Sugarcane yield index and soil nutrient variability
Compare to CK treatment, the yield per hectare of FN41 sugarcane increased from 7%~17% under the bio-fertilizer amendment soil (BF1 and BF2) and compound fertilizer (CF). Furthermore, compared to CK, BF1, BF2 and CF treatments significantly increased (P < 0.05) plant height, stem weight and effective stem. However, sugarcane stem diameter under CF, BF1and BF2 treatments revealed no significant difference compared to CK treatment (Table 1). Compared with CK and CF treatments, soil pH was significantly higher (P < 0.05) in both BF1 and BF2 treatments. However, CF treatment significantly reduced soil pH compared with CK. Moreover, soil organic carbon and available potassium were not impacted in all the treatments compared to CK treatment. Compared to CK treatment, soil total nitrogen was significantly higher (P < 0.05) in both BF1 and BF2 treatments, whereas soil available nitrogen did not change considerably among all the treatments. The contents of total nitrogen, available nitrogen, total phosphorus and available potassium increased significantly by about 27–40%, 24–26%, 51–62% and 161–180%, respectively, with the increase in BF1 treatment group being the most significant (Table 2).
Table 1
Effects of different treatments on yield indexes of sugarcane
Treament | Yield Index |
| Sugar(%) | Plant Height(cm) | Stem Diameter(cm) | Single stem weight(kg) | Effective stem/ha | Yield /hm2 |
CK | 14.17 ± 0.20ab | 270.05 ± 3.74c | 2.56 ± 0.06a | 1.24 ± 0.06b | 4,068 ± 127b | 75,531 ± 4,736b |
CF | 13.43 ± 0.17b | 286.37 ± 8.10b | 2.78 ± 0.04a | 1.57 ± 0.07a | 4,569 ± 113a | 107,431 ± 6,172a |
BF1 | 14.32 ± 0.17a | 303.83 ± 1.82a | 2.77 ± 0.14a | 1.66 ± 0.12a | 4,867 ± 212a | 120,802 ± 12,526a |
BF2 | 13.82 ± 0.28ab | 300.99 ± 2.92ab | 2.72 ± 0.08a | 1.59 ± 0.08a | 4,668 ± 96a | 111,026 ± 7,650a |
Note: Different letters in each column indicate significant differences among the treatments at the 0.05 level. |
Table 2
Effects of different treatments on soil nutrient content of sugarcane
Treatments | Soil Chemical Properties |
| pH value | Soil Organic Carbon /(g ·kg− 1) | Total nitrogen /(g ·kg− 1) | Total phosphorus /(g· kg− 1) | Available nitrogen /(mg·kg− 1) | Available potassium /(mg·kg− 1) | Available phosphorus /(mg·kg− 1) |
CK | 4.93 ± 0.05b | 17.70 ± 2.69a | 1.30 ± 0.07b | 0.32 ± 0.03b | 90.73 ± 7.32b | 54.23 ± 6.63b | 45.26 ± 6.13a |
CF | 4.59 ± 0.07c | 20.75 ± 1.85a | 1.48 ± 0.05ab | 0.46 ± 0.03a | 102.17 ± 3.49ab | 107.04 ± 13.66a | 49.71 ± 3.66a |
BF1 | 5.43 ± 0.11a | 24.48 ± 2.79a | 1.74 ± 0.18a | 0.46 ± 0.06a | 113.44 ± 8.09a | 146.15 ± 12.94a | 48.81 ± 9.89a |
BF2 | 5.35 ± 0.06a | 24.81 ± 2.88a | 1.72 ± 0.10a | 0.50 ± 0.03a | 105.99 ± 2.99ab | 128.37 ± 21.23a | 45.62 ± 1.68a |
Note: Different letters indicate a significant difference among treatments based on the LSD test (p < 0.05). |
Effect of different fertilizers on rhizosphere microbial community and diversity
In order to assess the effects of different treatments on microbial Alpha diversity in sugarcane rhizosphere soil, We plotted the box-line diagrams (Fig. 1). The rarefection curve showed the richness of observed OTU, which proved that the depth of sample sequencing was enough to show microbial Alpha diversity (Fig. S1). According to the result, rhizosphere microbial α-diversity (Shannon, Sobs, Chao, and Ace) indices were significantly (P ≤ 0.05) affected by fertilizer, but there were differences in the degree of influence between fungi and bacteria. (Table S1). At the bacteria, treatments BF1 and BF2 produced the highest significant Shannon indices respectively, compared with CK and CF, and highest Sobs,Ace and Chao indices were recorded in treatment BF2 (Table S1). On the other hand, at the fungi, except for Shannon and Ace were not significantly affected by fertilizer treatment, treatment BF2 registered the highest Sobs and Ace indices compared with other treatments (Table S1).
