Microstructure and biodegradation of long-established Salix psammophila sand barriers on sand dunes

Abstract

Salix psammophila has been extensively used as a sand barrier material for various desertification control applications over the years. Thus, elucidating the long-term degradation processes of this sand barrier in desert environments is of great importance. In this study, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemometric methods were used to evaluate and compare the structure and performance of the S. psammophila sand barrier during degradation. The results clearly showed that the structure and performance of the S. psammophila sand barrier varied in the different vertical sections of the barrier. With the increase in the setting period of the sand barriers, the atmospheric exposure section (AES) and stable sand buried section (SSBS) exhibited deterioration and decay, respectively. The mass loss rate was SSBS>AES>ASDI, which also exhibited different degrees of decrease in mechanical properties such as in the modulus of rupture, ultimately resulting in lodging, damage, and the loss of the function of the S. psammophila sand barrier in preventing wind–sand movement and fixing quicksand. Microstructural changes showed that after eight years of setting, the vessel and parenchyma cells were severely damaged and the corresponding chemical components, such as cellulose, hemicellulose, and lignin, were degraded to a certain extent. The decrease in the crystallinity index values based on the XRD analysis confirmed the deterioration and obvious changes in the crystallinity, which affected the strength of the S. psammophila sand barrier. The FT-IR analysis indicated that several characteristic peaks of cellulose, hemicellulose, and lignin in the AES and SSBS sections disappeared or were weakened compared with the ASDI section. Comprehensive analysis showed that the primary reason for the serious deterioration in AES was the aging caused by exposure to continuous UV radiation in the atmospheric environment, while the serious decay of SSBS was mainly caused by microbial and fungal activity in the sandy environment, ultimately leading to the degradation of the S. psammophila sand barrier. Our findings suggest that it is necessary to further strengthen the anti-aging and anti-corrosion measures in the resource utilization process of the S. psammophila sand barrier in the future. • Long-established Salix psammophila sand barriers on sand dunes, the AES and SSBS exhibited deterioration and decay phenomena, respectively. • The main explanation for the severe deterioration of the AES was the aging caused by exposure to continuous strong UV exposure in the atmospheric environment. • The serious decay of the SSBS was primarily caused by the microbial and fungal activities in the sandy environment. • It is necessary to further strengthen anti-aging and anti-corrosion measures in the resource utilization process of S. psammophila sand barriers.