小兴安岭原始红松混交林林隙土壤不同形态氮含量

Concentrations of different nitrogen forms in gaps of natural Pinus koraiensis mixed forest in Xiao Xing'anling Mountains

以小兴安岭地区红松混交林(椴树红松混交林、云冷杉红松混交林和枫桦红松混交林)大、中、小3个林隙为研究对象,对林隙和郁闭林分土壤铵态氮(NH4+-N)、硝态氮(NO3--N)、可溶性全氮(TSN)、可溶性有机氮(SON)、微生物氮(MBN)和全氮(TN)含量进行分析,探讨不同混交林林隙中土壤氮形态特征。结果表明:林隙和郁闭林分土壤以有机氮为主,占TN 98%以上。林隙中土壤NO3--N含量高于NH4+-N含量;SON含量高于NH4+-N和NO3--N含量。红松混交林中土壤NH4+-N、NO3--N、SON和MBN含量在大、小林隙之间以及林隙与郁闭林分之间差异显著,尤其是MBN含量表现为郁闭林分>小林隙>中林隙>大林隙,与林隙面积呈极显著负相关;3个林型中NO3--N/TN和MBN/TN随着林隙面积增大而减小;椴树红松混交林和云冷杉红松混交林林隙中NH4+-N/TN、TSN/TN和SON/TN随林隙面积增大而减小,枫桦红松混交林林隙中随林隙面积增大而增大。林隙和郁闭林分中土壤TSN与SON均呈现极显著正相关;林隙土壤NH4+-N与NO3--N和MBN呈显著相关,但在郁闭林中未表现出此关系。

The concentrations of different nitrogen（ N） forms in soil（ ammonium N（ NH4＋-N）,nitrate N（ NO3--N）,total soluble N（ TSN）,soluble organic nitrogen N（ SON）,microbial biomass N（ MBN） and total N（ TN）） were investigated under gaps with different sizes in three Korean pine（ Pinus koraiensis） mixed forests（ i. e.,Tilia-Korean pine mixed forest,spruce-fir-Korean pine mixed forest,and birch-Korean pine mixed forest） in Xiao Xing’anling Mountains.The results showed that organic N was the dominant form of TN,accounting for more than 98% of TN. Concentration of NO3--N was higher than that of NH4＋-N,and SON concentration were higher than NH4＋-N and NO3--N. Concentrations of NH4＋-N, NO3--N, SON and MBN showed significant differences between large and small forest gaps and between forest gaps and closed forests. Especially,MBN was in the order of closed forests 〉 small gap 〉 medium gap〉 large gap,showing a significant negative correlation with gap size. NO3--N / TN and MBN / TN decreased with the increase of gap size in the three forests. NH4＋-N / TN,TSN / TN and SON / TN decreased with the increase of gap size in the Tilia-Korean pine mixed forest gaps and spruce-firKorean pine mixed forest gaps,but increased with the increase of gap size in the birch-Korean pine mixed forest gaps. Significant correlations were observed between TSN and SON in forest gaps and closed forests. NH4＋-N was significantly correlated with NO3--N and MBN in forest gaps,but such relationships were not found in the closed forests.