The dominant bacteria phyla were Actinobacteria, Proteobacteria, Acidobacteria, Cyanobacteria, Firmicutes, Planctomycetes Bacteroidetes, Chloroflexi, Gemmatimonadetes and Nitrospirae in all fertilizer treatments soil (Fig. 2A). and the dominant fungi phyla were Ascomycota, Basidiomycota, Zygomycota, Ciliophora, Ochrophyta, Chytridiomycota, Choanomonada, Glomeromycota, Schizoplasmodiida and Blastocladiomycota (Fig. 2B). Although the dominant phyla of rhizosphere microorganisms in all soils were consistent, changes in the relative abundances of the dominant taxa were observed across different treatments (Table S2). In bacteria, there was a lower abundance of Actinobacteria and a higher abundance of Acidobacteria and Chloroflexi in soils with BF addition comparing with CK and CF (Fig. 2A), and in the OTU level, the addition of fertilizer reduced the number of OTU unique to bacteria in soil, but the degree of decrease was related to the type of fertilizer (Fig. 2C). In addition, Ascomycota had absolute abundance advantage in rhizosphere fungi. Compared to CF, BF treatment has more Ciliophora, Ochrophyta and Zygomycota (Fig. 2B). In OTU level, the addition of bio-fertilizer make it have more unique fungal OTU, specifically, CF reduced the number of unique OTUs (Fig. 2D).
The Spearman's heatmap showed the relationship between microbial diversity and soil traits (Fig. 3A), and the Spearman heatmap correlation analysis between major microbial genera and physiochemical soil variables were also illustrated in Fig. 3B. In bacteria, TP significantly affected the diversity index of bacteria and showed significant positive correlation with Shannon, Ace, Sobs and Chao (Fig. 3A). In addition, there was a significant correlation between TP, pH, AK and TN and most of the bacterial genera in bacterial top30. Among them genus Acidobacteria, Anaerolineaceae and Nitrospira had a significant positive correlation with soil pH while Bacillus, Rhizomicrobium, Frankiales, Saccharibacteria and Bradyrhizobium were observed to have a significant negative correlation with pH. Furthermore, Haliangium, Nitrospira and Nitrosomonadaceae had a strongly significant positive correlation with TN, but Bradyrhizobium registered a significant negative correlation with TN (Fig. 3B). In fungi, TN and AK had a significant positive correlation with Sobs (Fig. 3A). Meanwhile, Fusarium showed a significant negative correlation with AP and AK, Ascomycota also showed a significant negative correlation with TP and AK. It is noteworthy that Chalazion showed a significant positive correlation with SOC and TN,and the part of these observations were also confirmed in RDA analysis with the top 10 genera.
A Non-metric multidimensional scaling (NMDS) analysis showed a clear distinction in bacterial and fungal community composition at CK, CF and BF (Fig. 4A and D). In all the treatments, the bacterial community were distinct from each other based on their NMDS1 axis, however, fungal community composition showed distinct variation among the treatments at their NMDS2 axis. Based on redundancy analysis (RDA), results revealed that soil variables (pH, AN, AK, TN, TP, SOC) affected the soil microbial community at different treatments. The X and Y canonical axes explained 40.71% and 17.12%, 30.55% and 17.86% of the observed bacterial and fungal species dynamics, respectively. It is worth noting that, of all the soil variables investigated, pH (r2 = 0.8070, p-value = 0.0005) and AK (r2 = 0.7988, p-value = 0.001) in bacteria, SOC (r2 = 0.6974, p-value = 0.0025), TN (r2 = 0.7558, p-value = 0.0020), pH (r2 = 0.6640, p-value = 0.0045) and AK (r2 = 0.6303, p-value = 0.0085) in fungi were observed as important drivers shaping and controlling microbial community (Fig. 4C and F; Table S3). Meanwhile, the results of Adnois test indicated significant differences between different fertilizer treatment groups (Table 3), and VPA analysis showed that soil physicochemical factors explained 80.09% and 73.31% of the variance for bacteria and fungi, respectively, with pH explaining a higher percentage of the variance for fungi (23.88%) than for the bacterial (9.91%) group (Fig. S2).
Table 3
Analysis of bacteria and fungi Adonis
| CK | CF | BF1 | BF2 |
| R2 | P | R2 | P | R2 | P | R2 | P |
CK | | | 0.593 | 0.001 | 0.439 | 0.002 | 0.525 | 0.001 |
CF | 0.447 | 0.007 | | | 0.472 | 0.004 | 0.605 | 0.002 |
BF1 | 0.741 | 0.005 | 0.654 | 0.003 | | | 0.3 | 0.005 |
BF2 | 0.734 | 0.004 | 0.606 | 0.006 | 0.478 | 0.005 | | |
Note: Pairwise comparison of four groups of fertilization measures, the value of R2 represents the degree of explanation of sample differences, and the higher the value of R2, the higher the degree of explanation of differences in groups. The left lower triangle represents bacteria, the right upper triangle represents fungi, R2 > 0.75 is usually interpreted as a clear separation, R2 > 0.5 indicates separation, and R2 < 0.25 indicates a group that is difficult to separate. (p < 0.05). |
Differential microorganisms under different fertilizer treatments
According to the results of DESeq2, we identified 220 genus including 98 upregulated genus and 122 downregulated genus after the comparison between CK and BF2 in the bacteria, 86 genus (up = 40, down = 46) between CK and CF, 29 genus (up = 19, down = 10) between CF and BF2, respectively (Table S4). Such as Latescibacteria, Actinobacteria, Acidobacteria and Nordella were significantly enriched in the comparison of CF and BF2, however, Actinospica, Jatrophihabitans, Leifsonia and Sinomonas were significantly reduced (Fig. 5C). In the fungal community, 4 (CK vs CF), 29 (CK vs BF2) and 28 (CF vs BF2) differential genera were identified in the comparison groups of the different treatments, respectively (Fig. 5D-F). Such as Mrakia, Saccharomycetales, Obertrumia and Galactomyces were significantly enriched after BF2 treatment compared to the control group, Phallus, Ascomycota and Thysanophora were significantly reduced (Fig. 5E). The identified differentially genus were showed by Volcano plot (Fig. 5). In the Volcano plot, p < 0.05 was set as the cut-off criterion of significant difference.
