Abstract: The temporal and spatial dynamics of soil respiration were studied in maize fields with normal and low planting densities in Northeast China and the effects of soil temperature and air relative humidity on the soil respiration rate were analyzed. Results indicated that the diurnal variation of soil respiration showed a single-peak curve. However, the maximum peak appeared at 12:00-15:00 for maize normal planting density and 11:00-16:00 for maize low planting density. Soil respiration had lower rates in positions which were far from maize plants at the ecosystem level. Overall, soil respiration showed higher rates at maize normal planting density than at maize low planting density. The correlation coefficients between soil respiration and temperature or air relative humidity were different among different measuring positions and these correlation coefficients reached a significant level (P<0.01). Soil respiration was positively correlated with the soil temperature and negetively with air relative humidity.

Key words: free-living nitrogen-fixing bacteria, soil, associate nitrogen-fixing bacteria, phyllosphere.