3.1 Effects of intercropping sweet potato in a banana orchard on the population and diversity of the soil bacteria and fungi community
It can be seen from Table 1 that during May to September, the number of soil bacterial communities of intercropping sweet potato was 476.00-511.67 and that of banana monoculture was 397.67–451.00. The number of soil bacterial communities of intercropping increased by 28.67%, 5.54%, and 11.42% respectively in different months compared with that of monoculture, and the difference in May and September reached a significant level, but in July, there was no significant difference between intercropping and monoculture. The Ace and Chao1 indexes of community abundance of soil bacteria in intercropping were higher with 1859.18-1874.71 and 1861.28-1911.12 respectively than the 1458.26-1748.65 and 1478.19-1719.86 of the monoculture. The difference between the two treatments reached a significant or very significant level. The Shannon index of bacterial community diversity in the intercropping soil was 9.29–9.51, higher than that of 7.99–9.16 in the monoculture, and the difference reached a significant or extremely significant level in different months. The results showed that intercropping sweet potato in banana orchard could significantly improve the number, abundance, and diversity of the bacterial community in the soil.
Table 1
Quantity and diversity index of the bacterial community in the soil in sweet potato intercropping and monoculture in a banana orchard.
Treatment
|
Number of colonies (pieces)
|
Ace index
|
Chao1 index
|
Shannon index
|
May/A
|
511.67 ± 14.22Aa
|
1870.39 ± 25.71Aa
|
1861.28 ± 50.34Aa
|
9.29 ± 0.03Aa
|
May/B
|
397.67 ± 17.62Bb
|
1458.26 ± 54.62Bb
|
1478.19 ± 55.27Bb
|
7.99 ± 0.13Bb
|
July/A
|
476.00 ± 2.65Aa
|
1859.18 ± 12.28Aa
|
1911.12 ± 43.57Aa
|
9.51 ± 0.11Aa
|
July/B
|
451.00 ± 34.18Aa
|
1748.65 ± 41.78Ab
|
1719.86 ± 95.24Ab
|
9.16 ± 0.15Ab
|
Sep/A
|
484.67 ± 18.15Aa
|
1874.71 ± 16.35Aa
|
1907.80 ± 27.12Aa
|
9.45 ± 0.04Aa
|
Sep/B
|
435.00 ± 15.59Ab
|
1570.61 ± 95.21Bb
|
1624.03 ± 66.76Bb
|
8.61 ± 0.04Bb
|
Samples were taken in May, July, and September. May/A = Intercropping treatment in May. May/B = Monoculture treatment in May. July/A = Intercropping treatment in July. July/B = Monoculture treatment in July. Sep/A = Intercropping treatment in September. Sep/B = Monoculture treatment in September. Different lowercase letters and uppercase letters indicate that there are significant differences between the two treatments in the same month at the levels of P < 0.05 and P < 0.01, respectively. |
The population of the fungal community in the soil subject to intercropping during May, July, and September was 154.33-198.33, and more than 112.00-147.00 in the monoculture (Table 2). But the difference between the two treatments did not reach a significant level. The Ace and Chao1 indexes of soil fungi community in intercropping were 568.17-735.51 and 451.54-653.29, respectively, higher than 514.66-687.47 and 375.37-541.45 in monoculture. However, only in May, the difference in the Chao1 index between the two treatments reached a significant level, while the other differences were not significant. The Shannon index of soil fungi in intercropping was 5.92–6.72, and that of monoculture was 5.27–6.57. The Shannon index in intercropping in May and September was higher than that of the monoculture, while that of intercropping in July was lower than that of the monoculture, but the difference between the two treatments in three months was not significant. The results showed that intercropping sweet potato had a certain effect on the number, abundance, and diversity of soil fungi in the banana orchard.
Table 2
Quantity and diversity index of the fungi community in the soil in sweet potato intercropping and monoculture in a banana orchard.
