Allelopathic Effect Of Cinnammum Camphora Leaf Litter On The Growth And Main Physiological Characteristics Of Three Kinds Of Crops

A pot experiment was conducted to investigate the allelopathic effect of decomposing leaf litter of caraphov?Cinnammum camphora? on the growth and resistance physiology and photosynthetic characteristics of the three recipient crops cabbage?Brassica chinensis?, lettuce?Lactuca sativa?, Eggplant?Solanum melongena?. Four levels of leaf litter addition were applied to soil ?namely A1?25 g·pot-1?, A2?50 g·pot-1?and A3?100 g·pot-1? and CK ?no leaf litter added??. Leaf litter of each treatment was mixed with 10 kg soil and then the mixture was loaded into a pot and the vegetable seed was sown in every pot. The growth indicators?plant height, ground diameter, leaf area and biomass, etc.? and several indicators of resistance physiology after decomposition of leaf litter were determined at 20,40,60,80 d.respectively. And the determination of crop photosynthetic physiological indexes were conducted at 60, 80 d ?sunny? respectiely. At 30,50,70,90 d, the contents of soil microbial biomass C and N and the contents of soil nitrate nitrogen and ammonium nitrogen were measured for each receptor crops. The results were as follows:1. The decomposition of camphor leaf litter showed inhibition on ground diameter, height, biomass, leaf development of the three recipient crops. And it showed "dose effect" and "time effect", have obvious role in promoting fruition later period for eggplant. Furthermore, the inhibition effect to the recipient crops was consistent with the role of the chlorophyll and leaf development. The decline of photosynthetic ability caused the reduce of synthesis for organic matter. And then the development of leaves were limited resulting in the decrease of photosynthetic area. All of these were bound to affect the accumulation of organic matter and ultimately reflected in the form of plant growth.2. The decomposition of litter camphor leaves showed significant inhibitory effect on photosynthetic pigment content of three crops. And the effect of inhibition enhanced with the increment of leaf litter; the application of leaf litter reduced the net photosynthetic rate ?Pn?, stomatal conductance ?Gs?, transpiration rate ?Tr?, and water use efficiency ?WUE? compared with CK. And the concentration of intercellular CO₂ ?d? with all leaf litter treatments were both higher than CK; With the increasing of leaf litter amount in soil, the maximum net photosynthetic rate ?Pn max?, apparent quantum efficiency ?AQY?, RuBP carboxylation efficiency ?CE?, light respiration rate ?Rp? and dark respiration rate ?Rd? of three crops were declined under the saturation condition of light and CO₂, but the light compensation point ?Lcp?, light saturation point ?Lsp?, CO₂ saturation point ?Csp?, CO₂ compensation point ?Ccp? showed different trends due to different receptors crops.3. At the early stage of decomposition of litter camphor leaves ?20-40 d?, The content of MDA in leaves of recipient plants were significantly increased under different treatment ?P<0.05?. The activities of superoxide dismutase ?SOD? and catalase?CAT? were accelerated with the increase of leaf litter addition. But the activity of peroxidase?POD? was inhibited. The content of soluble sugar ?SS? was increased, while the content of soluble protein ?SP? was reduced. With the extension of decomposing time, the difference in contents of CAT, SOD, POD and MDA in crop with various processing were significantly decreased. The effect of promoting the content of SS has been weakened, even has no obvious difference between the groups, While the content of soluble protein ?SP? were still significantly inhibited for the three crops, with the increasing of the litter leaf dose, the inhibition was stronger, and the continue time was longer. Except for the small cabbage at 80 days, the content of the three kinds of receptor crops SP in A3 treatment has been lower than CK ?P< 0.05?.4. The allelopathic synthesis effects ?SE? of litter camphor leaves enhanced along with litter leaf amount increased, and showed a trend of increase after decreases first with the extension of decomposition time. This was consistent with the inhibition effect of the three kinds of crops in morphological growth. On the whole, the levels of sensitive for different recipient plants were different to the inhibition of allelopathic of camphor leaf litter. Here were the average SE for three crops with different decomposition way:cabbage ?BC? of SE ?average -0.385?, lettuce ?LS? of SE ?average -0.415?, eggplant ?SM? of SE ?average -0.360?. We can see that lettuce is the most sensitive, and the inhibition effect on lettuce was the strongest. While the inhibition effect on eggplant was the weakest, eggplant showed more tolerance. So eggplant was more suitable for intercropping with camphor or close planting.5. It was found that the content of nitrate nitrogen and ammonium nitrogen of all the disposed soil significantly reduced in a certain period of time ?less than 50 d of decomposition?, in contrast with the change of carbon and nitrogen content in soil microbial biomass. To late stage of decomposition ?70 to 90 days?, the difference of nitrate nitrogen and ammonium nitrogen content for the three receptors to various crops with different leaf litter process was significantly reduced. It indicated that the influence of leaf litter decomposition on soil mineralization nitrogen content is weakened gradually. In the whole cultivating period, the dynamic change of soil nitrogen mineralization is the same with the growth trend of crop, which showed that the effectiveness of decomposing the litter camphor leaves to influent soil nitrogen is likely to be important factor affecting the growth of receptor plant.6. The addition of different amount of camphor leaf litter was significantly increased the contents of soil microbial biomass C and microbial biomass N, This may be due to the addition of plant leaf litter to the soil to provide a rich organic matter, and promote a large number of soil microbial reproduction, It is possible that the allelochemicals released from decomposition of leaf litter promoted the growth of soil microorganisms. From the perspective of the dynamic changes of different processing at different time stages, the contents of soil microbial biomass increased rapidly. However, with the time of leaf litter decomposition, and then slowly decreased and the differences between the treatments were gradually reduced.In conclusion, the decomposition process of camphor leaf influenced the balance of antioxidant protection enzymes system for receptor crops, the accumulation of osmotic adjustment substances, caused the peroxide damage to cells, leaded to the cellular structure damage and loss of function, the lower chlorophyll content and photosynthetic capacity though released harmful substances. At the same time, the decomposition process of camphor leaf affected the form of crop growth and biomass accumulation though influencing the soil microbial biomass and available nutrients supply. With the further decomposition of leaf litter, the inhibition effect on the growth of three recipient plants were weaken.