沙地不同密度樟子松人工林土壤矿化氮质量分数与矿化特征

Soil Mineralized Nitrogen Content and Mineralization Characteristics of Pinus sylvestris var.mongolica Plantations with Different Densities in Sandy Land

为阐明密度对樟子松人工林土壤无机氮空间分布的影响,确定有利于有效氮素循环的最佳密度,选择密度为350、750、850、1000、1200和2970株·hm^(-2)的樟子松人工林为研究对象,采用室内恒温培养法,测定分析了土壤矿化氮质量分数与净氮矿化速率。结果表明:随着樟子松造林密度增大,土壤NH_(4)^(+)-N、NO_(3)^(-)-N和矿质氮质量分数先增加后减少,在1000株·hm^(-2)时达到峰值;净氨化速率、净硝化速率和净氮矿化速率先增后减。土壤NH_(4)^(+)-N、NO_(3)^(-)-N、矿质氮质量分数主要集中在0~20 cm,呈现出表聚性。随着土层加深,净氨化速率、净硝化速率和净氮矿化速率均逐渐减小,40~100 cm土层显著小于0~40 cm。相关性分析表明,土壤氮矿化指标与人工林株高、枯落物厚度及土壤有机碳(SOC)、全氮(TN)、碱解氮(AN)质量分数相关关系显著。通过RDA分析发现,土壤全氮、有机碳能够作为土壤氮矿化过程中的主要养分指示因子。由此表明,不同密度樟子松人工林土壤具有不同的氮矿化特征,合理的造林密度对沙地土壤有效氮质量分数有积极影响,造林密度为1000株·hm^(-2)时,土壤氮有效性最优。

The experiment was conducted to understand the effect of density on the spatial distribution of soil inorganic nitrogen in Pinus sylvestris var.mongolica plantation,and determine the optimal density for the effective nitrogen cycle.The method of indoor thermostatic culture was used to the determine and analyze the changes of soil mineralized nitrogen contents and net nitrogen mineralization rates of the P.sylvestris var.mongolica plantations in the Horqin sandy land under different afforestation densities of 350,750,850,1000,1200 and 2970 ind.·hm^(-2).With the increase of planting density of P.sylvestris var.mongolica,the contents of ammonium nitrogen(NH_(4)^(+)-N),nitrate nitrogen(NO_(3)^(-)-N)and mineral N content increased first and then decreased,reaching the peak at 1000 ind.·hm^(-2),and the net ammonification rate,net nitrification rate and soil net N mineralization rate also showed the same trend.The contents of soil NH_(4)^(+)-N,NO_(3)^(-)-N and mineral nitrogen in plantations with different densities decreased with soil depth and mainly concentrated in 0-20 cm,showing the surface accumulation.The soil net N mineralization rates were all decreased with the increase of soil depths,and the 0-40 cm soil layer was much greater than those of 40-100 cm soil layer.Mineralization indicators were significantly correlated with plant height and litter thickness,soil organic carbon(SOC),total nitrogen(TN)and available nitrogen(AN).The redundancy analysis showed that TN and SOC could be used as the main nutrient indicators in the process of soil nitrogen mineralization.The nitrogen mineralization characteristics of different density Mongolian pine plantations were different.When the afforestation density was 1000 ind.·hm^(-2),the soil of P.sylvestris var.mongolica had the best nitrogen mineralization indexes and the soil nitrogen was the most effective.