Effects of Cadmium Stress on Mycelial Growth and Antioxidant Systems in Agaricus subrufescens Peck

Agaricus subrufescens Peck is a nutrient-rich edible fungi with a distinctive flavor, but most varieties are sensitive to cadmium (Cd), making cadmium contamination common during cultivation. Currently, excessive fertilizer uses and increased solid waste are exacerbating cadmium contamination in soils. Since A. subrufescens utilize agricultural residues like straw and livestock manure as cultivation substrates, Cd can be adsorbed readily, leading to secondary accumulation. In this study, the toxic effects of and response mechanisms to different Cd concentrations with respect to mycelial growth, heavy metal accumulation, and antioxidant systems of A. subrufescens were systematically investigated. The results indicated that the mycelia exhibited Cd accumulation capacity, with accumulation levels positively correlated with stress concentration. At a Cd concentration of 5 mg/L, the intracellular Cd concentration in the mycelia reached approximately 800 mg/kg. As the Cd concentration increased, the efficiency of Cd uptake by mycelia correspondingly decreased. Cadmium stress (≥0.5 mg/L) significantly inhibited mycelial growth and induced morphological abnormalities, with the mycelia exhibiting yellowing. Furthermore, Cd induced dose-dependent oxidative stress. Hydrogen peroxide and MDA levels peaked at a Cd concentration of 2 mg/L, reaching 2.26 μmol/g and 8.98 nmol/g, respectively, indicating heightened lipid peroxidation. Low concentrations of Cd (≤2 mg/L) promoted increases in ASA and GSH activity. SOD, POD, GR, and APX activities significantly increased, with the ASA-GSH cycle synergistically scavenging ROS. CAT activity remained persistently inhibited, APX/GR activity was suppressed, and total sugar metabolism was disrupted, leading to the collapse of antioxidant defenses. In summary, depending on the Cd concentration, A. subrufescens mycelia exhibit markedly different responses at low versus high concentrations. This study provides a foundation for further research into the application of edible fungi in heavy metal-resistant cultivation.