Responses of soil nematode abundance and food web to cover crops in a kiwifruit orchard.

Soil biodiversity plays an important role in both agricultural productivity and ecosystem functions. Cover crop species influence the primary productivity of the ecosystem and basal resources. However, it remains poorly understood how different cover crop treatments influence the community of soil nematodes in an orchard ecosystem. In this study, field experiments were conducted to investigate the effects of cover crop treatments with different species numbers, i.e., no cover crop (CK), two cover crop species (C2), four cover crop species (C4), and eight cover crop species (C8), on weed biomass, together with composition, abundance, and metabolic footprint of soil nematode community in a kiwifruit orchard. As compared to the CK group, the groups of cover crop treatments had lower weed biomass, which decreased with the increase of the cover crop diversity. Moreover, for the abundance of total nematodes, fungivores exhibited higher levels in C4 and C8 treatments than that in CK, bacterivores had a higher abundance in C4 treatment, and plant parasites had a higher abundance in C2 and C8 treatments. Cover crop treatments also changed the structure of nematode community and enhanced the nematode interactions and complexity of nematode community network. In addition, C4 increased the Wasilewska index but decreased the plant-parasite index. The metabolic footprints of fungivores were higher in cover crop treatments compared with CK, and C4 and C8 also increased the functional metabolic footprint of nematode. Soil nematode faunal analysis based on nematode metabolic footprints showed that C8 improved the soil nutrient status and food wed stability. Mantel test and redundancy analysis showed that soil microbial biomass nitrogen and carbon, organic carbon, nitrate nitrogen, moisture content, pH, and cover crop biomass were the main factors that affect soil nematode community. In conclusion, cover crop treatments with four or eight plant species displayed a positive role in weed control, improvement of soil health, and promotion of energy flow in the soil food web through the increase in the metabolic footprints of nematodes in kiwifruit orchard.

Coordinative Management of Soil Resources and Agricultural Farmland Environment for Food Security and Sustainable Development in China.

Major problems in China's pursuit of sustainable agricultural development include inadequate, low-quality soil and water resources, imbalanced regional allocation and unreasonable utilization of resources. In some regions, overexploitation of soil resources and excessive use of chemicals triggered a web of unforeseen consequences, including insufficient use of agricultural resources, agricultural non-point source pollution and land degradation. In the past decade, China has changed its path of agricultural development from an output-oriented one to a modern, sustainable one with agricultural ecological civilization as its goal. First, the government has formulated and improved its laws and regulations on soil resources and the environment. Second, the government has conducted serious actions to ensure food safety and coordinated management of agricultural resources. Third, the government has planned to establish national agricultural high-tech industry demonstration zones based on regional features to strengthen the connection among the government, agri-businesses, scientific community and the farming community. As the next step, the government should improve the system for ecological and environmental regulation and set up a feasible eco-incentive mechanism. At the same time, the scientific community should strengthen the innovation of bottleneck technologies and the development of whole solutions for sustainable management in ecologically fragile regions. This will enhance the alignment between policy mechanisms and technology modes and effectively promote the sustainable development of agriculture in China.

Fertilization drives distinct biotic and abiotic factors in regulating functional groups of protists in a 5-year fertilization system.

Introduction: Protists play an important role in nutrient cycling, microbiome stability and soil fertility maintenance. However, the driving force of protistan functional groups remains poorly understood in agricultural ecosystems. Methods: We investigated the impacts of fertilization regimes on the diversity, composition and functional groups of protists and further disentangled the effects of multiple factors shaping the community composition of functional groups in a 5-year fertilization regime (CK, no fertilization; M, organic fertilization; MNPK, combined inorganic and organic fertilization; NPK, inorganic fertilization). Results: Fertilization significantly changed the community composition of protists rather than diversity. The MNPK treatment significantly increased the relative abundance of phototrophs and decreased that of the parasites and consumers. Partial least squares path modeling indicated that fertilization indirectly regulated protistan consumers via changes in the P content, which affected the composition of consumers mainly by regulating fungal community composition. Soil moisture (SM) and available phosphorus (AP) were identified as the top predictors for the composition of parasites, and the composition of phototrophs was mainly affected by SM, indicating that parasites and phototrophs were more sensitive to abiotic factors in the fertilization system. Discussion: Taken together, our findings highlight that fertilization significantly affects the composition of functional groups of protists and their biotic or abiotic regulatory processes, which have implications for the potential changes in their ecosystem functions for soil management systems.

