Effect of PGPR on growth and nutrient utilization of Elymus nutans Griseb at different temperatures

Abstract

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that facilitate plant growth and can be used in the restoration of ecosystems. However, PGPR vary in their temperature tolerance, and few studies have investigated the effect of temperature on PGPR-mediated growth promotion or PGPR inoculum colonization. Therefore, we isolated and purified rhizosphere bacteria from the rhizosphere soil of Elymus nutans Griseb (EnG), collected from the Qinghai-Tibet Plateau. Selective culture media were used to assess whether these strains possess plant growth-promoting abilities and to measure the magnitude of their plant growth-promoting ability. Then screen out the strains (S1, S2, S3, S4, and S5) with strong plant growth-promoting ability for identification. To demonstrate the growth-promoting effects of the selected PGPR, we conducted a study. In this study, we simulated three temperature gradients (10°C, 15°C, and 20°C) during the growing season of EnG on the Tibetan Plateau. Furthermore, we established four incubation substrate treatments: T1(addition of PGPR but no addition of NPK fertilizers), T2 (neither PGPR nor NPK fertilizers addition), T3 (addition of PGPR both and NPK fertilizers), and T4 (addition of NPK fertilizers but not PGPR), to explore the effects of PGPR on the growth and nutrient (NPK) utilization efficiency of EnG at different temperatures. The results revealed that compared with those under T2, the plant height (PT) and dry weight under, T1 increased by 51.72% - 70.67% and 24.99-51.25%, respectively. The soluble sugar (SS) and soluble protein (SP) content significantly increased by 59.37% and 369.66%, respctively, at 10 °C (p < 0.05) and by 100.17% and 94.5%, respectively, at 15 °C (p < 0.05). Compared with those under T4, the physiological efficiencies of N (NPE) at 15 °C and 20 °C significantly decreased by 40.43% and 72.11%, respectively, under T3. In summary, these showed that this PGPR (S1, S2, S3, S4, and S5) promoted the growth of EnG on the Tibetan plateau and improved its nutrient utilization efficiency.

Fig 1. General location and climatic parameters of three sampling sites.

Three randomly selected areas where Elymus nutans Griseb was growing vigorously. The map, base map, shape files, and map data were obtained from the National Geographic Information Public Service Platform “TianDiTu” (https://cloudcenter.tianditu.gov.cn/dataSource), the specific URL of the web page for retrieving this data is: https://cloudcenter.tianditu.gov.cn/administrativeDivision/. The map base layer has been reviewed and approved with the approval number GS (2024) 0650. The base map is unmodified.

Fig 2. The effects of different treatments on the growth of EnG at different temperatures.

T1(addition of PGPR but no addition of NPK fertilizers), T2 (neither PGPR nor NPK fertilizers), T3 (addition of PGPR and NPK fertilizers), and T4 (no addition of PGPR but addition of NPK fertilizers).

Fig 3. Effect of different treatments on plant height (PT), dry weight (DW), and plant chlorophyll (Chl)content.

Lowercase letters indicate differences between treatments and uppercase letters indicate differences between temperatures.

Fig 4. Effect of different treatments on root length (RL), number of root branches (RB), root surface area (RSA), and root average diameter (RD).

Lowercase letters indicate differences between treatments and uppercase letters indicate differences between temperatures.

Fig 5. Effect of different treatments on soluble sugars (SS), and soluble proteins (SP)content.

Lowercase letters indicate differences between treatments and uppercase letters indicate differences between temperatures.

Fig 6. Effect of different treatments (T3 and T4) on nutrient utilization.

Physiological efficiency of nitrogen (NPE), phosphorus (PPE), potassium (KPE), agronomic efficiency of nitrogen (NAE), phosphorus (PAE) and potassium (KAE), and apparent recovery efficiency of nitrogen (NRE), phosphorus (PRE) and potassium (KRE) content. * means p < 0.05, ** means p < 0.01, *** means p < 0.001, ns means no significant difference.

Fig 7. Relationship between plant growth factors and nutrient utilization.

(a) Spearman’s correlation between the relative abundance of PE, AE, and RE, and Plant growth factors. *, **, and *** represent significant correlations at the 0.05, 0.01, and 0.001 levels. (b) Mantel test between nutrient utilization and indicators of plant growth. In Figure (a), the thickness and color of the lines are indicated by Mantel’s p/r values, illustrating the degree of correlation’s significance and intensity. Figure (b) employs a heatmap, where the color gradient communicates that blue denotes a positive correlation, whereas red indicates a negative one. PT, plant height; DW, dry weight; Chl, plant chlorophyll; RL, root length; RB, number of root branches; RSA, root surface area; RD, root average diameter; SS, soluble sugars; SP, soluble proteins.