Mapping Chinese annual gross primary productivity with eddy covariance measurements and machine learning.

Annual gross primary productivity (AGPP) is the basis for grain production and terrestrial carbon sequestration. Mapping regional AGPP from site measurements provides methodological support for analysing AGPP spatiotemporal variations thereby ensures regional food security and mitigates climate change. Based on 641 site-year eddy covariance measuring AGPP from China, we built an AGPP mapping scheme based on its formation and selected the optimal mapping way, which was conducted through analysing the predicting performances of divergent mapping tools, variable combinations, and mapping approaches in predicting observed AGPP variations. The reasonability of the selected optimal scheme was confirmed by assessing the consistency between its generating AGPP and previous products in spatiotemporal variations and total amount. Random forest regression tree explained 85 % of observed AGPP variations, outperforming other machine learning algorithms and classical statistical methods. Variable combinations containing climate, soil, and biological factors showed superior performance to other variable combinations. Mapping AGPP through predicting AGPP per leaf area (PAGPP) explained 86 % of AGPP variations, which was superior to other approaches. The optimal scheme was thus using a random forest regression tree, combining climate, soil, and biological variables, and predicting PAGPP. The optimal scheme generating AGPP of Chinese terrestrial ecosystems decreased from southeast to northwest, which was highly consistent with previous products. The interannual trend and interannual variation of our generating AGPP showed a decreasing trend from east to west and from southeast to northwest, respectively, which was consistent with data-oriented products. The mean total amount of generated AGPP was 7.03 ± 0.45 PgC yr-1 falling into the range of previous works. Considering the consistency between the generated AGPP and previous products, our optimal mapping way was suitable for mapping AGPP from site measurements. Our results provided a methodological support for mapping regional AGPP and other fluxes.

Generalist Taxa Shape Fungal Community Structure in Cropping Ecosystems.

Fungi regulate nutrient cycling, decomposition, symbiosis, and pathogenicity in cropland soils. However, the relative importance of generalist and specialist taxa in structuring soil fungal community remains largely unresolved. We hypothesized that generalist fungi, which are adaptable to various environmental conditions, could potentially dominate the community and become the basis for fungal coexisting networks in cropping systems. In this study, we identified the generalist and habitat specialist fungi in cropland soils across a 2,200 kms environmental gradient, including three bioclimatic regions (subtropical, warm temperate, and temperate). A few fungal taxa in our database were classified as generalist taxa (~1%). These generalists accounted for >35% of the relative abundance of all fungal populations, and most of them are Ascomycota and potentially pathotrophic. Compared to the specialist taxa (5-17% of all phylotypes in three regions), generalists had a higher degree of connectivity and were often identified as hub within the network. Structural equation modeling provided further evidence that after accounting for spatial and climatic/edaphic factors, generalists had larger contributions to the fungal coexistence pattern than habitat specialists. Taken together, our study provided evidence that generalist taxa are crucial components for fungal community structure. The knowledge of generalists can provide important implication for understanding the ecological preference of fungal groups in cropland systems.

[Consumption Capacity of N2O in Paddy Soil and the Response Mechanism of nosZ-I-containing Communities].

