T.Z. Liu, J.M. Zhang, Z.W. Mao and R.J. Li
College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, Guangdong 510642, China; Guangdong Engineering Research Center of Grassland Science

SUMMARY Endophytic diazotrophic bacteria have been found within many graminaceous plants in the last decades and may contribute to nitrogen (N) nutrition through biological nitrogen fixation while promoting growth and stress tolerance to host plants. Their colonization and growth promotion were reported to be affected by plant N nutrition level. However, little is known on effects of endophytic diazotrophic bacteria and their interaction with N fertilization on turfgrass. A study was conducted to evaluate the growth and turf quality of ‘TifEagle’ bermudagrass in response to inoculation with endophytic diazotroph bacteria at different rates of N fertilization. Diazotrophic strains 7D and BM13 were previously isolated from native common bermudagrass. Bacterial colonization was applied by soaking ‘TifEagle’ bermudagrass plants for 24 h with liquids of the two diazotrophic strains respectively. Four rates of N fertilizer with urea at 0, 2, 4 and 8 g m-2 were applied to the inoculated and non-inoculated ‘TifEagle’ bermudagrass once a month after planting. Results showed that the growth rate, clipping yield, turf quality and shoot dry biomass increased with increased N fertilizer rates. Inoculation with diazotrophic strains in the absence of N fertilization resulted in growth promotion, however at 8 g m-2 of N fertilization, there was a significant decrease for root dry biomass compared to the non-inoculated plants. These results suggest that high N fertilization might inhibit the biological N fixation by endophytes in root systems. These findings could be helpful in the use of endophytic bacteria to supply bermudagrass and other turfgrass with biologically fixed N. Keywords diazotroph, fertilization rates, biological nitrogen fixation, 'TifEagle' bermudagrass, quality

Significance of this study What is already known on this subject? Turfgrass needs frequent application of nitrogen to meet growth requirements and compensate for nitrogen loss through frequent clippings removal. However, excessive use of nitrogen fertilizers has been associated with environmental pollution. It has been suggested that endophytic diazotrophic bacteria may be an efficient means for supplying graminaceous plants with biological nitrogen fixation. What are the new findings? The study showed that inoculation with diazotrophic strains in the absence of nitrogen fertilization resulted in growth promotion of bermudagrass. The application of higher amounts of nitrogen fertilizer undermined the effect of inoculation. What is the expected impact on horticulture? The diazotrophic strains may be potentially effective turfgrass growth promoting bacteria agents. They have a potential to be utilized as a biofertilizer for a wide variety of plants in various climatic and edaphic conditions.

E-mail: jimmzh@scau.edu.cn  

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Received: 19 April 2016 | Accepted: 1 July 2016 | Published: 29 August 2016 | Available online: 29 August 2016