| The final decomposition of litter is achieved through the enzymatic reaction of the biological communities in the soil detritus food web.Soil faunas can not only directly participate in the transformation and decomposition of organic matter in soil and litter through feeding,breaking and digesting,but also can indirectly affect the synthesis,secretion and activity of soil enzymes through selectively feeding on microbes,inoculating and propagating microbial propagules and altering the structure of microbial community.These further regulate the mineralization of carbon and nitrogen and release of nutrients in soil and litter.The decomposition from fresh litter to coarse humus is a continuous organic process.Changes in micro-climate environment,substrate quality and biota as the decomposition proceeded will inevitably affect the bio-activity involved in degradation,which has greatly mutated the effects of soil fauna on enzyme activity during litter decomposition.However,the studies so far have not clearly clarified the interactional mechanism between soil fauna and microbes in the litter detritus food web.Therefore,the four litter species,including the Minjiang fir?Abies faxoniana?,birch?Betula albo-sinensis?,poplar?Populus simonii?and bamboo?Fargesia spathacea?,were taken as subjects.Soil fauna was repelled by adding naphthalene to forest floor of the corresponding subalpine forest in field,the effects of soil fauna on the nine kinds of enzyme activity?including invertase,?-glucosidase,cellobiohydrolase,polyphenol oxidase,peroxidase,urease,N-acetyl-?-N-glucosaminidase,leucine arylamidase and acid phosphatase?were tested in decomposing litter using litterbag method from April 2016 to April 2018 in a subalpine forest of western Sichuan.The purpose of this research was to provide a reference for understanding the interactional mechanism between soil fauna and microbes during the material circulation of the detritus food web.The main results are as follows:?1?The soil faunal inhibitor?naphthalene?could effectively inhibit the individual density and species richness of arthropods involved in decomposing leaf litter.The inhibition rates on individual densities of arthropods of poplar,birch,fir and bamboo were 30.6269.11%,64.1875.45%,64.8873.86%and 49.7066.76%,respectively;the corresponding inhibition rates on species richness of arthropods were 39.4453.77%,39.1963.03%,43.7060.91% and 19.1546.72%,respectively.Litter type,sampling time and their interaction had a significant influence on the individual density and species richness of arthropods in litterbags.?2?Throughout the decomposition period,the activities of invertase,?-glucosidase,cellobiohydrolase,polyphenol oxidase and peroxidase in the control group?soil arthropod involved?were 38.9485.30 mg·g-1·d-1,7.6636.83?mol·g-1·h-1,0.898.13?mol·g-1·h-1,1.943.08?mol·g-1·h-1 and 2.7326.88?mol·g-1·h-1,respectively;and those in the treatment group?soil arthropod removed by naphthalene application?were13.6272.72 mg·g-1·d-1,5.0132.73?mol·g-1·h-1,0.466.61?mol·g-1·h-1,1.342.25?mol·g-1·h-1 and 1.6412.89?mol·g-1·h-1,respectively.The enzyme activities related to the carbon transformation showed obvious dynamic as the decomposition proceeded,and there were significant differences in enzyme activities among different types of litter.Soil fauna could significantly promote the activities of invertase,?-glucosidase and cellobiohydrolase,but had insignificant effects on the activities of polyphenol oxidase and peroxidase.?3?During the study period,the activities of urease,N-acetyl-?-N-glucosaminidase,leucine arylamidase and acid phosphatase in the control group were 2.803.12 mg·g-1·d-1,4.5528.88?mol·g-1·h-1,0.361.07?mol·g-1·h-1 and 22.1942.68?mol·g-1·h-1,respectively;and those in the treatment group were 2.252.98 mg·g-1·d-1,2.8018.58?mol·g-1·h-1,0.466.61?mol·g-1·h-1 and 16.5835.72?mol·g-1·h-1,respectively.Similarly,the enzyme activities related to the nitronge and phosphorus transformation showed obvious dynamic with the changes in decomposition time and litter type as the decomposition proceeded.The activities of urease,?-N-acetylglucosaminidase,leucine aminopeptidase and acid phosphatase were significantly promoted in the presence of soil fauna.?4?Compared with the coniferous species,litters of the broad-leaved species had higher enzyme activities related to carbon,nitrogen and phosphorus transformation.There was a significant correlation between the individual density and species richness of soil fauna in litterbag and nitrogen content,lignin content and C/N rate during the study period.Moreover,the enzyme activities related to activity of carbon,nitrogen and phosphorus transformation significantly correlation with the individual density and species richness of soil fauna in litterbag and soil temperature on the forest floor.In conclusion,the soil faunal inhabitor?naphthalene?can effectively restrict the soil arthropod community involveing litter decomposition,which can be used to study the ecological function of soil arthropod in subalpine forest.Soil fauna showed different positive effects on the enzyme activities of carbon,nitrogen and phosphorus transformation during litter decomposition in the subalpine forest of Western Sichuan.However,this promoting effect significantly varied with the change of enzyme type and had closely related relationgship with the substrate quality and hydrothermal conditions during decomposition. |
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