A Comparative Study of the Cellular Microscopic Characteristics and Mechanisms of Maize Seedling Damage from Superabsorbent Polymers

Superabsorbent polymers (SAPs) as soil moisture conditioners have been increasingly used in agriculture, but conflicting results were reported regarding the effects of SAPs on crop growth. In this study, both laboratory cultivation and analysis were conducted to investigate the effects of different SAPs on the growth and physiology of crops under water-saving agricultural practices. Maize (Zea mays L.) seedlings were cultivated using distilled water or three different SAP hydrogels, sodium polyacrylate (SP), potassium polyacrylate (PP), and sodium polyacrylate embedded with phosphate rock powder (SPP), as growth media. Growth characteristics of the model plant and damage were assessed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that both the SP and PP treatments had pronounced negative effect on the hydrogels of growth of maize seedlings. The SPP treatment appeared to facilitate the stem-leaf growth and had no obvious adverse effect on root growth. All the three hydrogel treatments caused varying degrees of damage to the organizational structure and cellular morphology of the roots, with the SP and PP treatments causing the most severe damage; the membrane system of root cells was damaged by both SP and PP treatments. An excessive accumulation of sodium and reduction of calcium occurred in the roots may be responsible for the observed damage to the cell membrane system, which, in turn, may have promoted the wilting of the cells.