Effects of fertilizer treatments on rhizosphere microbial biomarkers and functions
Linear discriminant effect size (LEfSe) analysis was conducted to identify and select unique microbial taxa significantly related to each fertilizer treatment. The biomarkers bacterial and fungal community were depicted in cladograms, and linear discriminant analysis (LDA) scores ≥ 3.5 and LDA ≥ 3 were then performed respectively (Fig. 6A and C). The biomarkers associated with treatments varied across the fertilizer. The bacterial and fungal community LDA analysis detected 66 (CK = 24, CF = 16, BF1 = 26, BF2 = 0), 98 (CK = 20, CF = 15, BF1 = 21, BF2 = 42) biomarkers for different fertilizer respectively (Fig. 6A and C). The higher score biomarker bacterial of BF1 treatment belonged to phyla Acidobacteria and Anaerolineaceae; that of CF belonged to Alphaproteobacteria, Gaiellales and Frankiales. Meanwhile, in fungi, the higher score biomarker of BF2 belonged to Cystofilobasidiaceae, Mrakia, Pinnularia and Tremellomycetes; that of CF belonged to unclassified Dothideomycetes and Tremellales (Fig. 6C). In addition, regarding KEGG, 44 pathways were significantly difference in third-level pathways (LDA > 2.5, P < 0.05, Fig. 6B), including 29 pathways with significantly difference in BF1, such as Genetic information Processing, Global and overview maps and Energy metabolism. 7 pathways were significantly difference in CF, such as Environmental information Processing, Lipid metabolism and Xenobiotics biodegradation and metabolism (Fig. S4). The BF1 treatment group had the most differential pathways. Meanwhile, there were 14 fungal FUNGuild (CK = 4, CF = 6, BF1 = 0, BF2 = 4), of which BF2 mainly included Pathotroph and Animal Pathogen, Pathotroph-Saprotroph and Fungal Parasite-Undefined Saprotroph were in CF (LDA > 2.0, P < 0.05, Fig. 6D and S5).
In the bacteria, of the top 30 genera identified by a support vector machine (Fig. S3), Woodsholea, norank_Latescibacter, Bauldia, Myxococcales, Oryzihumus were all identified as important variables that significantly contributed to the class separation between CK and CF, Anaerolinea, Vicinamibacter, Syntrophobacter, Anaerolineaceae were the more important genera for the difference between CK and BF2, and more attention need to be paid to the more important role of norank_ Anaerolineace, Vulgatibacter, Paenibacillus, Achromobacter and Roseiarcus for their differentiation between CF and BF2. (Fig. 7A). On the other hand, in the fungi, Hydnodontaceae, norank_ Agaricomyce, Saccharomycetales, Ascomycota, Glomeromycota between CK and CF, Ascomycota, Obertrumia, Salpingoeca, Monosiga, Discicristoidea between CK and BF2, Cochliobolus, Sordariales, Dothideomycetes, Pleosporales, Acrospermum between CF and BF2 had a greater contribution to the variability between groupings than other genus, respectively (Fig. 7B).
Network analysis of soil microbial communities(co-occurrence network)
Co-occurrence network analysis was used to assess interactions across dominant populations, and only the significant correlations (r2 > 0.4, p < 0.05) were shown in this network. The results revealed a lower number of links in the BF2 in the bacteria, and in the fungi, the BF1 feature networks had the least number of links (Table S5). Further insight into the bacterial and fungal genera network illustrated the lowest mean degree, centralization-closeness, network centralization and clustering coefficient values in BF2 than other treatments (Table S6). Some genus, such as norank_Acidobacteria, norank_Anaerolineaceae, Bacillus and Roseiflexus had a higher relative abundances and clustering coefficient in the bacterial network of BF1. The genus Candidatus_Solibacter, norank_Nitrosomonadaceae, Nitrospira and norank_Acidimicrobiales of CF in bacterial network had the largest clustering coefficient compared with other treatments (Fig. 8C and Table S7). In fungal network, Fusarium had the highest clustering coefficient values in CF compared to other treatments, however, BF2 had the lowest clustering coefficient value (Fig. 8D and F, Table S8).