An integrated belowground trait-based understanding of nitrogen-driven plant diversity loss.

Belowground plant traits play important roles in plant diversity loss driven by atmospheric nitrogen (N) deposition. However, the way N enrichment shapes plant microhabitats by patterning belowground traits and finally determines aboveground responses is poorly understood. Here, we investigated the rhizosheath trait of 74 plant species in seven N-addition simulation experiments across multiple grassland ecosystems in China. We found that rhizosheath formation differed among plant functional groups and contributed to changes in plant community composition induced by N enrichment. Compared with forb species, grass and sedge species exhibited distinct rhizosheaths; moreover, grasses and sedges expanded their rhizosheaths with increasing N-addition rate which allowed them to colonize belowground habitats. Grasses also shaped a different microenvironment around their roots compared with forbs by affecting the physicochemical, biological, and stress-avoiding properties of their rhizosphere soil. Rhizosheaths act as a "biofilm-like shield" by the accumulation of protective compounds, carboxylic anions and polysaccharides, determined by both plants and microorganisms. This enhanced the tolerance of grasses and sedges to stresses induced by N enrichment. Conversely, forbs lacked the protective rhizosheaths which renders their roots sensitive to stresses induced by N enrichment, thus contributing to their disappearance under N-enriched conditions. This study uncovers the processes by which belowground facilitation and trait matching affect aboveground responses under conditions of N enrichment, which advances our mechanistic understanding of the contribution of competitive exclusion and environmental tolerance to plant diversity loss caused by N deposition.

Responses of Soil Microbial and Nematode Communities to Various Cover Crop Patterns in a Tea Garden of China.

As one of the typical farmland ecosystems, tea gardens are of vital importance in China. The purpose of this study was to quantify the dynamic of soil properties, soil microbial diversity, and nematodes, as affected by various cover crop patterns in a Tanjiawan tea garden in Hubei Province, China. Four cover crop patterns were established as following: naturally covered of bare land and mixed planting with two species, four species, and eight species. The results revealed that soil organic matter, pH, and total phosphorous content were significantly related to cover crop patterns. The number of nematodes increased with cover crop diversity, and the percentage of plant parasitic nematodes in cover crop treatments was lower than in naturally covered bare land. A higher diversity of cover crops increased the number of bacterivores and fungivores, thereby enhancing the bacterial decomposition pathway of soil organic matter. Both soil nematodes and microbial communities showed significant seasonal changes under different cover crop patterns. The soil food webs were more stable and mature under cover crops with two species and four species. Combined with the results of a structural equation model, we found that soil properties, characterized by the total nitrogen, available phosphorus, NO3--N, and soil organic matter, were significantly correlated with soil nematodes and microbial communities. In addition, acterivores and plant parasites were significantly negatively correlated with omnivores/predators. Our results implied that soil properties and seasonal changes influence the relationships between cover crops, soil nematodes, and microbial communities. These findings provide a theoretical basis for future studies on interactions between soil properties, soil microorganisms, and nematodes in tea gardens.

Nitrogen Deposition Reduces the Diversity and Abundance of cbbL Gene-Containing CO2-Fixing Microorganisms in the Soil of the Stipa baicalensis Steppe.

CO2 fixation by autotrophic microbes has a significant effect on the carbon cycle in temperate grasslands. Nitrogen (N) deposition in soil has been steadily increasing for decades, which has consequences for soil microorganisms. However, the impact of this deposition on the diversity and abundance of CO2-fixing soil microorganisms remains unclear in temperate grasslands. In the present study, the cbbL gene, a key gene in the Calvin-Benson-Bassham cycle that encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, was used to study CO2-fixing microbes under different rates of N addition (0, 15, 30, 50, 100, and 150 kg N ha-1 yr-1) in a 9-year field experiment in a temperate grassland. The results showed that N addition led to significant reductions in cbbL gene abundance and genetic diversity and altered cbbL gene community composition. High N addition enhanced the relative abundances of Acidiferrobacterales and Rhizobiales but reduced those of Burkholderiales and Rhodobacterales. Structural equation modeling further revealed that N addition primarily reduced cbbL genetic diversity by increasing the soil NO3-N content and decreasing the soil pH. N addition indirectly reduced cbbL gene abundance, possibly by increasing the soil N/phosphorus (P) ratio and decreasing the soil pH. These findings suggest that N addition increases the soil available N and causes soil acidification, which may inhibit growth of CO2-fixing microbes to some extent.

