Soil Biochemical Characteristics In Different Land Use Systems And Their Relationships With Soil Respiration And N₂O Emission

As an important part of carbon and nitrogen cycle, soil respiration (CO2) and nitrous oxide (N2O) emission have attracted considerable attention during the last decades because of their contribution to global warming. The biological processes particularly microbial processes play a dominant role in soil respiration and N2O emission processes. Different soil with different microorganisms and substrate will result in different soil respiration and N2O emissions.The thirteen types of soil from different land use system in Jiangsu Province were collected and their biochemical characteristics were analyzed in this study. In ortder to investigate the effect of the aforementioned soil biochemical characteristics on soil respiration and N2O emission, an indoor incubation experiment with and without NH4NO3 input under the condition of a constant soil temperature (25 ℃) and soil moisture (0.30g·g-1) was carried out.The results showed that the biochemical characteristics of soils in the different land use systems and CO2 and N2O emissions from different soils greatly varied with each other. In generally, the highest abundance of bacteria was found in the orchard soil, the highest abundance of actinomycosis occurred in the meadows and the highest abundance of fungi appeared in the woodlands. The abundance of bacteria or actinomycosis in the bamboo soil was the lowest among all of the soils, and the orchard soil had the lowest content of fungi. The contents of soil microbial biomass carbon and nitrogen generally followed the order of the orchard soil> woodland> cropland. Correlation analysis indicated that there was the positive correlation between soil oganic carbon and soil total nitrogen (P<0.01), or between microbial biomass carbon and nitrogen (P<0.01), or between the abundance of soil bacteria and the contents of microbial biomass carbon and nitrogen, while the abundance of soil actinomycosis and soil fungi were positive correlation against soil organic carbon and total nitrogen contents (P<0.05). Whether the exogenous nitrogen existed or not, stepwise regression analysise suggested that soil respiration could be quantitatively determined by a linear combination of the soil bacteria and soil pH. At the absence of the exogenous nitrogen, N2O emission was mainly depended on the values of soil bacteria and ammonium nitrogen. When the exogenous nitrogen was added, N2O emissions was only depended on the values of soil bacteria. N2O emissions were positively correlated with CO2 emissions (P < 0.01). Moreover, the average of CO2 emissions per gram nitrogen was positive correlation against soil organic carbon, total nitrogen contents and the abundance of soil fungi (P< 0.05), while having negative correlation with the ratio of soil microbial biomass carbon to soil microbial biomass nitrogen (P< 0.05). N2O conversion rate per gram nitrogen was positive correlation against the abundance of soil bacteria (P< 0.01). Stepwise regression analysise suggested that the average of CO2 emissions per gram nitrogen could be quantitatively determined by a linear combination of the soil microbial biomass carbon to soil microbial biomass nitrogen; N2O conversion rate per gram nitrogen was mainly depended on the values of soil bacteria.