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. 2020 Mar 10;10(4):164. doi: 10.1007/s13205-020-2099-4

Exogenous phosphorus-solubilizing bacteria changed the rhizosphere microbial community indirectly

Jun Liu 1, Wenyu Qi 1, Qiang Li 2,3,✉, Shu-Guang Wang 1,✉, Chao Song 1, Xian-zheng Yuan 1
PMCID: PMC7064692  PMID: 32206498

Abstract

Phosphate-solubilizing bacteria (PSB) have been widely used as biological fertilizer. However, its impact on the local microbial community has less been known. In this study, a mixture of PSB was inoculated into the tomato growth alone or combined with manure fertilizer. The growth parameter results showed that the combination use of PSB and compost could significantly increase the tomato growth and yield. The use of PSB could significantly increase pH, available phosphorus and several kinds of trace elements both in the rhizosphere and non-rhizosphere soil. The quantitative PCR and high-throughput sequencing results showed that the inoculated PSB did not become the dominant strains in the rhizosphere. However, the soil bacterial community structure was changed. The relative abundance of several indigenous bacteria, such as Pseudomonas, decreased, while the population of several bacteria, including Bacillus, Anaerolineaceae, Cytophagaceae, and Gemmationadaceae, increased. The redundancy analysis result showed that the soil properties had a great influence on the indigenous microbial community. In conclusion, the inoculated PSB could not colonize in the soil with a single inoculation. The PSB secreted small molecular organic acids to dissolve inorganic phosphorus and changed the soil properties, which changed the rhizosphere microbial community indirectly.

Electronic supplementary material

The online version of this article (10.1007/s13205-020-2099-4) contains supplementary material, which is available to authorized users.

Keywords: Phosphate-solubilizing bacteria, Rhizosphere, Microbial community, Soil

Introduction

Phosphorus is one of the major essential macronutrients for crop growth. It plays important roles in most plant metabolic processes. Generally, total phosphorus is about 0.02–0.5% (w/w) in the soil (Ferandez et al. 2007; Lian et al. 2019). Most of this exists or presents in an insoluble form, which cannot be absorbed by plants. Only 0.1% of the total phosphorus in natural soil is available for plant uptake (Zou et al. 1992; Wiens et al. 2019). That makes phosphorus a major limiting factor for plant growth in agricultural systems. However, plants usually have poor uptake for phosphate because phosphate anions (H2PO4−, HPO42−) in traditional phosphate fertilizer can rapidly form metal complexes with Ca2+, Fe3+, or Al3+ in soil (Qureshi et al. 2012). So traditional phosphate fertilizers are often less effective. Therefore, it is necessary to develop an economical and eco-friendly technology to improve the availability of phosphorus in soil.

Several bacterial species, particularly rhizosphere-colonizing bacteria, can solubilize insoluble inorganic phosphate and/or break down organic phosphorus into soluble phosphate (Li et al. 2015; Hanif et al. 2015). Current research suggests that the inoculation of phosphate-solubilizing bacteria (PSB) into crops has the potential to reduce the application rates of phosphate fertilizer by 50% without significantly reducing the crop yield (Jilani et al. 2007; Rady et al. 2019). The most generally accepted mechanism for PSB to solubilize mineral phosphorus is the production of organic acid with low molecular weight (Illmer et al. 1995; Delvasto et al. 2006). Low molecular weight organic acids can lower the soil pH, chelate the cations bound to the phosphate anions, or compete with phosphate for adsorption sites, by which the mineralized phosphorus can be released (Khan et al. 2009; Mander et al. 2012). Low molecular weight organic acids may also play an important role in the detoxification of pollutants, the bioavailability of heavy metals, and even microbial activity in soil conditions (Onireti et al. 2017).

