| Chinese cabbage (Brassica rapa) and radish (Raphanus sativus) were chosen as target species to test the effect of decomposing Zanthoxylum bungeanum leaf litter on the growth of them in an pot experiment. According to the annual litterfall of Zanthoxylum bungeanum in orchard, four levels of leaf litter addition including 0 g·pot-1(TCK),10 g·pot-1(T1),20 g·pot-1(T2) and 40 g·pot-1(T3) were used to treat Chinese cabbage, while 0 g·pot-1 SCK),15 g·pot-1(Si),30 g·pot-1(S2) and 60 g·pot-1(S3) were used to treat radish. All together,64 pots were used with 8 repeats for each level in each species. Four pots of each treatment were fertilized by BB fertilizer (N:29%, P:16%, K:10%) after the first sampling time, and they were fertilized for the second time after the second sampled time with 0.5 g·pot-1 for each fertilizing time. Seedlings were sampled from each pot on 30th,45th and 60th d after sowing, followed by determination of biomass and resistant physiology indexes. Photosynthetic indexes were determined on sunny day around 30th and 60th day after sowing. Meanwhile, gas chromatography-mass spectrometer (GC-MS) was used to indentify the chemical constitutes of Zanthoxylum bungeanum leaf litter and determine the relative content. The potential allelochemicals were primarily analyzed. The results were as follows:1 The inhibitory effects of decomposing Zanthoxylum bungeanum leaf litter indicated by Chinese cabbage fresh weight and modification of fertilization①When unfertilized, fesh weight of Chinese cabbage increased by low amount of leaf litter (T1) compared with CK, and slightly decreased by medium amount of leaf litter with non-significant differences at 30 d. However, when treated by high amount of leaf litter, it was decreased significantly. Fourty-five days after sowing, the fresh weight was significantly increased by addition of leaf litter, but the differences were not significant between leaf litter treatments. It indicated obvious allelopathic inhibition of Zanthoxylum bungeanum leaf litter at priniminary stage of decomposition (0-30 d), but after 45 d the allelopathic effect of leaf litter changed from inhibition into promotion. It was probably that the release of allelochemicals deceased while the release of nutrient increased as it was decomposing. Therefore, the inhibitory effect weakened or even disappeared while a large amount of nutrient released made the increase of Chinese cabbage growth at middle and later stages of decomposition.② After fertilized, the fresh weight of Chinese cabbage significantly inceased by leaf litter when compared with CK at 45 d. At 60 d, T2 treatment significantly increased the fresh weight while the effects of other leaf litter treatments were non-significant. The results of double factor variance analysis indicated significant interaction between the effect of decomposing leaf litter and the effect of fertilization at 45 and 60 d. Meanwhile, the allelopathic indexes (RI value) were lower after fertilized indicated the modification of fertilization on the promotor effect of decomposing leaf litter.2 The inhibitory effects of decomposing Zanthoxylum bungeanum leaf litter on photosynthetic pigment content and photosynthesis of Chinese cabbage① Pigment content of Chinese cabbage was significantly decreased by T2, T3 treatments at 30 d. This effect became non-significant at 45 d. However, at 60 d, the pigment content of Chinese cabbage was lower than CK after treated by leaf litter. This indicated the inhibitory effect of leaf litter on photosynthetic pigment content of Chinese cabbage, and this effect varied as the amout of leaf litter and time of treatment changed.② At 60 d the lowest net photosynthetic rate (Pn) was observed in CK, and it was significantly different from the value observed in T2 and T3. The differences of stomatal conductance (Gs) and intercellular CO2 concentration (Ci) between CK and leaf litter treatments were non-significant.3 The effects of decomposing Zanthoxylum bungeanum leaf litter on antioxidant protection system of Chinese cabbage① Thirty days after sowing, the peroxidase (POD) activity of T2 and T3 treatments were significantly lower than that of CK. Fourty-five days after sowing, inhibitory effect of POD activity by leaf litter treatments was still observed. This effect changed into promotion at 60 d and it showed significant difference between T2 and CK.② The effect of leaf litter on catalase (CAT) activity was not significant at 30～45 d, and it became inhibitory effect at 60 d.③ Thirty days after sowing, the activity of superoxide dismutase (SOD) was significantly inhibited by T3 treatment, but at 45～60 d the difference became non-significant.④ The malonaldehyde (MDA) content was significantly decreased by leaf litter at 30～45 d. At 60 d it increased by T2 treatment.⑤ Based on the analysis above, the inhibitory effect of allelochemicals that released from leaf litter waken in process of time.4. Effects of decomposing Zanthoxylum bungeanum leaf litter on the osmotic adjustment of Chinese cabbage① At 30 d, the differences of soluble protein content between leaf litter treatments and CK were non-significant. At 45～60 d, the soluble protein content were significantly decreased by leaf litter, which indicated obvious inhibition of soluble protein synthesis in Chinese cabbage.② At 30～45 d, soluble sugar of Chinese cabbage was decreased significantly by addition of leaf litter, and this inhibition increased as the amount of leaf litter increased. At 60 d, the differences between leaf litter treatment and CK were non-significant. These indicated that the carbohydrate metabolism of Chinese cabbage was disturbed by Zanthoxylum bungeanum leaf litter.5. Effects of decomposing Zanthoxylum bungeanum leaf litter on the growth and physiology of radishThe effects of Zanthoxylum bungeanum leaf litter on the fresh weight and photosynthetic characteristics of radish is similar to that of Chinese cabbage, but the effects on antioxidant protection and osmotic adjustment systems responsed negatively than that of Chinese cabbage. It is possible that individual volume of radish plant is bigger than that of Chinese cabbage so that the allelopathic effect is relatively weakened.on radish.6 Identification and analysis of secondary metabolites from Zanthoxylum bungeanum leaf litterIn total,45 constitutes which represented 99.58% volatile compounds of Zanthoxylum bungeanum leaf litter were indetified from GC-MS. The main substances were terpenoids. There were 24 terpenoids in total and represented 54.20% of the total volatile compounds. Among them,6 sesquiterpenes,3 diterpenes, 2 tetraterpenes were indentified. There were 4 steroids which represented 17.46% of the total volatile compounds. In addition,8 alkanes, one esters,2 phenols,2 heterocyclic compounds,2 fatty acids, one alkene and one enolate were indentified which represented 0.36%,12.79%,5.95%,5.86%,0.98%,1.55%and 0.25% of the total volatile compounds respectively. The main compounds with the relative content bigger than 5% were 1,8-cineol, linalool, linalyl acetate, aristolone, octacosane, stigmast-5-en-3-ol, (3b,24S)-, vitamin E and viminalol. Among them, 1,8-cineol, linalool and linalyl acetate have obvious allelopathic effects, while stigmast-5-en-3-ol, (3b,24S)-and viminalol have potential allelopathic effects. |
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