| Since the implementation of the"Grain to Green Programme",the vegetation cover of the Loess Plateau region has increased significantly,and the ecological function has been improved.The litter is an important carrier connecting the aboveground and belowground ecosystems.As a reservoir of nutrients in the ecosystem,its decomposition process plays an important role in the material cycle and energy flow of the ecosystem in the Loess Plateau region.The study of the effect of litter decomposition on soil carbon and nitrogen is of great significance for scientific guidance of vegetation restoration and reconstruction.As decomposers,soil faunas directly or indirectly affect litter decomposition by crushing and feeding on litter,as well as by altering the physicochemical properties and biological composition of microhabitats.However,most studies on litter decomposition in the Loess Plateau region have ignored the role of soil fauna,which has limited insights into the soil ecosystems of the region.In this study,we studied the litter of typical shrub-herb in the Liudaogou watershed in the northern Loess Plateau.The dynamics of the groups,individual numbers,and structure of soil fauna during litter decomposition in different habitats were systematically investigated.The relationship between soil fauna and the nutrient release rate of litter was quantified.The effects of litter type and soil fauna on litter decomposition and nutrient release under the effects of mowing cover,nitrogen addition,and anthill soil cover were comparatively analyzed.The main results of the study are as follows:（1）The litter type,decomposition time and its interaction had significant effects on the individual numbers and groups of soil fauna.The diversity index and evenness index of soil fauna showed that the habitats of the Natural fallow（NAF）were significantly higher than the Korshinsk peashrub（KOP）and Purple alfalfa（ALF）.The dominance index,individual numbers and group of soil fauna showed that the NAF were significantly lower than KOP and ALF.The overall soil fauna in the decomposition bag was dominated by mites,which accounted for about 55%～97%of all soil fauna.Temperature,humidity,and fresh litter production all directly or indirectly altered the decomposition process of litter in the mesh bags by affecting soil fauna activity.The limiting factor for the decomposition rate in the later stage of decomposition remains the litter quality rather than the soil animal community and microorganisms.For plants that are high in nitrogen content and readily decompose,the structure of the soil fauna community can alter the rate of decomposition by influencing microbial activity.（2）The effects of mowing cover on soil fauna were strongly influenced by site conditions.Mowing reduced the individual numbers of soil fauna in the litter layer of KOP and ALF habitats,while in NAF habitats,the individual numbers and diversity index of soil fauna were increased.The mowing cover had a more pronounced effect on soil microbial community structure in herb habitats.The mowing cover increased the number of soil bacteria and their community richness and diversity in the NAF habitat,increased the relative abundance of Acidobacteria phylum in all habitats,and decreased the proportion of Proteobacteria phylum.Mowing cover increased the abundance and diversity of fungi in the ALF habitat.The effects of mowing cover on soil fauna,microorganisms and soil nutrients showed significant differences with vegetation type.（3）Nitrogen addition significantly affected the decomposition characteristics of litter.When nitrogen was applied at 30 kg N hm-2 yr-1（N30）,carbon release of litter from both NAF and ALF habitats was promoted.Carbon release of litter from ALF habitats was suppressed when nitrogen was applied at 50 kg N hm-2 yr-1（N50）.Nitrogen addition promoted litter nitrogen release from ALF habitat,but the differences were small among the different gradient nitrogen treatments;whereas,nitrogen addition had a more pronounced effect on litter nitrogen changes in NAF habitat compared to the unapplied nitrogen treatment.There are differences in nitrogen preferences of soil faunas which result in interspecific competition and homogenization of soil fauna community structure.The individual number of soil fauna in the ALF and NAF habitats began to decrease at nitrogen addition of 100 kg N hm-2 yr-1,and the group number remained almost constant with the N50 treatment.Nitrogen addition had significant effects on the Oribatida,Mesostigmata and Prostigmata.The litter type significantly affected the individual and group number of soil fauna.The individual number of soil fauna was significantly higher in the ALF habitat than in the NAF habitat in the same nitrogen application treatment,and the individual number of soil fauna was highest in the N50 treatment in the ALF habitat at 2743,which was about 23.75 times higher than in the N50 treatment in the NAF habitat.Nitrogen addition stimulates plant growth and increases plant above and belowground biomass,which results in nitrogen input to the soil through litter and inter-root deposition.（4）Anthill soil covers significantly accelerated the release of nutrients from the litter.In the decomposition experiment for a total of 92 days,the carbon content of litter in CK（Control check,Adding litter）,CAM（Adding litter+anthill soil cover of Camponotus japonicus）,FOR（Adding litter+anthill soil cover of Formica sinensis）and ANT（Adding litter+colony of Camponotus japonicus）decreased by 15.06%,65.10%,70.06%,and 35.15%,respectively,compared with the initial values.The nitrogen content of litter was released by 0.49%,61.14%,61.14%,66.49%,and 33.57%.The phosphorus content of litter released-18.23%,45.94%,44.43%and 13.52%.The cover type significantly affected the individual number and group of soil fauna.In the litter layer,the dominant group of soil fauna varied among the different cover types.The CK was Oribatida,Mesostigmata and Isoptera.The CAM was Oribatida and Mesostigmata.The FOR is Oribatida,Mesostigmata and Prostigmata.The ANT was Mesostigmata and Astigmata.The overall trend of litter carbon,nitrogen and phosphorus decreased with decomposition time in the abandoned ant mound soil treatment due to the lack of arthropod predators.Camponotus japonicu nesting activities significantly altered soil properties and increased litter nutrient release during the pre-decomposition period,but their predatory activities reduced the contribution of small and medium-sized soil fauna and microorganisms to litter nutrient release to some extent.Soil faunas play an important role in the decomposition of litter and the input of soil organic carbon,and significantly contribute to litter decomposition through direct feeding and influencing the microbial community,etc.The influence of soil faunas on litter decomposition is affected by a variety of factors,such as the vegetation type and the physical and chemical properties of the soil.At the same time,the decomposition of litter by ground-dwelling macrofauna,such as ants,should not be ignored,which is conducive to the formation of"fertilizer islands"at the point scale.Mowing and nitrogen application significantly altered the habitat characteristics and food source quality of soil fauna,which in turn altered the characteristics of soil microbial community and litter decomposition rate.This paper reveals in detail the characteristics of soil fauna in the restored ecosystem of the Loess Plateau and the role of soil fauna in the process of litter decomposition,and explores the methods of soil fauna regulation in the Loess Plateau.The results of this study can provide scientific references for the advancement of the construction of vegetation cover in the Loess Plateau and the accurate assessment of its ecological benefits. |
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