| Forest management is an important way to achieve sustainable forest development.Tending thinning is a common means of forest management.After the cultivation and thinning of the Robinia pseudoacacia plantation in the southern part of the Taihang Mountains,the light in the forest increased,and the vine plant Clematis brevicaudata spread rapidly,threatening the normal growth of surrounding trees and eventually forming a large monoculture.This kind of damage of Clematis has also been reported in Qinghai.At present,the results of similar inter-plant hazard studies show different ways of action such as strangulation and allelopathy,but the hazard mechanism of Clematis is still lacking.Therefore,in this study,the Robinia pseudoacacia was used as the materials,and the extracts of Clematis brevicaudata roots,stems and leaves and litter at different concentrations of 5g/L?10g/L?20g/L?30g/L and 50g/L were prepared by water extraction method.Using distilled water as a control,the effects of different extracts on the seed germination and seedling growth of Robinia pseudoacacia were investigated to explore the possible hazard relationship between the two plants.The main conclusions are as follows:(1)Taking the seeds of Robinia pseudoacacia as the test object,germination test using the culture dish method.The allelopathic effect of the extract from Clematis brevicaudata on the germination of Robinia pseudoacacia was evaluated in the artificial climate chamber environment.The results showed that the extracts of roots,stems and leaves and litter had a slight promoting effect on the germination rate of seeds.The higher the concentration,the stronger the inhibition.At the concentration of 50g/L,the germination rate was reduced by 69.5%,56.9% and 60.2%,respectively.At the same time,the inhibition of germination length increased with the increase of concentration.At the concentration of 50g/L,the root,stem and leaf and litter extracts were reduced by 80.2%,69.6% and 75.65%,compared with the control group,respectively.Among them,the Clematis brevicaudata root extract treatment group had the greatest impact compared with the other two groups.(2)After three months of watering with extract,the effects of different extracts on the plant height,ground diameter and biomass of seedlings were consistent.With the increase of extract concentration,the content of each index decreased first and then increased.At the concentrations of 5g/L and 10g/L,the height increment,ground diameter increment and biomass of the seedlings treated with the three extracts were higher than the control group.As the concentration of the extract continued to increase,it gradually fell below the control group.When the concentration reached 50g/L,the indexes were significantly lower than the control,and the growth index of the root extract treatment group was lower than the other two groups.The net growth,net growth and biomass of Robinia pseudoacacia were 9.5%,27.6% and 31.8% lower than the control group,respectively.(3)With the increase of the concentration of the three extracts,the root surface area,root diameter and root density of Robinia pseudoacacia seedlings gradually decreased.When the concentration was lower than 20g/L,the difference was smaller than the control.When the concentration of the extract was increased,the indexes of the root system were significantly lower than the control,and there was a significant difference(P<0.05).Under the treatment of the higher concentration extract,the stem and leaf extract treatment group had the greatest influence on the roots of the seedlings.At a concentration of 50g/L,root surface area,root mean diameter and root density were 47.2%,46.7% and 34.2% lower than the control group,respectively.(4)The three extracts had little effect on the indexes of the antioxidant system of Robinia pseudoacacia seedlings at low concentration,almost no difference with the control.At the concentration higher than 20g/L,the roots and leaves of the seedlings were peroxidized.The content of H2O2 and MDA increased and soluble protein decreased.The index of protective enzyme system was higher than that of the control.At the concentration of 50g/L,the contents of SOD,POD and CAT in roots and leaves decreased,indicating that the protective enzyme system was damaged and the ability to scavenge reactive oxygen species was reduced.It affects the normal physiological and biochemical processes of seedling cells and causes irreversible damage to plants.(5)With the increase of the concentration of extract of Clematis brevicaudata,the Pn and Tr of seedlings decreased,and Sc and Pn showed consistency.The main reason for the limitation of net photosynthetic rate of Robinia pseudoacacia was stomatal factors.The concentration of liquid decreased and the concentration of CO2 in the cells decreased due to the decline of stomatal conductance.The photosynthesis showed a high concentration inhibition,and the inhibitory effect of root extract was the most significant.(6)Different concentrations of water extracts of Clematis brevicaudata had different effects on the germination and growth of Robinia pseudoacacia,which showed high concentration inhibition of seed germination rate and physiological process of seedling growth,which may be related to flavonoids,saponins and coumarins.It is related to coumarin chemical substances,but the components contained in the Clematis are relatively complex,and the influence on the growth physiology of the Robinia pseudoacacia is the result of a combination of various chemicals.When the concentration of these components accumulates to a certain extent in nature,it has a negative impact on the natural regeneration of Robinia pseudoacacia plantation and sustainable forest management.Scholars urgently need to carry out further relevant research... |
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