岷江上游半干旱河谷区3种林型土壤氮素的比较

比较研究了岷江上游半干旱河谷区辐射松人工林、油松人工林与邻近灌丛0-20cm、20-40cm、40-60cm土层土壤氮素和氮循环过程相关酶的特征,包括土壤有机碳、全氮、碳氮比、硝态氮、铵态氮、无机氮、微生物量氮含量及蛋白酶、脲酶、硝酸盐还原酶活性。结果表明,辐射松林和油松林各土层土壤有机碳含量、碳氮比和硝酸盐还原酶活性无显著差异,油松林土壤无机氮含量和脲酶活性显著高于辐射松林土壤,而辐射松林土壤微生物量氮含量是3种林型土壤中最高的,灌丛0-20cm土层土壤有机碳、全氮含量最高。此外,有机碳、全氮含量、脲酶活性随土层深度增加而降低;而硝酸盐还原酶活性却随土层深度的增加而增强;同时,各土层间蛋白酶活性差异较小。因此,植被类型对土壤氮素转化有一定影响,而从目前的土壤氮素状况来看,油松林土壤中植物可直接吸收利用的氮素高于辐射松林和灌丛;辐射松林土壤微生物固持的氮素含量最高。区域3种植被类型土壤氮素状况还受到半干旱气候因素的强烈影响。

Comparison of soil nitrogen status among three stand types in the semi-arid areas of upper reaches of the Minjiang River

Comparison of soil nitrogen status and corresponding enzyme activity in 0-20cm, 20-40cm, 40-60cm soil depths from the Pinus radiata plantation (PR), Pinus tabulaeformis plantation (PT) and shrub-land (SL) were investigated in semi-arid areas of the upper reaches of the Minjiang River. The total organic carbon (TOC), C/N, total nitrogen(TN), NO-3-N, NH+4-N, soil inorganic nitrogen(SIN), soil microbial biomass nitrogen(SMBN), soil protease(SP), soil urease(SU), soil denitrification enzyme(SDE) were measured. No significant differences were found in TOC, C/N and SDE in each soil layer between the PR and PT. Soil SIN and SU were significantly higher in the PT than those in the PR, while SMBN in the PR of all soil profiles were the highest among the three stand types. TOC and TN in the depth of 0-20cm from the SL were the highest. On the other hand, TOC, C/N ratio, TN and SU decreased, while SDE increased, with the increasing of soil depths. Simultaneously, SP had little different in soil layers. These results confirmed that stand types influenced nitrogen cycle. Therefore, in terms of the supply of soil nitrogen, the content of soil inorganic nitrogen in the PT was higher than the PR and SL, while SMBN of PR was the highest. In addition, the three sand types in this region had been strongly impacted by the semi-arid climate.