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Combined organic and inorganic fertilization can improve soil fertility in coal mine reclamation areas. However, the contribution of the bacterial community (especially its occurrence patterns) to soil physicochemical properties and enzyme activity needs further evaluation. The objective of this research was to clarify the bacterial community diversity, composition, and intraspecific interactions in response to combined organic and inorganic fertilizer application in coal mine reclamation areas in the Loess Hilly Region, China. Maize rhizosphere soil samples were collected under four fertilization regimes (CK, no fertilization control; NPK, compound inorganic fertilizer; M, organic fertilizer; and NPKM, combined organic and inorganic fertilization) in a 10-year field experiment in Gujiao city, Shanxi Province. Bacterial communities were characterized using high-throughput sequencing of the 16S rRNA gene V3–V4 region. A cross-treatment Spearman correlation network was constructed to explore the bacterial co-occurrence patterns. Compared with CK, NPK, M, and NPKM decreased the pH by 0.59%, 2.27%, and 0.12%; increased the soil organic carbon by 11.25%, 11.69%, and 27.05%; and significantly decreased the bacterial Shannon diversity by 3.68%, 0.14%, and 3.54%, respectively. Compared with CK, NPKM significantly increased sucrase, urease, and alkaline phosphatase activities (p < 0.05). Critically, oligotrophic Acidobacteria were significantly more abundant in CK than in the other treatments. Gemmatimonadetes were more abundant in NPK and M, and Actinobacteria, Bacteroidota, and Patescibacteria were more abundant in NPKM. In addition, network analysis revealed that the keystone taxa in the different fertilization treatments belonged to different network modules and were significantly correlated with soil nutrient content and enzyme activity. Simultaneously, the Actinobacteria enriched in NPKM formed specific clusters through strong symbiosis, and there were significant positive correlations among sucrase, urease, and alkaline phosphatase. In summary, long-term combined organic and inorganic fertilization improved maize rhizosphere soil fertility by regulating enzyme activity, bacterial community composition, and bacterial species interactions in coal mine reclamation areas in the Loess Hilly Region. [ABSTRACT FROM AUTHOR]

The application of manure (M) and straw (S) will increase the Olsen P and phosphorus activation coefficient (PAC) in soil. Clarifying the increasing trend of Olsen P and PAC is crucial for rational fertilization. This study fitted the equation between the accumulated P surplus, Olsen P, and PAC in four treatments for 28 years and analyzed the changes and rates of P fractions. The results showed Olsen P and PAC increase linearly with NPK and NPKS treatments; for every 100 kg ha−1 of P surplus, Olsen P increased by 5.9 and 6.7 mg kg−1, and PAC increased by 0.52% and 0.50%. With M and MNPK treatments, the sigmoid curve equation was the best fitting method. The equilibrium values were 167 and 164 mg kg−1 for Olsen P, and 10.4 and 10.2 mg kg−1 for PAC. There was a correlation between Al-P, Ca2-P, Resin-P, NaOH-Pi, C/N, SOC, and pH, which had the highest interpretation rates for Olsen P and PAC. Manure is significantly better than straw in improving Olsen P in red soil. It is recommended to reduce the amount of manure applied for a long time to avoid a zero increase in Olsen P. [ABSTRACT FROM AUTHOR]

Chickpea is an important leguminous crop that improves soil fertility through atmospheric nitrogen fixation with the help of rhizobia present in nodules. Non-rhizobia endophytes are also capable of inducing nodulation and nitrogen fixation in leguminous crops. The aim of the current study was to isolate, characterize and identify the non-rhizobia endophytic bacterial strains from root nodules of chickpea. For this purpose, more than one hundred isolates were isolated from chickpea root nodules under aseptic conditions and were confirmed as endophytes through re-isolating them from root nodules of chickpea after their inoculation. Nineteen confirmed endophytic bacterial strains revealed significant production of indole acetic acid (IAA) both in presence and absence of L-tryptophan and showed their ability to grow under salt, pH and heavy metal stresses. These strains were evaluated for in vitro plant growth promoting (PGP) traits and results revealed that seven strains showed solubilization of P and colloidal chitin along with possessing catalase, oxidase, urease and chitinase activities. Seven P-solubilizing strains were further evaluated in a jar trial to explore their potential for promoting plant growth and induction of nodulation in chickpea roots. Two endophytic strains identified as Paenibacillus polymyxa ANM59 and Paenibacillus sp. ANM76 through partial sequencing of the 16S rRNA gene showed the maximum potential during in vitro PGP activities and improved plant growth and nodulation in chickpea under the jar trial. Use of these endophytic strains as a potential biofertilizer can help to reduce the dependence on chemical fertilizers while improving crop growth and soil health simultaneously.

Chickpea is an important leguminous crop that improves soil fertility through atmospheric nitrogen fixation with the help of rhizobia present in nodules. Non-rhizobia endophytes are also capable of inducing nodulation and nitrogen fixation in leguminous crops. The aim of the current study was to isolate, characterize and identify the non-rhizobia endophytic bacterial strains from root nodules of chickpea. For this purpose, more than one hundred isolates were isolated from chickpea root nodules under aseptic conditions and were confirmed as endophytes through re-isolating them from root nodules of chickpea after their inoculation. Nineteen confirmed endophytic bacterial strains revealed significant production of indole acetic acid (IAA) both in presence and absence of L-tryptophan and showed their ability to grow under salt, pH and heavy metal stresses. These strains were evaluated for in vitro plant growth promoting (PGP) traits and results revealed that seven strains showed solubilization of P and colloidal chitin along with possessing catalase, oxidase, urease and chitinase activities. Seven P-solubilizing strains were further evaluated in a jar trial to explore their potential for promoting plant growth and induction of nodulation in chickpea roots. Two endophytic strains identified as Paenibacillus polymyxa ANM59 and Paenibacillus sp. ANM76 through partial sequencing of the 16S rRNA gene showed the maximum potential during in vitro PGP activities and improved plant growth and nodulation in chickpea under the jar trial. Use of these endophytic strains as a potential biofertilizer can help to reduce the dependence on chemical fertilizers while improving crop growth and soil health simultaneously. [ABSTRACT FROM AUTHOR]