Effects of minerals on litter decomposition and humification under earthworm activity
Litter decomposition is the main way for plants to import organic carbon into soil,the presence of earthworms and minerals alters the decomposition and humification of litter.In order to investigate the changes of organic element composition,dissolved organic carbon content and humification degree of maize stalk by earthworms and minerals after culture,in this study,corn straw(CS0)was used as a raw material and incubation under earthworm activity for 135 days by addition of montmorillonite and hematite(raw material∶mineral=7∶3,m∶m),respectively,which was labeled as:corn straw(CS),corn straw+montmorillonite(CSM),corn straw+hematite(CSF),corn straw+earthworm(CSE),corn straw+montmorillonite+earthworm(CSME)and corn straw+hematite+earthworm(CSFE).This study investigated the changes in organic elemental composition,dissolved organic carbon content,and degree of humification of corn straw by earthworms and minerals after incubation.The results of the study showed that carbon content was reduced in all treatment groups after the decomposition.The carbon content of CSM and CSF was reduced by an average of 46.01%compared to CS,indicating that minerals accelerated the decomposition of litter material.Earthworm activity did not significantly alter mineral decomposition of litter.Meanwhile,carbon isotope ratios(δ13C)decreased after litter decomposition,suggesting that 12C composition was more retained compared to 13C composition,especially under mineral addition.However,earthworm activity inhibited the loss of 13C,which was most pronounced in CSME.This suggested that minerals and earthworms affect the preferential decomposition of different fractions of litters.As shown in the composition and properties of dissolved organic matter(DOM),it was clear that the humification index(HIX)and bioindex(BIX)of DOM increased in CSM and CSF compared to CS after the incubation,indicating that the minerals promoted the degree of humification and bioavailability of litters.The humification of litter was further enhanced under earthworm activity.In addition,its SUVA254,SUVA260 and SUVA280 increased in the presence of earthworms and minerals,suggesting that minerals/earthworms enhanced its aromatization,hydrophobicity and molecular weight,especially for CSME.Therefore,the addition of montmorillonite and earthworms more significantly increase the degree of humification,hydrophobicity and aromaticity of DOM,and improve the stability of soil organic matter.
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