[Response of Bacterial and Fungal Communities to Chemical Fertilizer Reduction Combined with Organic Fertilizer and Straw in Fluvo-aquic Soil].

To investigate the effects of chemical fertilizer reduction combined with organic fertilizer and straw on bacterial and fungal communities in fluvo-aquic soil under a wheat-maize rotation system in North China, a field-oriented fertilization experiment was performed at a trial base in Ninghe District of Tianjin. The differences in composition, diversity, and structure of bacterial and fungal communities were evaluated using five fertilization patterns (chemical fertilizer, F; chemical fertilizer reduction, FR; chemical fertilizer reduction combined with straw, FRS; chemical fertilizer reduction combined with organic fertilizer, FRO; chemical fertilizer reduction combined with organic fertilizer and straw, FROS) using Illumina high-throughput sequencing technology. Further, the main soil environmental factors driving the alteration of bacterial and fungal communities under different fertilization treatments were explored in combination with soil chemical analysis. The results showed that adding organic fertilizer (FRO) significantly increased the SOM content. In comparison with the FRS treatment, the TP content in the FROS treatment significantly increased by 13.33%. The AP content increased significantly after applying the FRO and FROS treatment, and it increased by 18.03%-33.45% and 22.69%-38.72%, respectively, as compared to that with the other treatments. The NH4+-N content of FRO and FROS treatments was significantly higher than that of chemical fertilizer treatments (F and FR), which was 2.14 and 2.23 times that of F treatment, and 2.23 and 2.33 times that of FR treatment, respectively. Proteobacteria, Actinobacteria, Chloroflexi, and Acidobacteria were the dominant bacterial phyla for all treatments, with Ascomycota being the dominant fungal phylum. Based on the chemical fertilizer reduction combined with organic fertilizer, the addition of straw (FROS) significantly decreased the relative abundance of Actinobacteria. Under the FRS and FROS treatments, a significant decrease in the relative abundance of Gemmatimonadetes was observed. Moreover, the FROS treatment caused a significant decrease in the relative abundance of Planctomycetes and Verrucomicrobia. As for the fungal community, the relative abundance of Ascomycota was significantly increased under the treatments applying organic fertilizer (FRO and FROS). In comparison with the FR treatment, the FROS treatment significantly decreased the relative abundance of Mortierellomycota and Olpidiomycota, and the FRS treatment also showed a significant inhibitory effect on the relative abundance of Mortierellomycota. The Shannon index of bacterial community of the FROS treatment was significantly reduced by 1.26% and 1.25% in comparison with the F and FR treatments, respectively; the Chao1 index increased by 4.51% as compared with that of the F treatment. The Shannon index of bacterial community exhibited a significantly positive correlation with available phosphorus as well as ammonium content (P<0.05). In comparison to the FR treatment, the FRS, FRO, and FROS treatments significantly decreased the Shannon index of fungal community by 29.85%, 24.94%, and 25.73%, respectively. A significantly positive relationship between the Shannon index of fungal community and available phosphorus content was observed. The community structure of bacteria of the FROS treatment was significantly different from that of F, FR, and FRO treatments, with the soil moisture, total phosphorus, pH, and available phosphorus as the major driving factors; the fungal community structure of the FRO and FROS treatments showed significant difference from that of the F and FR treatments, and the fungal community structure was mainly altered by total nitrogen, available phosphorus, and total phosphorus. In summary, our results indicated that the bacterial and fungal communities in fluvo-aquic soil exhibited a relatively strong response to the chemical fertilizer reduction combined with organic fertilizer and straw; meanwhile, the fungal community was also significantly influenced by chemical fertilizer reduction with organic fertilizer. Therefore, the organic fertilizer and straw drive the changes in the bacterial and fungal community composition, while improving the soil physicochemical properties. The fluvo-aquic fungi were more sensitive to the organic materials than the bacteria. Soil P was a common important influencing factor for regulating the bacterial and fungal community structure, and it should be paid full attention during the agricultural cultivation of fluvo-aquic soil.

Characterization of Acid-Aged Biochar and its Ammonium Adsorption in an Aqueous Solution.