Soil microbes are an essential component of terrestrial ecosystems and play key roles in many vital ecosystem functions (Panke-Buisse et al. 2015). They play an important role in plant productivity, especially in the agricultural system. A variety of microorganisms can form symbiotic relationships with plants by supplying limited nutrients to them. Among them, nitrogen-fixing bacteria (Rosenblueth et al. 2018), arbuscular mycorrhizal fungi (Valyi et al. 2016), and ectomycorrhizal fungi are representative (Martin et al. 2016). The indigenous and native microbes have some key tolerance mechanisms/pathways which help the plant against abiotic stressors such as drought (Guerena et al. 2019), extreme temperature (Liu et al. 2019), soil salinity (Ben Laouane et al. 2019), acidity (Tullio et al. 2019), alkalinity (Abd-Alla et al. 2014), and heavy metals (Benjelloun et al. 2019). Several kinds of bacteria, such as Pseudomonas spp. (Weller et al. 2002), can produce antifungal metabolites to protect several major agricultural crops against diseases.

Several current studies have been focusing on the effects of PSB addition to the indigenous soil. The PSB can increase the phosphorous uptake and improve the plant yield both in pot experiments and under field conditions (Hong-yuan et al. 2015; Rasul et al. 2019). Several kinds of PSB show the ability to produce gluconic acid and indole acetic acid to display beneficial plant growth promotion effects (Otieno et al. 2015; Mehta et al. 2015). Some PSB also demonstrate potential as biocontrol agents against some plant pathogens (Rasul et al. 2019). Although PSB have been widely studied and applied, few researches considered PSB as invaders to the indigenous soil microbes. The impact of PSB on the indigenous microbial community has less been known, which limits the further usage of PSB.

To assess the influence of PSB inoculation on the indigenous soil microbial community, a mixture of PSB was inoculated into the tomato growth alone or combined with manure fertilizer. The growth parameters of tomato were observed to evaluate the application effect of PSB. The soil samples from rhizosphere and non-rhizosphere soil were collected. The physical and chemical properties of soil samples were analyzed. With quantitative PCR and high-throughput sequencing, the abundance and community structure of the rhizosphere and non-rhizosphere soil were monitored.

Materials and methods

Preparation of phosphate-solubilizing inoculant

A combination of three PSBs was used in this study. The enriched PSBs were obtained from different soil samples by the National Botanical Research Institute's phosphate growth medium (NBRIP) broth (Nautiyal 1999). The phosphorus dissolution ability and the taxonomic place of the PSBs are shown in S1 and Fig. S1. The PSB cultural media was cultivated for 3 days at 37 °C until the population up to 109 CFU/mL−1. The culture media was washed by deionized water three times. The final population of PSB inoculums after resuspension was 108 CFU/mL−1.

Experimental design and soil sampling

The tomato plants were grown in the greenhouse condition (day temperature, 26–30 °C; night temperature, 18–20 °C; photoperiod, 14-h light:10-h dark). The compost made by the farmland was used in this study. Three treatments were established in a randomized block design: (1) compost control (M), in which 1000 kg ha−1 compost was applied as the former plant seasons; (2) PSB inoculums (B), in which 100 kg ha−1 PSB bacterial fertilizer was applied; (3) compost-bacterial fertilizer (MB), in which the manure and bacterial fertilizer were applied together. All the fertilizers were applied as basal fertilizers before seeding of the tomato plants.

The rhizosphere and non-rhizosphere soil samples were collected at the first harvest. A spade was used to take out plants from soil. The soil loosely attached to the plant roots was gently shaken down and collected as the non-rhizosphere soil. The plant roots were vigorously vortexed in ddH2O to separate the soils tightly associated with roots. The separated soil solution was centrifuged at 8000 rpm for 10 min to collect rhizosphere soil. The collected soil from the three experimental groups was stored at − 80 °C for the future analysis. The soil sample in the same field was also collected as the untreated sample at the same time.

