[Impacts of Land Use Intensification Level on Fluvo-aquic Cropland Soil Microbial Community Abundance and Necromass Accumulation in North China].

Despite the essential role of soil microorganisms in nutrient turnover in soil ecological systems and the recognized paramount significance of microbial necromass to soil organic carbon accumulation, how microbial community abundance and necromass respond to land use intensification level regulation remains poorly understood. To address this knowledge gap, based on the land use intensification level, three treatments were set up[annual wheat-maize rotation (CC), alternating temporary grassland with wheat planting (TG), and perennial grassland (PG)], and a long-term fixed filed experiment was established to investigate the influences of the regulation of land use intensification level on bacterial and fungal community abundances; the accumulation of bacterial, fungal, and total microbial necromass; and their contributions to SOC sequestration using droplet digital PCR and amino sugar detection technologies. We further sought to determine the key factors driving the bacterial, fungal, and total microbial necromass C accumulation. Our results demonstrated that fungal community abundance was strongly affected by land use intensification level regulation compared to that of the bacterial community, which increased with decreasing land use intensification level. The total microbial necromass C predominated the SOC accumulation across all three land use intensification levels, which contributed 52.78%, 58.36%, and 68.87% to SOC, respectively, exhibiting an increasing trend with the decline in land use intensification level. Fungal necromass C accounted for more than 80% of the total microbial necromass C, indicating its predominance in the accumulation of the total microbial necromass C and active variation via the reduction in land use intensification level. There was no significant difference in bacterial necromass C (MurA) content, with the trend of CC

[Impacts of Co-application of Chemical Fertilizer Reduction and Organic Material Amendment on Fluvo-aquic Soil Microbial N-cycling Functional Gene Abundances and N-converting Genetic Potentials in Northern China].

The emerging environment-associated issues due to the overuse of inorganic fertilizers in agricultural production are of global concern despite the benefit of high yields. Eco-friendly organic materials with the capability to fertilize soil are encouraged to partially replace mineral fertilizer. The N cycle conducted by soil microorganisms is the most important biogeochemical process, dictating the N bioavailability in farmland ecosystems; however, little is known about how organic material amendment affects soil microbial N cycling under chemical fertilizer reduction. Hence, a fixed field trial with five fertilization practices was implemented to experimentally alter microorganisms essential for the soil N cycle, including conventional chemical fertilization (NPK), reduced chemical fertilization (NPKR), reduced chemical fertilization plus straw (NPKRS), reduced chemical fertilization plus organic fertilizer (NPKRO), and reduced chemical fertilization plus organic fertilizer and straw (NPKROS). The microbial N-cycling gene abundances and associated N-converting genetic potentials were evaluated using real-time quantitative PCR. In comparison to conventional chemical fertilization (NPK), organic addition significantly increased the amounts of heterotrophic microbes involved in organic N decomposition, N fixation, and N reduction; however, it reduced autotrophic microbes performing ammonia oxidization. Consequently, the overall proportion of heterotrophic microbes was remarkably enhanced, and the autotrophic proportion was correspondingly lowered. The fertilization practice shift significantly improved N fixation and gaseous N emission potentials, whereas it suppressed NO3- leaching potential. A significant discrepancy among five fertilization treatments was observed based on functional gene abundances (PERMANOVA, P=0.002),as revealed by distance-based redundancy analysis (db-RDA), with NH4+ as the dominant factor. Organic fertilizer addition was beneficial for heterotrophic N functional microorganisms, with simultaneous input of straw augmenting such an effect. Pearson's correlation analysis revealed that N storage and gaseous N emission potentials were both substantially negatively correlated with NH4+; NO3- leaching potential was notably negatively associated with SOC and TN but significantly related to NH4+. In conclusion, chemical fertilizer reduction combined with organic material amendments, a main fertilization recommendation, may enhance soil N storage, diminish N loss by leaching, and mitigate the environmental risk of N2O emission. This deserves attention considering that healthy and sustainable agricultural soil environment can be cultivated from the view of microbial N-cycling.

[Effects of tillage managements on soil microbial community structure in soil aggregates of fluvo-aquic soil]. / 耕作方式对潮土土壤团聚体微生物群落结构的影响.

In order to explore the impacts of different tillage managements on the structure and diversity of microbial community in fluvo-aquic soil, the phospholipid fatty acid (PLFA) method was used to determine microbial community composition in soil aggregates. Four tillage treatments were set up in Qihe County, Shandong Province, including rotary tillage with straw return (RT), deep ploughing with straw return (DP), subsoiling with straw return (SS) and no-tillage with straw return (NT). Our results showed that DP treatment significantly increased the amount of fungal PLFAs and fungi/bacteria ratio in >5 mm soil aggregates compared with RT. DP could provide favorable conditions for fungi reproduction, facilitate soil organic matter storage and soil buffering capacity. DP increased the amount of PLFAs in 5-2 mm soil aggregates, reduced the gram-positive (G+) /gram-negative (G-) bacteria ratio in the soil, and improved soil nutritional status. In addition, DP improved the microbial abundance index in <0.25 mm soil aggregates. In general, DP could not only increase the abundance of bacteria and fungi in soil aggregates, but also improve the microbial community structure of soil aggregate, which help increase soil carbon sequestration capacity and keep soil microbial diversity to a certain extent. Results of the redundancy analysis showed that the total PLFAs, PLFAs of bacteria, G- bacteria and actinomycetes in soil aggregates are closely correlated with soil organic carbon, while PLFAs of G+ bacteria had a strong correlation with soil total nitrogen concentration. In each treatment, microbial communities in larger sizes of soil aggregates were mainly affected by the ratio of organic carbon to total nitrogen, soil moisture, pH, and mass fractions of soil aggregates, while the microbial communities in smaller sizes of soil aggregates were affected by the concentrations of organic carbon and total nitrogen.

