State Key Laboratory of Efficient Production of Forest Resources, College of Biological Sciences and Technology (Box 162), Beijing Forestry University, Qinghua East Road 35, Haidian District, Beijing 100083, P.R. China.
Tree Physiol. 2024 Feb 11;44(3). doi: 10.1093/treephys/tpae020.
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.
氮（N）在减轻树种盐胁迫方面起着重要作用。我们研究了两种不同的杨树（耐盐的胡杨和盐敏感的银白杨×（加拿大杨×毛白杨）（中林 35-44，中林 35-44））在铵（NH4+）和硝酸盐（NO3-）吸收方面的基因型差异及其对盐度耐受性的重要性。在 1 mM NH4+和 1 mM NO3-供应下，盐胁迫 7 天后，中林 35-44 的总 N 含量、生长和光合作用显著降低，而胡杨的盐度影响不明显。15NH4+示踪和根系通量分析表明，盐胁迫下的杨树保留了对铵的吸收，这与根系中铵转运体（AMTs）的上调有关，因为在盐胁迫下，测试的四种 AMTs 中有两种在胡杨（即 AMT1.2、2.1）和中林 35-44（即 AMT1.1、1.6）中显著增加。值得注意的是，胡杨与盐敏感的杨树在盐度下对硝酸盐的维持方式不同。15NO3-示踪和根系通量分析表明，胡杨维持硝酸盐的吸收和运输，而盐敏感的中林 35-44 对硝酸盐的吸收能力有限。盐胁迫增加了胡杨中硝酸盐转运体（NRTs）NRT1.1、1.2、2.4、3.1 的转录，而盐胁迫 7 天后，中林 35-44 中 NRT1.1、2.4、3.1 的转录水平下降。此外，盐胁迫刺激质膜 H+-ATPases（HAs）HA2、HA4 和 HA11 的转录，有助于胡杨中 H+-泵的激活和 NO3-的吸收。然而，在中林 35-44 中，HAs 的盐刺激作用不明显，在胁迫根中观察到 HA2 转录物的减少。我们得出的结论是，盐胁迫降低了 NRTs 和 HAs 的转录本，降低了中林 35-44 吸收 NO3-的能力，导致氮素供应有限。相比之下，胡杨维持 NH4+和 NO3-的供应，减轻盐胁迫的负面影响。