Tomato growth parameters

The plant height, root activity, and photosynthetic rate were measured at the first harvest. Plant height was measured from stem base to top. 100 plants of each experiment were measured. The root activity was measured by the tripheyetetrazolium chloride (TTC) method (Ruf and Brunner 2003). The photosynthesis rate was measured in the morning with a portable photosynthesis system (Li-6400XT, LI-COR Inc., Lincoln, NE). The yield of tomato was counted when the planting season was over.

Soil property analysis

The soil samples were shook with a soil to water ratio of 1:2.5 for 1 h, and then static settled. The supernatants were used for determining soil pH and conductivity. Soil organic carbon was determined using the K2Cr2O7 oxidation spectrophotometric method. The automatic Kjeldahl method (Varley 1966) was used for total nitrogen estimation. Soil ammonium and nitrate was extracted with 1 M KCl solution at a soil to water ratio of 1:4 for 1 h and quantified using the spectrophotometric methods. Soil available phosphorus was extracted with 0.5 M NaHCO3 solution and then measured by the ammonium molybdate spectrophotometric method. Soil available potassium was extracted with ammonium acetate and measured using a flame atomic absorption spectrophotometer. Soil available trace elements were extracted by diethylenetriaminepentaacetic acid and measured using an atomic absorption spectrophotometer.

DNA extraction

The total soil DNA of each sample was extracted from 0.25 g fresh soil with a TIANamp Soil DNA Kit (TIANGEN Biotech, Beijing, China) following the manufacturer’s instructions. The quantity and quality of DNA extracts were assayed using a Nanodrop One UV–VIS Spectrophotometer (Thermo Fisher Scientific, Wilmington, DE, USA). The DNA extracts were stored at − 80 °C for future analyses.

Detection of total bacteria in soil

The abundances of total bacteria were quantified by absolute quantification of 16S rRNA gene copies using quantitative PCR (QPCR) method. The qPCR experiment in this research followed the protocol used in the previous research of Guo et al. (2017). Bacterial 16S rRNA primers used in this research were K90 (5′-GCGGTGGAGCATGTGGTTTA-3′) and K94 (5′-GATAAGGGTTGCGCTCGTTG-3′).

Bacterial 16S rRNA gene amplification and high-throughput sequencing

The PCR and high-throughput sequencing of 16S rRNA amplicons were carried out by Biozeron (Shanghai, China) using an Illumina MiSeq platform.

The V4–V5 region of the bacteria 16S ribosomal RNA gene was amplified by PCR using primers 515F 5′-barcode-GTGCCAGCMGCCGCGG)-3′ and 907R 5′-CCGTCAATTCMTTTRAGTTT-3′, where barcode is an eight-base sequence unique to each sample. Amplicons were then purified and quantified for the library generation. Then the amplicon library was paired end sequenced (2 × 300) according to the standard protocols.

Bioinformatics and statistical analysis

Raw fastq files were demultiplexed and quality-filtered using QIIME2 (version 2018.8). All reads were then clustered into Operational Taxonomy Units (OTUs) with 97% similarity with the chimeric sequences removed by the software. The OTUs were aligned against the SILVA database (SSU 115) using confidence threshold of 70% (Amato et al. 2013) to identify the taxonomy of each 16S rRNA sequences. The identified taxonomy of each OTU in the phylum and genus level is shown in Tables S2 and S3.

The alpha diversity indices including Chao1, ACE, Shannon and Simpson indices were calculated following the Vegan package in R. Redundancy analysis (RDA) was performed in dplyr package in R.

Results

Growth characteristics of tomatoes

The yield and plant growth characteristics were significantly different between the experimental groups (P < 0.05) (Fig. 1). The tomatoes grown using PSB inoculation and compost together gained the highest average yield, which was 3.47 kg per plant. The average plant height of the PSB group was 187.3 mm, which was not significantly different to that of the compost group (188.1 mm). But the combined group was significantly higher than the other two groups, which is 192.5 mm. The root activity of the PSB group was 84% that of the compost group. At the same time, the root activity of the combined group was 114% that of the compost group. The photosynthetic rate showed the same trend, the usage of PSB inoculation reduced the photosynthetic rate by 6.9%, while the combination increased by 4%.

