Characteristics Of Soil Nematode Community In Alpine Meadow In Northern Tibet, China

As the most numerous metazoan,nematodes ubiquitously distributed in all types of soilworldwide.Due to the close relationships with other biota in soil food web as well as withplant community,nematode plays a critical role in almost all soil processes which providesnecessary ecosystem functionings particular maintaining the stabilization and thepromotion of the biogeochemical cycling and energy flow.Besides,it was also beingconsidered as the potential bioindicator to assess the environmental impacts on soilecosystem.Current attentions have been paid on soil nematode community structure and itsrelations with evionmental changes.So far,the studies of soil nematode are still in theinfancy in the regions of Tibetan plateau.Alpine meadow,which is the largest and most important ecosystems in Northern Tibet,extensively distributed in this region.This type of meadow is one of the typical ecosystemsin Tibetan plateau.To study the effect of vegetation on soil nematode community inTibetan plateau,we selected three representative plant communities:Po(Potentilla spp.),Kp(Kobresia pygmaea),and K1(Kobresia littledalei)as sample plots,based on thedominant species of each plant community.The sample plots are situated at N31°31′38″-N31°32′02″,E92°04′03″-E92°04′16″ in Naqu County in the Naqu region of the TibetAutonomous Region,China.Application of soil nematode individual density,communiy composition,Nutritionstructure characteristic index and biodiversity index,to analyse the feature of soil nematodecommunities in cold alpine.Respectively,we set up sample plots in both enclosure(3a)and grazing land in alpinemeadow.The following soil chemical properties were tested:pH,soil organic matter,totalnitrogen,phosphorus and kalium.The characteristics of soil nematode communities,as wellas the relationship between soil nematode community and soil chemical properties,wereanalyzed to understand the effect of grazing on alpine meadow,and the role of enclosure for the recovery of degraded alpine meadow in northern Tibet.The main conclusions show as follows:(1)A total of 33,038 nematodes,which were classified to nematode phylum,2 classes,6orders,51 families and 93 genera,were collected during the surveys.Average individualdensity was 847 nematodes per 100g dry soil.The results were mostly within the scope ofprevious reports,and nematodes obviously appeared to aggregate in the upper soil layers.(2)The ranking of quantities in different alpine meadow soils are following:Potentilla<Kobresia littledalei<K.pygmaea,differences of quantities are distinctive.the rankingsequence of genus number is opposite:Potentilla>Kobresia littledalei>K.pygmaea.Quantities of nematode and genus number are largely fluctuated in growth period.Revivingperiod has the largest number,flourishing period has the second,withered period is theleast.The seasons change trend consistent with individual density of soil nematode.(3)The rank of biodiversity is Potentilla>K.pygmaea>Kobresia littledalei.Evennessand dominance index of Kp were significantly higher than the other two kinds of plantcommunity.(4)The research indicated soil nematode tropic composition varied from one plantcommunity to another in alpine meadows.Herbivorous and bacterivorous nematodes werethe major nematode communities in the area.The relative abundance of herbivorous toomnivorous and/or predatory nematodes obviously varied in different plant communities.An analysis of the constitution of the c-p groups showed all cp2 groups were thepredominant groups in all three plant communities,and all cp-groups were mainlyr-strategists.Kobresia pygmaea was the most common food source for nematodes.Kobresia littledalei had the lowest nematode density,possibly because limited foodavailability limits the reproduction of cp-1 and cp2 nematodes.The result of analysis of theplant parasite index indicated the Potentilla community was easier for nematodes topopulate when compared to he other two kinds of plant community,whereas the data fromthe maturity index(MI),PPI/MI and cp5 demonstrated nematode stability in Potentilla washighest among three plant communities.(5)The fungal to bacterial feeder ratio and Nematode Channel Ratio showed bacterialdecomposition was the major decomposition pathway in the soil organic substancedecomposition system.Correlation of nutritional groups and environmental factors showedomnivorous/predatory nematodes were affected significantly by water content during dryperiods,while a close relationship was found between soil pH and fungivorous nematodes,which was obviously affected by electrical conductivity(EC)during periods of rapid growth.The abundance of bacterivorous nematodes was only correlated to pH during the dry season.The presence of different plant communities leads to effects on water content,soil formation and the distribution of nutrients.The analysis related to water content,pH and EC reveals plant communities have important influences on the functional structure of nematode communities.Differences in nematode community structure in different meadows preliminarily indicate the potential for using nematodes as environmental indicator species.(6)Short-term enclosure(3a)increase the biodiversity and abundance of soil nematodes,and reduce the proportion of the plant of predatory nematodes.Enclosure made the alpine meadow ecosystem to develop in the direction of more stable.WI index reflects in grazing intensity biggest alpine meadow vegetation flourishing period(August),high grazingintensity,the health of the soil is worst,and,further overload will cause degeneration of the alpine meadow.