According to its characteristics, biochar originating originating from biomass is accepted as a multifunctional carbon material that supports a wide range of applications. With the successfully used in reducing nitrate and adsorbing ammonium, the mechanism of biochar for nitrogen fixation in long-term brought increasing attention. However, there is a lack of analysis of the NH4+-N adsorption capacity of biochar after aging treatments. In this study, four kinds of acid and oxidation treatments were used to simulate biochar aging conditions to determine the adsorption of NH4+-N by biochar under acidic aging conditions. According to the results, acid-aged biochar demonstrated an enhanced maximum NH4+-N adsorption capacity of peanut shell biochar (PBC) from 24.58 to 123.28 mg·g-1 after a H2O2 modification. After the characteristic analysis, the acid aging treatments, unlike normal chemical modification methods, did not significantly change the chemical properties of the biochar, and the functional groups and chemical bonds on the biochar surface were quite similar before and after the acid aging process. The increased NH4+-N sorption ability was mainly related to physical property changes, such as increasing surface area and porosity. During the NH4+ sorption process, the N-containing functional groups on the biochar surface changed from pyrrolic nitrogen to pyridinic nitrogen, which showed that the adsorption on the surface of the aged biochar was mainly chemical adsorption due to the combination of π-π bonds in the sp2 hybrid orbital and a hydrogen bonding effect. Therefore, this research establishes a theoretical basis for the agricultural use of aged biochar.

The Roles of Bacteria in Soil Organic Carbon Accumulation under Nitrogen Deposition in Stipa baicalensis Steppe.

Grassland soil organic carbon (SOC) accounts for 15.5% of the SOC in reservoirs of terrestrial carbon (C) and is a major component of the global C cycle. Current and future reactive N deposited on grassland soils may alter biogeochemical processes and soil microbes. Microorganisms perform most of the decomposition on Earth and shift SOC accumulation. However, how variation in the identity and composition of the bacterial community influences SOC is far from clear. The objective of this study is to investigate the responses of SOC concentration to multiple rates of N addition as well as the roles of bacteria in SOC accumulation. We studied SOC storage and bacterial community composition under N addition treatments (0, 1.5, 3.0, 5.0, 10.0, 15.0, 20.0, and 30.0 g N·m-2 yr-1) in a 6-yr field experiment in a temperate grassland. We determined the soil inorganic nitrogen concentration and pH in a 0-10 cm soil layer. We used high-throughput genetic sequencing to detect bacteria. N addition led to significant increases in the concentrations of SOC. N addition reduced the soil pH but increased the NO3-N and NH4-N levels. The bacterial diversity was highest under low nitrogen addition. N addition increased the relative abundance of Proteobacteria, and Proteobacteria became the second dominant phylum under high N addition. Structural equation modeling further revealed that soil pH and bacterial community structure have an impact on SOC under N deposition. Nitrogen-regulated SOC is associated with Proteobacteria and Planctomycetes. These findings suggest that N deposition may alter the SOC content, highlighting the importance of understanding changes in the bacterial community for soil nutrients under N deposition.

Integration of behavioural tests and transcriptome sequencing of C. elegans reveals how the nematode responds to peanut shell biochar amendment.

Biochars have drawn wide attention as adsorbents, carbon sequesters and soil re-mediators. However, these substances are ambiguous regarding their effects on the motility, phenotypic changes and potential adaptative mechanisms of soil organisms. This study investigated how peanut shell biochar (PBC) affects the C. elegans model via a one-choice selection test and RNA-seq analysis. The results showed that C. elegans were able to select either PBC or a water control, and a clear preference for PBC was observed after 48 h of exposure, with the chemotaxis index (CI) reaching approximately 1.0. The nematode preferences for PBC vs sterile PBC/graphite were not significant, which demonstrated that initial microorganisms and appearances were not the reasons for the worms' selection, but the selection behaviour was instead determined by volatile odours. The treatments also showed that biochar amendment significantly decreased the body length, brood size and superoxide dismutase (SOD) activity of C. elegans to 960.20 ± 15.23 µm, 173.22 ± 4.56, 165.81 ± 3.82 U/mL SOD, respectively. Then, a possible molecular mechanism of PBC-induced developmental and reproductive effects on C. elegans was explored. Differential gene expression analysis was performed, and 1625 genes (1425 up- and 225 downregulated genes) were regulated in response to PBC treatment. The top 20 regulated genes were col genes (col-129; col-81; col-139; col-71), bli-6, perm-4 and his-24, which indicated that cuticle collagen synthesis, eggshell formation and/or heterochromatin in postembryonic growth may be disrupted following exposure to PBC. Therefore, our study suggested that quality standards be used to test nematode preferences and responses to biochar amendment, with the aim of safe application in soils, seedling substrates or fertilizers.