Fig. 1.

Fig. 1

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The growth characteristics of tomatoes in all experimental groups

Soil properties

The pH of the experimental group varied from 7.32 to 7.42, while the pH of untreated soil was 7.08. The usage of compost and PSB inoculation significantly increased the soil pH and conductivity (P < 0.01) (Table 1). However, there was no significant difference in soil pH between the experimental groups. The conductivities of the rhizosphere and non-rhizosphere soil in the compost were 228.5 and 232.0 μs/cm3, while those in the combined group were 236.0 and 231.4 μs/cm3, respectively. The two experimental groups using compost did not show significant differences in their soil conductivity (P < 0.01). The conductivities of the rhizosphere and non-rhizosphere soil in the PSB group were 212.7 and 206.0 μs/cm3, which did not reach the levels of the compost and combined groups but were significantly higher than the untreated soil (142.8 μs/cm3). PSB inoculation did not change most of the major soil element concentrations, except that of soil available phosphorus. The available phosphorus concentration increased from 66.4 to 78.2 mg/kg in the non-rhizosphere soil after inoculation with PSB and increased to 94.1 mg/kg in non-rhizosphere soil when PSB was used in combination with compost. The combination of compost and PSB inoculation did not significantly affect most of the soil major element concentrations, except that of soil available phosphorus, which was higher than that of other groups.

Table 1.

The major physical and chemical characteristics of soil samples (means ± standard deviations, n = 3)

pH Conductivity
(us/cm3)		 NO3−-N
(mg/kg)		 NH4+-N
(mg/kg)		 Total N
(g/kg)		 Organic C
(g/kg)		 Available P
(mg/kg)		 Available K
(mg/kg)
U 7.08 ± 0.02a 142.81 ± 3.44a 54.65 ± 3.17a 3.12 ± 0.21a 0.73 ± 0.02a 10.3 ± 0.53a 66.4 ± 1.49a 103.19 ± 2.59a
M–R 7.43 ± 0.05c 228.5 ± 0.94c 66.66 ± 4.42c 6.67 ± 0.19d 1.26 ± 0.13c 28 ± 0.17bc 75.3 ± 2.22bc 126.49 ± 6.19b
M–NR 7.38 ± 0.04bc 232 ± 4.82c 64.97 ± 3.67c 6.5 ± 0.15d 1.26 ± 0.06c 28.7 ± 0.33bc 72.5 ± 2.17b 126.8 ± 3.64b
B–R 7.32 ± 0.02b 212.7 ± 4.35b 55.98 ± 4.03ab 4.42 ± 0.32b 0.85 ± 0.04ab 11.6 ± 0.16a 71.91 ± 0.86b 104.7 ± 3.85a
B–NR 7.36 ± 0.09bc 206 ± 5.96b 56.52 ± 4.65ab 5.57 ± 0.44c 0.92 ± 0.01b 11.3 ± 0.22a 78.2 ± 3.47c 102.6 ± 5.05a
MB–R 7.35 ± 0.06bc 236 ± 4.45c 68.78 ± 1.08c 6.58 ± 0.61d 1.4 ± 0.04d 27.3 ± 2.26b 93.19 ± 0.23d 133.7 ± 1.76b
MB–NR 7.08 ± 0.02a 142.81 ± 3.44a 54.65 ± 3.17a 3.12 ± 0.21a 0.73 ± 0.02a 10.3 ± 0.53a 66.4 ± 1.49a 103.19 ± 2.59a
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Letters indicate Tukey’s honest significant difference tests with p < 0.05 among treatments

There were low concentrations of Cu, Ca, and Mg in the soil in all groups (Table 2). The available Zn, Mn, and Fe concentrations showed no significant differences in the compost and untreated soil, and were 3.1, 1.2, and 4.3 mg/kg, respectively. However, PSB inoculation increased the availability for Zn, Mn, and Fe. The available concentration of these trace elements was increased to 4.1, 2.1, and 5.3 mg/kg in the non-rhizosphere soil, respectively. The combined usage of PSB inoculation and compost further increased the Zn, Mn, and Fe concentrations to 5.1, 2.7, and 6.0 mg/kg in the non-rhizosphere soil, respectively.