The long-term flooding anaerobic environment in paddy soils is conducive to denitrification, which is one of the most important reasons for N2O emissions. N2O can be transformed to nitrogen gas (N2) by bacteria and archaea containing nitrous oxide reductase (N2OR) encoded by the nosZ gene, which is the only known biological pathway of N2O consumption in soil. nosZ-I is known to be typical in denitrifying bacteria, which is one of the clades of the nosZ gene and is mainly possessed a Tat signal peptide motif. Although many researchers have studied N2O emission characteristics of paddy soil, the capacity of N2O consumption and the response mechanism of related functional microorganisms in paddy fields is not yet clear. To verify the effect of exogenous N2O on N2O consumption and nosZ-I gene, a pot trial experiment was performed under anaerobic conditions. We collected intact soil cores from flooding paddy fields at a 0-5 cm depth, and exogenous N2O gas was input through the bottom of flooding paddy soil cores. Meanwhile, a control treatment (CK) with no additional N2O gas was also performed. The dynamic characteristics of the added exogenous N2O concentration through the intact soil cores, the content of inorganic nitrogen, and DOC were systematically monitored. In addition, the change in the nosZ-I population diversity and community composition were investigated by high-throughput sequencing approaches, with the purpose of revealing the N2O uptake ability of flooded paddy soil and the response mechanism of the nosZ-I population. The results showed that 97.39% of exogenous N2O diffused into the soil cores, and only 0.72%-7.75% of exogenous N2O escaped from the soil surface. The N2O released in the headspace of soil cores could continue being absorbed and consumed by the flooding soil column. In addition, 67.10% of the N2O escaped to the headspace was consumed in exogenous N2O treatment after 192 h of incubation, which was higher than that in CK treatment, and the N2O consumption rate increased by 144.2% than that in CK treatment. Meanwhile, the consumption of NH4+-N, NO3--N, and DOC consumed during exogenous N2O addition treatment was 19.65%, 16.29%, and 8.41% higher than that in CK treatment, respectively. However, the diversity of the nosZ-I gene community had no significant difference; the community composition of nosZ-I-containing bacteria changed significantly after 192 h when exogenous N2O was input. The abundances of OTU5004, OTU5065, OTU960, and OTU1282 (Proteobacteria) significantly increased, which were the dominant bacterial strain of nosZ-I gene on the OTU level. Compared with the initial sample and CK, the abundance of the OTU5004 strain increased by 7.3% and 4.63%, and the abundance of the OTU5265 strain (Azoarcus sp.) increased by 0.33% and 0.15%, respectively. The result indicated that the flooding paddy soil column at the soil layer of 0-5 cm has a strong N2O absorption and consumption ability. In summary, compared with CK, the addition of exogenous N2O significantly accelerated the N2O consumption rate, improved the consumption potential of flooding paddy soil column, promoted carbon and nitrogen conversion, and changed nosZ-I community composition. These results would provide a new reference for reducing atmospheric N2O emissions.

Large-scale patterns of soil antibiotic resistome in Chinese croplands.

Soil is a vital reservoir of antibiotic resistance genes (ARGs), but we still know little about their distribution in cropland soils and the main driving forces. Here we performed an investigation for ARGs patterns in 105 cropland soils (planted with maize, peanut or soybean) along a 2, 200 km transect in China using high-throughput quantitative PCR approaches. Totally, 204 ARGs were detected, with a higher diversity found in central China than that in northeast and south China. The most abundant (top 50%) and highly shared (present in >50% samples) ARGs regarded as core resistome were dominated by multidrug resistance genes such as oprJ, acrA-05 and acrA-04. Regressive analyses revealed that the relative abundance of total ARGs and core resistome both had significant relationships with mobile genetic elements (MGEs). Anthropogenic factors including the consumption of plastic films and soil properties including heavy metals showed good correlations with the diversity of ARGs. Structural equation modelling analysis further explained that anthropogenic factors were the main forces shaping the ARGs patterns. These findings highlight the importance of human activities in shaping soil antibiotic resistome in the croplands, providing potential management strategies to mitigate the dissemination of ARGs to humans via food chain.

[Impact of Dicyandiamide (DCD) and 3,4-Dimethylpyrazole Phosphate (DMPP) on Ammonia-oxidizing Bacteria and Archaea in a Vegetable Planting Soil].

Nitrification inhibitors (NIs) dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) showed significant effects in the inhibition of nitrification and the improvement of the utilization efficiency of nitrogen fertilizer in agricultural soils. However, the effects of different NIs on ammonia-oxidizing bacteria (AOB) and archaea (AOA) is still unclear. To verify the inhibitory effect of DCD and DMPP on AOB and AOA, a pot experiment was performed, including Urea, Urea+DCD, and Urea+DMPP treatments. The dynamics of NH4+-N and NO3--N and nitrification potential among different treatments were measured. In addition, real-time PCR and high-throughput sequencing approaches were applied to investigate the changes in the AOB and AOA population abundance and composition. The results revealed that the concentrations of NH4+-N in Urea+DCD and Urea+DMPP treatments were 213% and 675% higher than that in the CK treatment, respectively. However, the concentrations of NO3--N and the nitrification potentials were 13.3% and 37.2%, and 20.4% and 82.4% lower than that in CK treatment, respectively; Furthermore, the copy numbers of the bacterial and archaeal amoA gene were 51.2% and 56.5%, and 6.0% and 27.0% lower than that in the CK treatment, respectively. However, the diversity indexes of AOB and AOA communities, including evenness and richness, exhibited no significant differences after addition of DCD and DMPP. The nork-environmental-samples, unclassified-Nitrosomonadaceae, unclassified-Bacteria, and Nitrosospira, were the predominant genera of the AOB community. The no rank-Crenarchaeota, no rank-environmental-samples and Nitrososphaera were the predominant groups in the AOA community. Summarily, application of DCD and DMPP significantly delayed the transformation of NH4+-N, decreased the formation of NO3--N, inhibited the abundance and changed the composition of AOB and AOA communities. DMPP had a stronger inhibitory effect on nitrification, and on AOB and AOA than DCD. Therefore, compared with DCD, DMPP had a better application prospect regarding the improvement of the nitrogen utilization efficiency in vegetable soil.

