Comparison of soil nitrogen status among three stand types in the semi-arid areas of upper reaches of the Minjiang River
岷江上游半干旱河谷区3种林型土壤氮素的比较

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.