Physiological Characteristics and Nitrogen Absorption/Distribution Features of Salix matsudana Under Different Nitrogen Stresses

Abstract

This chapter discusses the growth, nitrogen absorption/distribution, and physiological responses of Salix matsudana seedlings cultured in hydroponic solution with different nitrogen sources ammonium nitrogen (${{{\text{NH}}_{4}}^{ + }}$–N ) or nitrate nitrogen (${{{\text{NO}}_{3}}^{ - }}$–N)); inadequate, medium, high, or excessive nitrogen. Results showed that S. matsudana biomass increased with increasing nitrogen concentration to a certain extent. S. matsudana growth was inhibited by excessive nitrogen concentration, and the inhibition rate of ${{{\text{NH}}_{4}}^{ + }}$–N was higher than that of ${{{\text{NO}}_{3}}^{ - }}$–N. S. matsudana showed absorption preference toward ${{{\text{NH}}_{4}}^{ + }}$–N than ${{{\text{NO}}_{3}}^{ - }}$–N under the same nitrogen concentration. at.% content, ¹⁵N absorption, and Ndff% exhibited the following trend in different organs of S. matsudana: root > stem > leaf. Moreover, ${{{\text{NH}}_{4}}^{ + }}$–N content was higher than that of ${{{\text{NO}}_{3}}^{ - }}$–N, and the difference intensified with increasing nitrogen concentration. Excessive and inadequate nitrogen concentrations of ${{{\text{NH}}_{4}}^{ + }}$–N and ${{{\text{NO}}_{3}}^{ - }}$–N exerted different effects on physiological parameters in roots and leaves. Root activity under excessive concentrations of ${{{\text{NH}}_{4}}^{ + }}$–N and ${{{\text{NO}}_{3}}^{ - }}$–N decreased by 50.61 % and increased by 19.53 %, respectively, compared with that of the control group. Root length, root surface area, average root diameter, root volume, and root tips were lower by 30.92, 29.48, 19.44, 27.01 and 36.41 %, respectively, in ${{{\text{NH}}_{4}}^{ + }}$–N treatment and by 1.66, 5.65, 1.49, 5.06, and 25.72 %, respectively, in ${{{\text{NO}}_{3}}^{ - }}$–N treatment than those in the control group. This result indicated that high ${{{\text{NH}}_{4}}^{ + }}$–N concentrations elicited stronger stress effect on S. matsudana than ${{{\text{NO}}_{3}}^{ - }}$–N. Therefore, the effect of ${{{\text{NH}}_{4}}^{ + }}$–N on S. matsudana could be alleviated to some extent by adding ${{{\text{NO}}_{3}}^{ - }}$–N to improve the remediation of water polluted by nitrogen.