| Forest-grass compound is an important ecological restoration mode in the national ecological construction, and is also one of the most effective ways to restoring the vegetation in the construction of ecological defense in the upper reaches of Yangtze River, where Eucalyptus grandis is one of the most important planting tree species, and is usually planted by forest-grass compound. In order to increase the income of farmers, crops like pasture, food, and vegetable are usually intercropped or interplanted in the forest at the early of period of the afforestation. But the intercropping of forest and various grasses are carried out at the near ripe or ripe forest. On one hand, the decomposing leaf litter of E grandis can provide nutrition to the undergrowth, but on the other hand allelochemicals from decomposing leaf litter also negatively affect the growth of grass in the intercropping system of E. grandis plantation and grass. However, there is little knowledge on the produce, degradation, and its allelopathic effect on the peripheral plants under the decomposition of E grandis leaf litter. Hence, the research of influence rule of allelopathy and degradation dynamic of E grandis leaf litter on crop is very meaningful for the restoration of ecosystem diversity and sustainable forest management in the E. grandis plantation.Fresh leaf litter were randomly collected from a10-yaer-old E. grandis plantation as experimental materials in this study, and the dynamic change of the relative content of allelochemicals and nutrient in leaf litter were compared under the conditions of40%soil moisture,80%soil moisture, and natural terms. Pot experiment was used to study the effect of decomposing leaf litter with three different contents include30g/pot (A1),60g/pot (A2), and90g/pot (A3) on growth and physiological characteristics of Cichorium intybus, Setaira viridis (L.) Beauv, and Eremochloa ophiuroides. Additionally, the mehod of culture was used to investigate the effect of water extract of fresh failed leves with three concentrations (0.5%,1%, and10%) on the seed germination and seeding growth of the three grasses. The main results are followed:1. The decomposition rate of E grandis leaf litter was highest in80%soil moisture, lowest in40%soil moisture, and that in natural condition was medium. The decomposition rate in summer was relatively higher, and that in winder was relatively slower. The dry matter remaining rate in80%soil moisture and natural condition was significant lower than that in40%soil moisture after July, and the dry matter remaining rate in80%soil moisture was also lower natural condition from August.2. Under the40%and80%soil moisture, the content of Nitogen in E. grandis leaf litter first incrased and then decreasd, and the content of lignose, cellulose, Carbon (C), Phosphorus (P), Potassium (K), Magnesium (Mg), and Calcium (Ca) decreased monotomously. In the natural condition, the release pattern of lignos was leaching-accumulation-release, C and K was continuous release, Mg and Ca released first and then accumulated, and the pattern of P was accumulation.3. There were36chemical substances detected in the initial samples of leaf litter of E. grandis, and which can be divided into9categories due to their chemical structures and properties, and nineteen of which were terpenoids, and accouting for52.78percent of them, which are the main allelochemicals. The relative content of alpha-Pipene nd1,8-Cineole were12.48%and19.61%, respectively, and were higher among all the chemical substances. The relative content of total chemical compositions and major allelochemicals decreased over time, and the biggest dorp was found in natural condition, whereas, smallese decrease was observed in40%soil humidity. Furthermore, the rates of decline were faster in early stage of decomposition, and the release rates of terpenoids were more than80%under these three contitions.4. The decomposing leaf litter of E. grandis can inhibit the growth and the accumulation of biomass of Cichorium intybus, Setaira viridis (L.) Beauv, and Eremochloa ophiuroides, the inhibition effect went up with the increase of the content of leaf litter. There was no significant difference found in the growth traits among the different experiment groups in the three grasses, when the distilled leaf litter of E. grandis were added in the soil. This shows that no significant influence of leaf litter on the physical properties of soil, and allelochemical was the main factor to influence the grass growth.5. The decomposing leaf litter of E. grandissignificantly inhibited the synthesis of photosynthetic pigments (chlorophyll a, chlorophyll b and cartenoids) of C. intybus, S. viridis, and E. ophiuroides. The photosynthetic rate, stomatal conductance, transpiration rate, and the response to CO2concentration and lingt intensity in three treatments were significantly lower than those in control group (P<0.05). The photosynthesis of leaf decreased that unltimately inhibited the the growth and the accumulation of biomass of grasses.6. The resistance physiology traits of C. intybus, S. viridis, and E ophiuroides’were influenced by allelopathy from the decomposing leaf litter of E. grandis. There was no significant difference in the activity of SOD, CAT, and POT between CK and treatments. The activity of three enzymes decreased with time and the amoungt of processing. At the day of90, the activity of three enzymes in treatments were significant lower than those in CK (P<0.05). The more leaf litter contained in the soil, the moer significant effect had in the content of MDA. The MDA content in the treatment with90g leaf litter was significant hiher than that in CK at the dat of30,60, and90(P<0.05). The soluble sugar and free proline content went up with the increase of leaf litter content at all time points, while the change of soluble protein contents was opposite. There were significant diffenerces found between CK and treatments with60and90g leaf litter in these three indexes at all tested time points (P<0.05).7. Besides, the extracts of fresh leaf litter of E grandis with concentration of0.5%and1%can improve the germination potential and germination index of E. ophiuroides, the germination potential, germination index, germination rate, the length of radicle and germ, and the fresh weight and dry weight of seedling were inhibited by the allelochemicals of extracts, and the inhibitory effect enhanced with the increase of concentration. The effect level of10%concentration was significant greater in germination and seedling growth than those of1%and0.5%concentractions, and CK (P<0.05).In conclusion, the decomposing of E. grandis leaf litter can not only provide nutrients to the undergrowth, but allelochemicals had various degrees of inhibitory on the germination, growth and development of grasses at different growth stages. Results of this study could provide scientific theoretical basis for the Forest-grass compound, biodiversity conservation, rational management in the intercropping system of E. grandis plantation and grass, and also provide some reference to evaluate scientifically the ecological value of E. grandis plantation. |
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