Replant problem and soil toxicity of passion fruit (Passiflora edulis Sims) in China

We investigated the soil toxicity in passion fruit plantations, the effects of old soils on the growth of the replanted passion and changes in photosynthetic parameters, physiological and biochemical parameters in the passion fruit leaves. In laboratory bioassays, we found that older soils of 1-, 2- and 3-year plantations significantly inhibited the root length of lettuce and passion fruit. The growth parameters (stem girth and perimeter, vine length, leaf area and shoot dry weight of passion fruit seedlings were significantly decreased when cultured in the older soils, compared with the virgin soils. Photosynthesis in the replanted seedling leaves cultured in the older soils were significantly lower than that cultured in the unplanted soils. The activity of antioxidant enzymes [superoxide dismutase (SOD), Peroxidase (POD) and catalase (CAT)] were significantly decreased in the replanted seedling leaves, along with decrease in insoluble carbohydrate and soluble protein. In replanted seedling leaves, the level of malondialdehyde (MDA) and abscisic acid (ABA) significantly increased, but the levels of indole-3-acetic acid (IAA) and cytokinins (ZR) of significantly decreased. Thus the older soils of passion fruit plantations have negative effects on the replanted passion fruit seedlings, suggesting the presence of soil autotoxicity in passion fruit plantations.