东北温带次生林采伐干扰对土壤氮矿化的影响

Effect of Harvest Cutting on Soil Nitrogen Mineralization in the Temperate Secondary Forests of Northeast China

在黑龙江省帽儿山地区对经过不同强度采伐1 a 后的次生林,采用PVC 管原位培养法测定土壤净氮矿化速率和净氮硝化速率的变化,结果表明,0～10 cm 土层的土壤平均净氮矿化速率和净氮硝化速率从大到小依次为皆伐后造林、皆伐后农作、50%强度采伐、25%强度采伐和对照,各采伐处理的0～12 cm 土层土壤质量含水量均显著高于对照（P〈0. 05）,净氮矿化速率和净氮硝化速率与土壤质量含水量呈显著正相关（P〈0. 05）,同时采伐亦增加了土壤中的有机碳含量,这说明采伐引起土壤含水量和有机碳含量增加是导致净氮矿化速率和净氮硝化速率升高的主要原因.此外,采伐还引起了土壤无机氮含量的变化,在生长季各采伐处理土壤硝态氮平均含量均显著高于对照（P〈0. 05）,而土壤铵态氮平均含量则显著低于对照（P〈0. 05）,各采伐处理土壤无机氮以硝态氮为主,对照则以铵态氮为主.上述结果表明该地区的森林经过采伐干扰后,可导致土壤硝态氮含量增加,土壤氮素流失风险亦增加.

A field experiment was carried out using a PVC tube in?situ incubation method to explore effect of harvest cut?ting on soil net nitrogen ( N) mineralization rate and net nitrification rate in temperate secondary forests one year after the felling operation varying in intensity in the Maoershan region of Heilongjiang Province. Results show that in terms of means of soil net N mineralization rates and net nitrification rates in the 0-10 cm soil layer, the treatments followed an order of afforestation after clear cutting>farming after clear cutting>50% of the stand volume removed>25% of the stand volume removed > control. Soil water content in the 0-12 cm soil layer was significantly higher in the harvested plots than in the control. Both net N mineralization rate and net nitrification rate were significantly and positively related to soil water con?tent. Harvesting also increased soil organic carbon content. All the findings suggest that the increased soil water and organic carbon are the main causes of the increase in soil net N mineralization rate and net nitrification rate after harvest cutting. In addition, harvest cutting also triggered change in soil inorganic N content. During the growing season, the means of NO3-?N contents in the harvested plots were significantly higher than that in the control, while the means of NH4+?N were quite the contrary. Soil inorganic N was dominated with NO3-?N in the harvested plots, and with NH4+?N in the control. The above findings suggest that harvest cutting may increase NO3-?N content in the soil, and hence, the risk of losing soil nitrogen in this region.