Symbiotic Performances of Three Mesorhizobium huakuii Strains Inoculated to Chinese Milk Vetch Varieties.

In this experiment, 4 varieties of Chinese milk vetch (Xinyang, Minzi No. 6, Minzi 8487711, and Shishou) were used as host plants and inoculated with 3 strains of rhizobium (CCBAU 2609, M. h 93, and 7653R). The differences in their morphology, yield, and nodule characteristics at different growth stages were studied and the reasons for these differences were analyzed to explore the exclusivity between different varieties of Chinese milk vetch and strains of rhizobium. Results showed no significant difference in plant height and whole-plant dry weight at seedling stage under different treatments but significant differences in these characteristics at full flowering stage. The results indicated that Minzi 8487711 and Shishou were significantly better than the other varieties. During the whole growth period, the growth indexes and nodule characteristics of the 4 varieties inoculated with strain 7653R were better than those of the varieties inoculated with other strains. At full flowering stage, compared with that of the control group, the biomasses of Xinyang, Minzi No.6, Minzi 8487711, and Shishou had increased by 2.04, 2.84, 1.56, and 2.69-fold, respectively, and nitrogenase activities increased by 3.82, 9.60, 6.21, and 15.18%, respectively. Significant differences in the exclusivity between varieties and strains were observed. Minzi No.6-7653R and Shishou variety-7653R had the strongest exclusivity. The results showed that 7653R was a broad-spectrum and high-efficiency rhizobium strain. 7653R is recommended to be used in combination with Chinese milk vetch varieties, such as Minzi 8487711 and Shishou, to obtain advantages in yield and nitrogen fixation in production.

[Effects of Transgenic Maize with cry1Ab and Epsps Genes C0030.3.5 on the Abundance and Community Structure of Soil Nitrogen-fixing Bacteria].

In order to evaluate the potential risk of planting transgenic corn on soil nitrogen-fixing microorganisms, in 2015, rhizosphere and non-rhizosphere soil samples were collected at the jointing stage, tassel stage, milky stage, and ripening stage, and the effects of transgenic maize with the cry1Ab and epsps genes on the abundance and diversity of soil nitrogen-fixing bacteria were studied by real-time quantitative PCR and T-RFLP. The results showed that the copy number of the diazotrophic nifH gene in the rhizosphere and non-rhizosphere soil of transgenic maize with the cry1Ab and epsps genes (C0030.3.5) and its parental maize (DBN318) showed a trend where it first increased and then decrease with the growth stages, ranging between 2.99×107 and 7.02×107 copies·g-1. The abundance of the diazotrophic nifH gene in the rhizosphere soil and non-rhizosphere soil gene showed no significant difference between TM and PM in the same growth stage (P>0.05). The correlation analysis showed that the abundance of the diazotrophic nifH gene was positively correlated with the content of organic matter, but negatively correlated with water content. T-RFLP analysis yielded 14 T-RFs of different lengths, and 43-bp and 155-bp fragments were the dominant population. The community composition of nitrogen-fixing bacteria was the same as that of TM and PM in the rhizosphere soil and non-rhizosphere soil, and there was no significant difference between the TM and PM populations in the same growth period (P>0.05). The Shannon index and Evenness index of the diazotrophic nifH gene showed a trend where they first increased and then decreased with the growth period, and there was no significant difference in the Shannon index and Evenness index in the same growth stage between the rhizosphere and non-rhizosphere soil samples. Principal component analysis(PCA) indicated that the composition of nitrogen-fixing bacteria was not different between TM and PM. Redundancy analysis (RDA) showed that soil ammonium, nitrogen, and pH were significantly correlated with composition of nitrogen-fixing bacteria.

Litter mixture dominated by leaf litter of the invasive species, Flaveria bidentis, accelerates decomposition and favors nitrogen release.

