科尔沁沙地草地营造樟子松人工林对土壤化学和生物学性状的影响

以科尔沁沙地东南缘沙质草地和不同年龄樟子松（Pinus sylvestris var. mongolica）人工林（15、24和30年生）为对象，研究草地造林对土壤pH，土壤C、N、P含量，无机N（铵态氮、硝态氮）含量，C、N矿化速率，微生物生物量C含量以及土壤酶（脲酶、转化酶和过氧化氢酶）活性的影响.结果表明：草地造林初期，林地土壤C、N、P含量逐渐降低，随着林龄增加而逐渐恢复；与草地相比，24年生樟子松人工林土壤C、N、P含量最低，分别下降29%、34%和33%，而30年生樟子松人工林土壤C和N含量与草地差异不显著.草地造林能够影响土壤无机N存在形式，使土壤铵态氮含量逐渐增加，硝态氮含量下降.草地造林对土壤潜在N矿化速率和硝化速率影响不显著，但能够改变土壤C矿化速率，不同林龄樟子松人工林土壤C矿化速率依次为：24年生>30年生>草地>15年生.草地造林初期，土壤微生物生物量C含量和土壤转化酶活性明显降低，随着林龄的增加又逐渐增加；草地造林对土壤脲酶活性影响不显著，而使土壤过氧化氢酶活性逐渐增加.科尔沁沙地草地造林能够显著改变土壤化学和生物学性状，且随着林龄的变化而有所差异.

Effects of grassland afforestation with Mongolian pine on soil chemical and biological properties in Keerqin Sandy Land

Taking one grassland and 15-, 24-, and 30 years old Mongolian pine (Pinus sylvestris var. mongolica) plantations in the southeast of Keerqin Sandy Land as test objects, this paper studied the effects of grassland afforestation on the soil chemical and biological properties, including pH value, C, N, and P concentration, inorganic N concentration, C and N mineralization rates, microbial biomass C, and enzyme activities. At the early stage of afforestation, the concentration of soil C, N, and P decreased; but with increasing stand age, they recovered gradually. Compared with those in grassland, the soil C, N, and P concentration in 24 years old plantation decreased by 29%, 34%, and 33%, respectively, but the soil C and N concentration in 30 years old plantation had less difference. Afforestation led to an increase of soil NH₄⁺-N concentration and a decrease of soil NO₃-N concentration, but had less effects on the soil N mineralization and nitrification rates. The soil C mineralization rate was decreased in the order of 24 years old plantation >30 years old plantation > grassland >15 years old plantation. Soil microbial biomass C and invertase activity decreased at the early stage of afforestation, but recovered with increasing stand age. After afforestation, soil urease activity had less change, but soil catalase activity increased gradually. Our results indicated that in Keerqin Sandy Land, grassland afforestation with Mongolian pine had significant effects on the soil chemical and biological properties, and the effects differed with stand age.