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Ammonium and nitrate affect sexually different responses to salt stress in Populus cathayana.

Nitrogen (N) fertilization is a promising approach to improve salt tolerance. However, it is poorly known how plant sex and inorganic N alter salt stress-induced Na+ uptake, distribution and tolerance. This study employed Populus cathayana Rehder females and males to examine sex-related mechanisms of salt tolerance under nitrate (NO3 - ) and ammonium (NH4 + ) nutrition. Males had a higher root Na+ efflux, lower root-to-shoot translocation of Na+ and higher K+ /Na+ , which enhanced salt tolerance under both N forms compared to females. On the other hand, decreased root Na+ efflux and K+ retention, and an increased ratio of Na+ in leaves relative to shoots in females caused greater salt sensitivity. Females receiving NH4 + rather than NO3 - had greater net root Na+ uptake, K+ efflux and translocation to the shoots, especially in leaves. In contrast, males receiving NO3 - rather than NH4 + had increased Na+ translocation to the shoots, especially in the bark, which may narrow the difference in leaf damage by salt stress between N forms despite a higher shoot Na+ accumulation and lower root Na+ efflux. Genes related to cell wall synthesis, K+ and Na+ transporters and denaturized protein scavenging in the barks showed differential expression between females and males in response to salt stress under both N forms. These results suggested that the regulation of N forms in salt stress tolerance was sex-dependent, which was related to the maintenance of the K+ /Na+ ratio in tissues, the ability of Na+ translocation to the shoots, and the transcriptional regulation of bark cell wall and proteolysis profiles. This article is protected by copyright. All rights reserved.