Effects Of Thinning On The Decomposition Of Fine Roots And Litter In Xiaoxing’anling Natural Forest

Tending thinning is an important way of forest management.Tending thinning directly or indirectly affects the decomposition of fine roots and litter by changing the temperature and humidity,light conditions,growth status of trees,shrubs,and herbs in the forest,as well as soil properties.Meanwhile,the decomposition of litter and fine roots determines their cycling and transportation with soil nutrients and energy,thereby affecting the material and energy cycling of the entire forest ecosystem.In order to promote the nutrient circulation in the secondary forest in the Xiaoxing’an Mountains and improve soil fertility,this paper studied the decomposition of fine roots and litter in the secondary forest in the Xiaoxing’an Mountains.The research area is located in the Dongfanghong Forest Farm of the Forestry Experimental Bureau led by Xiaoxing’an Ridge.Set 30 m × Seven 30 meter experimental plots,including A(thinning intensity 10%),B(15%),C(20%),D(25%),E(30%),and F(35%),were used as control plots.The plots without thinning were also recorded as CK.Conduct fine root and litter decomposition experiments in July 2021,and investigate relevant indicators of forest stands,soil,and microorganisms.Using analysis of variance,compare the nutrient matrix,biomass,mass residue rate,nutrient residue rate,and decomposition rate coefficient of fine roots and litter under different tending and thinning intensities;Pearson correlation analysis was conducted on the decomposition rate coefficient of fine roots and litter with their initial nutrient matrix.The chemical nutrients of fine roots and litter are enriched or released during decomposition.The decomposition trends of various elements in fine roots and litter are different,but both have the highest mass residue rate of N element and the lowest mass residue rate of K element over a one-year decomposition period.According to the Olson decay model,the coefficient k characterizing the decomposition rate was calculated,and it was found that the time for fine root decomposition was 50% from1.57 to 2.44 years,and 95% from 6.8 to 19.6 years.The decomposition time of 50% of litter is between 0.94 and 1.24 years,and the decomposition time of 95% is between 4.05 and 6.37 years.The decomposition rate of litter is significantly faster than that of fine roots.The random forest model was used to fit the relationship between the characteristics of stands,soil and microorganisms under different thinning intensities and the nutrient release of fine roots and litter,and to predict the nutrient release of fine roots and litter.The results of random forest model showed that the nutrient release of litter and fine roots was mainly driven by their initial chemical matrix and stoichiometric ratio,microbial carbon,nitrogen and carbon nitrogen ratio.In addition,tree biomass has a significant driving effect on fine root decomposition;Soil bulk density,soil available potassium,and soil organic carbon have significant driving effects on litter decomposition.Using principal component analysis,establish a sample evaluation model to determine the intensity of thinning that is more conducive to nutrient and energy cycling within the forest.To reduce the dimensionality of 37 indicators of forest stand,soil,microorganisms,litter,and fine roots,the principal component analysis of the sample plot scores from high to low is: D(25%)>B(15%)>C(20%)>A(10%)>CK(0%)>F(35%)>E(30%).It indicates that under different thinning intensities,plots under 25% thinning intensity are more conducive to the decomposition of fine roots and litter.