Influencing Mechanisms Of Warming And N Addition On The Stability Of Soil Aggregates And Nutrient Characteristics In Alpine Swamp Meadow Of The Qinghai-Tibet Plateau

Climate warming and increasing deposition of atmospheric nitrogen are important phenomena of global climate change,which will have a significant impact on the structure and function of terrestrial ecosystems.The Qinghai-Tibet Plateau is a sensitive area of climate change,with the largest and most extensive permafrost area in the middle and low latitudes of the world.Under the influence of global climate change,the fragile ecosystem of the Qinghai-Tibet Plateau is undergoing profound changes.The alpine swamp meadow is a sensitive habitat on the Qinghai-Tibet Plateau that is highly susceptible to the impact of climate change.Aggregates,as the basic unit of soil structure,are also the main storage place of soil nutrients.Therefore,studying the stability of soil aggregates and the mechanism of nutrient accumulation in marsh meadows on the Qinghai-Tibet Plateau under the background of climate warming and atmospheric nitrogen deposition is conducive to better exploring the mechanism of alpine ecosystems regulating climate change,with a view to providing a theoretical basis for future research on the impact of climate change on alpine ecosystems.This study selected alpine swamp meadows in the Fenghuoshan area on the Qinghai-Tibet Plateau as the research object.A simulated warming and nitrogen deposition experiment was conducted using an open top chamber and external N addition.The experiment included warming treatment,N addition treatment,andsimultaneous warming and N addition treatment.Soil samples were collected fro-m0-10 cm,10-20 cm,and 20-30 cm soil layers,and the required aggregates were separated using dry and wet sieving methods.Their particle size distribution was analyzed the stability indicators and carbon and nitrogen content were measured,and their response mechanisms under warming,N addition,and their interact-ion were analyzed.The main conclusions were drawn as follows:(1)The composition of soil aggregates in the three deep soil layers of the alpine meadow on the Qinghai-Tibet Plateau is dominated by macro-aggregates(>0.25 mm)and micro-aggregates(0.053~0.25 mm).The storage of organic carbon and total nitrogen stored in the macro-aggregates and their contribution to the original soil carbon and nitrogen are the highest,while NA-silt+clay(<0.053 mm)are the lowest.(2)The effect of warming on the particle size distribution of aggregates isn’t significant;The interaction of N addition,warming,and N addition has a significant impact on the distribution of aggregates in different particle sizes;The effect of warming treatment on the average weight diameter(MWD)of aggregates was not significant,but on the geometric mean diameter(GMD)was significant;The N addition treatment has a significant impact on the MWD and GMD of aggregates;The interaction treatment of warming and N addition has a significant impact on the MWD of aggregates,and has a very significant impact on GMD.(3)Warming significantly reduced the organic carbon content of the surface and middle soil layers,but had no significant effect on the total nitrogen content of the middle soil layers.Therefore,it also reduced the C/N ratio of these two soil layers,but the effect was not significant;In the N addition treatment,the low nitrogen treatment N1 only significantly increased the organic carbon conte nt of the middle soil layer,but the N addition treatment had no significant effect on the total nitrogen of each soil layer,so the C: N ratio of each soil layer did not change significantly;The interaction of warming and N addition significantly reduced soil organic carbon content,while significantly reducing soil total nitr ogen content,thus significantly reducing the C/N ratio of each soil layer.(4)There are significant differences in the effects of warming and N addition on organic carbon in soil aggregates among different particle sizes.Both warming significantly reduced the organic carbon storage in macro-aggregates and increased the organic carbon storage in micro-aggregates in surface soil.However,in middle and deep soil layers,both warming increased the organic carbon storage in macro-aggregates and decreased the organic carbon storage in micro-aggregates,but their effects were not significant.For the organic carbon storage in powder and clay particles,there is an increasing trend in the surface soil,while a decreasing trend in the middle and deep soil.The effect of N addition treatment on the organic carbon storage of various particle size aggregates was not significant.Warming and N addition simultaneously can significantly reduce the organic carbon storage of aggregates in the three soil layers.(5)There are significant differences in the effects of warming and N addition on the total nitrogen storage in soil aggregates among different particle sizes.Warming treatment can reduce the total nitrogen storage in large and micro-aggregates and increase the total nitrogen storage in NA-silt+clay,but neither change is significant;N addition treatment can increase the total nitrogen storage of macro-aggregates in each layer of soil in the short term,but has no significant effect on the total nitrogen storage of micro-aggregates and silt+clay.Warming and N addition simultaneously can significantly reduce the total nitrogen storage of aggregates in the three soil layers.In summary,N addition has a relatively low impact on soil nutrients,while warming has a higher impact on soil nutrients than N addition.For soil aggregates,warming and N addition did not have a significant impact on their stability,but their effects on internal nutrients and stability were consistent with the response of the original soil;Interactive treatment can significantly reduce the storage of organic carbon and total nitrogen in the soil,as well as the storage of organic carbon and total nitrogen in aggregates,thus also reducing the C: N ratio of aggregates.