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 (NO 3 - ) and ammonium (NH 4 + ) 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 NH 4 + rather than NO 3 - had greater net root Na + uptake, K + efflux, and translocation to the shoots, especially in leaves. In contrast, males receiving NO 3 - rather than NH 4 + 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.