[Differential Responses of Rhizospheric nirK- and nirS-type Denitrifier Communities to Different Phosphorus Levels in Paddy Soil].

Phosphorus is an essential life element, which can affect the activities and functions of denitrifiers. Both nirK and nirS genes can code nitrite reductase; however, it remains unclear whether nirK- and nirS-containing denitrifers respond differentially to changes in the availability of phosphorus in paddy soil. In this study, P-deficient paddy soil was used to grow rice plants. Three phosphorus levels established by applying P fertilizer at a rate of 0 mg·kg-1 (CK), 15 mg·kg-1 (P1), and 30 mg·kg-1(P2), respectively. The abundance and community structure of nirK- and nirS- containing denitrifers were determined using quantitative PCR and high-throughput sequencing techniques. Results indicated that nirK- and nirS-containing communities responded differentially to changes in the P levels. The nirS-containing communities are more sensitive to the changes in P in both rhizosphere and bulk soil samples. In addition, the abundance of nirS genes was 2-3 times higher in the P2 treatment than in the CK treatment. Furthermore, the nirS community structure is also clearly differed from the CK treatment. However, P addition only induced partial modification of the community structure and abundance of nirK-containing denitrifiers. Moreover, compared to the bulk soil with each phosphorus level, the nirS community structure in the rhizosphere soil changed significantly; however, only the P2 treatment induced significant increases in the abundance of the nirS gene. In contrast, no significant differences in the abundance and composition of nirK-containing denitrifers were detected between rhizosphere and bulk soils under different phosphorus levels. Collectively, application of phosphate fertilizer in P-deficient paddy soil could significantly increase the abundance of nirK- and nirS-containing denitrifiers, changing their community structures, with nirS-type showing a greater sensitivity than nirK-type denitrifiers. In comparison, the denitrifying communities in the rhizosphere were more sensitive to variable P levels than that in the bulk soil. Compared to bulk soils, rice growth shifted the community structure of nirS- and nirK-containing denitrifiers in rhizosphere soils at each level of P, but failed to induce significant changes in their abundance (except for P2) that could cause a significant increase in nirS abundance. These results could provide a theoretical basis for exploring the effects of fertilization on soil denitrification.

Multiple factors drive the abundance and diversity of the diazotrophic community in typical farmland soils of China.

Biological nitrogen fixation plays an important role in nitrogen cycling by transferring atmospheric N2 to plant-available N in the soil. However, the diazotrophic activity and distribution in different types of soils remain to be further explored. In this study, 152 upland soils were sampled to examine the diazotrophic abundance, nitrogenase activity, diversity and community composition by quantitative polymerase chain reaction, acetylene reduction assay and the MiSeq sequencing of nifH genes, respectively. The results showed that diazotrophic abundance and nitrogenase activity varied among the three soil types. The diazotrophic community was mainly dominated by Bradyrhizobium, Azospirillum, Myxobacter, Desulfovibrio and Methylobacterium. The symbiotic diazotroph Bradyrhizobium was widely distributed among soils, while the distribution of free-living diazotrophs showed large variation and was greatly affected by multiple factors. Crop type and soil properties directly affected the diazotrophic ɑ-diversity, while soil properties, climatic factors and spatial distance together influenced the diazotrophic community. Network structures were completely different among all three types of soils, with most complex interactions observed in the Red soil. These findings suggest that diazotrophs have various activities and distributions in the three soil types, which played different roles in nitrogen input in agricultural soil in China, being driven by multiple environmental factors.

