Distribution Characteristics Of Forest Soil Organic Carbon And Its Influencing Factors In Different Climate Zones In Ningxia

It is helpful to reveal the response mechanism of forest soil organic carbon to climate change for exploring the elevation patterns of soil organic carbon in different climatic zones.And it can provide a theoretical basis for scientific management of forest carbon pools and response to climate change.Ningxia is located on the transition zone from semi-arid to aridity,and its ecological environment is relatively fragile.The Liupan Mountains in the south of Ningxia,and the Luoshan Mountains in the middle,as green ecological barriers and water conservation forest areas,have the ecological functions of maintaining biodiversity,conserving water and soil,preventing wind and fixing sand,etc.,and are important ecological safety barriers in the northwest of China.Luoshan(temperate arid continental climate)and Liupanshan(warm temperate semi-humid climate)belong to different climate types,and they are ideal areas for studying the response of forest soil organic carbon to climate change.In this study,soil samples of 0-10,10-20 and 20-40 cm soil layers were collected along the same elevation gradient(1700?2600 m)in the Liupan Mountains and Luoshan Mountains to determine the soil organic carbon content and basic physical and chemical properties,and the effects of climate,vegetation and soil factors on forest soil organic carbon in different climate zones in Ningxia were systematically investigated by combining climatic and vegetation factors,and by means of random forest models and structural equation models.The results show that:(1)The content of soil organic carbon in Liupanshan was significantly higher than that in Luoshan,with obvious surface accumulation,and decreased with the increase of soil depth.With the increase of altitude,the soil organic carbon content in Luoshan increased significantly,while the soil organic carbon content in Liupanshan increased first and then decreased.(2)In the 0-10 cm soil layer,the soil physical and chemical indexes of Luoshan Mountain showed significant differences at different elevations.the variation of soil particle composition in the other soil layers was not significant within different altitudes.Soil organic carbon content was the highest at the altitude of 2300?2500 m,and significantly higher than that at the altitude of 1700?2100 m.(3)In the 0-10 cm and 10-20 cm soil layers,the pH,electrical conductivity and organic carbon content of Liupan Mountain showed significant differences at different elevations.The variation of soil particle composition was not significant within different altitudes.Soil organic carbon content was the highest at the altitude of 2300?2500 m,and significantly higher than that at the three altitudes of 1700?2300 m.(4)The soil organic carbon density in Liupan Mountain ranged from 2.90?7.99 kg/m2,and the organic carbon stock of forest soil from 0 to 100 cm was 5.349 Tg;the soil organic carbon density in Luoshan Mountain ranged from 0.99 to 6.84 kg/m2,and the organic carbon stock of forest soil from 0 to 60 cm was 0.151 Tg.(5)The random forest model showed that the dominant factor affecting the variation of organic carbon content along the elevation in Liupan Mountain was soil electrical conductivity.Soil pH was the dominant factor affecting the variation of organic carbon content along the elevation in Luoshan Mountain.(6)The structural equation model showed that the NDVI was the dominant factor influencing the variation of soil organic carbon content in forests from 0 to 10 cm in different climatic zones of Ningxia.The soil organic carbon content of 10?20 cm was mainly affected by the mean annual temperature and soil bulk density;the soil organic carbon content of 20?40 cm was mainly affected by pH and electrical conductivity;the soil organic carbon content of 40?60 cm was mainly affected by electrical conductivity.