Study On Litter Decomposition Of Dominant Species In Forest And Grassland Of Qilian Mountains

Litter decomposition is an important process of ecosystem material cycle,which maintains the normal operation of the ecosystem.Qilian Mountain,as a high mountain system in Northwest China,is an important ecological barrier area,and the area of forest and grassland is relatively large.The study on the decomposition dynamics and influencing factors of main litter in forest and grassland ecosystem of Qilian Mountains provides a theoretical basis for the preliminary study on the material cycle process of forest and grassland ecosystem of Qilian Mountains,and provides a reference for the ecological protection of Qilian Mountains.Qinghai spruce(Picea crassifolia)is the dominant species of forest in Qilian Mountains,which is greatly affected by altitudes and canopy closures.For this reason,different altitude gradients and canopy closures were set to study the leaf litter decomposition dynamics of Picea crassifolia forest.Meanwhile,the litter production and dynamics of Picea crassifolia forest were studied under different altitude gradients.Carum carvi and Elymus nutans are the dominant species in subalpine meadow of the Qilian Mountains,the litter of grassland is mainly mixed decomposition,and the decomposition form is easy to be affected by the environment,which has both standing and lodging.For this reason,standing and lodging conditions were set to study the litter decomposition dynamics,and the litter of the two dominant species were mixed in a ratio of one to one to study the effect of mixture on decomposition.Litterfall was collected and litter decomposition was analyzed.The main results are summarized as follows:(1)The annual litterfall production of Picea crassifolia is about 4 t?ha;¹?yr;¹,in which the leaf litterfall accounts for a large part of all litter production.The higher the altitude,the smaller the litterfall production.For each part,the production of leaf litterfall is the highest in autumn and summer,and the litterfall production of branch,bark,and reproductive organs is the highest in summer.The decomposition of Qinghai spruce leaf litter in early period was faster than that in the late period,and the loss of leaf litter decomposition in the early period accounted for more than 66%of the entire decomposition period.The sequence of decomposition rate at different altitudes is K₃₀₅₀>K₂₈₅₀>K₃₂₅₀>K₃₄₅₀.The order of decomposition rate under different canopy densities is K_low>K_middle>K_high.The time required to decompose 50%of leaf litter is about 6 yr.Altitudes and canopy closures affect the temperature and humidity which are important factors to litter decomposition.The results indicates that the microenvironment affect litter decomposition and production.(2)The litter of two dominant species in subalpine meadows decomposes faster in the early stage than in the later stage,and the loss of litter decomposition in the early stage accounts for 50?70%of the total decomposition period.The litter decomposition rate of the mixture is sum of each species composition rate in the early decomposition stage and non additive effect in the late decomposition stage.The litter decomposition rate of Carum carvi is the highest,followed by mixture litter and then Elymus nutans litter.The decomposition rate of lodging litter is faster than that of standing litter,and it takes about 3 yr to decompose 50%of lodging litter.The temperature and humidity under lodging condition are higher than that of standing condition.The results showes that the decomposition rate of litter is related to species and microenvironment,and the mixture of litter can accelerate decomposition.(3)In the initial lignocellulose content of Picea crassifolia leaf and dominant species in subalpine meadow,the cellulose content is the most.In subalpine meadow,the initial cellulose content of dominant species'litter affectes the decomposition rate.Generally,hemicellulose first accumulates and then degrades,cellulose continues to degrade,and lignin accumulates in the most of the decomposition time.The accumulation of lignin in leaf litter of Picea crassifolia reached the maximum at 1.1yr,however,lignin has been degraded in mixed litter of dominant species in subalpine meadows,it indicates that lignin degradation is accelerated after mixing.Hemicellulose and cellulose degraded faster under lodging litter decomposition in the dominant species of subalpine meadows,while lignin degraded faster under standing litter decomposition,it indicates that light irradiation accelerate lignin degradation.The degradation of lignin and cellulose accelerates in summer and slows down in winter,while the degradation of hemicellulose accelerates in winter or autumn.