Distribution Characteristics And Influencing Factors Of SOC And Soil PhytOC In The Karst Rocky Desertification Ecosystem,SW China

This research takes the typical representative of the Southwest China karst plateau gorge rock desertification comprehensive restoration demonstration area(Guanling-Zhenfeng Huajiang study area)as the research object.Eleven land use patterns(Zea mays land,Lonicera japonica land,Hylocereus undulatus land,Zanthoxylum bungeanum land,mingled forest of Z.bungeanum and H.undulatus,Pennisetum sinese land,abandoned land,natural grassland,shrubwood,Sabina chinensis forest,mingled forest of S.chinensis and L.lucidum.)were selected,and 0～5 cm,5～10 cm and 10～20 cm soil were collected to explore the basic physical and chemical properties of soil,soil organic carbon(SOC),phytolith,phytolith-occluded-carbon(PhytOC),and distribution characteristics.The SOC and PhytOC under different land use patterns were estimated,and the dominant influencing factors of SOC and PhytOC were explored.The influence law and driving mechanism of Karst land use pattern change on SOC and PhytOC were clarified.This study provides a theoretical reference for restoration of karst rocky desertification ecosystem and the optimization of land use structure and the realization of carbon neutral strategic goal in 2060.The main results are as follows:(1)The SOC content of mingled forest of S.chinensis and L.lucidum and S.chinensis forest was higher than that of the other nine land use patterns.Soil organic carbon storage of natural grassland was the highest,followed by mingled forest of S.chinensis and L.lucidum,and P.sinese land SOC content and Soil organic carbon storage is the lowest.In the soil profile,the SOC content of 11 land use patterns decreased with the deepening of the soil profile,and there was obvious surface enrichment phenomenon.Correlation analysis shows that the soil organic carbon of the11 land use types is closely related to environmental factors such as SOC and soil physical and chemical properties.In this study,the two environmental factors TP and pH are not significantly related to SOC content,but has a very significant correlation with TN,>2 mm gravel content,C:N,C:P,N:P,altitude,slope and the soil bulk density,indicating that the SOC content has a strong correlation with environmental factors such as TN,>2 mm gravel content,C:N and C:P.Among them,the content of gravel >2 mm is significantly correlated with the content of SOC and other environmental factors.There is a significant positive correlation between soil C,N,and P measurement ratios and organic carbon storage,and the two spatial environmental factors of slope and altitude are significantly correlated with SOC content and organic carbon storage.The results show that there is a strong correlation between the ratios of soil ecological stoichiometry in karst rocky desertification area.This shows that there is a strong correlation between the SOC content,organic carbon storage,and soil physical and chemical properties of the 11 land use types,and they are directly or indirectly affected by many factors.(2)In this study,the content of phytolith in each soil layer of the corn field was higher than that of other land use methods,and the content of mingled forest of S.chinensis and L.lucidum was the lowest.Correlation analysis showed that phytolith content was negatively correlated with pH,not with other environmental factors,but positively correlated with available silicon.Among the 11 land use patterns,the PhytOC content of P.sinese land was the highest in all soil layers.The PhytOC content of Z.bungeanum land and grassland was mainly concentrated in the subsurface and bottom layer.The PhytOC content of other land use patterns had obvious surface aggregation effect.The PhytOC was positively correlated with phytolith,available silicon and slope,but not with other environmental factors.The PhytOC in P.sinese land was significantly higher than mingled forest of S.chinensis and L.lucidum.,and there was no significant difference between the other land use patterns.There was no significant difference between the other land use patterns.There was a very significant correlation between phytolith carbon storage and PhytOC,SOC,TN and soil bulk density,and there was a significant correlation between phytolith carbon storage and slope,gravel content >2 mm and C:N,which indicating that there is a close correlation between PhytOC storage and SOC,and TN and soil bulk density are the key factors affecting PhytOC accumulation.(3)In this study,SOC and PhytOC are directly or indirectly affected by many factors,among which TN,altitude,TP,phytolith,C:N,C:P,N:P are the main factors affecting SOC and PhytOC,especially TP and C:N have more direct effects.There was no significant correlation between SOC content and PhytOC content,but there was a very significant correlation between SOC content and phytolith carbon storage,indicating that PhytOC accumulation was greatly affected by SOC.In general,SOC,PhytOC and environmental factors such as the basic physical and chemical properties of the soil are closely related.(4)Soil PhytOC/SOC increased with the increase of soil depth,indicating that the stability of soil PhytOC was enhanced with the deepening of soil profile.Soil PhytOC/SOC had no significant correlation with TP and p H,but had significant correlation with other environmental factors,which indicated that the stability of soil PhytOC in karst rocky desertification area of Southwest China was greatly affected by environmental factors.Generally speaking,soil organic carbon and PhytOC are closely related to soil physical and chemical properties and other environmental factors in southwest karst rocky desertification ecosystem.