Nitrogen–Salt Interaction Adjusts Root Development and Ion Accumulation of the Halophyte Suaeda salsa

Abstract

Nitrogen (N) application might exert a great impact on root (biomass, length) distribution, which possibly contributes to ion and nutrient uptakes. Here, we address the effects of N application on these characteristics to detect how N improves its salt tolerance. Suaeda salsa was subjected to four salt levels (0.5, 1.0, 1.5, and 2.0%) and three N treatments (NO3−-N: 0, 0.25, and 0.50 g·kg−1) in soil column experiments. The N applications performed a “dose effect” that significantly enhanced the growth of Suaeda at low salt levels, while negative effects were displayed at high salt levels. Moderate N markedly benefited from Na+ and Cl− uptake, which was approximately 111 mg and 146 mg per plant at a salt level of 1.0%. Exposure to a certain N application significantly enhanced topsoil root length at salt levels of 0.5% and 1.0%, and it was higher by 0.766 m and 1.256 m under N50 treatment than that under N0 treatment, whereas the higher salt levels accelerate subsoil root growth regardless of N treatment. Therefore, its interactive effects on root development and ion uptake were present, which would provide further theoretical basis for improving saline soil amelioration by N application. Regression analysis always showed that topsoil root length generated more positive and significant influences on ion uptake and vegetative growth than total root length. The results suggested that N application is beneficial to salt tolerance by altering root allocation so as to raise its elongation and gather more ions for halophyte in the topsoil.

Nitrogen Promotes the Salt-Gathering Capacity of Suaeda salsa and Alleviates Nutrient Competition in the Intercropping of Suaeda salsa/Zea mays L.

“…S. salsa and Z. mays L. are two kinds of highly nitrogen-demanding plants, and insufficient nitrogen adversely affects their growth [ 20 , 21 ]. It was not to be ignored that, as the most direct exposure to adversity, root structure and function are terribly important to enhance the uptake in soil nutrients and accelerate microbial activities [ 35 , 36 , 37 ].…”

“…Nitrogen is an important regulatory factor that acts on halophytes at different developmental stages in their life history [ 20 , 21 ]. Studies have shown that the NO 3 − -N application can promote the germination and vigor index of suaeda seeds [ 20 , 22 ].…”

“…Therefore, nitrogen might generate an important influence in the suaeda/maize intercropping. Nitrogen can obviously promote the accumulation of base ions in S. salsa , which effectively contributes to the remediation of saline soil in agriculture [ 21 ]. Due to the ability in accumulating salt of halophyte root, this migration process might be accelerated in the root zone of halophytes with nitrogen supply.…”

“…S. salsa (suaeda) is an annual euhalophyte with high aptitude in gathering Na + to the root zone, being considered an ideal species for saline soil remediation in several studies [ 21 , 24 ]. Z. mays L. (maize) is a salt-sensitive non-halophyte with a fibrous root system that produces an important influence with a rhizosphere capacity in nutrient activation in the intercropping [ 25 , 26 ].…”