[Variation of community structure and function of rhizospheric denitrifiers at tillering and booting stages of rice]. / æ°´ç¨»åˆ†è˜–æœŸå’Œå­•ç©—æœŸæ ¹é™ åç¡åŒ–èŒç¾¤è½ç»“æž„åŠåŠŸèƒ½å˜åŒ–.

We investigated the variation of denitrifying communities in rice rhizosphere at tillering and booting stages in comparison with bulk soils with a pot experiment. The techniques of quantitative polymerase chain reaction (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) were used to measure the abundance and community composition of denitrifiers (narG and nosZ), respectively. The results showed that the potential denitrification activity in the rhizosphere at tillering stage was significantly lower than bulk soils. No significant difference was detected between the rhizosphere and bulk soils at booting stage. The abundance of both narG- and nosZ-containing denitrifying bacteria was significantly higher in rhizosphere than in bulk soils at both tillering and booting stages. In comparison with narG-containing community, community composition and diversity of nosZ-containing bacteria were more sensitive to rice growth. In conclusion, the exudates of rice could induce significantly more denitrifying bacteria in rhizosphere, whose denitrifying activities were related to growth stage of rice. At the period with strong growth, the secretion of roots showed clear restriction to the functions of rhizospheric denitrifiers compared to booting stage.

Protist communities are more sensitive to nitrogen fertilization than other microorganisms in diverse agricultural soils.

BACKGROUND: Agricultural food production is at the base of food and fodder, with fertilization having fundamentally and continuously increased crop yield over the last decades. The performance of crops is intimately tied to their microbiome as they together form holobionts. The importance of the microbiome for plant performance is, however, notoriously ignored in agricultural systems as fertilization disconnects the dependency of plants for often plant-beneficial microbial processes. Moreover, we lack a holistic understanding of how fertilization regimes affect the soil microbiome. Here, we examined the effect of a 2-year fertilization regime (no nitrogen fertilization control, nitrogen fertilization, and nitrogen fertilization plus straw amendment) on entire soil microbiomes (bacteria, fungi, and protist) in three common agricultural soil types cropped with maize in two seasons. RESULTS: We found that the application of nitrogen fertilizers more strongly affected protist than bacterial and fungal communities. Nitrogen fertilization indirectly reduced protist diversity through changing abiotic properties and bacterial and fungal communities which differed between soil types and sampling seasons. Nitrogen fertilizer plus straw amendment had greater effects on soil physicochemical properties and microbiome diversity than nitrogen addition alone. Moreover, nitrogen fertilization, even more together with straw, increased soil microbiome network complexity, suggesting that the application of nitrogen fertilizers tightened soil microbiomes interactions. CONCLUSIONS: Together, our results suggest that protists are the most susceptible microbiome component to the application of nitrogen fertilizers. As protist communities also exhibit the strongest seasonal dynamics, they serve as the most sensitive bioindicators of soil changes. Changes in protist communities might have long-term effects if some of the key protist hubs that govern microbiome complexities as top microbiome predators are altered. This study serves as the stepping stone to promote protists as promising agents in targeted microbiome engineering to help in reducing the dependency on exogenous unsustainably high fertilization and pesticide applications.

Increased microbial functional diversity under long-term organic and integrated fertilization in a paddy soil.

Microbes play key roles in diverse biogeochemical processes including nutrient cycling. However, responses of soil microbial community and functional genes to long-term integrated fertilization (chemical combined with organic fertilization) remain unclear. Here, we used pyrosequencing and a microarray-based GeoChip to explore the shifts of microbial community and functional genes in a paddy soil which received over 21-year fertilization with various regimes, including control (no fertilizer), rice straw (R), rice straw plus chemical fertilizer nitrogen (NR), N and phosphorus (NPR), NP and potassium (NPKR), and reduced rice straw plus reduced NPK (L-NPKR). Significant shifts of the overall soil bacterial composition only occurred in the NPKR and L-NPKR treatments, with enrichment of certain groups including Bradyrhizobiaceae and Rhodospirillaceae families that benefit higher productivity. All fertilization treatments significantly altered the soil microbial functional structure with increased diversity and abundances of genes for carbon and nitrogen cycling, in which NPKR and L-NPKR exhibited the strongest effect, while R exhibited the least. Functional gene structure and abundance were significantly correlated with corresponding soil enzymatic activities and rice yield, respectively, suggesting that the structural shift of the microbial functional community under fertilization might promote soil nutrient turnover and thereby affect yield. Overall, this study indicates that the combined application of rice straw and balanced chemical fertilizers was more pronounced in shifting the bacterial composition and improving the functional diversity toward higher productivity, providing a microbial point of view on applying a cost-effective integrated fertilization regime with rice straw plus reduced chemical fertilizers for sustainable nutrient management.

