| Litter decomposition plays a key role in the material cycle and C cycle of terrestrial ecosystems,and the decomposition rate directly affects the energy turnover and C balance of global ecosystems.Understanding the mechanism of soil fauna's influence on litter decomposition is of great significance for a deeper understanding of forest carbon and energy cycles.At present,there are few studies on the relationship between soil fauna and forest litter decomposition in China;therefore,the contribution of soil fauna on litter decomposition cannot be accurately evaluated.In this study,we first established a data model based on the results of existing studies to analyze the relationship between soil fauna and litter decomposition.Meanwhile,from October 2016 to October 2018,we conducted field decomposition experiments.Further verified the reliability in a model on temperate forests by optimizing the field microenvironmental experimental method of designing PVC decomposition rings to simulate microenvironments.Thus,the influence of soil fauna on litter decomposition and its regulatory mechanism was revealed.The main results are as follows:(1)Based on the existing database analysis involving 64 different plant species and 120 different litter combinations,a total of 126 decomposition constants were analyzed.The results showed that the litter decomposition by soil fauna in China's forest ecosystem increased by 65%.Soil fauna have different impacts on different forest types due to different climate types.The decomposition rate of soil fauna in warm and humid environment is more obvious while that in dry and cold temperate forests is relatively low.The degree of impact of soil fauna on litter decomposition is in the following order:tropical forest>subtropical forest>temperate forest.(2)Litter quality greatly affects the decomposition of litter by soil fauna in China's forest ecosystem.Through fitting,it is found that soil fauna effect decreases with the increase of annual precipitation,annual temperature,N and cellulose(P<0.05).Soil animal effect increased with the increase of lignin,lignin/cellulose,lignin/N,C/N and N/P(P<0.05).Analysis shows that soil fauna effect is jointly controlled by annual precipitation,N content and C/N ratio(P<0.001).(3)Taking the litters of 16 common temperate arbor species in Maoershan secondary forest as the research object,the effects of soil fauna on litter decomposition in 2 years were studied.The results showed that the decomposition rates of 16 litters increased to different degrees with the participation of soil fauna.When soil fauna participate in litter decomposition,the litter decomposition rates of Padus maackii,Fraxinus mandshurica and Phellodendron amurense are faster,the decomposition constants(k)are 1.427,1.087 and 0.922 respectively.However,the litters of Quercus mongolica,Pinus koraiensis and Ulmus davidiana.var.japonica decomposed slowly with k values of 0.374,0.369 and 0.278 respectively.However,the effects and contribution rates of soil fauna on the decomposition of different species are different.Among them,the mass residual rate of Padus maackii after 2 years is only 0.5%while that of Ulmus davidiana.var.japonica is 52.9%.Soil fauna contributed 34.0%to the decomposition of Acer tegmentosum while Fraxinus mandshurica contributed only 2.0%.(4)Experiments on decomposition of soil fauna and litter in temperate forests found that litter quality in regional environment is the main factor affecting decomposition contribution of soil fauna.At the same time,the soil fauna impact scale of Padus maackii,Phellodendron amurense,Acer tegmentosum and Fraxinus mandshurica was significantly higher than that of other species.The soil fauna effect size of Quercus mongolica,Juglans mandshurica and Sorbus alnifolia is relatively small.Fitting the relationship between soil fauna effect and the initial litter quality,it was found that the N content,Ca content and non-structural carbohydrate(NSC)content in the litter quality were significantly positively correlated with the scale of soil fauna effect.Lignin content,tannic acid content,C/N and lignin/N have strong negative correlation with soil fauna effect.The results showed that the higher the content of decomposable substances(such as N,NSC and so on.)in litter quality,the higher the impact of soil fauna on litter decomposition of this species;On the contrary,the higher the content of lignin and tannic acid which are difficult to decompose,the lower the influence of soil fauna influence scale on the decomposition of this species.(5)The 16-common litter was divided into arbuscular mycorrhiza(AM)and ectomycorrhiza(EM)by mycorrhizal type.After two years of decomposition in the field,we found that the decomposition rate of AM host litter by soil fauna was more than double that of EM host.Comparing the different mycorrhizal types of litter quality,the AM litter was characterized by lower C/N and higher NSC,and the difference resulted in the effect of soil fauna on the rapid litter decomposition.(6)The amino sugar composition accumulated by apoplastic species responded to some extent to the influence of soil fauna stimulating microorganisms on decomposition.At the same time,the fitting soil fauna effect is significantly related to the contents of glucosamine,galactosamine and muramic acid(P<0.01).the response of microorganisms to litter decomposition cannot be separated from the destruction of physical structure of litter by soil fauna.Nutrients such as C source and N source in litter decomposed by soil fauna are more easily utilized by microorganisms.In addition,litter quality can further attract microorganisms to participate in decomposition by influencing soil fauna to participate in decomposition. |
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