| American ginseng (Panax quinquefolium L.) is an important perennial understory herb for its medicinal properties. It usually takes four years from seeding to harvest of fresh root; however, replanting problem in the same field significantly affects its growth and yield. Crop rotation has been an efficient tool in control continuous cropping problem in agriculture, but no suitable rotation crop and period in field soil after cultivated American ginseng four years has been set up until now. In this study, we analyzed the variation of soil fertility, phenolic acids, fugal community and plant pathogenic fungus in soil after cultivated American ginseng four years (AG), 1 year-(American ginseng-maize/wheat, R-1),3 year-(American ginseng-maize/ wheat*3, R-3),5-year-rotation (American ginseng-maize/wheat*5,R-5) and field soil that has been cultivated maize or wheat (M/W) in view of soil ecology; the growth of American ginseng seedlings were also surveyed in pot-and field-grown experiments in different soil samples. Our study provides basic data for understanding the mechanism of replanting problem and form efficient crop rotation system between American ginseng and main crops.The main results are summarized as follows:1. Through determination and analysis of soil fertility in three soil samples that after four-years cultivation of American ginseng from Beijing, Shandong and Jilin, we find that little difference is observed in soils between Beijing and Shandong cultivation region in soil organic matter (SOM), alkali-hydrolyzable nitrogen (AN), and available potassium (AK), these parameters are significantly lower (P<0.05) than those from Jilin cultivation region. The available phosphorous(AP) contents between root zone and bulk soil samples in three cultivation regions are different, which may be concerned about the amount of fertilization in each region; the pH is Beijing>Shandong>Jilin. The contents of AN, AP and AK in root zone soil of three cultivation regions are higher than that from bulk soil except that SOM and pH show no obvious regularity. Analyzed by Ward’s method and squared Euclindean distance measure, Soil fertility of Beijing and Shandong are closer, which is farther from that of Jilin.2. We determined the nutrients in AG, R-1, R-3, R-5 and M/W. Compared to M/W, the levels of AN, AP and AK in AG increase 20.66%(P<0.05),6.49% and 10.19%(P>0.05) respectively while the SOM, total nitrogen (TN) and total potassium (TK) decrease by 6.28-10.19%(P>0.05). After one-year-rotation with wheat/corn, the contents of available nutrients in soil decreases. After-three-years rotation with wheat/corn, the contents of AN, AK, TN and SOM are lower than that in AG significantly (P<0.05), but no great changes are found in contents of AP, TP and pH. The above parameters in R-5 get close to that of M/W.3. The contents of phenolic acids are measured using HPLC in AG from Beijing, Shandong and Jilin (involved root zone soil and bulk soil). The content of p-hydroxybenzoic acid, vanillic acid, vanillin, syringic acid, ferulic acid, benzoic acid, salicylic acid and cinnamic acid in root zone soil samples from Beijing and Shandong region are similar, which are significantly lower than that from Jilin (P<0.05); the content of p-coumaric acid in Beijing and Jilin’s soil samples are closer each other and higher than that from Shandong significantly (P<0.05). The total content of phenolic acid in Jilin is higher 477.66%、400.96%(P<0.05) than that from Beijing and Shandong separately. The variation trend between root zone soil and bulk soil in three soil samples is similar, but ratio of phenolic acids is different in three regions. The ratio of p-coumaric acid in Beijing and Shandong’s soil samples are the highest among nine phenolic acids, and followed by vanillic acid and salicylic acid; the ratio of vanillic acid in Jilin region is the highest, whereas vanillin and salicylic acid come second. In three regions, the contents of vanillic acid, vanillin, p-coumaric acid, ferulic acid in root-zone soil are significantly higher than that in bulk soil (P<0.05). It implies that fibrous roots of American ginseng can secrete phenolic acids into soil and vanillic acid, vanillin, p-coumaric acid, ferulic acid are main ingredients.4. The contents of phenolic acid in the root-zone soils from 13 samples have close relations with root disease, yield and soil nutrient content. The content of p-coumaric acid, vanillic acid, syringic acid, ferulic acid in root-zone soil with severe root disease index