Hongling Qin

Effect of long-term fertilization on bacterial composition in rice paddy soil

We investigated the effect of long-term fertilization on bacterial abundance, composition, and diversity in paddy soil. The experiment started in 1990 in Taoyuan Agro-ecosystem Research Station in China (111°33′ E, 28°55′ N). The molecular approaches including real-time quantitative PCR, terminal restriction fragment length polymorphism, and clone library construction were employed using 16S rRNA gene as genetic marker. Application of inorganic fertilizers did not affect bacterial abundance, and rice straw incorporation combined with inorganic fertilizers significantly (P < 0.05) increased bacterial abundance with shifts in bacterial community composition. Among phylogenetic groups, γ-Proteobacteria was responsive to all fertilization regimes while Acidobacteria was relatively stable to fertilization practices. Inorganic fertilizer mainly affected γ-Proteobacteria and δ-Proteobacteria, while rice straw incorporation influenced β-Proteobacteria and Verrucomicrobia. Therefore, long-term fertilization can affect abundance and composition of bacterial communities in paddy soil.

Influence of fertilisation regimes on a nosZ-containing denitrifying community in a rice paddy soil

BACKGROUND Denitrification is a microbial process that has received considerable attention during the past decade since it can result in losses of added nitrogen fertilisers from agricultural soils. Paddy soil has been known to have strong denitrifying activity, but the denitrifying microorganisms responsible for fertilisers in paddy soil are not well known. The objective of this study was to explore the impacts of 17-year application of inorganic and organic fertiliser (rice straw) on the abundance and composition of a nosZ-denitrifier community in paddy soil. Soil samples were collected from CK plots (no fertiliser), N (nitrogen fertiliser), NPK (nitrogen, phosphorus and potassium fertilisers) and NPK + OM (NPK plus organic matter). The nitrous oxide reductase gene (nosZ) community composition was analysed using terminal restriction fragment length polymorphism, and the abundance was determined by quantitative PCR. RESULTS Both the largest abundance of nosZ-denitrifier and the highest potential denitrifying activity (PDA) occurred in the NPK + OM treatment with about four times higher than that in the CK and two times higher than that in the N and NPK treatments (no significant difference). Denitrifying community composition differed significantly among fertilisation treatments except for the comparison between CK and N treatments. Of the measured abiotic factors, total organic carbon was significantly correlated with the observed differences in community composition and abundance (P < 0.01 by Monte Carlo permutation). CONCLUSION This study shows that the addition of different fertilisers affects the size and composition of the nosZ-denitrifier community in paddy soil.

Phosphorus status and risk of phosphate leaching loss from vegetable soils of different planting years in suburbs of Changsha, China.

Abstract The aim of the study was to develop an index to assess the environmental risk of P loss potential in vegetable soils with chronic difference of plantation in the suburbs of Changsha, Hunan Province, China. Chemical methodology was used to study soil phosphorus status and the relationships between available P in soil and potential soil leaching P. The results showed that there was a significant linear relationship between Olsen P and CaCl 2 -P or P concentration in soil solution. Olsen P increased sharply when either CaCl 2 -P or P concentration in soil solution reached a certain level. It was confirmed that 80 mg kg −1 of Olsen P was the critical value of soil P leaching in the vegetable soils. P leaching probability over the critical was assessed by GIS and indicator Kriging and four secondary risks of phosphorus leaching loss were defined. In the area with vegetable cropping for over 30 yr (Chenjiadu) and 10–15 planting years (Huangxingzhen), the indices of phosphorus leaching loss risk were 3 and 2.93, respectively. These two areas belonged to strong secondary of risk of phosphate leaching loss. In the new vegetable planting field less than 2 yr (Ningxiang), the index was 0.06, which had almost no risk of phosphorus leaching. In vegetable soils in the suburban region of Changsha, the phosphorus leaching peotential is high and the phosphorus leaching loss is related to chronic length of vegetable cropping.

Effects of Subsoiling on Soil Moisture Under No-Tillage for Two Years

Abstract In order to improve the water use efficiency under conservation tillage, the effects of subsoiling on soil moisture under no-tillage were studied. An experiment of 40 cm subsoiling in a field kept under no-tillage for 2 years was operated from 2005 to 2006. Based on the data of the soil moisture and crop yield, the physical basis of subsoiling for water conservation and yield increase was analyzed. The results showed that the soil water storage under subsoiling, from the soil surface to a depth of 100 cm was more than that under no-tillage for the growth season. In the 0–100 cm soil depth, the soil moisture in 50–100 cm depth under subsoiling was more compared with no-tillage, which increased when its drought and decreased when its rainy with the increase in soil depth. Compared with no-tillage, subsoiling could reduce the water consumption of oats in the 0–50 cm depth and increase the water consumption in the 50–100 cm depth. Also, subsoiling increased the yield by 18.29% and the water use efficiency by 16.8% in a two-year average. The effects of subsoiling on water conservation and yield increase were affected by precipitation, and a well-proportioned rainfall was better to increase yield and water use efficiency. Meanwhile, subsoiling decreased bulk density, which increased with the available precipitation. Subsoiling under no-tillage is the effective rotation tillage to contain more soil moisture and improve water use efficiency in ecotone of North China.

