Effect of Long-Term Fertilization on Soil Enzyme Activities Under Different Hydrothermal Conditions in Northeast China

Human activities have altered weather patterns by causing an increase in greenhouse gas. The effects of climate change have been studied, including effects on some ecosystems throughout the world. There are many studies on changes in the soil due to climate change, but much of them did not extend their research to soil enzyme that integrates information on soil microbial status and soil physical-chemical conditions. Meanwhile, there are lots of experimental fields established to study effects of long-term fertilization on soil enzyme activities, but many did not compare the difference of soil enzyme activities and did not analyze the effect of climatic factors on soil enzyme activities with long-term fertilization under different hydrothermal conditions. In this study, we compared soil enzyme activities of three long-fertilization stations which had different hydrothermal conditions in Northeast China, and analyzed the relationship of hydrothermal condition, soil chemical properties with soil enzyme activities. Hydrothermal conditions （annual temperature and total rainfall） decreased in order of Gongzhuling （Jilin Province, China ） Harbin （Heilongjiang Province, China） Heihe （Heilongjiang Province, China） over the course of the long-term fertilization experiment. Sunshine hours showed the longest in Gongzhuling, the second in Heihe, and the last in Harbin. However, the order of soil enzymes was not in agreement with hydrothermal conditions. Overall, the order of soil enzymes for the same treatment among three stations was consistent in 2008 with in 2009. Correlation analysis demonstrated that different soil enzymes achieved the different affected levels by climatic factors under different fertilization treatments. Urease activity showed a significant relationship with sunshine hours in no fertilizer （CK） treatment （R=-0.91, P0.01） and relative humidity in mineral fertilizers plus manure （MNPK） treatment （R=0.82, P0.05）. Phosphatase activity exhibited a negative correlation with annual mean temperature, annual mean maximum temperature and annual mean minimum temperature, and their correlation coefficients were separately -0.83, -0.79, and -0.83 at P0.05 in CK treatment. Invertase activity was highly and positively correlated with sunshine hours in CK treatment （R=0.94, P0.01）. Catalase activity showed significant negative correlations with minimum relative humidity in CK treatment （R=-0.81, P0.05）, and positive correlations with sunshine hours in M treatment （R=0.83, P0.05）. There were no climatic factors which strongly affected on dehydrogenase in all treatments. Soil enzyme activities were closely related to the soil chemical properties. Soil urease activity was positively correlated with available P （P0.05）. With exception of correlation between invertase and total P at P0.05, phosphase, invertase, catalase, and dehydrogenase showed significant positive correlations with soil chemical properties （P0.01）. It was a comprehensive process that biologic and abiotic factors were effect on soil enzyme activities under different fertilization treatments. To sum up, the variation of hydrothermal conditions in different climate zones and soil chemical properties affect integrally metabolic activity and metabolic finger print of microbial communities in black soil.