Mixing with native broadleaf trees modified soil microbial communities of Cunninghamia lanceolata monocultures in South China

Abstract

Mixing with different broadleaf trees into the monocultures of Cunninghamia lanceolata is widely adopted as an efficient transformation of the pure C. lanceolata forest. However, it is unclear how native broad-leaved trees influence the belowground ecological environment of the pure C. lanceolata culture plantation in nutrient-poor soil of South China. Herein, we aimed to investigate how a long-time mixing with native broadleaf trees shape soil microbial community of the pure C. lanceolata forest across different soil depth (0-20 cm and 20-40 cm) and to clarify relationships between the modified soil microbial community and those affected soil chemical properties. Using high-throughput sequencing technology, microbial compositions from the mixed C. lanceolata-broadleaf forest and the pure C. lanceolata forest were analyzed. Network analysis was utilized to investigate correlations among microorganisms, and network robustness was assessed by calculating network natural connectivity. Results demonstrated that the content of soil microbial biomass carbon and nitrogen, total phosphorus and pH in mixed forest stand were significantly higher than those in pure forest stand, except for available phosphorus in topsoil (0-20 cm). Simultaneously, the mixed C. lanceolata-broadleaf forest has a more homogeneous bacterial and fungal communities across different soil depth compared with the pure C. lanceolata forest, wherein the mixed forest recruited more diverse bacterial community in subsoil (20-40 cm) and reduced the diversity of fungal community in topsoil. Meanwhile, the mixed forest showed higher bacterial community stability while the pure forest showed higher fungal community stability. Moreover, bacterial communities showed significant correlations with various soil chemical indicators, whereas fungal communities exhibited correlations with only TP and pH. Therefore, the mixed C. lanceolata-broadleaf forest rely on their recruiting bacterial community to enhance and maintain the higher nutrient status of soil while the pure C. lanceolata forest rely on some specific fungi to satisfy their phosphorus requirement for survive strategy.

Keywords: microbial community structure; microbial symbiotic network; mixed Cunninghamia lanceolata-broadleaf forest; pure Cunninghamia lanceolata forest; soil microbial diversity.

Figure 1

The proportion of the top 10 microorganisms in the relative abundance of bacterial (A) and fungal (B) communities under different forest stands. The abscissa is the name of the sample, and the ordinate is the proportion of species in the sample. Columns of different colors represent different genera, and the length of the column represents the proportion of genera. MC20 and MC40 represent the soil layers of 0–20 cm and 20–40 cm of the mixed Cunninghamia lanceolata-broadleaf forest, respectively. PC20 and PC40 represent the 0–20 cm and 20–40 cm soil layers of the pure C. lanceolata forest, respectively.

Figure 2

Lefse analysis of soil bacterial (A) and fungal (B) communities in different soil layers of two different stands. Significantly discriminant taxon nodes are colored, and the branch areas are shaded according to the highest ranked group for that taxon. When the taxon was not significantly differentially represented among the sample groups, the corresponding node was colored white. Highly abundant and selected taxa are indicated. Refer to Figure 1 for abbreviations of different forest stands in different soil depth.

Figure 3

Alpha diversity of bacterial (A) and fungal (B) communities in different soil layers of different forests. The horizontal bar in the box represents the median. The top and bottom of the box represent the 75th and 25th percentiles, respectively. The asterisks above the horizontal line indicate significant differences between the two groups, *P < 0.05, **P < 0.01, and ***P < 0.001. Refer to Figure 1 for abbreviations of different forest stands in different soil depth.

Figure 4

Principal coordinate analysis of different soil layers in two forest stands based on the Bray-Curtis distance. The beta diversity index was calculated by vegan package of R language, and Table (A) or (B) is the result of the multivariate analysis of variance performed using the Adonis function. *P < 0.05. Refer to Figure 1 for abbreviations of different forest stands in different soil depth.

Figure 5

Correlation network of soil microbial bacterial (A) and fungal (B) communities in different stands and soil layers. Only the species association with extremely significant correlation was shown (|r| > 0.8 and P < 0.05), in which different nodes represent different species. The size of the node is proportional to the relative abundance of the species. Different colors represent the phylum of the species. The red connection indicates a positive correlation, the blue connection indicates a negative correlation, and the number of lines indicates the intensity of the connection between the nodes. Refer to Figure 1 for abbreviations of different forest stands in different soil depth.

Figure 6

The natural connectivity of microbial networks in different soil layers of two different stands. Natural connectivity of bacterial and fungal networks was calculated and evaluated by using fastnc (https://github.com/wqssf102/fastnc) software to reveal the stability of bacterial (A) and fungal (B) networks, respectively. Refer to Figure 1 for abbreviations of different forest stands in different soil depth.

Figure 7

Mantel's correlation analysis between soil properties and soil microbial communities. The color of the right box represents the spearman correlation r value between environmental factors, *P < 0.05, **P < 0.01, ***P < 0.001, the left edge width corresponds to the Mantel 's r statistic of distance correlation, and the edge color represents the statistical significance P value based on 999 permutations.

Figure 8

Correlations between the top 10 phyla in relative abundance and environmental factors in bacterial (A) and fungal (B) communities. The color represents the correlation coefficient, the black asterisk is the P-value of the correlation, the circle is the important value analyzed by multiple regression, and the bar chart on the right is the interpretation degree of environmental factors to each biological data in multiple regression.