Ronggui Hu

Impact of Long-Term Fertilization on the Composition of Denitrifier Communities Based on Nitrite Reductase Analyses in a Paddy Soil

The effect of long-term fertilization on soil-denitrifying communities was determined by measuring the abundance and diversity of the nitrite reductase genes nirK and nirS. Soil samples were collected from plots of a long-term fertilization experiment started in 1990, located in Taoyuan (110°72″ E, 28°52″ N), China. The treatments were no fertilizer (NF), urea (UR), balanced mineral fertilizers (BM), and BM combined with rice straw (BMR). The abundance, diversity, and composition of the soil-denitrifying bacteria were determined by using real-time quantitative PCR, terminal restriction fragment length polymorphism (T-RFLP), and cloning and sequencing of nirK and nirS genes. There was a pronounced difference in the community composition and diversity of nirK-containing denitrifiers responding to the long-term fertilization regimes; however, less variation was observed in communities of nirS-containing denitrifiers, indicating that denitrifiers possessing nirK were more sensitive to the fertilization practices than those with nirS. In contrast, fertilization regimes had similar effects on the copy numbers of nirK and nirS genes. The BMR treatment had the highest copy numbers of nirK and nirS, followed by the two mineral fertilization regimes (UR and BM), and the lowest was in the NF treatment. Of the measured soil parameters, the differences in the community composition of nirK and the abundance of nir denitrifiers were highly correlated with the soil carbon content. Therefore, long-term fertilization resulted in a strong impact on the community structure of nirK populations only, and total organic carbon was the dominant factor in relation to the variations of nir community sizes.

Soil Nitrous oxide and Carbon dioxide emissions following incorporation of above- and below-ground biomass of green bean

Information on soilxa0N2O and CO2 emissions from above- and below-ground biomass of legume crops is limited in scientific literature. Therefore, a laboratory study was conducted to evaluate the differences in soilxa0N2O and CO2 emissions from the above- and below-ground biomass of green bean. Leave and shoot (LS) and root nodule (Nod) of green bean were incorporated into soil and incubated for 53xa0days. N2O and CO2 emissions were measured throughout the 53-day study period. Incorporation of organic residues significantly (pxa0≤xa00.05) increased N2O and CO2 emissions. However, the Nod treatment yielded higher emissions of N2O as compared to LS treatment. Cumulative N2O emissions were 13-fold and fourfold in Nod and LS treatment as compared to the control, respectively. CO2 emissions were higher in LS treatment than that of Nod treatment. Cumulative CO2 emissions were 2.15-fold and 1.15-fold in LS and Nod treatments as compared to the control, respectively. The results of current study suggest that below-ground biomass of legume crops produces higher N2O emissions while CO2 emissions were higher in above-ground biomass.