Table 2.

The concentration of trace elements in soil samples (means ± standard deviations, n = 3)

Available Zn
(mg/kg)		 Available Mn
(mg/kg)		 Available Fe
(mg/kg)		 Available Cu
(mg/kg)		 Available Ca
(mg/kg)		 Available Mg
(mg/kg)
U 3.1 ± 0.06a 1.2 ± 0.03a 4.3 ± 0.06c 0.1 ± 0.02a 0.2 ± 0.01a ND
M–R 3.4 ± 0.05ab 1.1 ± 0.05a 3.2 ± 0.01a 0.1 ± 0.01a 0.2 ± 0.01a ND
M–NR 3.5 ± 0.15b 1.2 ± 0.03a 3.8 ± 0.07b 0.1 ± 0.01a 0.2 ± 0.01a ND
B–R 4.2 ± 0.03c 2.1 ± 0.03b 5.3 ± 0.03d 0.1 ± 0.01a 0.2 ± 0.01a ND
B–NR 4.11 ± 0.13c 2.1 ± 0.09b 5.3 ± 0.1d 0.1 ± 0.01a 0.2 ± 0.01a ND
MB–R 5.1 ± 0.22d 2.7 ± 0.1c 6 ± 0.1e 0.1 ± 0.01a 0.2 ± 0.01a ND
MB–NR 3.1 ± 0.06a 1.2 ± 0.03a 4.3 ± 0.06c 0.1 ± 0.02a 0.2 ± 0.01a ND
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Letters indicate Tukey’s honest significant difference tests with p < 0.05 among treatments

There was little difference in all soil characteristics between the non-rhizosphere and rhizosphere soils. This indicated that the influence of plants was not significant.

Effects of PSB and manure on bacterial communities

There was no significant difference in soil microbial abundance among all the experimental groups, which was almost 1012 copies per gram of soil (Fig. 2). This indicated that the soil could only provide a limited living space for microorganisms.

Fig. 2.

Fig. 2

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The bacterial abundance in all soil samples. Bars represent standard deviations (n = 3)

Bacterial 16S rRNA genes were sequenced using the Illumina MiSeq platform. Quality and chimera filtration of the raw data produced a total of 215,591 high-quality sequencing reads from seven groups, with an average of 30,798 reads (ranging from 27,495 to 33,871) (Table 3). The read numbers, coverage, number of OTUs, and statistical estimates of species richness and diversity indexes from each sample at a genetic distance of 3% are presented in Table 3. Finally, at a 97% sequence identity, these high-quality sequences were clustered into 10,326 OTUs in total, and each library contains different phylogenetic OTUs ranging from 1782 to 2351.

Table 3.

The information and diversity index for Illumina sequencing

Sample ID Reads 0.97
OTU Ace Chao Coverage Shannon Simpson
B–NR 30,663 1888 2178 2167 0.987 6.31 0.0039
B–R 28,200 1846 2159 2148 0.985 6.18 0.0068
M–NR 27,495 1897 2169 2159 0.986 6.38 0.0043
M–R 33,871 1916 2200 2215 0.988 6.23 0.0052
MB–NR 30,179 2026 2369 2351 0.985 6.32 0.0047
MB–R 32,460 1998 2295 2283 0.987 6.28 0.0052
U 32,723 1455 1782 1814 0.988 4.46 0.1057
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The diversity and richness indices of all experimental groups were calculated to illustrate the complexity of each group (Table 3). The ACE and Chao indices were designed to quantify the species richness. The ACE index of untreated soil was 1782, while those of other experimental groups were significantly higher, ranging from 2159 to 2369. The Chao index showed the same trend, which ranged from 2148 to 2351, while in untreated soil it was 1814. The Shannon and Simpson indices were often used to quantify the diversity. The Shannon index ranged from to 4.46 to 6.38, that of the experimental soil samples was significantly higher than that of the untreated soil. The Simpson index of untreated soil was 0.1057, which was significantly higher than that of the experimental soils. The alpha diversity indexes showed that the usage of compost and PSB inoculation improved the soil microbial species richness and diversity.

