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sur le développement des zones arides et semi-arides

Titre : Effects of Plant Diversity on CO2 and CH4 Fluxes in Artificial Grassland Ecosystemsin Semi-Arid Regions

Auteur : 李惠珍

Grade : Master 2022

Université : Inner Mongolia University

Résumé
As the largest ecosystem in the world,grassland ecosystem plays a key role in the greenhouse gas balance of the atmosphere due to its source-sink effect on CO2and CH4.The impact of species diversity level on greenhouse gas exchange flux is mainly concentrated in wetlands and forests,while there is little research on artificial grassland,especially the research on greenhouse gas flux in non growing seasons.In this study,Leymus chinensis,Bromus inermis,Medicago sativa,and Melissitus ruthenica were chosen to construct sown pastures,with three plant diversity levels（1,2,4 species,respectively ;representing three diversity gradients）.The annual dynamic detection of greenhouse gas（CO2and CH4）fluxes and soil physicochemical factors will be carried out for 2consecutive years from 2020 to 2021.The annual dynamic changes of greenhouse gases and soil physical and chemical properties were explored,the annual emissions of greenhouse gases were quantified,and the influencing factors affecting greenhouse gas fluxes were further clarified.The main research conclusions are as follows :（1）Plant diversity levels had no significant effect on aboveground biomass.The leaf area index in 2021 was significantly higher than that in2020,and there was no significant difference in forage yield between different years.In 2020,the leaf area indices of species diversity levels in1,2 and 4 were 1.08,0.94 and 0.80,respectively ;The forage yields of the four species diversity levels were 1239.32,1229.94 and 1049.20 kg hm-2,respectively.In 2021,the forage yields of the 1,2,and 4 species diversity levels were 1214.29,1124.18 and 1157.72 kg hm-2,respectively.（2）The level of plant diversity had no significant effect on CH4and CO2fluxes,and the artificial grassland community was always a CH4sink and a CO2source.The CH4flux ranged from 2.64 to 2.86 kg C hm-2yr-1,and the CO2flux ranged from 29.50 to 31.74 g C m-2yr-1.The cumulative CH4uptake at species diversity levels 1,2 and 4 were 2.64,2.66 and 2.86 g C m-2,of which the CH4uptake in non-growing seasons accounted for 33.57～38.34%of the total annual CH4uptake ;the total annual cumulative CO2emissions for species diversity levels 1,2 and 4were 29.50,30.25 and 31.74 g C m-2,of which the CO2emission in the non-growing season accounted for 14.46～16.17%of the total annual CO2emission.（3）The annual warming potential of forage grass under different plant diversity levels in 2021 was higher than that in 2020.（4）CH4flux was significantly negatively correlated with air temperature,5 cm ground temperature,10 cm ground temperature,and p H,but was significantly positively correlated with soil moisture,soil total carbon content,soil nitrate nitrogen content,soil total nitrogen content,and microbial nitrogen content.correlation（P<0.05）.There was no significant correlation between CO2flux and the above indicators.In conclusion,the increase of species diversity will increase CH4uptake and CO2emission,and the non-growing season greenhouse gas flux cannot be ignored,which is of great significance for studying the contribution of artificial grassland ecosystems to global greenhouse gas emissions.

Mots clés : species diversity ;mixed sowing of beans and grass ;greenhouse gas ;non-growing season ;growing season ;warming potential ;

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