| In recent years,changes in atmospheric nitrogen deposition and rainfall patterns caused by human activities is becoming increasingly globalized,which is bound to have an impact on terrestrial ecosystems.In this context,the degradation of desert grassland ecosystems is becoming a topic of widespread concern.Soil nematodes play an important role in the material circulation and energy flow of the ecosystem and are often used as biological indicators to monitor the environment.This study explored the response characteristics of soil nematodes in the Stipa breviflora desert through steppe to changes in water and nitrogen deposition through long-term field control experiments.The main results are as follows:1.A total of 41 genera of soil nematodes was obtained in the study area.The dominant community genera were Acrobeles,Acrobeloides,Cervidellus,Aphelenchus,Helicotylenchus,Tylenchorhynchus,Chiloplacus,Aphelenchoides.The increase in precipitation significantly increased the nematode abundance compared with nitrogen addition and was especially obvious in the last year of the experiment(2019).Under different water and nitrogen control,the N50(kg·N·hm-2·a-1)nematode abundance increased significantly.the species diversity gradually increased under dynamic conditions.2.In terms of functional groups of nematodes,the number of bacterial-eating nematodes in the 0-10 cm soil layer was the largest(40.72%?49.97%of the total),and the number of omnivorous nematodes was the lowest.Rain-increasing conditions were conducive to the increase of micro-eating nematodes,while rain-reducing was the opposite.The addition of N50 nitrogen level inappropriate water and nitrogen was more conducive to the growth of micro-eating nematodes.Rain-reducing N100 treatment reduced the number of fungal-eating nematodes.Increasing rainfall and nitrogen application increased the number of herbivorous nematodes,and nitrogen application would reduce the number of predator/omnivorous nematodes,but there was no significant change in the inter-annual dynamics.3.From the perspective of community structure-function index,nitrogen addition had a stronger influence on nematode richness than water factor,and higher nitrogen addition significantly increased nematode richness.A single addition of nitrogen had no significant effect on the evenness index and dominance index of nematodes and did not change the diversity and stability of the nematode community.Changing in vegetation characteristics of precipitation enhancement did not increase plant productivity and therefore did not affect nematode diversity.Under the dynamic treatment of the year,the soil mineralization pathway was affected by micro-nematodes,and the organic matter was mainly degraded by bacteria.The flora analysis shows that the water-nitrogen interactive treatment improved the soil anti-interference ability as a whole,and the food web was structured.4.Soil ammonium nitrogen,nitrate nitrogen,water content,pH,plant diversity and biomass were the main environmental factors that affect nematode community changes.The changes in soil nitrogen content and vegetation characteristics represented that the increase in the quality and quantity of nematode food resources had increased the number of partial nutrient k-strategists(cp1 and cp2).With the increase of nitrogen gradient,the pH gradually decreased,and the dominant genus of the cp3 group and the group of those who prefer the r strategy(cp4 and cp5)decreased accordingly.In summary,the comprehensive treatment of the changes in soil nematode community structure for three years indicated that under different water and nitrogen interactions,the stability of the soil food web in the Stipa breviflora desert steppe had been improved,and the stability of the underground food web in the Stipa breviflora desert steppe ecosystem had gradually increased. |
PDF Full Text Request