[Effect of Dicyandiamide on N2O Emission in Fallow Paddy Field and Rape Cropping].

The emissions of greenhouse gas in winter are often neglected, and the latest research results showed that N2O emissions in fallow paddy field and winter oilseed rape are still large, research on mitigating the N2O flux and the mechanism behind them is of significance for mitigating N2O emissions from agricultural soil. By using static chamber techniques and molecular biology techniques, the N2O emission as well as the community composition and abundance of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) from fallow paddy field, rape cropping with and without DCD treatment in Taoyuan agricultural ecological experiment station of the Chinese Academy of sciences were measured. The results showed that the addition of DCD significantly inhibited N2O emissions in fallow paddy field and rape cropping by 36.7% and 23.6%, respectively. The application of DCD in fallow paddy field inhibited the abundance of AOA and AOB by 59.3% and 73.7%, respectively, but only changed the community structure of AOA. The addition of DCD in rape cropping only changed the community structure and inhibited the abundance of AOB. This research showed that DCD application could effectively mitigate the N2O emissions in fallow paddy field and winter rape cropping under different mitigation mechanisms.

[N2O Consumption Ability of Submerged Paddy Soil and the Regulatory Mechanism].

A large number of researches showed that the N2O negative emissions from flooding paddy fields, peatlands and other wetlands ecosystem were frequent and considerable, which is of great significance on alleviating the greenhouse gas effect. However, there are few reports about the transformation and microbial mechanism of N2O between atmosphere and paddy soil. The slurry of surface paddy soil (0-5 cm) was incubated in laboratory conditions, and the effect of enhanced N2O concentrations in headspace on the N2O consumption capacity of submerged paddy soil and the response of nosZ gene abundance were explored. The results showed that, paddy soil under flooding and anaerobic conditions harbored very strong potential of N2O reduction along with a relatively high nosZ gene abundance (108 copies·g-1 dry soil at DNA level). Regression analysis presented the N2O concentrations in headspace were positively correlated (r2=1, P<0.001) to the N2O consumption rates of paddy soil slurry, indicating the high N2O concentration could stimulate the N2O consumption power, to a very high rate of 4567.99 µg·(m2·h)-1. Meanwhile, there were no significant differences in the high abundance of nosZ gene among N2O treatments, demonstrating the nosZ gene abundance at DNA level might not be the main controller of N2O consumption ability in submerged paddy soil and further study on the key microbial factor is needed.

Long-term balanced fertilization increases the soil microbial functional diversity in a phosphorus-limited paddy soil.

The influence of long-term chemical fertilization on soil microbial communities has been one of the frontier topics of agricultural and environmental sciences and is critical for linking soil microbial flora with soil functions. In this study, 16S rRNA gene pyrosequencing and a functional gene array, geochip 4.0, were used to investigate the shifts in microbial composition and functional gene structure in paddy soils with different fertilization treatments over a 22-year period. These included a control without fertilizers; chemical nitrogen fertilizer (N); N and phosphate (NP); N and potassium (NK); and N, P and K (NPK). Based on 16S rRNA gene data, both species evenness and key genera were affected by P fertilization. Functional gene array-based analysis revealed that long-term fertilization significantly changed the overall microbial functional structures. Chemical fertilization significantly increased the diversity and abundance of most genes involved in C, N, P and S cycling, especially for the treatments NK and NPK. Significant correlations were found among functional gene structure and abundance, related soil enzymatic activities and rice yield, suggesting that a fertilizer-induced shift in the microbial community may accelerate the nutrient turnover in soil, which in turn influenced rice growth. The effect of N fertilization on soil microbial functional genes was mitigated by the addition of P fertilizer in this P-limited paddy soil, suggesting that balanced chemical fertilization is beneficial to the soil microbial community and its functions.

