Characteristics And Influencing Factors Of Carbon Flux In Desert Steppe On The Northern Slope Of Tianshan Mountains

Desert steppe is a grassland type widely distributed in the piedmont plain to the middle and low mountains on the northern slope of the Tianshan Mountains in Xinjiang.It plays an important role in regulating the carbon budget of the grassland ecosystem on the northern slope of the Tianshan Mountains.In order to elucidate the variation characteristics of carbon flux in the desert steppe on the northern slope of the Tianshan Mountains and its response to environmental factors.In this study,the desert steppe on the northern slope of the Tianshan Mountains was taken as the object,based on the observation data of the micro-meteorological observation system and the Li-840 CO₂ infrared analyzer from 2020 to 2021,the change characteristics of carbon flux in the desert steppe and the influence of environmental factors on it were analyzed.The main results are as follows:（1）The shallow soil temperature and humidity in the desert steppe had obvious diurnal variation characteristics,soil temperature in spring and summer gradually decreased with the increase of soil depth,and the soil temperature in autumn and winter increased with the increase of soil depth.Path analysis shows that the change of soil temperature in desert grassland is mainly driven by the direct action of air temperature,and then indirectly affected by soil humidity.5 cm soil moisture fluctuates periodically in spring,summer and autumn,soil moisture fluctuations are not obvious in winter.（2）From June to September,the net ecosystem carbon exchange of the desert steppe had an obvious diurnal variation trend,with carbon absorption during the day and carbon emission at night,the monthly average net ecosystem carbon exchange rate ranged from-0.89～0.64μmol·m^-2·s^-1.Ecosystem respiration has obvious diurnal variation,ecosystem respiration was higher during the day and tends to be flat at night,the monthly average ecosystem respiration ranged from 0.25～4.13μmol·m^-2·s^-1.Soil respiration first increases during the day and then decreases,and the diurnal variation trend is relatively gentle at night,the maximum value appeared at 12:00-16:00,and the minimum value appeared around 6:00-7:00,the monthly average soil respiration ranged from 0.19～2.80μmol·m^-2·s^-1.（3）Photosynthetically active radiation was the dominant factor affecting the net ecosystem carbon exchange during the day,and the two were in line with the right-angle hyperbolic model,and the net ecosystem carbon exchange during the day decreased with the increase of photosynthetically active radiation;The relationship between ecosystem respiration and 5 cm soil temperature conformed to an exponential model,and Q₁₀ was between 1.58～2.82.The relationship between ecosystem respiration and 5 cm soil moisture was a quadratic function,too low or too high soil moisture would inhibit it.Redundancy analysis showed that 5 cm soil moisture,air temperature and photosynthetic effective radiation were the key factors affecting the net ecosystem carbon exchange and ecosystem respiration in desert steppe.The soil respiration was jointly affected by 5 cm soil temperature and 5 cm soil moisture;The best fitting model between soil respiration rate was R_s=-0.024+0.099T_s-5.726SM+0.288T_sSM.（4）Ecosystem respiration and soil respiration under different precipitation treatments had obvious diurnal trends;ecosystem respiration under three precipitation treatments（28 mm,18 mm,5 mm）increased significantly compared with CK by 216.81%,153.27%and 39.35%,the soil respiration increased significantly by 22.93%,23.20%,12.07%.Ecosystem respiration has a linear relationship with 5 cm soil water content,and soil respiration has a quadratic function relationship with 5 cm soil water content.