[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.

[Effects of Conversion of Forest to Arable Land on the Abundance and Structure of the cbbL-Harboring Bacterial Community in Albic Soil of the Hilly Region of Northeast China].

Soil CO2 fixer, which plays an important role in soil carbon cycling, can convert CO2 into organic matter. However, the effect of land-use change on the abundance and community structure of soil CO2 fixer is poorly understood. Examining the community of functional microbes that encode the large subunit of ribulose-1, 5-bisphosphate carboxylase/oxygenase under the conversion of land-use patterns may provide valuable information for promoting soil carbon sequestration ability and sustainable use. In this study, we investigated how the abundance and community diversity of the CO2-fixing bacteria responded to conversion of forest to arable land in the hilly region of Northeast China. We found that the abundance of soil cbbL-harboring bacteria was substantially lower in arable land (2.57×108 copies·g-1, soil) compared to forest (7.30×108 copies·g-1, soil), while the cbbL/16S rRNA gene ratio did not differ significantly between the two treatments. The values of the Shannon and Chao1 index decreased significantly with the conversion of forest to arable land, but the Simpson index was in contrast to these results. Neighbor-joining phylogenetic tree and principal coordinates analysis (PCoA) both demonstrated that the composition of the cbbL-harboring bacterial community was significantly affected by land-use change. Soil cbbL gene abundance and Shannon diversity significantly positively correlated with pH, and significantly negatively correlated with AP and NO3-, indicating that the changes in soil pH and available nutrients caused by land-use change greatly affected soil cbbL abundance and diversity. Meanwhile, pH, NO3-, available phosphorus (AP) and NH4+ significantly correlated with soil cbbL-harboring bacterial community structure. In conclusion, a 25-year long-term conversion of forest to arable land changed the community structure of soil cbbL-harboring bacteria, and soil pH, AP and available N played crucial roles in controlling the ecological properties of soil cbbL-harboring bacteria.

[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.

Molecular characterization and expression pattern of two pheromone-binding proteins from Spodoptera litura (Fabricius).

Pheromone perception is thought to be mediated by pheromone-binding proteins (PBPs) in the lymph surrounding the olfactory receptors. We cloned and characterized two PBP genes (SlitPBP1 and SlitPBP2) from the common cutworm, Spodoptera litura (F.; Lepidoptera: Noctuidae), which encode PBPs belonging to two different PBP groups. Western blot analysis of the crude antennal extracts with SexigPBP1 antibody revealed a single immunoreactive band (much stronger in male than in female) of approximately 16 kDa, in agreement with the calculated values for SlitPBPs. From genomic DNA, two introns and a similar exon/intron structural pattern were identified in each PBP genes, but the introns differed in length within and between PBP genes. The expression patterns of two SlitPBP genes, with respect to tissue distribution and sex, were further investigated by reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time PCR. Although the two PBP genes were expressed only in the antennae of both sexes, reflecting the antennal specificity of PBPs, the transcription levels of PBP genes differed between the sexes and the genes. The transcription levels of SlitPBP1 and SlitPBP2 in females were only 2.1% and 7.0%, respectively, relative to those in males, and the levels of PBP2 compared with PBP1 were 31.4% and 95.3% in males and females, respectively. These differential expression levels might suggest different roles played by the two SlitPBPs in the perception of sex pheromone both in males and females.

Molecular characterization of two pheromone binding proteins and quantitative analysis of their expression in the beet armyworm, Spodoptera exigua Hübner.

Pheromone binding proteins (PBP) play an important role in insect pheromone communication. However, the PBP for the beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae), an important agricultural pest worldwide, remains unaddressed. We report the cloning of two PBP genes, SexigPBP1 and SexigPBP2, from the antennal cDNA of S. exigua by reverse transcriptase-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends-PCR (RACE-PCR). The deduced PBP amino acid sequences are characteristic of the odorant binding protein (OBP) family, although the two PBPs are only 44% identical. From an analysis of the genomic DNA, two introns and a similar intron/extron structural pattern were identified in each of the two PBP genes. RT-PCR analysis revealed that the two PBP genes are only expressed in antennae. Real-time PCR further indicated that the expression of SexigPBP1 is much higher than that of SexigPBP2, regardless of sex. However, the female expression levels for SexigPBP1 and SexigPBP2 are about 39% and 73%, respectively, relative to male levels. Finally, phylogenetic analysis suggested that PBPs from the Noctuidae are divided into three distinct groups based on the primary sequences.