Differential Responses of Nitrifier and Denitrifier to Dicyandiamide in Short- and Long-Term Intensive Vegetable Cultivation Soils

Abstract Nitrification inhibitors, such as dicyandiamide (DCD), have been shown to decrease leaching from urea- and ammonium-based fertilizers in agricultural soils. The effect of nitrification inhibitors on nitrifier and denitrifier in short- and long-term intensive vegetable cultivation soils was poorly understood. In this study, the pot trial was conducted to investigate the differential responses of nitrifier ( amoA -containing bacteria) and denitrifier ( nirK -containing bacteria) to DCD in short-(soil S) and long-term (soil L) intensive vegetable cultivation soils. Quantitative polymerase chain reaction (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) were employed to detect the abundance and composition of amoA- and nirK -containing communities. The results indicated that application of DCD led to a consistently higher NH 4 + -N concentration during the whole incubation in soil L, while it was quickly decreased in soil S after 21 days. Furthermore, DCD induced more severe decrease of the abundance of amoA -containing bacteria in soil L than in soil S. However, the abundance of the nirK- containing community was not significantly affected by DCD in both soils. Long-term vegetable cultivation resulted in a super-dominant amoA -containing bacteria group and less divergence in soil L compared with soil S, and DCD did not cause obvious shifts of the composition of ammonia-oxidising bacteria (AOB). On the contrary, both amoA- and nirK -containing bacterial compositions were influenced by DCD in soil S. The results suggested that long-term intensive vegetable cultivation with heavy nitrogen fertilization resulted in significant shifts of AOB community, and this community was sensitive to DCD, but denitrifiers were not clearly affected by DCD.

Elevated N2O emission by the rice roots: based on the abundances of narG and bacterial amoA genes

Rice fields are an important source of nitrous oxide (N2O), where rice plants could act as a key factor controlling N2O fluxes during the flooding-drying process; however, the microbial driving mechanisms are unclear. In this study, specially designed equipment was used to grow rice plants and collect emitted N2O from the root-growing zone (zone A), root-free zones (zones B, C, and D) independently, at tillering and booting stages under flooding and drying conditions. Soil samples from the four zones were also taken separately. Nitrifying and denitrifying community abundances were detected using quantitative polymerase chain reaction (qPCR). The N2O emission increased significantly along with drying, but the N2O emission capabilities varied among the four zones under drying, while zone B possessed the highest N2O fluxes that were 2.7~4.5 times higher than those from zones C and D. However, zone A showed N2O consumption potential. Notably, zone B also harbored the highest numbers of narG-containing denitrifiers and amoA-containing nitrifiers under drying at both tillering and booting stages. This study demonstrates that drying caused significant increase in N2O emission from rhizosphere soil, in which the higher abundance of AOB would help to produce more nitrate and significantly higher narG-containing microbes would drive more N2O production and emission.

Abundance of transcripts of functional gene reflects the inverse relationship between CH4 and N2O emissions during mid-season drainage in acidic paddy soil

Agricultural management significantly affects methane (CH4) and nitrous oxide (N2O) emissions from paddy fields. However, little is known about the underlying microbiological mechanism. Field experiment was conducted to investigate the effect of the water regime and straw incorporation on CH4 and N2O emissions and soil properties. Quantitative PCR was applied to measure the abundance of soil methanogens, methane-oxidising bacteria, nitrifiers, and denitrifiers according to DNA and mRNA expression levels of microbial genes, including mcrA, pmoA, amoA, and nirK/nirS/nosZ. Field trials showed that the CH4 and N2O flux rates were negatively correlated with each other, and N2O emissions were far lower than CH4 emissions. Drainage and straw incorporation affected functional gene abundance through altered soil environment. The present (DNA-level) gene abundances of amoA, nosZ, and mcrA were higher with straw incorporation than those without straw incorporation, and they were positively correlated with high concentrations of soil exchangeable NH4+ and dissolved organic carbon. The active (mRNA-level) gene abundance of mcrA was lower in the drainage treatment than in continuous flooding, which was negatively correlated with soil redox potential (Eh). The CH4 flux rate was significantly and positively correlated with active mcrA abundance but negatively correlated with Eh. The N2O flux rate was significantly and positively correlated with present and active nirS abundance and positively correlated with soil Eh. Thus, we demonstrated that active gene abundance, such as of mcrA for CH4 and nirS for N2O, reflects the contradictory relationship between CH4 and N2O emissions regulated by soil Eh in acidic paddy soils.