| Under the background of global change,changes in nitrogen deposition and precipitation patterns will directly or indirectly affect various soil fauna and related ecosystems in the underground soil food web.On the one hand,ants as "soil engineers" play a bottom-up effect on the food web.On the other hand,the ant's predatory effect will produce a nutritional cascade through the top-down effect.Nitrogen deposition and changes in precipitation patterns may have direct or indirect effects on ant communities.Nonetheless,there are not many studies on ants for nitrogen deposition and alternations in precipitation patterns.The traditional methods of simulating nitrogen deposition and precipitation on soil fauna are based on understory,ignoring the absorption and interception of nitrogen and precipitation by the forest canopy and other related ecological processes.This experiment relies on the field experiment control platform of "Canopy Simulated Nitrogen Settlement" in Jigongshan Nature Reserve,Xinyang City,Henan Province,which explores the effects of canopy simulated nitrogen deposition and precipitation on ant communities by 7 treatments: Canopy Nitrogen Addition 25 kg N ha-1yr-1(CAN25);Canopy Nitrogen Addition 50 kg N ha-1yr-1(CAN50)Understory Nitrogen Addition 25 kg N ha-1yr-1(UAN25);Understory Nitrogen Addition 50 kg N ha-1yr-1(UAN50);Canopy Water Addition(30% additional precipitation,CW);Canopy Nitrogen and Water Addition(Canopy Nitrogen Addition 25 kg N ha-1yr-1+30% additional precipitation,CNW);Control(CK).Mainly study the following scientific questions:(1)How do different nitrogen addition methods and nitrogen addition concentration affect the ant community?(2)How does the main effect of enhancement of precipitation and nitrogen-water interaction affect the ant community?In response to the above scientific issues,this study used trap methods to capture ants to determine the effects of nitrogen application and rain enhancement on ants.The research results are as follows:(1)There was a significant difference between the effects of simulated nitrogen deposition in canopy nitrogen application and in understory on ant abundance and relative abundance.Compared with understory nitrogen application,canopy nitrogen application significantly increased ant abundance,but the effect of nitrogen deposition on different ant species was not consistent,which was mainly shown as follows: for dominant species,canopy nitrogen application significantly increased the relative abundance of Carebara melasolena,but significantly reduced the relative abundance of Pheidole zoceana;For the more common species,canopy nitrogen application significantly reduced the relative abundance of Crematogaster osakensis and Nylanderia flavipes.compared with understory nitrogen application.The effect of different nitrogen concentration on the abundance of ants was as follows: the relative abundance of Carebara melasolena was significantly increased by low nitrogen compared with high nitrogen.The Shannon Weiner index and evenness index of all the treats with nitrogen application increased significantly,while the dominance index and species richness index decreased significantly.Compared with understory nitrogen application,the low nitrogen level in the forest canopy significantly increased the number of Shannon Weiner finger and evenness index of ants,but there was no significant difference to the diversity indexes of ants.Our results show that the simulated nitrogen deposition in the canopy significantly increases the physicochemical properties of soil moisture content,microbial biomass carbon nitrogen,total organic carbon and total phosphorus compared with the application of nitrogen under the canopy.This suggests that the deposition of canopy nitrogen may contribute to the growth of plants and other soil organisms by promoting the dynamics of soil nutrients,and further provide a favorable environment for ant food sources,leading to an increase in ant population and community diversity under crown nitrogen application.(2)The effects of simulated canopy nitrogen application and precipitation on ant abundance and diversity were significantly interactive.Compared with the control group,both canopy nitrogen application and precipitation-increasing treatment significantly increased ant abundance,but the effect of nitrogen application on ant abundance was not significant in the precipitation-increasing situation.Similarly,under the application of nitrogen,the effect of precipitation on ant abundance was not significant.Compared with the control group,ant abundance was significantly increased under the combined treatment of nitrogen application and precipitation.The responses of different ant species to canopy nitrogen application and precipitation enhancement were inconsistent,which were mainly shown as: compared with the control group,canopy nitrogen application and precipitation enhancement both significantly increased the dominant species Carebara melasolena,but significantly reduced the relative abundance of dominant species Pheidole zoceana.However,in the case of precipitation increasing,the relative abundance of Pheidole zoceana was significantly increased by nitrogen application.The response of the more common species to nitrogen application was significantly increased only in the precipitation-increasing situation,but its response to precipitationincreasing was significantly decreased.The simulated canopy nitrogen application and precipitation had significant interaction effects on ant diversity indexes.No matter whether the precipitation was increased or not,canopy nitrogen application significantly increased the number of Shannon Weiner index and evenness index of ants.On the contrary,no matter whether nitrogen was applied or not,precipitation significantly reduced the number of Shannon Weiner index and evenness index.However,these two indexes were significantly increased under the combined treatment of nitrogen application and precipitation,indicating that canopy nitrogen application had a more obvious promoting effect on ant diversity.Both dominance index and species richness index were significantly reduced by canopy nitrogen application in both precipitation-increasing scenarios.Under the condition of no nitrogen application,increasing precipitation significantly increased the dominance index of ants but significantly reduced their species richness index.However,under the condition of nitrogen application,the effect of increasing precipitation on dominance index and species richness index was not significant.Under the combined treatment of nitrogen application and precipitation,these two indexes were significantly reduced compared with natural conditions,indicating that canopy nitrogen application had a more obvious inhibitory effect on ant dominance and abundance.To sum up,the simulated nitrogen deposition in canopy,especially the low nitrogen application in canopy,has a significant promoting effect on ant population and diversity.Although increasing the number of ants,increasing precipitation is not conducive to increasing the diversity of ants.The reason may be that increasing precipitation significantly increases the number of dominant species,Carebara melasolena,but significantly reduces the number of dominant species,Pheidole zoceana and more common species,leading to an increase in the dominance index of ants under the precipitation treatment.Compared with natural conditions,the number of ants,the number of Shannon Weiner index and the evenness index were significantly increased under the combined treatment of nitrogen application and rainfall increase,and the dominance and richness were significantly reduced,indicating that the number and diversity of ants were more obvious in response to nitrogen application.This means that under the background of global changes in the future,the interaction of multiple factors such as nitrogen deposition and precipitation is more conducive to the reproduction and survival of ants,and hence to the maintenance of the structure and function of the ecosystem by ants. |
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