Responses Of Carbon Exchange In Different Types Of Wetland Ecosystems In Qinghai Lake To Simulated Warming And Nitrogen Deposition

In the past hundred years,increasing global temperature and increasing atmospheric nitrogen deposition have caused significant changes in the carbon and nitrogen cycle of terrestrial ecosystems.Due to the unclear characteristics of regional climate change in the alpine wetland of Qinghai Lake and the uncertainty of future carbon and nitrogen cycles,it is of great significance to study the response of different types of wetland ecosystem carbon exchange in Qinghai Lake to simulated warming and nitrogen deposition.In order to explore the response characteristics of the carbon exchange components of different types of wetland ecosystems to nitrogen addition under warming conditions and their environmental driving factors.In this study,Ikeulan Wayan Station(Heyuan Wetland)and Niaodao Station(Lakeside Wetland)were selected as the research objects.The open-top temperature chamber was used to elevate passive temperature and the artificial nitrogen application was used to simulate the atmospheric nitrogen deposition.There are four treatment methods:control,warming,nitrogen addition and both warming and nitrogen addition.The LI-6400 XT photosynthesis instrument and static chamber method were used to determine the carbon exchange components of the wetland ecosystem from May to September 2020.At the same time,the site surface soil temperature,soil water content,above-ground biomass,below-ground biomass,soil p H values,total soil nitrogen and total soil carbon were measured,and the following conclusions were drawn after the integrated analysis:(1)The surface soil temperature of Wayan Station and Niaodao Station showed a unimodal trend throughout the growing season,but the soil temperature of Niaodao Station had a higher average value on the scale of the growing season.Warming,nitrogen application and interaction not only increase the soil temperature(about1.00 °C)at the depth of 0-20 cm in the two wetlands,but also promote their seasonal changes.(2)The soil water content of different depths in Wayan Station showed obvious unimodal changes throughout the growing season.While the soil water content of Niaodao Station in the growing season is increasing during the day,the lakeside wetland of Niaodao Station is more sensitive to climate change than the river source wetland of Wayan Station.(3)The above-ground biomass of Wayan Station showed an inverted V-shaped change trend during the whole growing season.The Niaodao Station showed an increasing trend,and the above-ground biomass of Niaodao Station was larger in the growing season.The below-ground biomass of 0-10 cm soil layer in Wayan station is higher than that of 10-20 cm soil layer.The increase in temperature promoted the increase of the above-ground biomass of plants in Wayan Station,but reduced the below-ground biomass.Nitrogen application and interaction significantly promoted the above-ground biomass and the rate of plant fall.The below-ground biomass of Niaodao Station has been increasing month by month as a whole,and both the warming and the interaction have significantly promoted the increase of above-ground biomass and below-ground biomass.(4)The temperature increase and nitrogen application treatments increased the soil p H of the two sites,and the interaction of temperature increase and nitrogen application had little effect on it.The limitation of low temperature in alpine wetland is more obvious than the limitation of nitrogen.The total nitrogen and total carbon content of the soil at different depths at Wayan Station roughly presents an inverted U-shaped seasonal variation,and the content of the 0-10 cm soil layer is more than that of the 10-20 cm soil layer.Niaodao Station showed a trend of first increasing and then decreasing on the growing season scale.Increasing temperature significantly reduced the soil total nitrogen and total carbon content in the topsoil layer of Wayan Station,while the nitrogen application treatment and the interaction increased.Increasing temperature has little effect on the total nitrogen and total carbon of the soil at the Niaodao Station,but the nitrogen application and the interaction are significantly reduced.(5)The day-to-month change trend and peak time of the carbon exchange components in the wetland ecosystems of Wayan Station and Niaodao Station under different treatments are different.The seasonal changes of net ecosystem exchange(NEE)carbon in the two wetlands both showed obvious U-shapes.The absorption rate reached the maximum in July.The warming treatment promoted the NEE of the two wetlands in the early stage and inhibited the NEE in the later stage.Nitrogen application and alternate treatment had a greater promotion effect on the increase of NEE in the two wetlands,but did not reach a significant state(P>0.05).The seasonal variation characteristics of ecosystem respiration(ER)under different treatments all showed obvious bell-shaped,but the peak time of appearance was different.The warming treatment inhibited the ER of the Wayan station wetland,and the nitrogen application and the interactive treatment promoted the ER of the Wayan station wetland.Increasing temperature,nitrogen application and interaction all promoted the ER of the Niaodao Station wetland.The seasonal variation characteristics of gross ecosystem productivity(GEP)under different treatments all showed an obvious inverted V-shaped trend,and reached the maximum in July.The warming treatment inhibited the GEP of the Wetland in Wayan Station,but promoted the GEP of the Wetland in Niaodao Station.Both the nitrogen application treatment and the interaction promoted the GEP of the two wetlands.(6)The carbon exchange components of the Wayan station wetland ecosystem under different treatments have a significant correlation with the surface soil layer(0-20cm)soil temperature,soil water content,underground biomass,and soil total nitrogen(P<0.05),different The carbon exchange components of the wetland ecosystem of the Niaodao Station under the treatment had a significant correlation with soil temperature and soil water content(P<0.05).The carbon exchange components of the two wetland ecosystems are all linearly related to the surface soil temperature,and the ecosystem carbon exchange components and environmental elements between the treatments have a relatively consistent correlation,indicating that the soil temperature is the ecological environment of the Qinghai Lake wetland.The key influencing factors of system carbon exchange under climate change scenarios(temperature rise and atmospheric nitrogen deposition).In summary,this study analyzed the response characteristics of the carbon exchange components of different types of wetland net ecosystems in Qinghai Lake to simulated warming,nitrogen addition and their interactions,and also explored the changes in carbon exchange in different alpine wetland ecosystems.Environmental driving factors and related results provide data support for future wetland ecosystem carbon exchange scale extrapolation and model prediction.