Seasonal patterns of rhizosphere microorganisms suggest carbohydrate-degrading and nitrogen-fixing microbes contribute to the attribute of full-year shooting in woody bamboo Cephalostachyum pingbianense

Abstract

Compared with the ordinary single-season shooting among woody bamboos in Poaceae, the attribute of full-year shooting in Cephalostachyum pingbianense represents a unique shooting type or mechanism. Nevertheless, except for the overall physiological mechanism, the effect of ecological factors, especially soil microorganisms, on this full-year shooting characteristic remains unclear. In this study, 16S rRNA and ITS rRNA genes were sequenced using the Illumina platform. Our aims were to detect the seasonal changes in rhizospheric microbial communities of C. pingbianense and to discover the correlations of soil microbes with soil properties and bamboo shoot productivity. The results showed that seasonal change had no significant effect on bacterial alpha diversity, but significantly affected bacterial and fungal community structures as well as fungal richness. Among all soil properties examined, soil temperature, soil moisture and organic matter were the predominant factors affecting bacterial community diversity and structure. Soil temperature and soil moisture also significantly influenced fungal community structure, while available phosphorus had the greatest effect on fungal diversity. In each season, bacterial genera Acidothermus, Roseiarcus, and Bradyrhizobium, along with fungal genera Saitozyma, Mortierella, Trichoderma, etc., were dominant in bacterial and fungal communities, respectively. Bacterial community functions in four seasons were dominated by chemoheterotrophy, cellulolysis, and nitrogen fixation. Saprotrophic fungi occupied a high proportion in soil samples of all seasons. In addition, correlation analysis revealed that the bamboo shoot productivity was positively correlated with multiple microbial taxa involved in carbon and nitrogen cycles. It is proposed that highly abundant microbes involved in carbohydrate degradation and nitrogen fixation in the rhizosphere soil may contribute to the attribute of producing bamboo shoots all year round in C. pingbianense. This study is among the few cases revealing the connection between bamboo shooting characteristics and soil microorganisms, and provides new physiological and ecological insights into the forest management of woody bamboos.

Keywords: Cephalostachyumpingbianense; bamboo shooting; microbial function; rhizosphere microbe; seasonal variation.

Figure 1

Soil physicochemical properties (A–H) and bamboo shoot number (I) of C. pingbianense in the four seasons. Different uppercase and lowercase letters in each subgraph indicated significant differences at p < 0.01 and p < 0.05 levels respectively, and error bars represented standard deviation (SD). TN, total nitrogen; TK, total potassium; AP, available phosphorus; HN, hydrolyzable nitrogen; AK, available potassium; OM, organic matter; ST, soil temperature; SM, soil moisture; BSN, bamboo shoot number; Sp, spring; Su, summer; Au, autumn; Wi, winter.

Figure 2

Alpha and beta diversity of rhizosphere microbes in C. pingbianense in different seasons. (A,B) Chao1 indexes of bacterial (A) and fungal (B) communities. (C,D) Shannon indexes of bacterial (C) and fungal (D) communities. (E,F) Principal coordinate analysis (PCoA) of bacterial (E) and fungal (F) communities based on the Bray-Curtis distance algorithm. significant differences at p<0.05 level

Figure 3

Microbial community composition in rhizosphere of C. pingbianense in four seasons. (A,B) Relative abundances of main bacterial (A) and fungal (B) community phyla. (C,D) Heatmaps showing the top 30 abundant bacterial (C) and fungal (D) genera.

Figure 4

Functional prediction of rhizosphere microbes in C. pingbianense in four seasons. (A) Heatmap showing the top 30 bacterial ecological functions by total abundance in the samples. (B) Significant difference test among groups in bacterial phenotypes. (C) Fungal functional group composition of samples in four seasons. The size of circles in (C) reflected the total abundance of corresponding species in samples of all seasons, and the thickness of lines represented the abundance of that species in the sample of a certain season.

Figure 5

LEfSe analysis of fungal abundance in rhizosphere of C. pingbianense in four seasons. (A) Cladogram showing taxa with different abundance values of fungal community. (B) LDA bar chart of fungal community.

Figure 6

Redundancy analysis of soil properties and bacterial (A) or fungal (B) community in rhizosphere of C. pingbianense. TN, total nitrogen; TK, total potassium; HN, hydrolyzable nitrogen; AP, available phosphorus; AK, available potassium; OM, organic matter; ST, soil temperature; SM, soil moisture.

Figure 7

Heatmaps showing correlations between chosen factors and the first 20 genera of bacteria (A) and fungi (B). Color depth represented the magnitude of correlation R value. *0.01 < p ≤ 0.05; **0.001 < p ≤ 0.01; ***p ≤ 0.001; BSN, bamboo shoot number; ST, soil temperature; SM, soil moisture; AK, available potassium; TN, total nitrogen; OM, organic matter; TK, total potassium; HN, hydrolyzable nitrogen; AP, available phosphorus.