Study On Mixed Decomposition And Nutrient Release Dynamics Of Litters In Subtropical Forest

Litter decomposition plays an important role in maintaining the structure and function of the whole forest ecosystem as well as the nutrient balance and biomass cycle of the forest ecosystem.At present,most scholars have conducted more studies on the decomposition of litters of single tree species,but few studies have been conducted on the interaction between the decomposition of litters of different tree species combinations,and the regulatory mechanism of the decomposition of multiple tree species is still unclear.This paper selected the subtropical evergreen broad-leaved forest of Pinus massoniana Lamb,Lithocarpus glaber,Quercus glauca Thunb,Choerospondias axillaris,litter leaf mixed according to different tree species composition and species diversity gradient,including 4 single tree litter leaf,6 group two tree species composition,four groups of three tree species combination and 1 set of four tree species combination,a total of 15 species combination.Litter leaves from different tree species combinations were placed into the corresponding tree cluster combinations of evergreen broad-leaved forests in January 2019 for in-situ decomposition experiment,and collected once a month for 12 times.Due to the traditional method namely artificial eye identification tree takes charge,especially to the litter decomposition of leaf late after big beating the artificial are hard to identify tree species in this study,through the establishment of the near infrared spectral model to quantitative analysis of the tree species composition and carbon,nitrogen and phosphorus content is to investigate dynamic change and litter decomposition of leaf mixed hybrid decomposition effect,tree species diversity on the influence of the mixed litter decomposition and nutrient release dynamics,the main results were as follows:(1)Quality of different tree species combination litter leaf residue rate with the increase of the decomposition time showed a downward trend,through the 365 days after the decomposition,a single tree species combination litter leaf quality residual rate is 47.93%-64.33%,use Olson negative exponential attenuation model of different tree species composition and species diversity gradient fit litter quality retention rate of the leaf,degree of fitting the model and the quality retention rate is good(R2>0.9148,P<0.01),can be seen by the K value stone oak decompose fastest(K=0.625),Choerospondias axillaris to decompose the slowest(K=0.411).The mass residual rate of litters in the two tree combinations was 54.3%-63.9%,and Pinus massoniana Lamb-Choerospondias axillaris showed the fastest decomposition(K=0.567).Pinus massoniana Lamb-Quercus glauca Thunb had the slowest decomposition(K=0.430).The mass residual rate of litters in the three tree species combinations was 55.7%-63.73%,among which Pinus massoniana Lamb-Choerospondias axillaris-Quercus glauca Thunb combination had the fastest decomposition(K=0.530),while Pinus massoniana Lamb-Quercus glauca Thunb-Lithocarpus glaber had the slowest decomposition(K=0.434).After 365 days of decomposition,the mass residual rate decreased to 63.02%.The decomposition coefficient(K value)is 0.465.With the increase of decomposition time of litters,the leaf mass residual rate of different tree species showed a trend of gradual decline,among which the two tree species combinations showed the fastest decline,and the mass residual rate of Pinus massoniana Lamb-Quercus glauca Thunb-Lithocarpus glaberwas the slowest decline.With the increase of diversity gradient of tree species,the decomposition rate of litters first increased and then decreased.(2)the decomposition rate of litters leaves of different tree species combinations was fitted with the Olson negative exponential attenuation model,and the fitting effect was better with the experimental data(R2>0.9232,P<0.01).The decomposition rate of Lithocarpus glaber was the fastest.Choerospondias axillarisdecomposition is the slowest,Pinus massoniana Lamb-Choerospondias axillaris combination decomposition is the fastest.Pinus massoniana Lamb-Quercus glauca Thunb assemblage decomposed the most slowly,among the three tree species assemblage Pinus massoniana Lamb-Choerospondias axillaris-Quercus glauca Thunb assemblage decomposed the most quickly,Pinus massoniana Lamb-Quercus glauca Thunb-Lithocarpus glaber decomposed the most slowly.The decomposition coefficient(K value)of litters of four species combinations was 0.465,and the decomposition rate model of litters of different species combinations was basically consistent with the mass residual rate of litters,indicating that the model's estimation of the decomposition rate of litters of different species combinations was in line with the actual situation.(3)quantitative analysis was carried out with OPUS software to select the optimal model for mass percentage of litters and spectral prediction of carbon,nitrogen and phosphorus content of four dominant species.The correlation coefficients between predicted and measured values were high,indicating that the leaf weight of litters of the four dominant species was suitable for NIRs technique and could be applied to the determination of mixed decomposition of forest litters.The regression analysis of the predicted mass ratios of four dominant species in different combinations and the actual mass ratios of four dominant species in different combinations shows that the correlation coefficients between the predicted and actual mass ratios of litter leaves of four dominant species and the predicted and actual values of carbon,nitrogen and phosphorus content in different combinations are relatively high.Therefore,the infrared spectrum prediction model of litters leaves of four dominant species is suitable for litters decomposition study in this experiment.(4)The addition of different patterns of Choerospondias axillaris,Quercus glauca Thunbang and shigerao all promoted the decomposition rate of Pinus massoniana Lamb.Among them,the combination of Choerospondias axillaris and Quercus glauca Thunbshan had the strongest promoting effect on the decomposition of Pinus massoniana Lamb.The mixed decomposition rate of Pinus massoniana Lamb,Choerospondias axillaris and Lithocarpus glaber was increased by different species diversity gradient.Moreover,with the increase of tree species diversity,the gradient mixing decomposition of different tree species had a stronger promoting effect on Pinus massoniana Lamb.The four species diversity combinations had the strongest effect on the decomposition rate of Choerospondias axillarisand respectively.Two species diversity gradient mixed decomposition and three species diversity gradient promoted the decomposition rate of Quercus glauca Thunb.The mixed decomposition rate of the four species was inhibited.(5)with the decomposition of litters,the carbon(C)content in litters leaves of four species of tree species and the carbon(C)content in litters leaves of different species of tree species showed a direct release pattern,with an overall downward trend.With the decomposition of litters,the nitrogen content in litters leaves of the four dominant species and the nitrogen(N)content in litters leaves of different species diversity basically showed a enrichment pattern,with an overall upward trend.With the decomposition of litters,phosphorus(P)content in litters leaves of four dominant species and phosphorus(P)content in litters leaves of different species diversity basically showed an enrichment and release pattern,with an overall rising trend.