The Studies On The Effects Of Fertilization On Soil Nematode Community Structure In Alpine Meadow On The Qinghai-tibetan Plateau

With the enhancement of human activities and the intensification of global climate change,the atmospheric nitrogen and phosphorus deposition is increasing,which has a major impact on the structure and function of grassland ecosystems,and grasslands around the world have undergone different degrees of degradation.The alpine meadow on the Qinghai-Tibetan Plateau is vital grassland ecosystem in China,and nitrogen and phosphorus deposition have an important impact on it.Studies have shown that fertili-zation can restore degraded grasslands,and the abundant nematodes in the soil are very sensitive to environmental changes.The community composition of nematode changes can be used to reflect the health of the soil ecosystem.However,there is no consistent conclusion about the response and mechanism of soil nematode community in alpine meadow to nitrogen and phosphorus input.Therefore,this paper takes the soil nematode community in the long-term fertilization plot of the alpine meadows on the Qinghai-Tibetan Plateau as the research object.By collecting soil samples before and after fer-tilization in 2017,we studied the soil nematode community before and after fertilizatio n?control treatment,single application of nitrogen fertilizer,single application of phos-phorus fertilizer,nitrogen and phosphorus mixed fertilizer?changes in characteristics and composition,with a view to revealing the influence mechanism of long-term ferti-lization on the nematode community structure of alpine meadows on the Qinghai-Ti-betan Plateau.Through research and analysis,the following main results and conclusions are showed that:1.Soil nematode abundance increased from 100.45?strip/100 g dry soil?before fertilization to 667.81?strip/100 g dry soil?after fertilization.Among them,the single application of nitrogen fertilizer increased from 109.54?strip/100 g dry soil?to 631.78?strip/100 g dry soil?,and it was maximum of abundance when treated with moderate fertilization(10 g·m^-2);the single application of phosphorus fertilizer increased from96.80?strip/100 g dry soil?to 503.95?strip/100 g dry soil?,and as the fertilizatio n concentration increased,the abundance decreased;the nitrogen and phosphorus mixed fertilizer increased from 94.87?strip/100 g dry soil?to 904.95?strips/100 g dry soil?,also with the fertilization concentration increased,the abundance decreased.It showed that fertilization significantly increased the soil nematode abundance?6.65 times before fertilization?,and the effect of nitrogen and phosphorus mixed fertilization was the most significant,and the two caused a significant synergistic effect.The soil nematode spe-cies decreased from 50 genera before fertilization to 45 genera after fertilization,and the dominant genera of soil nematodes decreased from six before fertilization to four after fertilization,indicating that fertilization can also reduce the species diversity of soil nematodes and the dominant genera.2.After fertilization the soil nematode evenness index,Shannon-Wiener index,maturity index and plant parasitic index increased,indicating that fertilization increased soil nutrients,plant roots were not easily infected by plant-feeding nematodes,above-ground vegetation growth was better,and the soil ecology system tends to be stable.Fertilization will also significantly increase soil nematode biomass and metabolic index,and the community-weighted mean?CWM?volume of the nematode responds differ-ently to different fertilization.But the biomass,metabolic index and CWM value of nematodes are the highest in the medium nitrogen fertilizer(10 g·m^-2),indicating that this concentration of nitrogen fertilizer is the most suitable for nematode growth,and the nematode has the highest utilization rate of carbon.Nematode biomass and meta-bolic index are positively correlated with soil nutrients and water content,and signif i-cantly negatively correlated with soil pH,indicating that nematodes prefer to live in weakly acidic,rich food resources and relatively humid environments.3.After fertilization the abundance of nematodes with lower c-p value increased,with higher c-p value decreased.It shows that fertilization lead to decrease of abun-dance and even loss of species of the nematodes with large body size,long generation cycle and environmental sensitivity,and changes soil nematodes to r-strategists with small body size,short generation cycle and high reproduction rate,which is related to the sensitivity of different nematode species to fertilization disturbance.At the same time,fertilization make the decomposition pathway of soil food web be transformed from the bacterial decomposition pathway to the fungal and bacterial co-decomposition pathway,indicating that the soil food web tends to be mature and stable,which is related to increase the number of fungal nematodes caused by fertilization.In conclusion,fertilization can relieve the limitation of soil nutrients on nematodes and vegetation growth in alpine meadows on the Qinghai-Tibetan Plateau.But should pay attention to the effect of fertilization concentration,Single application of medium concentration nitrogen fertilizer,single application of low concentration phosphorus fertilizer or low concentration nitrogen phosphorus mixed fertilizer can promote the growth of soil nematodes and vegetation in alpine meadows,stabilize the soil ecosys-tem,and facilitate the recovery of degraded alpine meadows.