蚯蚓活动下矿物对凋落物分解及腐殖化的影响

Effects of minerals on litter decomposition and humification under earthworm activity

凋落物分解是植物向土壤输入有机碳的主要途径,蚯蚓和矿物的存在会改变凋落物的分解及其腐殖化。为探究培养后蚯蚓和矿物对玉米秸秆的有机元素组成、溶解性有机碳含量以及腐殖化程度的变化,本研究以玉米秸秆(CS0)为原料,分别通过添加蒙脱石和赤铁矿(原料∶矿物=7∶3,m∶m),在蚯蚓活动下进行135 d培养,标记为:玉米秸秆(CS)、玉米秸秆+蒙脱石(CSM)、玉米秸秆+赤铁矿(CSF)、玉米秸秆+蚯蚓(CSE)、玉米秸秆+蒙脱石+蚯蚓(CSME)、玉米秸秆+赤铁矿+蚯蚓(CSFE)。研究结果表明,分解后各处理组碳含量均有所减少。其中,与CS相比,CSM和CSF的碳含量平均减少46.01%,表明矿物加快了凋落物的分解。蚯蚓活动没有显著改变矿物对凋落物的分解。同时,凋落物培养后碳同位素比值(δ^(13)C)降低,表明^(12)C较^(13)C相对富集保留,尤其矿物添加下更为明显。但蚯蚓活动减弱^(13)C的损失,在CSME中最明显。这表明矿物和蚯蚓会影响凋落物不同组分的优先分解。从溶解性有机质(DOM)的组成和性质可知,培养后与CS相比,CSM和CSF的DOM的腐殖化指数(HIX)和生物指数(BIX)增大,表明矿物提高凋落物的腐殖化程度和生物可利用性。在蚯蚓活动下凋落物的腐殖化会进一步增强。此外,蚯蚓和矿物存在下其SUVA254、SUVA260和SUVA280增大,表明矿物/蚯蚓提高了其芳香化、疏水性和分子量,尤其是CSME最为显著。因此,蒙脱石和蚯蚓的添加更能显著增加DOM的腐殖化程度、疏水性和芳香性,提高土壤有机质的稳定。

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(δ^(13)C)decreased after litter decomposition,suggesting that ^(12)C composition was more retained compared to ^(13)C composition,especially under mineral addition.However,earthworm activity inhibited the loss of ^(13)C,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.