农田防护林根际与非根际土壤氮素形态特征

Characteristics of Nitrogen Forms in Rhizosphere and Non-rhizosphere Soil of Farmland Shelter Forests

探讨根际与非根际土壤氮素形态变化,以阐明农田防护林地对土壤氮循环的影响,为农田防护林的建设管理提供依据。该研究选取黑龙江省拜泉县樟子松纯林、落叶松纯林、樟子松×落叶松混交林3种典型农田防护林型的土壤,测定土壤理化指标、氮素形态指标及氮转化功能基因拷贝数的变化。结果表明,混交林根际土壤的酸性程度高于纯林,其中,樟子松纯林根际土壤pH显著高于其他林型,落叶松纯林土壤电导率最高,其根际电导率值高达(53.33±2.54)μS/cm,混交林土壤容重显著大于纯林(P<0.05);混交林两树种的根际土壤全氮、铵态氮、硝态氮含量均显著高于各自纯林(P<0.05),表明混交林土壤氮素成分在3种林型中最优;与其他林型相比,樟子松纯林根际土壤功能基因拷贝数(amoA-AOA、amoA-AOB、nirS、nosZ、narG、nifH)都处于较低的水平,表明其影响了土壤氮转化速率,降低了土壤铵态氮、硝态氮的含量;冗余分析(RDA)结果表明,农田防护林氮素形态变化与土壤理化指标和氮转化功能基因密切相关,amoA-AOA基因与amoA-AOB基因分别为研究区根际与非根际土壤影响最大的因子,说明硝化作用在土壤氮转化中占主导位置。综上,防护林型的适宜建设程度由大到小为:混交林、落叶松纯林、樟子松纯林。

To explore the changes of soil nitrogen forms in rhizosphere and non rhizosphere,in order to clarify the impact of farmland shelter on soil nitrogen cycle,and to provide basis for the construction and management of farmland shelter,in this study,three types of shelter in Baiquan County of Heilongjiang Province were selected as the research objects,including pure forest of Pinus sylvestris var.mongholica Litv.,pure forest of Larix gmelinii(Rupr.) Kuzen.and a mix of Pinus sylvestris var.mongholica Litv.and Larix gmelinii(Rupr.) Kuzen.The changes of soil physical and chemical indexes,nitrogen form indexes and copy number of nitrogen transformation functional genes were measured.The results showed that the acidity of rhizosphere soil of mixed forest was higher than that of pure forest.Among them,the pH value of rhizosphere soil of Pinus sylvestris pure forest was significantly higher than that of other forest types.The soil conductivity of Larix pure forest was the highest,and its rhizosphere conductivity value was as high as(53.33±2.54) μs/cm,the soil bulk density of mixed forest was significantly higher than that of pure forest(P<0.05).The contents of total nitrogen,ammonium nitrogen and nitrate nitrogen in rhizosphere soil of mixed forest were significantly higher than those of pure forest(P<0.05),indicating that the soil nitrogen of the mixed forest was the best among the three forest types.Compared with other forest types,the copy numbers of soil functional genes(amoA-AOA,amoA-AOB,nirS,nosZ,narG,nifH) in the rhizosphere of pure Pinus sylvestris stand were at a low level,indicating that it affected the transformation rate of soil nitrogen and reduced the content of soil ammonium nitrogen and nitrate nitrogen.The results of RDA showed that the changes of nitrogen forms in farmland shelter were closely related to soil physical and chemical indexes and nitrogen transformation functional genes.amoA-AOA gene and amoA-AOB gene were the largest influencing factors of rhizosphere and non rhizosphere soils in the study area,indicating that nitrification played a dominant role in soil nitrogen transformation.In conclusion,the suitable construction degree of shelter forest type from the most to the least was mixed forest、pure Larix forest、pure Pinus sylvestris forest.