),冻融交替显著增加了土壤无机氮含量。

Changes of intensity and frequency of soil freezing-thawing cycles are important factors affecting the N cycle in the riparian ecosystem in eastern mountain of Liaoning province. The freezing-thawing cycles could affect soil nitrogen cycles through microbial biomass and community. The study was carried out in Dahuofang experimen- tal forest watershed. The effect mechanism of freezing-thawing cycles on inorganic nitrogen content of soil was re- vealed, which could provide the references for assessing the risk of N loss in the riparian ecosystem. The results show that soil inorganic nitrogen content is in an increasing trend with the increasing times of freezing-thawing cy- cles. Different freezing temperature has the significant effect on inorganic nitrogen. The inorganic nitrogen contents are 34. 9 -0. 9 mg.kg-1 and 37. 2-0. 8 mg-kg-1 after 10 freezing-thawing cycles with the -5℃/＋5℃ and -20 ℃/＋5 ℃ treatments,which are 1.21 and 1.41 times of initial inorganic nitrogen content of soil samples,re- spectively. Furthermore, freezing-thawing cycles and its temperature difference have the significant effect on soil NH4-N content （P 〈0. 01 ）. After 10 freezing-thawing cycles, soil NH4＋ -N content is 4-10 times of soil samples for ＋ 5 ℃treatment. Freezing-thawing cycles have the significant influences on soil NO3- -N content （ P 〈 0. 05 ）, while its temperature difference has not the significant influences on NO3--N content（ P 〉 0. 05 ）. The response of soil microbial biomass nitrogen content to freezing-thawing cycles is significant（ P 〈 0.01 ）.