| Increasing concentrations of greenhouse gases due to the development of the industrial progression and increased human activity cause global climate change,including global warming and changes in precipitation patterns,with a sustained increase in total annual precipitation in mid-latitudes.At the same time,global nitrogen deposition increases significantly with the burning of fossil fuels and the application of fertilizers in agriculture.These global climate change factors seriously affect the structure and function of terrestrial ecosystems by influencing the ecology,flora and fauna,and the life activities of microorganisms.Ants are globally distributed in a wide range of habitats and dominate terrestrial ecosystems with high biomass,high density and diversity.On the one hand,ant nesting has an indirect effect on soil greenhouse gas emissions by influencing the physical structure of the soil,nutrient cycling and the composition of the biological community;on the other hand,ants directly influence soil greenhouse gas emissions through their respiration and their own metabolic behavior.Therefore,studies on the impact of ants on soil greenhouse gas emissions can help to understand and address the global warming phenomenon.However,there is a lack of research on ant greenhouse gas emissions and few studies have focused on the impact of ants on soil greenhouse gas emissions in the context of global change.This thesis presents a global meta-analysis of the effects of ants on greenhouse gas emissions in recent years,and relies on the established field control experiment platform of the National Field Scientific Observation and Research Station for Forest Ecosystems in Dabie Mountains,Henan Province,to investigate the effects of ants on soil greenhouse gas emissions under two global change factor control experiments,namely nitrogen deposition and rainfall.The study on the effect of ants’nests on soil greenhouse gas emissions was carried out under two global change factor control experimental treatments:increased nitrogen deposition and increased precipitation.The experimental platform consisted of four treatments:control（C）,canopy N addition（N）,canopy increased precipitation（W）and canopy N addition and increased precipitation（NW）,which were randomly distributed in four groups of 16 plots.In each treatment plot,three nests of Pheidole zoceana（leaf-cutting ants）and non-nesting soils were selected for in situ measurements of soil CO2,CH4 and N2O emissions using a trace gas analyzer,and soil physicochemical properties were analyzed under each treatment.The study addresses the following two scientific questions:1)What is the effect of ant nests on soil greenhouse gas emissions and 2)Is there a significant interaction between nitrogen deposition,rainfall and ant nests on soil greenhouse gas emissions?The main findings are as follows:（1）This paper conducted a global meta-analysis by integrating the effects of ants on greenhouse gas emissions and found that for CO2,in forest,grassland and wetland ecosystems,ant nests significantly contributed to soil CO2 emissions;in desert ecosystems,ants significantly suppressed soil CO2 emissions;and in mining areas,ants had no significant effect on soil CO2 emissions.For CH4,in forest ecosystems,ants significantly contribute to soil CH4 emissions;in grassland ecosystems,ants have no significant effect on soil CH4 emissions;and in wetland ecosystems,ants significantly suppress soil CH4 emissions.For N2O,ants significantly promoted soil N2O emissions in forest,grassland and wetland ecosystems.In this experiment,ant nests in forests were found to significantly contribute to soil CO2 and CH4 emissions,but unlike the results of the meta-analysis,they did not significantly contribute to soil N2O emissions.（2）In this study,the control of greenhouse gas emissions from ant nests and non-ant nest soil under nitrogen addition and precipitation treatment was studied.The results showed that for CO2,there was a significant interaction between nitrogen addition,precipitation enhancement and ant nest on soil CO2 emission:under the background of ambient rainfall,nitrogen addition promoted the CO2 emission of ant nest soil（+5%）,while under the background of increased precipitation,nitrogen addition significantly reduced the CO2 emission of ant nest soil（-8%）.The results of the structural equation model showed that under the background of ambient rainfall,nitrogen addition had a direct positive effect on the promotion of ant nests on soil CO2 emissions,while under the background of increased rainfall,nitrogen addition had no significant effect on the promotion of ant nests on soil CO2 emissions.For CH4,there was a significant interaction between nitrogen addition and ant nests on soil CH4 uptake:under the background of environmental nitrogen deposition,ant nests significantly reduced soil CH4 uptake（-30%）,while under the background of nitrogen addition,ant nests had no significant effect on soil CH4 uptake.The results of the structural equation model showed that nitrogen addition directly affected the inhibitory effect of ant nests on soil CH4 absorption.For N2O,there was a significant interaction between nitrogen addition and ant nests on soil N2O emissions.Nitrogen addition would change the insignificant inhibitory effect of ant nests on soil N2O emissions into insignificant promoting effect.There was also a significant interaction between increased rainfall and ant nests on soil N2O emissions.In the context of ambient rainfall,ant nests significantly inhibited soil N2O emissions（-57%）.In the context of increased rainfall,ant nests significantly promoted soil N2O emissions（+45%）.The results of the structural equation model showed that nitrogen addition may affect the promoting effect of ant nests on soil N2O by indirectly inhibiting soil MBC,while increased precipitation may affect the promoting effect of ant nests on soil N2O by directly affecting and increasing soil MBN.（3）From the annual scale,the ant nest will significantly promote the emission of soil greenhouse gases.Under the nitrogen deposition treatment,the greenhouse gas emissions of the ant nest will increase by an additional 6%of the global warming potential.Under the increased precipitation treatment,the greenhouse gas emissions of the ant nest will increase by an additional 88%of the global warming potential.Under the nitrogen addition and increased precipitation treatment,the greenhouse gas emissions of the ant nest will increase by an additional 11%of the global warming potential.Through investigation,the density of ant nests in the study area is about 1.59per square meter,and the area is about 1.36%.Combined with the area of ant nests,it is found that ant nests only increase the global warming potential of forest soil by about3‰.Therefore,if the area and density of ant nests are not considered,the contribution of ant nests to greenhouse gas emissions will be overestimated.In summary,the results of both meta-analysis and experimental studies show that in forest ecosystems,ants promote soil CO2 emissions and inhibit soil CH4 uptake,and are a hotspot for greenhouse gas emissions in forests.At the same time,there was some interaction between N deposition,increased precipitation and ant nests on different GHG emissions,which may be caused by N addition and rainfall increase changing soil physicochemical properties or affecting soil biomass and microbial activities in ant nests.Nitrogen addition,rainfall and both N addition and rainfall treatments lead to an increase in the GWP of ant nests,but the contribution of ant nests to global warming decreases in the context of N addition and rainfall.Under future scenarios of increased nitrogen deposition and increased rainfall,the status of ant nests as hotspots for soil greenhouse gas emissions may change to some extent. |
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