大兴安岭北部天然针叶林土壤氮矿化特征

采用顶盖埋管法对大兴安岭地区天然针叶林(樟子松林、樟子松-兴安落叶松混交林和兴安落叶松林)土壤铵态氮(NH~+_4-N)、硝态氮(NO~-_3-N)、净氮矿化速率进行研究,并探索土壤理化性质与氮矿化之间的相关性,为大兴安岭地区森林生态系统土壤养分管理及森林经营提供帮助。结果表明:观测期内(5—10月)3种林型土壤无机氮变化范围为31.51—70.42 mg/kg,以NH~+_4-N形式存在为主,占比达90%以上,且与纯林相比混交林土壤无机氮含量较高。3种林型土壤净氮矿化、净氨化、净硝化速率月变化趋势呈V型,7、8月表现为负值,其他月份为正值。净氮矿化速率变化范围樟子松林为-0.54—1.28 mg kg~(-1) d~(-1)、樟子松-兴安落叶松混交林为-0.13—0.55 mg kg~(-1) d~(-1)、兴安落叶松林为-0.80—1.05 mg kg~(-1) d~(-1)。土壤净氨化过程在土壤氮矿化中占主要地位,占比达60%以上。3种林型土壤净氮矿化、净氨化及净硝化速率垂直差异显著,0—10 cm土层矿化作用明显高于10—20 cm土层(P0.05)。土壤氮矿化速率与土壤含水量、土壤有机碳含量、土壤C/N、枯落物全氮含量和枯落物C/N均存在显著相关性。不同类型的森林土壤及枯落物的质量也存在差异,进而影响土壤氮矿化特征。

Soil nitrogen mineralization characteristics of the natural coniferous forest in Northern Daxing'an Mountains, Northeast China

The characteristics of the ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), and nitrogen mineralization rate were investigated using the method of in situ top-closed incubation in natural coniferous forests (Pinus sylvestris var. mongolica forest, Pinus sylvestris var. mongolica-Larix gmelinii mixed forest, and Larix gmelini forest) in Daxing''an Mountains. This study was aimed at comparing the characteristics of soil nitrogen mineralization in different forest types, and exploring the correlation between soil physical and chemical properties and nitrogen mineralization, which will help to improve soil nutrient and forest management in the Daxing''an Mountains. The results showed that the soil inorganic nitrogen in three forest types ranged from 31.51 to 70.42 mg/kg, of which > 90% was in the form of NH₄⁺-N during the observation period (5-10 months). The soil inorganic nitrogen content in the mixed forest was higher than that in the pure forest. The net nitrogen mineralization, ammonization, and nitrification rates of the three forest types were all negative in July and August and positive in other months with a clear seasonal pattern of a V-type change. The range of net nitrogen mineralization rate of the three forest types was -0.54 to 1.28 mg kg^-1 d^-1 (Pinus sylvestris var. mongolica forest), -0.13 to 0.55 mg kg^-1 d^-1 (Pinus sylvestris var. mongolica-Larix gmelinii mixed forest), and -0.80 to 1.05 mg kg^-1 d^-1 (Larix gmelini forest), respectively. The soil net ammonization dominated in the process of the soil nitrogen mineralization, and accounted for > 60% of the total amount of soil nitrogen mineralization. The vertical net nitrogen mineralization, net ammonization, and net nitrification rates were significantly different among the three forest types, with a significantly higher rate (P < 0.05) in the 0-10 cm soil layer than that in the 10-20 cm soil layer. Soil nitrogen mineralization rates were significantly correlated (P < 0.05) with soil moisture content, organic matter content, soil C/N, total nitrogen content, and C/N of the litter. We concluded that the characteristics of soil nitrogen mineralization were affected by the different quality of soils and litter in different forest types in the Daxing''an Mountains.