Decomposition Characteristics Of Litters In Wild Rhododendron Forests Under Artificial Control

Baili Rhododendron National Forest Park(short for "Baili Rhododendron")is located at the junction of Qianxi County and Dafang County in northwest Guizhou Province.It is the largest and densest native rhododendron forest with a wild rhododendron distribution area identified thus far in China.Rhododendron delavayi Franch and Rhododendron agastum Franch are the main group species and dominant species of Rhododendron.According to the preliminary investigation of the team,the rhododendron forest in the Baili Rhododendron forest is mainly composed of old rhododendrons,with few new seedlings under the forest and serious accumulation of dead leaves and humus,resulting in slow decomposition of litters and serious obstruction of natural regeneration within the community.In recent years,"Baili Rhododendron" has made great efforts to develop tourism,and the problems facing the cuckoo forest have been aggravated by man-made damage and interference.In the long run,if it is not protected,the survival of the rhododendron population will be threatened,and the ecological environment and sustainable development of the Baili Rhododendron scenic spot will be extremely unfavorable.In this paper,a laboratory experiment was conducted to add exogenous nitrogen,phosphorus,alkaline substances and three different microbial agents to the litter of Rhododendron delavayi,Rhododendron agastum and mixed forest to explore the effects of artificial control measures on thedecomposition of rhododendron litters and to provide a new idea for the degradation of litters in the Baili Rhododendron forest area and artificial assistance in the natural regeneration of the wild rhododendron community.In this study,an indoor decomposition test was used to collect litters in the test basket with the extension of decomposition time to study the decomposition characteristics of litters in different stands under different treatments.An indoor decomposition experiment was conducted on three species of litters from Rhododendron delavayi,Rhododendron agastum and mixed forest for 5 months(from the end of November 2021 to the end of April 2022).In the experiment,we applied high and low levels of nitrogen,phosphorus,and the alkaline substance alkali lime to test baskets containing litter from Rhododendron delavayi,Rhododendron agastum and mixed forests,as well as three different microbial agents.Only one foreign substance is applied to the test basket of each stand.The changes in lignin,cellulose,hemicellulose,enzyme activities and organic acid contents in litters after 20,50,90 and 140 days of application of exogenous substances were studied and analyzed.The results show the following:(1)There was no significant difference in the final decomposition rate of the three stands after half a year of decomposition,in the order from large to small: mixed forest > Rhododendron agastum > Rhododendron delavayi.After the application of different exogenous substances,the final decomposition rate of the threekinds of forest litter changed significantly.The final decomposition rate of Rhododendron delavayi litter under the organic fertilizer treatment was the highest(80.25%),the final decomposition rate of Rhododendron agastum litter under the high concentration phosphorus treatment was the highest(82.22%),and the overall decomposition rate of mixed forest litters was lower than that of Rhododendron delavayi and Rhododendron agastum and was the highest under the HS treatment(69.49%).(2)The contents of lignin,cellulose and hemicellulose in litters of different stands varied in the decomposition process.Stand types and treatment methods had major effects and interactions on the contents of lignin,cellulose and hemicellulose in the litters of the three stands.The addition of low concentrations of nitrogen and phosphorus can promote the decomposition of the three litters.The most effective measures to accelerate the decomposition of different rhododendron litters are different: organic fertilizer for Rhododendron delavayi litter is the best,it is effective to apply low concentrations of nitrogen and plant microbial agents to the litter of Rhododendron agastum,and the addition of alkali lime is the best for mixed forest litter.The correlations between the contents of lignin,cellulose and hemicellulose in litters of the three stands and the four measured enzymes and final decomposition rates were alsodifferent.(3)There are certain differences in enzyme activities due to different litter types and treatments,and the correlation between the enzyme activities of different litters and different treatments is different.The application of exogenous nitrogen and phosphorus can improve the activity of sucrase in the litter of Rhododendron delavayi,Rhododendron agastum and mixed forest to varying degrees,but the high concentration of nitrogen has little effect on the activity of sucrase.The application of high concentrations of nitrogen and three microbial agents had a better effect on the activity of cellulase in the mixed forest and had a more obvious effect on the activity of acid phosphatase in Rhododendron delavayi and Rhododendron agastum.The application of exogenous phosphorus can also promote the activity of polyphenol oxidase in mixed forest litter.No correlation was found between the activity of polyphenol oxidase in the three stands and the treatment.The acid phosphatase of Rhododendron delavayi was negatively correlated with the addition of high concentrations of alkali lime.The activities of acid phosphatase,sucrase and cellulase of Rhododendron agastum were positively correlated with high nitrogen concentrations.Only cellulase and high nitrogen content in litters of mixed forest were significantly correlated.(4)The content changes of 8 organic acids in different stand types were different under different treatments.The total amount of organic acids in the control group was in the order of mixed forest,Rhododendron delavayi and Rhododendron agastum(from high to low).Exogenous nitrogen and phosphorus can increase the organic acid and citric acid contents of Rhododendron delavayi,and low exogenous concentrations of nitrogen increased the total organic acids in Rhododendron charming.Compared with the two single stands,the total amount of organic acids in the mixed stand was higher overall,and the addition of high concentrations of nitrogen and phosphorus most obviously promoted the increase in organic acid content.Oxalic acid and tartaric acid in the leaves of the three litters were stably present and could be detected and will not disappear due to the application of exogenous substances,and tartaric acid is 3-9 times as much as oxalic acid on the whole.Oxalic acid content decreased with increasing nitrogen concentration,while other organic acid contents were inversely proportional to nitrogen concentration.