Synergistic effects of nano-hydroxyapatite and zeolite on chromium tolerance in Pleioblastus pygmaeus: Physiological, biochemical and molecular evidence

Soil contamination by chromium (Cr) is one of the most pressing constraints on sustainable agriculture and crop productivity. The current work evaluated whether 100 mg/L nano-hydroxyapatite (n-HAP) combined with 25 g/kg zeolite (Ze) can act synergistically to relieve Cr-induced toxicity in Pleioblastus pygmaeus , a bamboo taxon recognized for its strong phytoremediation capacity. The trial was carried out inside a greenhouse under tightly regulated conditions; the plants received a range of Cr doses (0–150 mg L −1 ) and were supplied with n-HAP and Ze, applied either separately or as a co-treatment. The data showed that the two amendments markedly improved mineral acquisition (P, Mg, Mn, K, Ca), promoted biomass gain and helped preserve photosynthetic pigments. Moreover, the combined treatment enhanced enzymatic and non-enzymatic antioxidant defenses, reduced chromium accumulation and translocation, improved membrane stability and relative water content, and increased the accumulation of osmoprotectants, including proline and polyamines. At the molecular level, the combined application significantly upregulated the antioxidant-related genes SOD , POD , CAT , and PAL , consistent with enhanced oxidative stress tolerance. Overall, these physiological, biochemical, and molecular responses demonstrate the synergistic effects of nano-hydroxyapatite and zeolite in improving chromium tolerance in P.pygmaeus . The proposed complementary mechanisms involve reduced chromium bioavailability together with enhanced nutrient acquisition and antioxidant defense, providing a promising strategy for the sustainable remediation of chromium-contaminated soils.