Treatment
|
Number of colonies (pieces)
|
Ace index
|
Chao1 index
|
Shannon index
|
May/A
|
198.33 ± 48.52Aa
|
735.51 ± 74.49Aa
|
653.29 ± 54.09Aa
|
5.92 ± 0.92Aa
|
May/B
|
143.00 ± 44.19Aa
|
659.87 ± 94.06Aa
|
465.19 ± 87.11Ab
|
5.27 ± 0.69Aa
|
July/A
|
164.33 ± 45.28Aa
|
726.27 ± 152.18Aa
|
618.71 ± 91.93Aa
|
6.35 ± 0.48Aa
|
July/B
|
147.00 ± 45.08Aa
|
687.47 ± 161.94Aa
|
541.45 ± 115.33Aa
|
6.57 ± 0.31Aa
|
Sep/A
|
154.33 ± 63.07Aa
|
568.17 ± 42.07Aa
|
451.54 ± 5.74Aa
|
6.72 ± 0.68Aa
|
Sep/B
|
112.00 ± 69.40Aa
|
514.66 ± 33.32Aa
|
375.37 ± 82.64Aa
|
6.25 ± 0.13Aa
|
Samples were taken in May, July, and September. May/A = Intercropping treatment in May. May/B = Monoculture treatment in May. July/A = Intercropping treatment in July. July/B = Monoculture treatment in July. Sep/A = Intercropping treatment in September. Sep/B = Monoculture treatment in September. Different lowercase letters and uppercase letters indicate that there are significant differences between the two treatments in the same month at the levels of P < 0.05 and P < 0.01, respectively. |
3.2 Effects of sweet potato intercropping in the banana orchard on the main bacterial phyla and population composition of the soil
The composition and relative abundance of soil bacterial community structure at the phylum classification level are shown in Fig. 2. Proteobacteria, Actinobacteria, Acidobacteria, Chloroflex, Bacteroidetes, and Gemmatimonadetes were the dominant bacteria in the banana plot soil, which accounted for more than 88%. During May to September, the relative abundances of these six main bacterial phyla were 31.83–41.04%, 13.83–26.94%, 15.03–20.38%, 10.86–11.65%, 3.87–5.77%, and 2.71–4.43%, respectively, and that of the monoculture were 19.20-27.86%, 20.07–24.13%, 12.00-18.39%, 21.91–24.73%, 2.02–4.90%, and 0.33–2.39%, respectively. The relative abundances of Proteus, Acidobacteria, Bacteroidetes, and Blastomonas in intercropping were greater than those of the monoculture, and their monthly average abundances were increased by 67.92%, 8.64%, 64.37%, and 327.76% respectively. In May and September, the relative abundances of Proteus and Blastomonas were significantly higher than those of the monoculture, while the monthly average relative abundances of Actinomycetes and Campylobacter decreased by 12.62% and 51.65% compared with the monoculture. The results showed that the intercropping of sweet potato in the banana plot had a great effect on the community structure and composition of the main bacterial phyla in the soil, and the relative abundance of Proteus, Acidobacteria, Bacteroides, and Blastomonas increased significantly, but the relative abundance of Actinomycetes and Campylobacter reduced.
The composition, structure, and relative abundance of the main bacterial populations in soil between the intercropping of sweet potato and the monoculture were quite different. Among the detected bacterial populations, the dominant bacterial populations with relative abundance of more than 1% in the soil intercropped with sweet potato in May and September were AD3, Acidothermus, Subgroup_6, and Acidobacteriales, and the relative abundances of other non-dominant populations were 81.78% and 78.29%. While dominant populations in the monoculture were AD3, Acidothermus, Elsterales, Acidobacteriaceae_Subgroup_1, Conexibacter, WPS-2, and Gammaproteobacteria_Incertae, and the relative abundances of other populations were 51.17% and 64.62%. But in July the dominant bacterial populations in the intercropping were AD3, Acidothermus and Subgroup_6, Conexibacter, and Acidobacteriales, the relative abundance of other populations was 80.7%, and those of the monoculture were AD3, Acidothermus, Subgroup_6, Elsterale, Acidobacteriaceae_Subgroup_1, Conexibacter, WPS-2, and Gammaproteobacteria_Incertae, the relative abundance of other populations was 72.98%. Among these dominant soil bacterial populations, the relative abundance of AD3, Acidothermus, Elsterales, Acidobacteriaceae_Subgroup_1, Conexibacter, and WPS-2 was lower than that in the monoculture, and the difference reached a significant or extremely significant level, while the relative abundance of Subgroup_6 and other populations was significantly or extremely significantly higher than that in the monoculture (Fig. 3). The results showed that sweet potato intercropping in the banana orchard had a significant effect on regulating the composition and structure of the soil bacterial population, the relative abundance of the soil dominant bacterial population was reduced, and that of the non-dominant bacterial population increased. The relative abundance of the non-dominant population increased by 10.58–58.81%.
