Community structure of soil diazotrophs in coastal Casuarina equisetifolia varieties and the environmental drivers.

内容摘要

Casuarina equisetifolia is a typical coastal shelterbelt tree species. The characteristics of soil diazotrophic microbial communities among different varieties of C. equisetifolia remain poorly understood. In this study, we investigated the physicochemical properties, structure of soil diazotrophic communities and their key driving factors across six varieties (Xingwang, Fada, Qiantou, Ping'an, Ruyifeng, and Jixianglong) from the National C. equisetifolia Germplasm Repository in Hui'an, Fujian Province. The results showed that: 1) There were significant differences in soil physicochemical properties among different varieties, with soil moisture ranging from 7.7% to 15.6%, organic matter content from 6.3% to 9.8%, and clay proportion from 0.1% to 0.3%. All variables, as well as the activities of N-acetyl-glucosaminidase (25.77-92.12 nmol·g-1·h-1) and leucine aminopeptidase activity (12.18-59.04 nmol·g-1·h-1) were highest in 'Ruyifeng'. 2) The abundance of nifH gene ranged from 4.5×105 to 1.6×106 copies·g-1 soil, with the highest value being observed in 'Jixianglong'. The α-diversity indices of diazotrophic microbial communities (based on the nifH gene) were significantly higher in Ping'an than in the other varieties. Principal coordinate analysis based on Bray-Curtis distance revealed relatively high diazotrophic microbial community similarity between Jixianglong and Xingwang, as well as between Qiantou and Fada, whereas the Ping'an exhibited the most distinct community composition. 3) The dominant diazotrophs across all six varieties were Bradyrhizobium (relative abundance>40%), and there were significant differentiations in community composition. The community composition of Ping'an variety differed most markedly from others. 4) Soil moisture, pH, and organic matter cotent were the main factors driving diazotrophic abundance, with organic matter content having the most significant effect. Organic matter content and clay fraction were identified as key drivers of community diversity. Structural equation modeling showed that soil pH and moisture had significant negative effects on diazotrophic abundance but positive effects on diversity. In conclusion, different varieties of C. equisetifolia significantly influence the abundance and diversity of diazotrophic communities by modulating rhizosphere soil conditions, thereby playing a key role in the construction of coastal protection forests and soil microbial succession. Among the varieties, Jixianglong was suitable for nitrogen-deficient coastal soils to enhance nitrogen supply, Ping'an could better adapt to environments with high variability or where rhizosphere stability was required, and Ruyifeng exhibited higher enzyme acti-vities in soils with relatively high organic matter content. 木麻黄是典型沿海防护林树种,但其不同品种土壤固氮微生物群落特征仍缺乏系统研究。本研究以福建惠安国家木麻黄种质资源库的6个品种(兴旺、发达、千头、平安、如意凤、吉祥龙)为对象,探讨土壤理化性质、固氮菌群落结构特征及其主要驱动因子。结果表明:1)不同品种木麻黄土壤理化性质差异显著,其中土壤含水率为7.7%～15.6%,有机质含量为6.3%～9.8%,黏粒比例为0.1%～0.3%,均以‘如意凤’品种最高。N-乙酰氨基葡萄糖苷酶活性(25.77～92.12 nmol·g-1·h-1)和亮氨酸氨基肽酶活性(12.18～59.04 nmol·g-1·h-1)也以‘如意凤’品种最高。2)固氮功能基因(nifH)丰度为4.5×105～1.6×106 copies·g-1,其中‘吉祥龙’最高;‘平安’品种固氮微生物群落(基于nifH基因)的α多样性指数显著高于其他品种;基于Bray-Curtis距离的主坐标分析表明,‘吉祥龙’与‘兴旺’、‘千头’与‘发达’间的固氮菌群落相似性较高,而‘平安’与其他品种差异最显著。3)6个品种的优势固氮菌均为慢生根瘤菌属(相对丰度>40%),但群落组成分化显著,‘平安’品种的群落组成与其他品种差异最突出。4)冗余分析表明,土壤含水率、pH和有机质含量是影响固氮菌丰度的主要因子,其中有机质作用最显著;而有机质和黏粒比例则是群落多样性的关键驱动因子。结构方程模型显示,土壤pH和含水率对固氮菌丰度呈显著负效应,但对多样性呈显著正效应。综上,不同品种木麻黄通过调节根际土壤环境,显著影响固氮菌群落的丰度与多样性,从而在滨海防护林构建与土壤微生物群落演替中发挥关键作用。其中,‘吉祥龙’适用于缺氮的沿海土壤以提升氮素供应,‘平安’适用于环境波动大或需维持根际微生境稳定的区域,‘如意凤’则在有机质丰富土壤中表现出更高的酶活性。.