模拟氮沉降对华北落叶松人工林土壤微生物碳和微生物氮的动态影响

为揭示过量的大气氮沉降对华北落叶松人工林土壤微生物碳、氮和土壤呼吸的影响,通过对照(N0:0 g/(m^2·a))、轻度施氮(N1:8 g/(m^2·a))、重度施氮(N2:15 g/(m^2·a))3个外源施氮水平下5年的野外定点试验和观测,模拟过量氮沉降条件下华北落叶松人工林土壤微生物碳、氮和土壤呼吸的变化,旨在阐明林下土壤微生物和呼吸对过量氮沉降的响应及其对土壤碳氮循环的影响。结果表明:在5-10月生长季中,土壤微生物碳和氮的平均含量分别为1 098.93,97.31 mg/kg,二者都随土层深度的增加呈下降趋势;轻度施氮促进土壤微生物碳和氮的增加,重度施氮抑制土壤微生物碳和氮的增加;土壤微生物碳和微生物氮从生长初期5月起,5-7月呈增加趋势,7月出现峰值,8月降低,9-10月小幅增加,呈现"N"形曲线。土壤微生物碳氮比为4.94~18.54,且随施氮量增加而减小。各氮处理下,华北落叶松人工林土壤呼吸速率5,6月较低,7-8月持续增加,并在8月达到最高,9-10月逐渐降低。相关分析表明,土壤呼吸与土壤全氮、含水量、微生物碳和微生物氮含量呈极显著正相关关系,与土壤有机质呈显著正相关关系。在全球变化背景下,研究结果可为进一步明确过量大气氮沉降对森林生态系统碳氮循环的影响途径和机制研究提供重要参考。

Effects of Simulated Nitrogen Deposition on Soil Microbial Carbon and Nitrogen Dynamics of Larix principis-rupprechtii Plantation

To examine the effects of excessive atmospheric nitrogen deposition on soil microbial carbon and nitrogen in Larix principis-rupprechtii plantation, we conducted fixed experiment plots and 5 years observation experiments to simulate the changes of microbial carbon, nitrogen, and soil respiration in soil of Larix principis-rupprechtii plantation with three nitrogen deposition treatments:CK (N₀:0 g/(m²·a)), light N level (N₁:8 g/(m²·a)), and severe N level (N₂:15 g/(m²·a)) to clarify the response of soil microorganism under excessive nitrogen deposition forest and the influence on soil carbon and nitrogen cycle. The results showed that the average content of soil microbial carbon and nitrogen was 1 098.93 and 97.31 mg/kg. In the May-October growing seasons respectively they showed a downward trend with the increase of soil depth. Light N addition promoted the increase of soil microbial carbon and nitrogen. Severe N addition inhibited the increase of soil microbial carbon and nitrogen. The content of soil microbial carbon and nitrogen increased from May to July and peaked in July, then decreased in August, slightly increased from September to October, and showed an "N" curve. The C/N of soil microbial was between 4.94 and 18.54, and decreased with the increase of N addition. The soil respiration rate of Larix principis-rupprechtii plantation was lower in May and June, continuously increased from July to August and reached the peak in August, then gradually decreased from September to October under different N treatments. The correlation analysis showed that soil respiration was significantly positively correlated with the content of soil total nitrogen, water content, microbial carbon and microbial nitrogen, and was positively correlated with soil organic matter. With the global change, the research results can provide important reference for further clarifying the impact of excessive atmospheric nitrogen deposition on carbon and nitrogen cycle in forest ecosystems.