Effect of Temperature on Soil Geochemical Properties and Accumulation of Heavy Metals in Brassica napus L.

Abstract

According to the Inter-Governmental Panel on Climate Change (IPCC, 2021), the earth has been warmed at 1.09°C since the pre-industrial era, and global surface temperature is likely to be higher by 1.0°C to 5.7°C by the end of the twenty-first century (2081-2100). However, the effects of increased temperature on soil properties and heavy metal uptake of plants have not been known well. In order to investigate the effects of soil temperature on soil geochemical properties and the accumulation of heavy metals in plants, we grew rapeseeds (Brassica napus L.) in pots filled with contaminated field soil at 4 different temperatures (22.5, 22.9, 23.7, and 24.6°C) in controlled growth chambers. The results showed that elevated temperature inhibited the growth of rapeseed, and the seed yields decreased by 37 % at 24.6°C compared to 22.5°C. In the case of accumulation of heavy metals in rapeseed, the values of partial correlation coefficient after controlling the growth stages followed this order: Zn (0.50) > Cd (0.21) > Cu (0.19) > As (0.15) > Pb (0.13). The concentration of Zn in rapeseed showed a significant moderate positive correlation with soil temperature (r=0.50). At the maturity stage, elevated soil temperature gradually increased the translocation factor (TF) of Zn, Cd, and Pb from root to shoot. Furthermore, concentrations of Zn and Cd in rapeseed were highly correlated during all growth stages, with a high positive correlation (r > 0.7). It indicates that if the soil is heavily contaminated with Cd, increased soil temperatures could affect the accumulation of Cd in plant tissues. In total and bioavailable concentrations of heavy metals in soil, no significant variations were observed with soil temperatures. When controlling the timing of sample variables, soil pH was positively correlated with soil temperature, whereas electrical conductivity (EC) and cation exchange capacity (CEC) was negatively correlated with soil temperatures. This study suggested that elevated soil temperature affected complex plant processes and soil geochemical properties, leading to loss of productivity and soil-to-plant transfer of heavy metals. It reveals that future global warming could result in unanticipated crop yield and quality reductions, and consequently, it may have detrimental effects on the health of animals and human beings.