The influence of phosphorus on leaf function, cadmium accumulation and stress tolerance of poplar leaves under cadmium exposure

A pot experiment was conducted to evaluate the effect of phosphorus (P) availability on leaf function, cadmium accumulation and stress tolerance of poplar leaves under cadmium exposure. The pot experiment consisted of two-factors including three Cd treatments and two P treatments, and a clone of Populus × euramericana was used as plant material. Leaf development and gas exchange were less inhibited by Cd exposure than that by P deficiency. Under different P levels, Cd accumulation increased with the increasing intensity and duration of Cd exposure, while Cd accumulation in leaves was inhibited by P deficiency. With sufficient P nutrition, Cd content and Cd concentration of leaves reached 300 μg plant−1 and 32 μg g−1 DW, respectively. Cd was preferentially enriched in leaf veins to avoid Cd poisoning in photosynthetic apparatus. In the absence of Cd exposure, P promoted WUEi via increasing photosynthesis rate. In contrast, P nutrition promoted WUEi under Cd exposure via regulating stomata aperture and reducing water loss via transpiration. The activities of antioxidants including GR and CAT were enhanced by P addition, as a result of the elevated expression of related genes (Gr chl, Gr cyt, Cat2, Cat3). The mechanisms underlying the promotive effect of P on leaf function and Cd tolerance are elucidated. Phosphorus promotes leaf function and Cd tolerance of poplar by enhancing photosynthetic process, stomatal regulation and antioxidant defense. Phosphorus shortage reduced the levels of phytohormones, while P addition contributes to stress tolerance via promoting the levels of phytohormones including ABA, JA and IAA. Salicylic acid (SA) promotes stress tolerance under Cd exposure via affecting the inducement of antioxidant enzymes. The improved Cd tolerance of leaves facilitates leaf carbohydrate production, promotes Cd bio-extraction and benefits xylem development of poplars growing under Cd exposure.