| Aiming to remedy the problem of soil cadmium contamination loquat orchard, this study used the biological species diversity principle of ecological system, via screening out of potential cadmium hyperaccumulator (Solanum photeinocarpum) from local orchard weeds for grfafting, and intercropping post-grafting generation of S. photeinocarpum with loquat, to study the effects of intercropping on ecophysiological characteristics, DNA methylation patterns and cadmium accumulation characteristics of two kinds of plants. The study was in order to screen out post-grafting generation of 5. photeinocarpum which could significantly reduce the cadmium content in loquat fruit, and reveal eco-regulatory mechanism of post-grafting generation of S. photeinocarpum reducing cadmium accumulation of loquat. This study would be important scientific significance and value on cadmium contaminated orchard of loquat and other fruit-producing areas. The main results were as follows:1. By using high soil cadmium concentration contamination screening method,6 kinds of cadmium hyperaccumulators or cadmium accumulators were screened out from 11 kinds of dominance orchard weeds. The screening efficiency was high. Gnaphalium affine, Galinsoga parviflora and Youngia erythrocarpa were cadmium hyperaccumulators, Solanum photeinocarpum was a potential cadmium hyperaccumulator, and Cardamine hirsuta and Galium aparine were cadmium accumulators.2. Using different concentrations of cadmium contamination (0-20 mg/kg) to deal with the annual loquat seedling from seed, the results showed that with the increase of soil cadmium concentration, the root biomass, stem biomass, leaf biomass, shoot biomass and chlorophyll content of loquat seedling from seed reduced, but there were no obvious symptoms of poisoning. These results showed the annual loquat seedling from seed had the strong patience to soil cadmium stress. The distribution of cadmium content in annual loquat seedling from seed was:roots> stems> shoots> leaves. With the increase of soil cadmium concentration, cadmium content in annual loquat seedling from seed increased, and cadmium accumulation amounts in shoots increased before soil cadmium concentration of 10 mg/kg and decreased after that concentration. Therefore, loquat seedling from seed could be used as the remedy material to renedy soil cadmium contamination orchard within the concentration of 10 mg/kg.3. Applying the straws of cadmium hyperaccumulators G parviflora, Y. erythrocarpa and S. photeinocarpum in cadmium contamination soil (10 mg/kg), and planting loquat seedling from seed, the results showed that the biomass of loquat seedling from seed was:S. photeinocarpum straw> G parviflora straw> not applying> Y. erythrocarpa straw, and the cadmium content was:S. photeinocarpum straw> Y. erythrocarpa straw> G. parviflora straw> not applying. The maxima cadmium accumulation amounts of two loquat seedling from seed were S. photeinocarpum straw. Therefore, S. photeinocarpum straw was the best material to improve soil cadmium contamination orchard remedy ability of loquat seedling from seed.4. Using different root stocks for grafting:ungrafted (UG), self-rooted grafting by the same one S. photeinocarpum seedling (SG), self-rooted grafting by two different sizes of S. photeinocarpum seedlings (DG) and grafting on the rootstock of wild potato (PG), showed that the shoot biomasses of SG, DG and PG decreased compared with UG, which was caused by the short planting time. Compared with UG, SG and DG increased cadmium content in S. photeinocarpum, and PG decreased that. Grafting increased DNA methylation rate of S. photeinocarpum with the order of PG > DG> SG> UG, and DNA methylation pattern changes was priority with hypermethylation with the order of PG> DG> SG versus UG, which would improve the resistance of S. photeinocarpum to cadmium stress.5. By study the cadmium accumulation characterics of post-grafting generation of S. photeinocarpum, the grafting did not cause the gene mutation in first post-grafting generation of S. photeinocarpum, but increased the biomass, cadmium content, cadmium accumulation amount, chlorophyll content, antioxidant enzyme (SOD, POD and CAT) activity and photosynthesis of first post-grafting generation of S. photeinocarpum with the order of PG1> UG1> SG1> DG1. DNA methylation level and DNA methylation pattern changes of first post-grafting generation of S. photeinocarpum were consistent with grafting contemporary, indicating that DNA methylation changes by grafting transfered to generation. The biomass, cadmium content and cadmium accumulation amount of second and third post-grafting generations of S. photeinocarpum were consistent with the trend of first generation, indicating that epigenetic changes caused by grafting could be stable transfered in post-grafting generation of S. photeinocarpum. Therefore, grafting could improve cadmium remedy ability of post-grafting generation of S. photeinocarpum, and this was a new method to meliorate hyper accumulator.6. The first post-grafting generation of S. photeinocarpum intercropping with loquat seedling from seed increased the biomass, cadmium content and cadmium accumulation amount in shoots, chlorophyll content, antioxidant enzyme (SOD, POD and CAT) activity, photosynthesis, soluble sugar content, total phosphorus content and total potassium content of two kinds of plants compared with monoculture respectively. These results suggested that post-grafting generation of S. photeinocarpum intercropping with loquat seedling from seed was a reasonable collocation method, which could promote the two kinds of plants growth and and improving cadmium remedy ability. In addition, intercropping with first post-grafting generation of S. photeinocarpum, DNA methylation level of loquat seedling from seed improved with the order of intercropping (PG1)> intercropping (DG1)> intercropping (SG1)> intercropping (UG1)> monoculture, and DNA methylation pattern changes was priority with hypermethylation with the order of intercropping (PG1)> intercropping (DG1)> intercropping (SG1)> intercropping (UG1) versus monoculture. These results indicated that intercropping improved the resistance of loquat seedling from seed.7. The pot and plot experiments showed that first post-grafting generation of S. photeinocarpum intercropping with grafted loquat tree and bearing loquat tree decreased cadmium contents in roots and young branches, and increased cadmium content in old branches compared with monoculture. The intercropping decreased cadmium contents in pericarp, sarcocarp and seed of loquat fruit compared with monoculture, and the order was monoculture> intercropping (UG1)> intercropping (SG1)> intercropping (DG1)> intercropping (PG1). The cadmium content in sarcocarp of loquat fruit the decreased of 8.97%-50.65% compared with monoculture, but it did not reach the standard of limit to green food (0.03 mg/kg). It might be related to soil cadmium concentration and loquat cultivar. By intercropping, the single fruit weight, longitude diameter, horizontal diameter of loquat fruit had no obvious change compared with monoculture. The total acid content of intercropped loquat fruit was lower than monoculture, but Vc content, soluble solid content and total sugar content of intercropped loquat fruit were higher than monoculture, indicating that intercropping with first post-grafting generation of S. photeinocarpum improved the nutritional quality of loquat fruit. Intercropping with grafted loquat tree and bearing loquat tree also increased cadmium remedy ability of first post-grafting generation of S. photeinocarpum with the order of PG1> DG1>SG1> UG1, and the remedy effect was obvious.To sum up, Aiming to soil cadmium contamination loquat orchard, first post-grafting generation of S. photeinocarpum intercropping with loquat was an effective way of phytoremediation, and intercropping with PG1 was best, followed by intercropping with DG1. |
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