is significantly higher 140.24-536.06%(P<0.05) than that of soil with light root disease index. Total content of phenolic acids is also higher 101.53%(P<0.05). The contents of p-hydroxybenzoic acid, syringic acid, benzoic acid, salicylic acid and p-coumaric acid in the root-zone soil with high root yield are lower 4.32-59.66%(P<0.05) than that soil with low root yield. With the higher nutrient levels of AN, AK and SOM, the content of vanillic acid, syringic acid, ferulic acid and p-coumaric acid in soil samples are higher 41.27-69.49%(P<0.05) than that in lower soil nutrients.5. The contents of syringic acid,p-coumaric acid, ferulic acid in AG are higher (P<0.05) than that in M/W, and decrease in R-1(P<0.05); after 3 and 5 years crop rotation, the contents of three phenolic acids in soil come close to that of M/W. The total content of phenolic acid in AG is higher than that of M/W (P<0.05); but there is no significant difference between soil after 3-5 years crop rotation and M/W in contents.6. We further amplified the ITS region of various fungi and digested the DNA fragment with Hinfl and HaeⅢ for T-RFLP patterns based on 49 identified fungi. A database including the fungus isolated mainly from American ginseng roots and root-zone soil was set up. It involves 40 species,25 genus, consisting of those from Alternaria, Cylindrocarpon, Fusarium, Phytophthora, Botrytis, Rhizoctonia, Trichoderma, Metarhizium and Penicillium. The database provides a basic tool for further study pathogenic fungi and bio-control fungi in field soil.7. On basis of TRF of ITS4 generated by HaeⅢ digestion and ITS IF generated by Hinf1 digestion separately, the diversity of fungal communities in soil is analyzed. The same trend is that Shannon-Wiener (H’)Simpson (D) and evenness (J) index all decreased in AG; however, Margalef (Ma) index increased (P>0.05) compared to M/W. The levels of the H’, and D index in R-5 are very close to M/W. The fungal community is similar in AG and R-1; and there exists no obvious difference between R-3, R-5 and M/W in the fungal community.8. On basis of TRF area generated by HaeⅢ digestion, we analyze variations of fungus in AG, R-1, R-3, R-5 and M/W. The main pathogenic fungi can be found in five soil samples on basis of database, however, the TRF area of pathogenic fungi in AG are bigger than that in other soil samples and some TRF area of pathogenic fungi in R-5 are similar to M/W. The results indicate that the TRF area of Fusarium, Cylindrocarpon, Botrytis cinerea, Phytophthora cactorum in AG are larger 22.17-191.28%(P>0.05) than that in M/W, and the TRF area of these pathogenic fungi in G-5 are smaller 26.32-59.60%(P>0.05) than AG. The TRF area of Trichoderma harzianum in AG is about 3.2 times (P>0.05) of M/W; the area of TRF in R-1, R-3 and R-5 is larger 317.82-663.72%(P>0.05) than that in AG, however, which has no evident regularity along with years.9. The growth of American ginseng seedlings in soil samples of AG, R-1, R-3, R-5 and M/W are observed by pot experiments. The results reveal that fresh, dried weight of root in R-1 and R-3 increase 21.68 and 23.80%(P>0.05),15.21 and 20.17% (P>0.05) separately compared to M/W. The fresh and dried root weight are similar between R-5 and MAV; the fresh weight increasing 45.05% and 49.61%(P<0.05), the dried weight increasing 42.53%、47.02%(P<0.05) compare to AG. The root disease index, ratio of diseased root and number of fibrous root are closer in R-1 and AG. Compare to AG, root disease index, ratio of diseased root decrease and number of fibrous root increase in R-3, R-5 and M/W (P<0.05).10. The field plot trials in soil with five-year wheat/maize rotation during a two-year period indicate that seedling emergency ratio is 92.71-98.61% in the first year and seedling survival ratio is between 80.56% and 87.33% in the second year among density of 100-800seeds/m2. The fresh and dried biomass of seedlings in summer and autumn have significant negative correlation with seeding density (r2=-1.00,P<0.01) in the second year. The concentration of phenolic acids varied in root zone soil of different growth stage and seedling. The contents of p-hydroxybenzoic acid and p-coumaric acid have significant negative correlations with seeding density (r2=-1.00, P<0.01) in summer of 2-year-old seedling. The fresh weight of single root is above 4.88 g in the condition that the density of seed is about 200～400 seeds/m2, which is a good choice in practical American ginseng garden. |
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