Long-distance responses of ginger to soil sulfamethoxazole and chromium: Growth, co-occurrence with antibiotic resistance genes, and consumption risk

The coexistence of antibiotics and heavy metals in agroecosystems is nonnegligible, which permits the promotion of antibiotic resistance genes (ARGs) in crops, thus posing a potential threat to humans along the food chain. In this study, we investigated the bottom-up (rhizosphere -> rhizome -> root -> leaf) long-distance responses and bioenrichment characteristics of ginger to different sulfamethoxazole (SMX) and chromium (Cr) contamination patterns. The results showed that ginger root systems adapted to SMX- and/or Cr-stress by increasing humic-like exudates, which may help to maintain the rhizosphere indigenous bacterial phyla (i.e., Proteobacteria, Chloroflexi, Acidobacteria and Actinobacteria). The root activity, leaf photosynthesis and fluorescence, and antioxidant enzymes (SOD, POD, CAT) of ginger were significantly decreased under high-dose Cr and SMX co-contamination, while a "hormesis effect" was observed under single low-dose SMX contamination. For example, CS100 (cocontamination of 100 mg/L SMX and 100 mg/L Cr) caused the most severe inhibition to leaf photosynthetic function by reducing photochemical efficiency (reflected on PAR-ETR, phi fPSII and qP). Meanwhile, CS100 induced the highest ROS production, in which H2O2 and O-2(center dot-) increased by 328.82% and 238.00% compared with CK (the blank control without contamination). Moreover, co-selective stress by Cr and SMX induced the increase of ARG bacterial hosts and bacterial phenotypes containing mobile elements, contributing to the high detected abundance of target ARGs (sul1, sul2) up to 10(-2)similar to 10(-1) copies/16S rRNA in rhizomes intended for consumption.