3.3 Effects of sweet potato intercropping in the banana orchard on the composition and structure of the main fungi phyla and population composition in the soil
At the phylum classification level, the composition and relative abundance of the soil fungal community in the banana orchard are shown in Fig. 4. During May to September, Ascomycota, Basidiomycota, Mortierellomycota, Rozellomycota, Chytridiomycota, and Glomeromycota were the dominant fungi, and the number of communities of these dominant fungi accounted for more than 86%. In which the relative abundances of Ascomycota were the highest with 46.79–68.88% for intercropping and 42.33–61.95% for monoculture. The relative abundances of the other five population groups in the intercropping were 13.43–36.53%, 2.81–4.63%, 0.76–2.93%, 0.45–1.27%, and 0.05–0.27% respectively, those in the monoculture were 13.9-24.88%, 2.91–4.31%, 0.35–2.85%, 0.24–0.99%, and 0.00-0.19% respectively. The monthly average relative abundance of the six dominant groups in intercropping was higher than that in monoculture, but only in July the relative abundance of Basidiomycetes and Coccidiomycetes was significantly higher than that in monoculture, and that of the remaining fungi community between intercropping and monoculture did not reach a significant level in three months. The results showed that intercropping sweet potato had an important regulatory effect on the relative abundance of Basidiomycetes and Coccidiomycetes in the banana plot soil, but had little effect on other fungal communities.
In different periods of banana growth, the composition and structure of soil fungal populations in intercropping with sweet potato were very different from those in monoculture (Fig. 5). In May, the relative abundance of soil fungi in intercropping reached more than 1% including Podzolica, Neocosmospora_rubicola, and Iodophanus, in which, the highest relative abundance was Neocosmospora_rubicola(19.43%), followed by Iodophanus_carneus (7.62%), and Saitozyma_podzolica༈4.81%༉. While there was only Saitozyma_podzolica and Neocosmospora in the banana monoculture, their relative abundance was more than 1%, being 15.42% and 1.00%, respectively. The relative abundance of Neocosmospora_rubicola and Iodophanus_carneus in intercropping was significantly higher than that of monoculture, and that of Saitozyma_podzolica was significantly lower than that of monoculture. There was no significant difference in the other fungal populations between intercropping and monoculture. In July, the dominant fungal population in the intercropping soil was made up of Saitozyma_podzolica, Neocosmospora_rubicola, Conocybe_anthracophila, Fusarium_equiseti, and Coprinopsis, and that in the monoculture was Saitozyma_podzolica, Neocosmospora_rubicola, and Fusarium_equiseti. The relative abundance of three populations including Neocosmospora_rubicola, Conocybe_anthrophila, and Coprinopsis_cladophylla in intercropping was significantly higher than that in monoculture, and there was no significant difference between other non-dominant populations between the two treatments. In September, only Saitozyma _podzolica and Neocosmospora_rubicola constituted the dominant fungal population in the intercropping soil, while those in the monocultured soil were Saitozyma_podzolica and Fusarium_equiseti. The relative abundance of other communities was less than 0.7%. The relative abundance of Neocosmospora_rubicol and Coprinopsis_clastophylla population in intercropping was significantly higher than that in monoculture, while that of the Fusarium_equiseti population was significantly lower than that in monoculture, and there was no significant difference in the other non-dominant fungal populations between intercropping and monoculture. In addition, the relative abundance of unclassified soil fungal populations was 47.27–71.80% in intercropping and 62.31–72.17% in monoculture. The results showed that the intercropping of sweet potato in the banana orchard could regulate the composition and structure of the main soil fungi population and the relative abundance of dominant populations was improved significantly and that of Saitozyma_podzolica and Fusarium_equiseti was reduced.