| Allelopathy which was widely distributed in nature plays an important role on the interpretation of interaction mechanism of individual plants and among species and plant communities. And it has important implications on agricultural and forestry production. Therefore, further study on allelopathy contributes scientific and practical significance. In this study, pot experiment by adding Tenjikukatsura (Cinnamomum japonicum) leaf litter to the soil in a way to simulate the natural decomposition was applied to study its effects on Impatiens (Impatiens balsamina) growth. Four litter addition treatments,0 g·pot-1 (CK),20 g·pot-1 (L20),40 g·pot-1 (L40),80 g·pot-1 (L80) were set. By determining the morphological index, resistance physiological index, photosynthetic indexes and observe their reproductive growth characteristics of Impatiens balsamina, we studied the allelopathy of Cinnamomum japonicum leaf litter. The chemical composition and relative content of Cinnamomum japonicum leaf litter and its stewing samples was identified by using GC-MS, and we inferred from leaf litter in allelopathic chemicals into the main ingredient. Meanwhile, in order to observe whether leaf litter addition had a significant impact on the growth by affecting the soil aeration, root growth and water permeability, we set up a parallel cooking blank experiment. The results were as follows:1. Cinnamomum japonicum leaf litter addition significantly inhibited impatiens diameter growth, biomass accumulation of aerial part and underground part of plat and the number of lateral branches, while no significant impact was observed on height growth.2. With the increasing amount of Cinnamomum japonicum litter addition, flowers of impatiens decreased clearly, and L40 and L80 treatment were significantly lower than CK. Although the flowering duration did not differ obviously among treatments, full-bloom stage of both treatments L40 and L80 delayed significantly compared to CK, early flowering stage of treatment L80 delayed three days as well. The number of capsules collected, the total weight of the seeds and their seed kernel weight of each treatment plant did not differ significantly. The overall seed weight of each capsule contained increased with the increasing amount of leaf litter, and the weight of treatment L80 was significantly higher than that of CK.3. Cinnamomum japonicum leaf litter addition had no significant effect on the H2O2 content overall, but the H2O2 content increased significantly at the beginning of squaring stage. Reactive oxygen scavenging system superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity of impatiens leaves were significantly lowerthan CK, but ascorbic acid (ASA) content increased with the elevated level of Cinnamomum japonicum litter addition at the beginning of squaring stage. Impatiens malondialdehyde (MDA) content increased with the increasing amount of Tenjikukatsura litter addition after squaring. It indicated that the non-enzymatic ROS scavenging system might be the more important antioxidant system for impatiens, and specially, ASA plays an important role at the beginning of squaring stage. Oxidative stress caused by Tenjikukatsura leaf litter addition may exceed scavenging ability of the two types of ROS scavenging scavenging system of impatiens, resulting in a significant reduction of the impatiens diameter and biomass accumulation. Osmolytes soluble sugars (SS) of Impatiens didn’t change with the increase of leaf litter addition in the whole process, neither did as soluble protein (SP) in the early budding and flowering, which indicated that Cinnamomum japonicum leaf litter might not affect these two osmotic substances.4. Chlorophyll content decreased in the whole growth process with the increase amount of Cinnamomum japonicum leaf litter addition, especially 58 days after transplanted, when chlorophyll contents of L40 and L80 were significantly inhibited. Impatiens net photosynthetic rate(Pn) and water use efficiency (WUE) were significantly inhibited by Tenjikukatsura leaf litter, while three gas exchange parameters Gs, Ciand Tr showed a substantially opposite trend. Light response characteristics under different light intensity illustrated that net photosynthetic rate in the order:CK>L20>L40>L80, and apparent quantum yield (AQY), maximum net photosynthetic rate (Pn max) and dark respiration rate (Rd) decreased with increase amount of leaf litter, while the light compensation point (Lcp) and light saturation point (L-sat) tended to increase. CO2 response characteristic parameter Pn showed a consistent trend with light response curve:CK>L20>L40>L80. With the increase amount of leaf litter applied, RuBP carboxylation efficiency (CE), maximum net photosynthetic rate (Pn max) and photorespiration rate (Rp) showed an overall decreasing trend, while the CO2 compensation point (Ccp) generally showed an increasing trend. Intercellular CO2 saturation point (Ci sat) of L20 treatment was the least, while L80 treatment was the maximum. It showed leaf litter treatment not only reduced the impatiens net photosynthetic rate, but also inhibited the ability to utilize poor light and low CO2 concentration.5. It is identified 68 kinds of chemical composition in Cinnamomum japonicum original leaf litter, accounted for 85.44% of total volatile oil content, which mainly contained 43 kinds of terpenes (41.44%), and 3 kinds of phenols (17.66%). There were 19 kinds of chemical composition identified from strewing Cinnamomum japonicum leaf litter, which constituted 72.1% of the total volatile oil content. These 19 kinds of compounds included four kinds of phenols (39.3%),2 kinds of alcohols (12.05%),5 kinds of terpenes (7.48%). It was presumed that coumarin, eucalyptus alcohol, cinnamic aldehyde, trans-caryophyllene and terpineol, etc. removed or reduced by cooking may be the main allelochemicals in Cinnamomum japonicum litter.6. Cooking leaf treatment had no significant effect on the growth of impatiens. Impatiens morphological indexes including diameter (33 d), height (33 d) and aboveground biomass (85 d), photosynthetic morphological indexes including net photosynthetic rate, H2O2 content (48 d), the antioxidant protective enzymes systems SOD activity (48 d), MDA content (48 d) and osmotic adjustment substance SS content (48 d) were not significantly different from control. Within the level of letter addition in this study, it is indicated that the added leaf litter would not affect soil aeration permeability significantly; allelochemicals released during decomposition of leaf litter were the main factor inhibiting the growth of impatiens.The foregoing analysis showed that Cinnamomum japonicum leaf litter in the soil released allelochemicals including coumarin, eucalyptus alcohol, cinnamic aldehyde, trans-caryophyllene and terpineol, etc., destructing non-enzymatic ROS scavenging system damaging the membrane system of Impatiens balsamina. Allelochemicals reduced net photosynthetic rate and weaken their ability to take advantage of low light and low concentrations of CO2 by destroying or inhibiting the synthesis of chlorophyll impatiens, resulting in diameter and biomass accumulation reduction. The inhibition of allelochemicals of Cinnamomum japonicum leaf litter on vegetative growth in the early days lead to the delay of early flowering season and Full-bloom stage in reproductive growth stage and the decline of total flowers, resulting in the decline of ornamental value. |
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