PubMed · 2026-06-08
Adding straw biochar to rice paddy soils can backfire under heat stress: while it mildly helps algae handle heavy metals at normal temperatures, at higher temperatures it amplifies metal toxicity, crashing algal populations and reducing their ability to keep cadmium and manganese out of the water.
At temperatures of 34°C and above, straw biochar switched from mildly protective to a stress amplifier, causing algal biomass to drop by over 60%.
The combined heat and biochar stress reduced algae's metal-trapping capacity by 44–48%, potentially allowing more cadmium and manganese to enter paddy water and rice grain.
A machine learning model (R² = 0.77) confirmed temperature and biochar dose are the strongest predictors of metal retention, underscoring that biochar recommendations must account for local climate conditions.
