| As one of the most active components in terrestrial ecosystems, soil fauna plays an important role in soil nitrogen cycling. Soil fauna diversity is influenced by land use patterns, and the difference of soil fauna species and quantities can directly or indirectly affect soil N mineralization. To understand the effects of soil fauna on N mineralization under different land uses, we conducted an experiment at three different land use patterns（i.e. poplar plantation, cropland and crop-poplar integrated system） with three treatments including control, nematodes exclusion, and soil fauna exclusion in a coastal area of northern Jiangsu. By application closed-up incubation method in field, the variations of soil mineral nitrogen contents, soil net N mineralization rates were analyzed. The experiment was carried out by randomized blocks design. The main results are as follows:（1）Nematodes exclusion and soil fauna exclusion significantly decreased the contents of soil NH4+-N,NO3--N and TMN（p<0.05）, and performed in order of control, nematodes exclusion, and soil fauna exclusion, which indicated that the soil fauna and nematodes might significantly contribute to increase the contents of NH4+-N,NO3--N and TMN. Also, in nematodes exclusion and soil fauna exclusion, the contents of soil microbial biomass nitrogen（MBN）, soil microbial biomass carbon（MBC） significantly decreased.The soil pH（p<0.05） significantly increased in nematodes exclusion and soil fauna exclusion treatments in 3 land uses, and the soil MBC/MBN significantly increased in poplar plantation and crop-poplar integrated system（p<0.01）, the soil MBC/MBN decreased in cropland.（2）Nematodes exclusion and soil fauna exclusion significantly decreased the rates of soil net N mineralization（p<0.05）, and performed from high to low in order of crop-poplar integrated system（0.17mg/kg/d）, cropland（0.12mg/kg/d）, and poplar plantation（0.14mg/kg/d）, and soil N mineralization process in 010cm layer was more easily influenced by soil fauna. The net N mineralization rate in different soil fauna treatments performed from high to low as order of control, nematodes exclusion, and soil fauna exclusion, which indicated that the soil fauna and nematodes might increase the net N mineralization rates.（3）The contents of NH4+-N,NO3--N,TMN showed significant seasonal variations in 3 land uses（p<0.05）. The seasonal variation of NH4+-N in 3 land uses all showed Summer>Autumn>Spring>Winter, seasonal variation of NO3--N and TMN showed Summer>Autumn>Spring>Winter in poplar plantation and crop-poplar integrated system while Autumn>Summer>Spring>Winter in cropland. Nematodes and soil fauna exclusions decreased the contents of NH4+-N, NO3--N, TMN in 4 seasons, but did not alter their seasonal variation trends.（4） In all sites, soil net N mineralization rates showed significant seasonal dynamic. Soil net N mineralization rate maximum both in poplar plantation and cropland appeared in autumn（0.25mg/kg/d, 0.29mg/kg/d, respectively）, but in poplar plantation and crop-poplar integrated system, soil net N mineralization rate maximum appeared in summer（0.45mg/kg/d）. Nematode and soil fauna exclusion all could lower the net N mineralization rates in spring, summer and autumn, while did not alter the net N mineralization rates in crop-poplar integrated system, but soil fauna exclusion affected the seasonal dynamics of net N mineralization rates in the poplar plantation and cropland. in poplar plantation and cropland, the net N mineralization rates showed summer>autumn>spring>winter with soil fauna exclusion, while autumn>summer>spring> winter with control. Repeated measurement analysis of variance showed that there were significant interaction effects between sampling times and soil fauna treatments（p<0.01）. |
