Abstract
Availability of nitrogen (N) in soil changes the composition and activities of microbial community, which is critical for the processing of soil organic matter and health of crop plants. Inappropriate application of N fertilizer can alter the rhizosphere microbial community and disturb the soil N homeostasis. The goal of this study was to assess the effect of different ratio of N fertilizer at various early to late growth stages of rice, while keeping the total N supply constant on rice growth performance, microbial community structure, and soil protein expression in rice rhizosphere. Two different N regimes were applied, i.e., traditional N application (NT) consists of three sessions including 60, 30 and 10% at pre-transplanting, tillering and panicle initiation stages, respectively, while efficient N application (NF) comprises of four sessions, i.e., 30, 30, 30, and 10%), where the fourth session was extended to anthesis stage. Soil metaproteomics combined with Terminal Restriction Fragment Length Polymorphism (T-RFLP) were used to determine the rhizosphere biological process. Under NF application, soil enzymes, nitrogen utilization efficiency and rice yield were significantly higher compared to NT application. T-RFLP and qPCR analysis revealed differences in rice rhizosphere bacterial diversity and structure. NF significantly decreased the specific microbes related to denitrification, but opposite result was observed for bacteria associated with nitrification. Furthermore, soil metaproteomics analysis showed that 88.28% of the soil proteins were derived from microbes, 5.74% from plants, and 6.25% from fauna. Specifically, most of the identified microbial proteins were involved in carbohydrate, amino acid and protein metabolisms. Our experiments revealed that NF positively regulates the functioning of the rhizosphere ecosystem and further enabled us to put new insight into microbial communities and soil protein expression in rice rhizosphere.
Highlights
Rice is the staple food for more than half of the world’s population (Xing and Zhang, 2010)
We investigated the effects of N application in four sessions (NF) on (i) soil N availability, uptake and percent nitrogen use efficiency (% Nitrogen Use Efficiency (NUE)), enzymatic activity and crop productivity; (ii) the associated microbial diversity using terminal restriction fragment length polymorphism (T-RFLP); and (iii) the protein profile of the nitrogen application (NT) and nitrogen in four sessions (NF) rhizospheric soils at late growing stage of rice through metaproteomics
Our study provides evidence that the application of nitrogen in four sessions (NF) was able to improve the physiological status of rice, especially at late growing stage, indicating higher leaf chlorophyll contents, increased NUE along with rice productivity in the NF treatment
Summary
Rice is the staple food for more than half of the world’s population (Xing and Zhang, 2010). Researchers have succeeded to increase the crop yield by developing improved rice varieties through molecular breeding, but the efforts are continued to further enhance the yield traits of rice genotypes in order to meet the growing demand for food (Kato et al, 2007; Xing and Zhang, 2010). For improving Nitrogen Use Efficiency (NUE) of crops and reducing off-field losses, it is pertinent to understand the molecular mechanisms accountable for N homeostasis in intensively N fertilized agriculture system. Estimation and monitoring of the N2O or N2 emission in rice paddy field is technically difficult, expression analysis of the catabolic genes regulating biological denitrification and production of N2O and N2 could be useful biomarkers for the determination of N loss in the system (Morales et al, 2010; Bouskill et al, 2012)
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