[Effects of Organic Fertilizer Combined with Biochar on Denitrifying Microorganisms and Enzyme Activities in Orchard Soil].

To study the effects of organic fertilizer combined with biochar on soil denitrification and denitrifying microbial community structure, this study took lemon orchard soil as the research object and adopted a pot experiment, setting up five fertilization treatments:no fertilization(CK), conventional fertilization(F), organic fertilizer(P), fertilizer+biochar(FP), and organic fertilizer+biochar(PP). The abundance and community structure of denitrifying microorganisms were studied using real-time quantitative PCR and T-RFLP. Redundancy analysis(RDA) was used to explore the environmental factors affecting the denitrifying microbial community structure, and PLS-PM analysis was used to explore the environmental factors affecting the denitrification potential of lemon orchard soil. The results showed as follows:① compared with that under the single fertilizer treatment(F), the organic fertilizer and biochar(P, FP, and PP) treatments significantly increased the denitrification potential of the soil, ranging from 147.8% to 1445.3%. The denitrification rate of soil treated with organic fertilizer combined with biochar was 23.8% lower than that treated with organic fertilizer alone. ② Compared with that in the CK treatment, fertilization treatment significantly increased the abundance of nirS and nirK denitrification microorganisms. Fertilizer treatments(F and FP) significantly reduced the abundance of nosZ denitrifying microorganisms. Biochar treatment significantly changed the diversity and uniformity of denitrifying microorganisms, but the specific law and mechanism quality remained unclear. ③ The results of RDA analysis showed that fertilization could affect the community structure of nirS, nirK, and nosZ denitrifying microorganisms by changing C/N, WC, NO3--N, SOC, AK, and AP. ④ PLS-PM analysis showed that soil denitrification was positively correlated with pH and the abundance of nirK denitrification microorganisms, and NO3--N indirectly affected soil denitrification by affecting the abundance of nirK denitrification microorganisms. In addition, the nirK microbial community was the dominant microbial community in soil denitrification in lemon orchards. In conclusion, organic fertilizer directly affected soil denitrification by regulating soil pH, whereas regulating NO3--N content affected nirK denitrification microbial abundance, indirectly affecting soil denitrification. The application of organic fertilizer combined with biochar could slow down the improvement of soil denitrification caused by single application of organic fertilizer, which is more suitable for promotion in orchards in this region.

[Effects of Chemical Fertilizer Reduction Combined with Organic Fertilizer Application on Bacterial Community Structure in Rhizosphere/Non-Rhizosphere Soil of Lemon].

The aim of this study was to examine the effects of different fertilization methods on the physicochemical properties and bacterial community structure of lemon rhizosphere/non-rhizosphere soil in order to provide theoretical basis for scientific and rational fertilization of orchards. A pot experiment was carried out, and six fertilization treatments were set up:control (CK), conventional fertilization (FM), organic fertilizer (P), fresh organic fertilizer (NP), 70% chemical fertilizer+30% organic fertilizer (70FP), and 50% chemical fertilizer+50% organic fertilizer (50FP). Chemical analysis, real-time fluorescence quantitative PCR, and terminal restriction fragment length polymorphism (T-RFLP) were used to study the effects of different fertilization treatments on the physicochemical properties of rhizosphere and non-rhizosphere soils, the abundance of the bacterial 16S rRNA gene, and bacterial community structure. Redundancy analysis (RDA) was used to explore the environmental factors affecting the bacterial community structure of lemon rhizosphere/non-rhizosphere soil. The results showed the following:① the pH and contents of organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, and nitrate nitrogen in rhizosphere/non-rhizosphere soil were significantly increased by reducing the amount of chemical fertilizer and applying organic fertilizer (50FP and 70FP) (P<0.05). Compared with conventional fertilization (FM) and single application of organic fertilizer (P and NP), the soil available P content, available K content, and nitrate nitrogen content increased by 24.76%-97.98%, 6.87%-45.11%, and 18.42%-55.82%, respectively. ② Fertilizer reduction combined with organic fertilizer significantly increased the abundance of soil bacteria and soil respiration intensity (P<0.05), and the abundance of soil rhizosphere bacteria and soil respiration intensity under the 50FP treatment increased by 15.83%-232.98% and 8.0%-162.5% compared with that under conventional fertilization and organic fertilizer alone, respectively. The bacterial abundance of rhizosphere soil was positively correlated with the pH and contents of organic matter, total nitrogen, and total phosphorus. ③ The PCoA and RDA analysis results showed that the single organic fertilizer and organic fertilizer and chemical fertilizer de-weighting of rhizosphere bacterial community structure and not adding fertilizer had a bigger difference between processing, and the main environmental factors influencing the rhizosphere/non rhizosphere bacterial community structure were organic matter, total nitrogen, total phosphorus, total potassium, alkali solution nitrogen, nitrate nitrogen, and available potassium. Fertilizer reduction combined with organic fertilizer could significantly increase soil nutrient content, increase soil bacterial abundance, and change the bacterial community structure of rhizosphere soil, and the 50FP treatment yielded better results. Therefore, 50% Chemical fertilizer+50% organic fertilizer (50FP) was a better fertilization method to improve the physical and chemical properties of orchard soil, increase the abundance of soil bacteria, and improve the soil respiration intensity.