[Effect of short-time drought process on denitrifying bacteria abundance and N2O emission in paddy soil].

In order to investigate the impact of drying process on greenhouse gas emissions and denitrifying microorganisms in paddy soil, wetting-drying process was simulated in laboratory conditions. N2O flux, redox potential (Eh) were monitored and narG- and nosZ-containing denitrifiers abundances were determined by real-time PCR. N2O emission was significantly increased only 4 h after drying process began, and it was more than 6 times of continuous flooding (CF) at 24 h. In addition, narG and nosZ gene abundances were increased rapidly with the drying process, and N2O emission flux was significantly correlated with narG gene abundance (P < 0.01). Our results indicated that the narG-containing deniteifiers were the main driving microorganisms which caused the N2O emission in the short-time drought process in paddy soil.

[N2O flux in winter and its affecting factors under different land use patterns].

Due to the low temperature in winter, the emissions of greenhouse gas are often neglected. And the latest research results showed that there is continuous N2O emission in winter, therefore, research on understanding the No2O flux regulation is important for evaluating agricultural soil N2O emission. By using static chamber techniques, the N2O emission from soils under different land use patterns including fallow paddy field, rape cropping, honey pomelo orchard and abandon land in Taoyuan agricultural ecological experimental station of Chinese Academy of Sciences was measured. The results showed that fallow paddy field and rape cropping N2O emissions were obviously higher than those of the honey pomelo orchard and abandon land, and the total N2O flux in winter decreased in the order of rape cropping > fallow paddy field > honey pomelo orchard > abandon land. Cumulative N2O emission was 0.502, 0.392, 0.162 and 0.075 kg x hm(-2), respectively. Fallow paddy field and rape cropping N2O emissions accounted for large proportions of the annual N2O emissions, while honey pomelo orchard and abandon land had small contribution to the annual N2O emissions. The correlation analysis results showed that for different land use patterns, when the soil temperature > 5 degrees C, N2O emissions in winter and soil temperature had significant positive exponential correlation, and had little to do with moisture. This research showed that: when the soil temperature > 5 degrees C, the soil temperature was the leading factor in N2O emissions in winter under different land patterns; When the soil temperature < 5 degrees C, other environmental factors had comprehensive influences on the N2O emissions.

[Effects of rice straw returning on the community structure and diversity of nitrogen-fixing gene (nifH) in paddy soil].

Taking a long-term fertilization experiment in Taoyuan Agro-ecosystem Research Station under Chinese Academy of Sciences as the platform, and selecting four treatments (no fertilization, CK; rice straw returning, C; nitrogen, phosphorus and potassium fertilization, NPK; and NPK+C) as the objects, soil samples were collected at the tillering, booting and maturing stages of rice, and the abundance, composition and diversity of nifH-containing bacterial community were measured by real-time quantitative PCR and terminal restriction fragment length polymorphism (T-RFLP), aimed to understand the effects of rice straw returning on the nifH-containing bacterial community in paddy soil. Compared with CK, treatments NPK+C and NPK increased the abundance of nifH-containing microorganisms significantly (except at tillering stage), and NPK+C had the highest abundance of nifH-containing microorganisms. Under the effects of long-term fertilization, the composition of nifH gene community in CK differed obviously from that in the other three treatments. The nifH composition had definite difference between C and NPK, but less difference between NPK and NPK+C. Long-term fertilization did not induce significant changes in nifH diversity. Therefore, long-term rice straw returning not only induced the changes of nifH gene community composition, but also resulted in a significant increase in the abundance of nifH-containing community, and hence, the increase of soil nitrogen fixing capacity.

[Effects of continuous cropping of vegetables on ammonia oxidizers community structure].

