| Detritus food web is an important channel for nutrient turnover through microbial biochemical decomposition in forest soils.Soil fauna accelerates litter decomposition and nutrient cycling not only directly by feeding and fragmenting plant litter and changing soil structure,but also indirectly by regulating microbial activity.Therefore,soil faunal diversity and function are closely related to carbon and nutrient cycling through detritus food web in forest soils.Some biocides(i.e.,naphthalene)have been widely used to investigate the ecological functions of soil fauna and some studies did found that naphthalene could effectively inhibit soil fauna.However,naphthalene can also impact soil nutrients,enzyme activity and microbial community,and this effect of naphthalene was called as “non-target effect”.Moreover,the non-target effect and its efficiency on soil respiration,nutrient turnover and microbial activity varied among different soil fauna,vegetation types and environmental conditions,representing great uncertainties in studying the ecological functions of soil fauna in various ecosystems.To explore the non-target effect of naphthalene,we conducted a two-year in situ experiment in a subalpine forest on the eastern Tibetan Plateau during January 2016 to December 2017 and measured soil respiration,soil dissolved carbon and nitrogen,enzyme activity,and microbial biomass carbon and nitrogen.We found that:(1)Naphthalene significantly decreased individuals and groups of soil macro-,mesoand micro-fauna.The average individuals and groups of soil fauna were 2477 and 162.59 in the control plots,and were 487.01 and 77.78 in the naphthalene plots,respectively.Compared to the control,the individuals of soil macro-fauna and meso-and micro-fauna were decreased by 78.51% and 80.79%,and the groups were decreased by 56.09% and 47.14%,respectively.(2)Naphthalene significantly decreased soil respiration,but its interaction with time was not significant.The seasonal dynamics of soil respiration rate in both naphthalene and control plots showed approximate single-peak curves,with the lowest and highest values in Janurary/February and August,respectively.The soil respiration were significant between naphthalene and control plots only in July and August 2017.(3)Contents of soil dissolved carbon(DC),ammonium and nitrate in both naphthalene and control plots decreased and then increased,but dissolved nitrogen(DN)remained stable during the growing season.Both the DC and DN contents were highest in April,but DC content was lowest in June and DN content was lowest in October.Naphthalene significantly affected DC and DN contents,but the effects were not significant for ammonium and nitrate.(4)The activities of invertase and urease increased and then decreased during the growing season,but the activities of nitrate reductase and nitrite reductase showed diverse patterns.Nitrate reductase were highest in April but lowest in August,and nitrite reductase were highest in October but lowest in June.Naphthalene had no significant effects on invertase,urease,nitrate reductase and nitrite reductase.(5)Microbial biomass carbon(MBC)and nitrogen(MBN)significantly changed over time.Specifically,MBC content increased and then decreased,but MBN content showed a reverse pattern during growing season.Both MBC and MBN contents were lowest in August,but MBC content was highest in June and MBN content was highest in April.The MBC/MBN ratio was lowest in April and maintained high levels in later periods.The different between naphthalene and control plots in MBC content were significant in April and October 2016,in MBN content was significant in August 2016,and in MBC/MBN ratio was significant in April and June 2017.In conclusion,naphthalene inhibited soil fauna community in the subalpine forest,and its non-target effect did not significantly changed soil respiration,soil nutrient content and microbial activity,but it has a slight effect on soil dissolved organic matter in some periods.We conclude that it is a feasible method by using naphthalene to investigate the ecological function of soil fauna community in the subalpine forest of western Sichuan. |
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