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Nitrogen (N) plays an important role in mitigating salt stress in tree species. We investigate the genotypic differences in the uptake of ammonium (NH4+) and nitrate (NO3−) and the importance for salt tolerance in two contrasting poplars, salt-tolerant Populus euphratica Oliv. and salt-sensitive P. simonii × (P. pyramidalis × Salix matsudana) (P. popularis cv. 35-44, P. popularis). Total N content, growth and photosynthesis were significantly reduced in P. popularis after 7 days of exposure to NaCl (100 mM) supplied with 1 mM NH4+ and 1 mM NO3−, while the salt effects were not pronounced in P. euphratica. The 15NH4+ trace and root flux profiles showed that salt-stressed poplars retained ammonium uptake, which was related to the upregulation of ammonium transporters (AMTs) in roots, as two of the four AMTs tested significantly increased in salt-stressed P. euphratica (i.e. AMT1.2 , 2.1) and P. popularis (i.e. AMT1.1 , 1.6). It should be noted that P. euphratica differs from salt-sensitive poplar in the maintenance of NO3− under salinity. 15NO3− tracing and root flux profiles showed that P. euphratica maintained nitrate uptake and transport, while the capacity to uptake NO3− was limited in salt-sensitive P. popularis. Salt increased the transcription of nitrate transporters (NRTs), NRT1.1 , 1.2 , 2.4 , 3.1 , in P. euphratica , while P. popularis showed a decrease in the transcripts of NRT1.1 , 2.4 , 3.1 after 7 days of salt stress. Furthermore, salt-stimulated transcription of plasmalemma H+-ATPases (HAs), HA2 , HA4 and HA11 contributed to H+-pump activation and NO3− uptake in P. euphratica. However, salt stimulation of HAs was less pronounced in P. popularis , where a decrease in HA2 transcripts was observed in the stressed roots. We conclude that the salinity-decreased transcripts of NRTs and HAs reduced the ability to uptake NO3− in P. popularis , resulting in limited nitrogen supply. In comparison, P. euphratica maintains NH4+ and NO3− supply, mitigating the negative effects of salt stress. [ABSTRACT FROM AUTHOR]

Objective The aim of this study was to evaluate the efficacy of metagenomic next-generation sequencing (mNGS) for the identification of Gram-negative bacteria (GNB) infections and the prediction of antimicrobial resistance. Methods A retrospective analysis was conducted on 182 patients with diagnosis of GNB infections who underwent mNGS and conventional microbiological tests (CMTs). Results The detection rate of mNGS was 96.15%, higher than CMTs (45.05%) with a significant difference (χ 2 = 114.46, P <.01). The pathogen spectrum identified by mNGS was significantly wider than CMTs. Interestingly, the detection rate of mNGS was substantially higher than that of CMTs (70.33% vs 23.08%, P  < .01) in patients with but not without antibiotic exposure. There was a significant positive correlation between mapped reads and pro-inflammatory cytokines (interleukin-6 and interleukin-8). However, mNGS failed to predict antimicrobial resistance in 5 of 12 patients compared to phenotype antimicrobial susceptibility testing results. Conclusions Metagenomic next-generation sequencing has a higher detection rate, a wider pathogen spectrum, and is less affected by prior antibiotic exposure than CMTs in identifying Gram-negative pathogens. The mapped reads may reflect a pro-inflammatory state in GNB-infected patients. Inferring actual resistance phenotypes from metagenomic data remains a great challenge. [ABSTRACT FROM AUTHOR]