Investigations were conducted on the effects of intensive application of chemical fertilizers in crop production on soil nitrifier communities and the relationship between nitrifier communities and soil nitrification ability. Two series of vegetable soils were selected from Huangxing, Changsha, reflecting continuous vegetable cropping with about 20 years and new vegetable field with only about 2 years vegetable growing history. In each series five independent topsoils (0-20 cm) were sampled and each soil was a mixture of 10 cores randomly taken in the same field. Terminal restriction fragment length polymorphism (T-RFLP) and quantity PCR (Q-PCR) were used to determine the composition and abundance of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) communities. Results indicated that long-term and continuous vegetable cropping obviously changed the compositions of both AOB and AOA amoA gene, soil pH and Olsen-P content were the dominant factors affecting the composition of AOB amoA. In the vegetable soils, although the copy number of AOA amoA gene was about 5 times higher than AOB amoA gene, no significant correlation was detected between AOA amoA gene abundance and soil nitrification rate. It was not sure whether long-term and continuous vegetable cropping could shift the abundance of AOB and AOA, but it resulted in the enrichment of some dominant AOB species and increase of soil nitrification potential (PNF).

[Effect of long-term application of nitrogen fertilizer on the diversity of nitrifying genes (amoA and hao) in paddy soil].

The aim of this study was to determine the effect of long-term (16 years) application of nitrogen fertilizer on the diversity of nitrifying genes (amoA and hao) in paddy soil on the basis of long-term paddy field experimental station (started in 1990) located in Taoyuan, with the molecular approaches of PCR, constructing libraries and sequencing. The fertilizer was urea and no fertilizer was as control. The Shannon index showed that long-term application of nitrogen fertilizer made the diversity of amoA gene descend while no effect on the diversity of hao gene. The LIBSHUFF statistical analyses demonstrated that both amoA and hao libraries of CK and N treatments were significantly different from each other and the rarefaction curves of libraries failed to meet the plateaus indicating that there were lots kinds of genes haven't been detected. The results of blasting with GenBank and the phylogenetic tree showed that the amoA genes detected in our study had a similarity with the uncultured gene of amoA, which showed some similar to Nitrosospira. Otherwise, the hao genes cloned showed a relationship to the genes of cultured bacteria such as Silicibacteria, Nitrosospira and Methylococcus, and the hao genes found in the N treatment dominated in alpha-Proteobacteria. These results suggest that long-term fertilization of nitrogen had significant impacts on the diversity or community of amoA and hao genes.

[Change characteristics of soil available nitrogen and phosphorus and heavy metal contents after long-term cultivation of vegetables].

Soil samples were collected from three vegetable fields under different years of cultivation in Changsha suburbs of Hunan Province, South-central China to study the accumulation characteristics, risks, and sources of soil available nitrogen and phosphorus and heavy metals in the fields. With the increasing year of vegetable cultivation, the soil NO3(-)-N, Olsen-P, and heavy metals contents in the fields increased significantly. The average contents of soil NO3(-)-N, Olsen-P, and Cd in the vegetable fields having been cultivated for 1-2 years in Ningxiang County, 10-15 years in Changsha County, and 30 years in Kaifu District were 21.1, 31.9 and 0.33 mg x kg(-1), 42.0, 146.9 and 0.52 mg x kg(-1), and 49.5, 219.9 and 1.40 mg x kg(-1), respectively. The cumulative index (CI) of soil heavy metals generally followed the sequence of Cd >> Cu > Pb > Ni > Zn. Principal component analysis and cluster analysis showed that compared with soil NH4 OAc-extracted potassium, pH, organic matter and NH4(+)-N, that were dominated by natural factors, the soil Olsen-P and NO3(-)-N had the similar accumulation characteristics with the soil heavy metals, being mainly controlled by fertilization. It was considered that the soil environment and health quality of the vegetable fields in Changsha suburbs were not optimistic. The longer the cultivation year of vegetables, the more the soil NO3(-)-N, Olsen-P, and heavy metals accumulated in the fields. The accumulation of these elements in the fields could be primarily due to the long-term fertilization.

[Discussion of laboratory diagnosis for echinococcosis].

Laboratory diagnosis is one of the main means for diagnosis of echinococcosis. With the continuing evolvement of immunology and immunology technology, the laboratory diagnosis of echinococcosis obtained an encouraging progress, and the sensitivity and specificity of diagnostic tests for echinococcosis further improved. This review summarizes the current information concerning stool test, diagnostic antigen, and immunological diagnostic methods of echinococcosis.