OTUs were identified into 40 prokaryotic phyla from the 16S rRNA gene sequences. Among them, 14 phyla were identified at an abundance > 1% in at least one group. As shown in Figs. 3 and 4, the dominant phyla (relative abundance > 5% in at least one sample) in the seven groups were Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexis, Cyanobacteria, Firmicutes, Gemmatimonadetes and Proteobacteria. Overall, the dominant populations of original soil microorganisms (Proteobacteria) were digested, and the microbial populations of Bacteroides, Gemmatimonadetes, Acidobacteria, and Firmicutes were enriched. In total, 676 genera were detected in all seven groups. Among them, 43 genera were identified at an average abundance > 1% in at least one group. Genus level analysis showed that Arthrobacter spp., the main strain of PSB, did not become the dominant bacteria in soil, which showed that PSB inoculation could not directly change the soil microbial population structure. At the genus level, plant growth-promoting bacteria such as Bacillus were enriched, and pathogenic bacteria such as Pseudomonas were digested.

Fig. 3.

Fig. 3

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Relative abundance and hierarchical cluster analysis of all samples at phylum level

Fig. 4.

Fig. 4

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Bacterial community heat map analysis of all samples at genus level. Top 30 genera were selected, and the color intensity of scale indicates relative abundance of each OTU read

Linking soil properties with bacterial communities

The redundancy analysis (RDA) (Fig. 5) of the soil physical and chemical properties and soil microbial diversity showed that the soil physical and chemical factors had a significant positive impact on the soil microbial community structure. Among the soil properties, the pH has the strongest effect, followed by the conductivity and NH4+-N. the RDA indicated that the improvement of the soil physical and chemical conditions could effectively promote the change in the soil microbial population structure.

Fig. 5.

Fig. 5

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The redundancy analysis on the bacterial community with the characteristics of soil

Discussion

In this research, the stain Arthrobacter spp. was inoculated into soil as the exogenous phosphate-solubilizing bacteria. Sequencing results showed that Arthrobacter spp. did not successfully colonize in the soil. However, the content of available phosphorus in soil increased significantly, which indicated that Arthrobacter spp. had strong life activities in soil after inoculation. Several studies have indicated that the PSB can colonize and locally enrich on the root and/or in the rhizosphere soils. That local enrichment made the low-abundance bacteria have an important effect on plant growth.

In this research, strains of Arthrobacter spp. were inoculated into soil as exogenous PSB. The sequencing results showed that Arthrobacter spp. did not successfully colonize in the soil. However, the available phosphorus content in the soil increased significantly, which indicated that Arthrobacter spp. had strong life activities in soil after inoculation. Several studies have indicated that PSB can colonize and locally enrich the root and/or rhizosphere soil (Chabot et al. 1996; Ahmad et al. 2018; Rocio Suarez-Moreno et al. 2019). This local enrichment can allow low-abundance bacteria to have an important effect on plant growth (Dawson et al. 2017).

Increased soil trace element contents were also observed in this study. This indicated that Arthrobacter spp. secreted small molecular organic acids to dissolve inorganic phosphorus in the soil (Table S1), which was consistent with previous studies (Rózycki 1985; Sun et al. 2018). The combined application of Arthrobacter spp. and compost provided enough organic carbon sources for Arthrobacter spp., which promoted the life activities of PSB and further increased the available phosphorus content in the soil. This promoted the growth of the tested tomatoes, and ultimately increased their yield.

