Coupling effects of water and nitrogen fertilization on root morphological characteristics of Moringa oleifera seedlings

Abstract

Moringa oleifera is a perennial tropical deciduous tree species, which has high economic value and cultivation purpose. In order to investigate the effects of different water (W) and nitrogen (N) additions on the root growth and traits of M. oleifera, we explored the response of root growth (e.g., root length, surface area, volume and average diameter of coarse and fine roots) of M. oleifera seedlings to the coupling of different soil water and nitrogen availabilities. There were three soil W gradients including 40% (low water, W1), 60% (medium water, W2), 80% (high water, W3) of field saturated water capacity (SWC), and four N application levels, including no notrigen (N0, 0 g·plant-1), low notrigen (N1, 0.6 g·plant-1), medium notrigen (N2, 1.8 g·plant-1), and high notrigen (N3, 3.6 g·plant-1). The results were as follows: (1) W treatment had no significant effects on the coarse and fine root traits. (2) N treatment significantly affected the coarse root length, surface area, volume, average diameter and specific root area (SRA), while only significantly influenced fine root average diameter and SRA. (3) Two-way ANOVA demonstrated that the interaction between W and N only dramatically affected fine root length; under the same W treatment, low N promoted but high N suppressed the coarse and fine root length, surface area and volume, suggesting that the coupling of N1 with W2, or N1 with W3 to some extent promoted the root growth. The study indicates that single W treatment does not change the root traits, N1 promotes but N3 inhibit the root growth, and the coarse root are more sensitive to N application than fine root thus the coupling of W and N can obviously regulate the root growth of M. oleifera. Therefore, in order to promote the growth and biomass accumulation of M. oleifera, usage and coupling percentage of water and nitrogen should be restrained and effectively enhance the water and nitrogen efficiency in practices.

Keywords

• coupling of water and nitrogen
• root traits
• fertilization
• cultivated species
• tropics