Characteristics and Mechanisms of Maize Seedling Damage By Superabsorbent Made of Acrylate Polymers.

Superabsorbent made of acrylate polymers (SAPs-A) dominates the agriculture market as soil moisture conditioners, but conflicting results were reported regarding the effects of SAPs-A on crop growth. In this study, the effects of SAPs-A on plants growth were investigated in greenhouse using maize seedling as an indicator plant.

The results showed that SAPs-A had a remarkable inhibitory effect on the growth of maize seedlings at the early growth stage and the effect was enhanced with increasing application rate. Scanning electronic microscopy (SEM) analysis of the cross-sections of the maize roots in soil culture showed that the organizational structure and cellular form of the maize root-end treated by SAPs-A were severely damaged, characterized by irregular cellular form, loose arrangement of cells and breakage of cortex parenchyma. Treatment with SAP hydrogels for one hour significantly increased MDA concentration in maize roots and decreased the activities of SOD and CAT. These changes increased with decreasing water absorption of the hydrogel. Addition of acrylic acid to growth medium inhibited the growth of maize seedlings at 2.5 mg/L, and the effect became significant at the concentration of 5 mg/L. Application of acrylic acid at the concentrations of 10 mg/L led to severe root-rot. The effects of acrylic acid and Na+ on inhibited crops growth appeared to be additive. The release and degradation of residual acrylic acid from SAPs-A increased with rising soil moisture content. Acrylic acid was completely degraded in 15-20 days, but Na⁺in SAPs-A released slowly in soil. These results indicate that the inhibitory effects of SAPs-A on crops growth are related to the high concentrations of Na+ and free acrylic acid, which are toxic to plants when roots penetrate through or near the hydrogels in soil.

Key Words: residual acrylic, Na+, SAP, adverse effect, soil moisture content