Jichen Wang

Wheat and Rice Growth Stages and Fertilization Regimes Alter Soil Bacterial Community Structure, But Not Diversity.

Maintaining soil fertility and the microbial communities that determine fertility is critical to sustainable agricultural strategies, and the use of different organic fertilizer (OF) regimes represents an important practice in attempts to preserve soil quality. However, little is known about the dynamic response of bacterial communities to fertilization regimes across crop growth stages. In this study, we examined microbial community structure and diversity across eight representative growth stages of wheat-rice rotation under four different fertilization treatments: no nitrogen fertilizer (NNF), chemical fertilizer (CF), organic–inorganic mixed fertilizer (OIMF), and OF. Quantitative PCR (QPCR) and high-throughput sequencing of bacterial 16S rRNA gene fragments revealed that growth stage as the best predictor of bacterial community abundance and structure. Additionally, bacterial community compositions differed between wheat and rice rotations. Relative to soils under wheat rotation, soils under rice rotation contained higher relative abundances (RA) of anaerobic and mesophilic microbes and lower RA of aerophilic microbes. With respect to fertilization regime, NNF plots had a higher abundance of nitrogen–fixing Cyanobacteria. OIMF had a lower abundance of ammonia-oxidizing Thaumarchaeota compared with CF. Application of chemical fertilizers (CF and OIMF treatments) significantly increased the abundance of some generally oligotrophic bacteria such those belonging to the Acidobacteria, while more copiotrophic of the phylum Proteobacteria increased with OF application. A high correlation coefficient was found when comparing RA of Acidobacteria based upon QPCR vs. sequence analysis, yet poor correlations were found for the α- and β- Proteobacteria, highlighting the caution required when interpreting these molecular data. In total, crop, fertilization scheme and plant developmental stage all influenced soil microbial community structure, but not total levels of alpha diversity.

Profiling of soil volatile organic compounds after long-term application of inorganic, organic and organic-inorganic mixed fertilizers and their effect on plant growth

The complexity of soil processes involved in the production, consumption and accumulation of volatile organic compounds (VOCs) makes hard to access the overall dynamics of VOCs in the soil. In this study, the field soil, applied with inorganic (CF), organic (OF) and inorganic-organic mixed (CFOF) fertilizers for ten years was evaluated for the emission of VOCs at different temperature and moisture levels. We identified 30-50 soil emitted VOCs representing the most common soil VOCs groups by using the solid-phase microextraction (SPME) fiber and gas chromatography-mass spectroscopy. The highest total emission of VOCs was found in OF treatment, but it was non-significantly different with CF treatment. The emission of VOCs was significantly increased with the decrease in moisture contents and increase in the temperature of the soil. Among different fertilizer treatments, the emission of VOCs was significantly higher in OF treatment at 5% moisture, and in CF and OF treatments at 35°C. Further, the VOCs emitted from soil treated with CFOF showed the highest increase in plant growth while CF and OF treatments showed similar results. The VOCs were also extracted from the soil using methanol to better understand the dynamics of VOCs. The abundance of VOCs extracted from the soil was 44-61%, while the richness was 65-70% higher than the VOCs emitted from the soil in different treatments. Taken together the results of emitted and extracted VOCs from the soil, we conclude that the fertilizers are able to discriminate among the VOC patterns of soil. In addition, most of the VOCs are retained in the soil and the emission of VOCs from soil depends on the type of VOCs, soil properties and environmental conditions; however, more research is required to find out better soil VOCs analysis methods.

Dynamic Response of Ammonia-Oxidizers to Four Fertilization Regimes across a Wheat-Rice Rotation System

Ammonia oxidation by microorganisms is a rate-limiting step of the nitrification process and determines the efficiency of fertilizer utilized by crops. Little is known about the dynamic response of ammonia-oxidizers to different fertilization regimes in a wheat-rice rotation system. Here, we examined ammonia-oxidizing bacteria (AOB) and archaea (AOA) communities across eight representative stages of wheat and rice growth and under four fertilization regimes: no nitrogen fertilization (NNF), chemical fertilization (CF), organic-inorganic mixed fertilizer (OIMF) and organic fertilization (OF). The abundance and composition of ammonia oxidizers were analyzed using quantitative PCR (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) of their amoA genes. Results showed that fertilization but not plant growth stages was the best predictor of soil AOB community abundance and composition. Soils fertilized with more urea-N had higher AOB abundance, while organic-N input showed little effect on AOB abundance. 109 bp T-RF (Nitrosospira Cluster 3b) and 280 bp T-RF (Nitrosospira Cluster 3c) dominated the AOB communities with opposing responses to fertilization regimes. Although the abundance and composition of the AOA community was significantly impacted by fertilization and plant growth stage, it differed from the AOB community in that there was no particular trend. In addition, across the whole wheat-rice rotation stages, results of multiple stepwise linear regression revealed that AOB played a more important role in ammonia oxidizing process than AOA. This study provided insight into the dynamic effects of fertilization strategies on the abundance and composition of ammonia-oxidizers communities, and also offered insights into the potential of managing nitrogen for sustainable agricultural productivity with respect to soil ammonia-oxidizers.

Grafting Resulted in a Distinct Proteomic Profile of Watermelon Root Exudates Relative to the Un-Grafted Watermelon and the Rootstock Plant

Abstract Grafting is commonly used to relieve damage caused by soil-borne diseases and to enhance the nutrient uptake in watermelon plants. Certain reports have shown the proteomic changes of plant tissues involved in grafting, while little information about the secretome after watermelon grafting is available. To gain insight into the root-secreted protein profile, root exudates of three types of seedlings (own-root watermelon (W), grafted-root watermelon (WB) and own-root bottle gourd (B)) were collected under hydroponic conditions, desalted and concentrated using Amicon ultracentrifugal filter devices, and separated by one-dimensional SDS–PAGE. Principal component analysis revealed that the protein profile was distinctly altered after grafting, and the diversity of root-secreted proteins of WB was significantly higher than that of W and B. Moreover, analysis by LC-QTOF/MS/MS revealed that some proteins associated with biotic and abiotic stress resistance appeared in response to grafting, such as disease resistance protein At4g27190, callose synthase, HVA22, and Clp protease. These results indicate that grafting can shift the root-secreted protein profile and thus could increase stress resistance. This study would help to reveal the mechanisms of disease resistance and growth promotion achieved through grafting.

Plant growth stages and fertilization regimes drive soil fungal community compositions in a wheat-rice rotation system

Fungal communities may have different response to fertilization under different conditions. Therefore, it is necessary to reveal the effects of fertilizations on fungal communities considering temporal heterogeneity at different crop stages. To address this, soil samples were collected across eight typical plant growth stages of a wheat-rice rotation system under four fertilization regimes: no nitrogen fertilizer (NNF), chemical fertilizer (CF), organic-inorganic mixed fertilizer (OIMF), and organic fertilizer (OF). Soil temperature and moisture that co-vary with plant growth stages were the strongest predictors of fungal community compositions; meanwhile, fertilization regimes also played important roles. Shannon index and the relative abundance of Ascomycota were consistently increased when compared OF treatment with CF and OIMF treatments, while CF treatment had a higher relative abundance of Zygomycota when compared with NNF and OF treatments. For the functional guilds, application of urea-nitrogen fertilizers (CF and OIMF treatments) significantly decreased the relative abundance of saprotrophs and symbiotrophs, while soil treated with OF had less relative abundance of pathotrophs when compared to inorganic fertilizers. Our study provided a detailed picture of how fungal community composition responded to fertilization regimes across different plant growth stages.