模拟氮沉降对温带阔叶红松林地土壤氮素净矿化的影响

以长白山阔叶红松混交林为研究对象,于2006—2008年原位模拟不同形态氮((NH4)2SO4、NH4Cl和KNO3)沉降水平(22.5和45kgN·hm-2·a-1),利用树脂芯法技术(resin-core incubation technique)测定了表层(有机层0～7cm)和土层(0～15cm)土壤氮素净矿化、净氨化和净硝化通量的季节和年际变化规律。同时,结合前人报道的有关林地碳、氮过程及其环境变化影响的结果,力求有效预估森林生态系统中氮素年矿化通量对大气氮沉降量和水热条件等因子变化的响应。结果表明,长白山阔叶红松林地土壤氮素年净矿化通量为1.2～19.8kgN·hm-2·a-1,2008年不同深度的土壤氮素年净矿化通量均显著高于2006和2007年(P<0.05)。随着模拟氮沉降量增加,土壤氮素净矿化通量也随之增加,尤其外源NH4+-N输入对净矿化通量的促进作用更为明显(P<0.05),但随着施肥年限的延长,这种促进作用逐渐减弱。与林地0～15cm土壤相比,氮沉降增加对0～7cm有机层氮素净氨化和净矿化通量的促进作用更为明显,尤其NH4Cl处理的促进作用更大。结合前人报道的野外原位观测结果,土壤氮素年净矿化通量随氮素沉降量的增加而增大,氮沉降量对不同区域森林土壤氮素净矿化通量的贡献率约为52%;氮沉降量(x1)和pH值(x2)可以解释区域森林土壤氮素年净矿化通量(y)变化的70%(y=0.54x1-18.38x2-109.55,R2=0.70,P<0.0001)。前人研究结果仅提供区域年均温度,未考虑积温的影响,这可能是造成年净矿化通量与温度无关的原因。今后的研究工作应该加强区域森林土壤积温观测,进而更加准确地预估森林土壤氮素的年净矿化通量。

Effects of simulated nitrogen deposition on soil nitrogen mineralization in a temperate broadleaf-Korean pine (Pinus koraiensis) forest

Taking a broadleaf-Korean pine (Pinus koraiensis) forest in Changbai Mountains of Northeast China as the object, an in situ experiment was conducted in 2006-2008 to study the effects of simulated nitrogen deposition on the seasonal and annual dynamics of soil net nitrogen mineralization, including net ammonification and net nitrification, in humus layer (0-7 cm) and uppermost mineral layer (0-15 cm) in the forest. The applied nitrogen forms were (NH4)2SO4, NH4Cl, and KNO3, and their application rates were 0, 22.5, and 45 kg N·hm-2·a-1. During the study period, the annual soil nitrogen mineralization flux in the forest was 1.2-19.8 kg N·hm-2·a-1. In the two soil layers, the net nitrogen mineralization flux was significantly higher in 2008 than in 2006 and 2007 (P<0.05). The soil net N mineralization rate was increased with nitrogen input, especially the input of (NH4)2SO4 or NH4Cl (P<0.05), but this promotion effect decreased with the extension of years. Nitrogen deposition, especially NH4Cl, had more obvious promotion effect on the net ammonification and net mineralization rates in humus layer than in the uppermost mineral layer. The previous researches on the annual fluxes of net nitrogen mineralization in forest soils in global scale also showed that the soil net nitrogen mineralization rate was increased significantly with increasing atmospheric nitrogen deposition, and the variation of atmospheric nitrogen deposition accounted for 52% of the variation of soil net nitrogen mineralization rates across the forests. In this study, nitrogen deposition (x1) and soil pH (x2) could explain 70% of the variation of soil net nitrogen mineralization rate (y) (y=0.54x1-18.38x2-109.55, R2=0.70, P<0.0001). The previous researches only provided the annual temperature in research areas, not considered the influence of the accumulative temperature, which could be the causes of non-relationship between soil nitrogen mineralization and temperature. The future research should pay more attention to the observation of soil accumulative temperature in different regional forests.