Previous studies (van Elsas et al. 2012) have shown that it is often difficult to obtain colonization of exogenous bacteria in in situ soil by a single inoculation. To improve the in situ colonization effect of exogenous PSB, in many studies, the bacteria were combined with biochar (Beheshti et al. 2017; Rafique et al. 2017). The use of biochar increases the application cost; however, whether the application effect decreases with time needs further experimental verification. In this study, the exogenous PSB alone failed to colonize in situ, but still improved the soil available phosphorus content and promoted crop growth. Therefore, the use of exogenous phosphorus-solubilizing bacteria alone may be one of multiple application schemes under different soil conditions.

In recent studies, many researchers have studied the efficiency of the application of phosphate bacteria in situ, but few of those studies focused on the soil community after the in situ use of PSB (Mehta et al. 2015; Bechtaoui et al. 2019; Rasul et al. 2019). Although exogenous Arthrobacter spp. did not successfully colonize into dominant bacteria, these bacteria did change the physical and chemical properties in the soil. Through the RDA (Fig. 5), it could be easily found that the microbial community was greatly influenced by the soil physical and chemical properties. In addition, PSB promoted plant growth. It may also have influenced the microbial community succession by plant root secretion.

The introduction of Arthrobacter spp. resulted in the decreased relative abundance of various heterotrophic microorganisms in local soil. Arthrobacter spp. might compete with the local microorganisms with similar niches, such as a carbon source and energy sources (Arrebola et al. 2019), according to the invasion model of exogenous microorganisms (Mallon et al. 2018). This competition may be responsible for the failure of Arthrobacter spp. to colonize in local soil. At the same time, the relative abundance of Bacillus sp., Anaerolineaceae sp., Cytophagaceae sp., Gemmationadaceae sp., and Nitrosomonadaceae sp. genera in the experimental group was increased. These bacteria have been reported to be associated with the decomposition of organic matter, such as cellulose (Liang et al. 2015; Aanderud et al. 2018), and soil nitrite nitrogen oxidation (Cheng et al. 2017). This indicated that the competitive release caused by Arthrobacter spp. drove the soil microbial population to exploit and utilize the part outside the niche occupied by Arthrobacter spp. The reproduction of these bacteria could further increase the content of soil elements and improve the diversity of soil microorganisms. Although the colonization of Arthrobacter spp. was not successful, its disturbance to the soil nutrition, microbial population, and niche had been preserved, and could affect the invasion of other exogenous bacteria in the future. Relevant studies (Filho-Lima et al. 2000; Alves et al. 2003; Velmourougane et al. 2017) have also confirmed that repeated introduction of biological fertilizers and probiotics can eventually lead to the successful local colonization of related exogenous microorganisms.

Conclusions

In conclusion, exogenous phosphorus-solubilizing bacteria did not form thermophilic bacteria in soil filling but altered the structure of the in situ bacterial community when used in combination with compost, which indirectly affected the structure of the in situ bacterial community. The change in plant metabolism caused by the change in the soil physical and chemical properties also affected the structure of the soil micro community, but its effect was weak.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Supplementary file1 (TIF 86 kb) (86.8KB, tif)
Supplementary file2 (TIF 342 kb) (342.7KB, tif)
Supplementary file3 (DOCX 18 kb) (18.7KB, docx)
Supplementary file4 (DOCX 12 kb) (12.9KB, docx)
Supplementary file5 (XLSX 13 kb) (13KB, xlsx)

Acknowledgements

This work was supported by the China Major Science and Technology Program for Water Pollution Control and Treatment (2017ZX07101003), the National Natural Science Foundation of China (21676161, 31500413) and Shandong Provincial Natural Science Foundation, China (BS2015SW004).

Compliance with ethical standards

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Human and animal rights

This article does not contain any studies with human participants or animals performed by any of the authors.

Contributor Information

Qiang Li, Email: liqiang67@lyu.edu.en.

Shu-Guang Wang, Email: wsg@sdu.edu.cn.

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