Study On Soil Aggregates And Their Stability Of Main Forest Types In Fengyang Mountain

Soil aggregates are the basic units of soil structure.The stability of soil aggregates influences the quality of soil structure.In order to explore the mechanism of soil cementing material on soil aggregate stability and reveal the mechanism of formation and stabilization of soil aggregates in subtropical area,this study determinated the contents of total soil organic carbon,soil humus,Fe and A1 oxides and soil water-stable aggregates in three soil layers(0?10cm?10?20cm?20?30cm),and analyzed the effects of soil organic cementing material and inorganic cementing material on the stability of soil aggregates based on four forest types(broad-leaved mixed forest,coniferous and broad-leaved mixed forest,Chinese fir forest,bamboo forest)in Fengyang Mountain Nature Reserve of Zhejiang Province.The main results are as follows:(1)The content of soil water-stable macroaggregates(WSA)(>0.25mm)in four forest types was above 90%.Soil WSA content,geometric mean diameter(GMD)and average mass diameter(MWD)in bamboo forest are lower than those in other forests,and the highest values were observed in Chinese fir forest.Soil aggregate MWD of bamboo forest ranged from 1.12 mm to 1.15 mm,which showed significant difference from the other three forest types(P<0.05).With the increased of soil depth,soil aggregate MWD increased gradually in Chinese fir forest,and first increased and then decreased in broad-leaved mixed forest,coniferous and broad-leaved mixed forest,and bamboo forest.(2)With the increased of soil depth,the content of soil organic carbon(SOC)and particulate organic carbon(POC)decreased gradually,while the content of soil mineral organic carbon(MOC)increased first and then decreased.Soil POC/SOC ratios of Chinese fir forest and bamboo forest were higher than those of broad-leaved mixed forest and coniferous and broad-leaved mixed forest.However,soil MOC/SOC ratios of Chinese fir forest and bamboo forest were lower than those of broad-leaved mixed forest and coniferous and broad-leaved mixed forest.With the increased of soil depth,soil humus(HS),humic acid(HA)and fulvic acid(FA)content,and humic acid/fulvic acid(HA/FA)decreased gradually.In all four forest types,soil HS content was the highest in the coniferous and broad-leaved mixed forest,while that was the lowest in Chinese fir forest.The HA content was the highest in bamboo forest,and FA content was the highest in coniferous and broad-leaved mixed forest.(3)The order of Fe and A1 oxides contents in different forms is Fed>Ald>Feo>Alo>Fep>Alp.In all four forest types,Fe oxide content increased gradually with the increased of soil depth.However,Al oxide content did not show a certain trend.In 0?10 cm soil layer,Fed content in Chinese fir forest was significantly larger than those in other forests(P<0.05),which was shown as Chinese fir forest>broad-leaved mixed forest>bamboo forest>coniferous and broad-leaved mixed forest.In 10?20 cm soil layer,Alp contents in coniferous and broad-leaved mixed forest and and Chinese fir forest were greater than that in bamboo forest.(4)Soil bulk density showed negative correlation with soil D,and significant positive correlation with MWD and GMD.Soil pH showed significant negative correlation with WSA,MWD and GMD,and positive correlation with soil D.Soil non-capillary porosity and total nitrogen content showed significant negative correlation with soil MWD and GMD,and significant negative correlation with soil D.There was a significant positive correlation between soil total organic carbon(SOC)and soil aggregates GMD(P<0.05).Mineral organic carbon(MOC)showed significant positive correlation with soil aggregate GMD(P<0.05),and significant negative correlation with soil aggregate D(P<0.05).The result of boosted regression tree(BRT)analysis showed that soil aggregate MWD was mainly influenced by Alp in various forms of Fe and Al oxides,which produced a 43.6%contribution rate,followed by Ald(23.5%)and the Fed(19.5%);Feo(6.9%),Alo(4%)and Fep(2.4%)had less effect.(5)The result of principal component analysis(PCA)showed that the contents of soil SOC,heavy organic carbon(HFOC),coarse-grain organic carbon(CPOC),fine-grained organic carbon(FPOC)and POC,non-capillary porosity(NCAP)and pH were the main factors that affected soil aggregate stability.The increase of soil SOC,HFOC,CPOC,FPOC,POC contents(P<0.05),soil NCAP and pH(P<0.01)would significantly promote soil aggregate stability.