鹽生固沙植物海馬齒(Sesuvium portulacastrum)根圈及根部內生微生物結構及功能研究

The structure and function of microbial communities in the rhizosphere and root endosphere of dune-stabilizing halophyte Sesuvium portulacastrum

海馬齒 (Sesuvium portulacastrum) 為海濱常見鹽生植物，對生育地鹽分逆境具高度耐受性，在海岸林營造上被應用於穩固砂丘。許多研究指出環境微生物與植物適應非生物逆境有密切關係，為瞭解環境微生物與海馬齒鹽鹼地適應特性的關係，本篇研究採集台南七股地區的海馬齒植體及生育地土壤樣品，藉由PacBio SMRT 16S rRNA基因定序技術，分析海馬齒根內、根圈及總體土壤微生物組成及功能，另外進行細菌分離及接種試驗以初步探索海馬齒根圈細菌是否能幫助植物在鹽分逆境下生長。由試驗結果發現，來自2個不同地點的海馬齒有相似的根內生細菌群落結構，而海馬齒根圈及總體土壤間細菌α多樣性相近，且細菌群落結構無顯著差異，顯示海馬齒地下部對根圈微生物相組成的影響並不明顯。數個細菌分類群在海馬齒根圈土壤較總體土壤有更高的豐度，且在前人研究結果中顯示可能具有植物促生特性，此外自海馬齒分離並具有植物促生特性的細菌，接種於苦楝苗木後展現出促進植物在鹽分逆境下生長的能力。藍菌門細菌為海馬齒根內生優勢菌群，推測可能與海馬齒鈉吸收能力及鹽分逆境適應有關。

Sesuvium portulacastrum is a common halophyte in coastal areas. Because of its excellent salt stress tolerance, S. portulacastrum is often used for coastal afforestation to stabilize sand dune. Many studies have pointed out that plant-microbe interactions impact stress tolerance of plants. To understand the microbial community structure and the effects of microbes on salt stress tolerance of S. portulacastrum, we performed the microbiome analysis of bulk soil, rhizosphere and endosphere of S. portulacastrum in Qigu District, Tainan, using bacterial 16S rRNA sequencing technology. Besides, we also evaluated the salt tolerance of plants inoculated with bacteria isolated from S. portulacastrum roots to identify bacterial isolates which may benefit plant growth under stress conditions. Our results showed that the structure of endophytic bacterial community in S. portulacastrum roots harvested from two different sites was similar. There was no significant difference of α-diversity and bacterial community structure between soils and rhizospheres, implying that the recruitment of environmental bacteria through root exudates secreted by S. portulacastrum is not evident. Compared to bacterial composition in bulk soils, several bacterial genera and species were enriched in the rhizosphere, with some possessing plant growth-promoting (PGP) characteristics based on previous studies. The growth-promoting effects were further validated on Melia azedarach L. seedlings under salt stress by supplying two potential PGP bacteria from S. portulacastrum. In addition, we observed that Cyanobacteria was the predominant microbial species in the S. portulacastrum root endosphere, which may be correlated with the salt tolerance of S. portulacastrum. Further studies will be required to assess the effects of microbial communities on salt tolerance in plants.