[Functional Genomics Analysis of Nitrogen and Phosphorus Transformation in Maize Rhizosphere Microorganisms].

Fertilizer reduction and efficiency improvement is an important basis for ensuring the safety of the agricultural ecological environment. Microorganisms are the key driving force for regulating the soil nitrogen and phosphorus cycle. Studying the nitrogen and phosphorus transformation function of rhizosphere microorganisms can provide a microbiological regulation approach for further improving the use efficiency of soil nitrogen and phosphorus. Based on the field micro-plot experiments of three typical farmland soils(phaeozem, cambisol, and acrisol), metagenomic sequencing technology was used to study the differences in functional genes and regulatory factors of maize rhizosphere microorganisms during soil nitrogen and phosphorus transformation. The results showed that the functional diversity of maize rhizosphere microorganisms was affected by soil type. The functional diversity of rhizosphere microorganisms in phaeozem and cambisol was mainly affected by water content and nutrient content, and that in acrisol was affected by total phosphorus(TP) and available phosphorus(AP). For soil nitrogen transformation, the gene abundance of related enzymes in the pathway of nitrogen transformation was the highest in the urease gene(ureC) and glucose dehydrogenase gene(gdh), which were 7.25×10-5-12.88×10-5 and 4.47×10-5-7.49×10-5, respectively. The total abundance of assimilatory nitrate reduction functional genes in acrisol was higher than that in phaeozem and cambisol, and the total abundance of functional genes related to other processes was the highest in cambisol. The abundance of functional genes encoding enzymes related to nitrogen metabolism was mainly driven by soil bacterial richness, total potassium(TK), and TP. For soil phosphorus transformation, the number of alkaline phosphatase genes(phoD) catalyzing organic phosphorus mineralization was 1093, and the number of acid phosphatase genes(PHO) was 42. The abundance of phoD was two orders of magnitude higher than that of PHO. In addition, fertilization had no significant effect on the abundance of phoD and PHO in the same soil type. Random forest analysis showed that the abundances of phoD and PHO were significantly affected by soil moisture, organic matter(OM), and total nitrogen(TN), but AP content had the greatest impact on PHO abundance. These results clarified the nitrogen and phosphorus transformation characteristics of maize rhizosphere microorganisms at the functional genomic level and enriched the molecular biological mechanism of the microbial nitrogen and phosphorus transformation function.

[Interactions of Fungi Community and Relationship with the Carbon Structure in Arable Mollisols with Gradient Organic Matter Content].

Fungi play an important role in the accumulation and transformation of soil organic matter (SOM) and nutrient cycling. To investigate the relationship between the fungal community and soil organic carbon functional groups under gradient SOM contents in arable mollisols, arable mollisols with 2%-9% SOM content were collected in Northeast China. Solid-state 13C-NMR technology was used to explore the differences in the functional group structure of SOM, and ITS high-throughput sequencing was used to investigate the fungal community structure. The potential interactions between different taxonomic groups of soil fungal community and their associations with organic carbon molecular structures were compared by constructing molecular ecological networks under low SOM (2%-5%) and high SOM (7%-9%) conditions. The 13C-NMR results indicated an increase in the relative abundance of Alkyl C (25.8% to 35.9%). The decrease in Alkyl C/O-Alkyl C indicated a smaller degree of decomposition in high SOM soils. Sordariomycetes and Mortierellomycotina dominated the fungal community and their relative abundance increased with the SOM gradient (P<0.05) from 14.33% to 28.17% and from 7.32% to 23.14%, respectively. The network analysis showed simpler ecological topological properties of the fungal community in low SOM soils, with lower numbers of nodes, edges, and average clustering coefficients than those in high SOM soils. A closer relationship between fungi and organic carbon functional groups, especially LOC, was observed in low SOM soils. The random forest model showed that LOC had the largest amount for fungal interactions in low SOM soils (10%), followed by recalcitrant organic carbon (ROC). In comparison, LOC contributed less to the variations in fungal interactions in high SOM soils (7.4%). With globally increasing soil carbon loss, the limition of the carbon resources, especially the reduction of LOC, may reduce the stability and ecological functions of soil fungal communities.