In natural ecosystems, invasive plant litter is often mixed with that of native species, yet few studies have examined the decomposition dynamics of such mixtures, especially across different degrees of invasion. We conducted a 1-year litterbag experiment using leaf litters from the invasive species Flaveria bidentis (L.) and the dominant co-occurring native species, Setaria viridis (L.). Litters were allowed to decompose either separately or together at different ratios in a mothproof screen house. The mass loss of all litter mixtures was non-additive, and the direction and strength of effects varied with species ratio and decomposition stage. During the initial stages of decomposition, all mixtures had a neutral effect on the mass loss; however, at later stages of decomposition, mixtures containing more invasive litter had synergistic effects on mass loss. Importantly, an increase in F. bidentis litter with a lower C:N ratio in mixtures led to greater net release of N over time. These results highlight the importance of trait dissimilarity in determining the decomposition rates of litter mixtures and suggest that F. bidentis could further synchronize N release from litter as an invasion proceeds, potentially creating a positive feedback linked through invasion as the invader outcompetes the natives for nutrients. Our findings also demonstrate the importance of species composition as well as the identity of dominant species when considering how changes in plant community structure influence plant invasion.

[Effects of tillage methods on soil physicochemical properties and biological characteristics in farmland: A review].

Tillage methods affect soil heat, water, nutrients and soil biology in different ways. Reasonable soil management system can not only improve physical and chemical properties of the soil, but also change the ecological process of farmland soil. Conservation tillage can improve the quality of the soil to different degrees. For example, no-tillage system can effectively improve soil enzyme activity. No tillage and subsoiling tillage can provide abundant resources for soil microbe' s growth and reproduction. No tillage, minimum tillage and other conservation tillage methods exert little disturbance to soil animals, and in turn affect the quantity and diversity of the soil animals as well as their population structure. Effects of different tillage methods on soil physical and chemical properties as well as biological characteristics were reviewed in this article, with the soil physical and chemical indices, enzyme activities, soil microbe diversity and soil animals under different tillage patterns analyzed. The possibility of soil quality restoration with appropriate tillage methods and the future research direction were pointed out.

[Effects of different vegetation restoration patterns on the diversity of soil nitrogen-fixing microbes in Hulunbeier sandy land, Inner Mongolia of North China].

By using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and sequence analysis, this paper studied the nifH gene diversity and community structure of soil nitrogen-fixing microbes in Hulunbeier sandy land of Inner Mongolia under four years management of five vegetation restoration modes, i. e., mixed-planting of Agropyron cristatum, Hedysarum fruticosum, Caragana korshinskii, and Elymus nutans (ACHE) and of Agropyron cristatum and Hedysarum fruticosum (AC), and mono-planting of Caragana korshinskii (UC), Agropyron cristatum (UA), and Hedysarum fruticosum (UH), taking the bare land as the control (CK). There existed significant differences in the community composition of nitrogen-fixing microbes among the five vegetation restoration patterns. The Shannon index of the nifH gene was the highest under ACHE, followed by under AC, UC, UA, and UH, and the lowest in CK. Except that UH and CK had less difference in the Shannon index, the other four vegetation restoration modes had a significantly higher Shannon index than CK (P < 0.05). The phylogenetic analysis showed that the soil nitrogen-fixing microbes under UA, UH, and UC were mainly of cyanobacteria, but the soil nitrogen-fixing microbes under AC and ACHE changed obviously, mainly of proteobacteria, and also of cyanobacteria. The canonical correlation analysis showed that the soil total phosphorus, available phosphorus, total nitrogen, and nitrate nitrogen contents under the five vegetation restoration modes had significant effects on the nitrogen-fixing microbial communities, and there existed significant correlations among the soil total phosphorus, available phosphorus, total nitrogen, and nitrate nitrogen. It was suggested that the variations of the community composition of soil nitrogen-fixing microbes under the five vegetation restoration modes were resulted from the interactive and combined effects of the soil physical and chemical factors.

[Effects of different fertilizer application on soil active organic carbon].

The variation characteristics of the content and components of soil active organic carbon under different fertilizer application were investigated in samples of calcareous fluvo-aquic soil from a field experiment growing winter wheat and summer maize in rotation in the North China Plain. The results showed that RF (recommended fertilization), CF (conventional fertilization) and NPK (mineral fertilizer alone) significantly increased the content of soil dissolved organic carbon and easily oxidized organic carbon by 24.92-38.63 mg x kg(-1) and 0.94-0.58 mg x kg(-1) respectively compared to CK (unfertilized control). The soil dissolved organic carbon content under OM (organic manure) increased greater than those under NPK and single fertilization, soil easily oxidized organic carbon content under OM and NPK increased greater than that under single chemical fertilization. OM and NPK showed no significant role in promoting the soil microbial biomass carbon, but combined application of OM and NPK significantly increased the soil microbial biomass carbon content by 36.06% and 20.69%, respectively. Soil easily oxidized organic carbon, dissolved organic carbon and microbial biomass carbon accounted for 8.41% - 14.83%, 0.47% - 0.70% and 0.89% - 1.20% of the total organic carbon (TOC), respectively. According to the results, the fertilizer application significantly increased the proportion of soil dissolved organic carbon and easily oxidized organic carbon, but there was no significant difference in the increasing extent of dissolved organic carbon. The RF and CF increased the proportion of soil easily oxidized organic carbon greater than OM or NPK, and significantly increased the proportion of microbial biomass carbon. OM or RF had no significant effect on the proportion of microbial biomass carbon. Therefore, in the field experiment, appropriate application of organic manure and chemical fertilizers played an important role for the increase of soil active organic carbon content and the effective control of its key components.

