Photosynthetic and rhizospheric response characteristics to Cd stress in five (hyper)accumulator species from two contrasting soils

Evaluating the adaptive responses of different plant species to different types of Cd-contaminated soils and selecting the most effective hyperaccumulator are essential for improving remediation efficiency. In this study, we evaluated the Cd accumulation capacity and adaptive responses of five common (hyper)accumulator: Amaranthus hypochondriacus (A.H), Solanum nigrum (S.N), Celosia argentea (C.A), Phytolacca acinosa (P.A), and Sedum plumbizincicola (S.P), which were grown in two typical Cd-contaminated soils from Renhua (RH) and Maba (MB) in southern China. The results demonstrated that photosynthetic and rhizospheric responses were key factors in mediating plant adaptation to Cd stress. Leaf Cd levels were between 40.4 and 152.9 mg kg^-1 in MB soil and between 9.9 and 541.4 mg kg^-1 in RH soil, with S. plumbizincicola and P. acinosa accumulating the most and least Cd, respectively. Amaranthus hypochondriacus and S. nigrum exhibited the greatest above-ground biomass in MB and RH soils, respectively, whereas P. acinosa consistently demonstrated the highest root biomass in both soils. Phytolacca acinosa also showed the highest concentration of photosynthetic pigments, with 42.8 ∼ 220.4 % higher than those of other species grown in RH soil, likely due to higher Cu uptake. Conversely, S. plumbizincicola exhibited the lowest levels of photosynthetic pigments, suggesting an inverse correlation between leaf Cd concentration and the accumulation of photosynthetic pigments. Phytolacca acinosa demonstrated significantly higher rhizospheric microbes compared to other species, with increases in bacteria, actinomycetes, and fungi ranging from 20.9 % to 30.7 %, 10.6-30.2 %, and 78.4-182.9 %, respectively. In addition, root-secreted oxalic and malic acids were elevated in all species, particularly in RH soil, helping to mitigate the restrictive effects of near-neutral pH on nutrient availability. These findings underscore that hyperaccumulator species employ unique physiological and rhizospheric strategies to manage Cd stress, with these strategies differing based on Cd exposure level and soil types.