The effect of biochar and green manure on soil physical and chemical properties
It could be seen from Table 1 that the application of biochar would significantly change the physical and chemical properties of the soil, and the combined application of biochar and green manure had a more significant impact on the physical and chemical properties of the soil. Compared with CK, both T1 and T2 treatments significantly increased the soil pH, porosity, alkali-hydrolyzable nitrogen, available phosphorus and available potassium content. Among them, in T2 treatment, soil pH, porosity, alkali-hydrolyzable nitrogen, available phosphorus and available potassium were increased by 19.09%, 19.74%, 9.38%, 19.13% and 14.30%, respectively, comparing to CK treatment. The soil bulk density of T1 and T2 treatments was reduced by 15.20% and 22.40%, respectively, compared with CK treatment, reaching to a significant level. The soil organic matter and soil cation exchange capacity of T1 and T2 treatments both increased, not reaching to a significant level yet.
Table 1
Effects of biochar and green manure on soil physical and chemical properties
Treatment
|
pH
|
Soil bulk density (g·cm− 3)
|
Soil porosity (%)
|
Organic matter (g·kg− 1)
|
Avail. N (mg·kg− 1)
|
Avail. P (mg·kg− 1)
|
Avail. K (mg·kg− 1)
|
CEC
(cmol·kg− 1)
|
CK
|
5.76b
|
1.25a
|
52.68c
|
40.28a
|
194.50b
|
154.46b
|
326.78b
|
17.70a
|
T1
|
5.83a
|
1.06b
|
58.93b
|
41.05a
|
208.84a
|
172.36a
|
357.85a
|
18.25a
|
T2
|
5.87a
|
0.97b
|
63.08a
|
41.92a
|
212.74a
|
184.01a
|
373.52a
|
18.80a
|
Within each column, means followed by different letters are significantly different according to Tukey’s test at p ≤ 0.05 |
The effect of biochar and green manure on soil fungal α diversity
9 soil samples were tested, and a total of 428,819 valid sequences were obtained, with average sequence of a single sample as 47,647. Based on 97% sequence similarity, under cluster analysis of the tested sequences, the average number of OTUs for all samples was 270。The total number of OTUs in the three treatments was 174, of which the OTUs of the T2 treatment were significantly higher than that of the CK (Fig. 1)。
It could be seen from Table 2 that there was no significant difference in fungal α diversity between T1 treatment and CK treatment, but the Shannon index of T1 treatment was greater than CK, and the Ace index and Chao index were smaller than CK, indicating that the application of biochar could increase soil fungi Diversity, but reduce the abundance of fungi. The Shannon index, Ace index and Chao index of T2 treatment were significantly greater than CK treatment, and Simpson index was lower than CK treatment, indicating that applying biochar while tugging green manure can effectively increase the diversity and abundance of soil fungi。
Table 2
Sequencing sequence and of soil fungi α Diversity
Treatments
|
Sequencing numbei
|
Shannon index
|
Simpson index
|
Ace index
|
Chao index
|
Coverage(%)
|
CK
|
51140.00
|
2.73b
|
0.15a
|
183.68b
|
186.33b
|
99.97
|
T1
|
49312.33
|
2.83b
|
0.14a
|
170.59b
|
170.93b
|
99.97
|
T2
|
42487.33
|
3.02a
|
0.13a
|
201.68a
|
202.12a
|
99.95
|
Within each column, means followed by different letters are significantly different according to Tukey’s test at p ≤ 0.05 |
The effect of biochar and green manure on soil fungal community structure
Effect of biochar and green manure on fungal community structure in horizontal soil
The results of the species annotation showed that a total of 30 fungal floras were obtained at the phylum level in all samples, and the average relative abundance < 1% was classified as other groups, and 10 taxa were obtained, as shown in Fig. 2. Among them, the more abundant phylum species are Ascomycota, an unclassified supergroup (SAR_k__norank), an unclassified fungus (unclassified_k_norank), Basidiomycota and Mucoromycota. Compared with CK, the abundance of Ascomycota treated with T1 and T2 decreased by 7.54% and 22.85%. The relative abundance of Basidiomycota treated with T1 and T2 increased by 130.30% and 276.00%, respectively, compared with CK treatment. The relative abundance of Mucoromycota treated with T2 was 44.66% lower than that treated with CK.
The abundance of soil fungi showed differences at different treatment levels. As shown in Fig. 3, Ascomycota and Schizoplasmodiida showed significant differences among the three treatments, and Ascomycota was relatively abundant in CK treatment. The highest relative abundance of Schizoplasmodiida was oberved in T2 treatment. It could be seen from Fig. 3 that among the top 13 of relative abundance for fungi in phylum level, the relative abundance of 8 flora in T2 treatment was higher than that in CK treatment。
The effect of biochar and green manure on fungal community structure in horizontal soil
The results of the species annotation show that a total of 151 fungal floras were obtained at the genus level in all samples, and the groups with an average relative abundance of < 1% were classified as other groups, and 23 groups were obtained, as shown in Fig. 4. Among them, the more abundant floras were an unclassified genus (unclassified_k_Microascaceae), Chaetomium, Talaromyces, Colpoda, and Fusarium. The relative abundance of an unclassified genus (unclassified_k_Microascaceae) belonging to Microascaceae in T2 treatment increased by 9.33% compared with CK treatment, and the relative abundance of Chaetomium decreased by 58.67%. The relative abundance of Talaromyces in T1 and T2 treatments increased by 273.51% and 230.12% compared with CK treatment, and the relative abundance of Colpoda increased by 6.58% and 74.80%, respectively. The relative abundance of Fusarium decreased by 39.22% and 23.10%, respectively.
Effect of Biochar and Green Manure on the Principal Components of Soil Fungal Community
The principal component analysis of soil colony structure based on the abundance of OTUs is shown in Fig. 5. The contribution of the PC1 axis and the PC2 axis to the difference in sample composition are 41.28% and 27.29%, respectively. It could be seen from Fig. 5 that the biological repetition in each treatment group was not quite well, but the distance between CK treatment and T2 treatment was relatively long, indicating that there was a significant difference in soil fungal community composition between biochar and green manure and conventional fertilization. T1 treatment had a cross-over to both CK and T2 treatment, indicating that application of only biochar had a certain effect on soil fungi, but combined application of green manure on the basis of biochar could much significantly change the microbial community structure。
Correlation analysis between community structure of soil dominant fungi and environmental factors
The correlation between the top 20 fungal species with relative abundance at the phylum level and soil factors is shown in Fig. 6. pH, SBD, AN, AK and AP all had significant effects on soil bacterial community structure. There was a significant negative correlation between Ascomycota and AK (P < 0.05), and a negatively correlation(P < 0.05) between SBD with unclassified_k__norank, Schizoplasmodiida and Basidiomycota. There was a significant correlation between AK, pH, AN and AP with schizoplasmodiida, in which AK and schizoplasmodiida had a very significant positive correlation (P < 0.01). Aphelidea and Blastocladiomycota were negatively correlated with environmental factors. Among the top 20 fungal communities in relative abundance, about 1/2 were positively correlated with environmental factors. The effects of SOM, CEC, AK, pH, AN and AP on soil fungal community structure were consistent.