[Optimization of conservation network system for inter-basin wetland ecosystem in Huang-Huai-Hai Region].

By using systematic conservation planning (SCP) method, and taking catchment as planning unit, an optimization of conservation network system for the inter-basin wetland ecosystem in Huang-Huai-Hai Region was conducted, with a comprehensive consideration of 3-dimensional (lateral, longitudinal and vertical) connectivity and Inter-basin Water Transfer Project and by the methods of irreplaceability analysis and gap identification. The efficacy of the optimized conservation network system was evaluated, as compared with the existing conservation network system. According to the principles of irreplaceability and connectivity, the wetland conservation gaps could be divided into two types, i.e. , be conserved in priority and in general. After the optimization, the conservation status of the inter-basin wetland ecosystem in Huang-Huai-Hai Region had an overall improvement. The conserved percentage of the wetland types was from about 20% up to 46.8%, and, for each wetland type, its conserved level increased to some extent, almost above 40%. Both in the near future and in the long term, more attention should be paid to the conservation of lake wetland. In addition, the integration of ecosystem service function and biodiversity and the combination of protection with restoration would be the main task for the wetland ecosystem conservation planning in the future.

[Diversity and community structure of soil ammonia-oxidizing bacteria in Hulunbeier Grassland, Inner Mongolia].

By the methods of polymerase chain reaction-denaturing gradient gel electrophoresis and sequence analysis, a comparative study was conducted on the diversity and community structure of soil ammonia-oxidizing bacteria in the Filifolium sibiricum steppe, Stipa baicalensis steppe, Leymus chinensis steppe, Stipa grandis steppe, and Stipa kryrowi steppe in Hulunbeier Grassland, Inner Mongolia. A significant difference was observed in the community structure of soil ammonia-oxidizing bacteria among the five steppes, with the similarity lower than 50%. The diversity of soil ammonia-oxidizing bacteria was the highest in F. sibiricum steppe, followed by in S. baicalensis steppe, L. chinensis steppe, S. kryrowi steppe, and S. grandis steppe. In the five steppes, Nitrosospira cluster 3 was the dominant group, and the Nitrosospira cluster 1, 2, and 4 as well as Nitrosomonas were also found. The community structure of soil ammonia oxidizing bacteria in F. sibiricum steppe was most complex, while that in L. chinensis steppe and S. grandis steppe was relatively simple. Correlation analysis indicated that there existed significant positive correlations between the diversity of soil ammonia-oxidizing bacteria and the soil moisture, total nitrogen, total organic carbon, and C/N ratio (P<0.05).

[Effect of plantation of transgenic Bt cotton on the amount of rhizospheric soil microorganism and bacterial diversity in the cotton region of Yellow River basin].

Traditional culture-dependent method and PCR-DGGE were adopted to investigate the amount of microorganism and bacterial diversity in rhizospheric soil of transgenic Bt cotton in four provinces of Yellow River basin at four growth stages, i.e., 30, 60, 90, and 120 days after sowing. In the same province and at the same growth stage, no significant difference was observed in the amount of microorganism in rhizospheric soils of transgenic and non-transgenic Bt cottons. Within the same province the amount of microorganism was mainly affected by growth stage; while in different provinces, it was greatly affected by regional conditions. In the four provinces, the bacterial diversity in rhizospheric soil of transgenic Bt cotton was abundant; and in the same province and at the same growth stage, there were no significant differences in the Shannon index, evenness, and richness of bacteria in rhizospheric soils of transgenic and non-transgenic Bt cottons. In different provinces, the bacterial diversity in rhizospheric soils was dependent on regional conditions, but the difference was rather small.