Responses of Earthworms to Organic Matter at Different Stages of Decomposition

This study was conducted to examine the responses of earthworms to soil organic matter and litter at different decomposition stages and their contributions in litter decomposition processes in southern subtropical areas of China. Two plantations were selected as the study sites: Site I was dominated by the exotic endogeic earthworm species Ocnerodrilus occidentalis; Site II was dominated by epigeic species Amynthas corticis. After the fallen litter and earthworms were removed or expelled, four treatments were set up as: reserving the top soil (0–5 cm, equal to H layer) (H), removing the top soil and adding fresh litter (Le), removing the top soil and adding semi-decomposed litter (Li), and a control with no top soil nor any litter (CK). Five randomized blocks that were enclosed with nylon nets on the top were set up in each site, and then the four treatments were arranged randomly in each block. After 2–3 months, earthworms were collected using the formalin method. The results showed that Ocnerodrilus occidentalis preferred Treatment H though it was found in Treatments Le and Li as well; Amynthas corticis preferred Treatment Li though sometimes it also appeared in Treatment H; and Amynthas sp., another epigeic species, was mainly present under Treatment Le and only appeared in Treatment H occasionally. These findings confirmed that earthworm species belonging to different ecological groups had different responses to organic matter at different decomposition stages. The impacts of earthworm communities dominated by O. occidentalis mainly appeared at the later periods of litter decomposition.

Organic Matter Decomposition in Red Soil as Affected by Earthworms

The earthworms Pheretima carnosaf Drawida gisti and Eisenia foetida were studied to compare theircontributions to the decomposition of various organic materials surface-applied on red soil in a 165-daygreenhouse experiment. The native species Pheretima caruosa and Drawida gisti were equally effective inaccelerating the decomposition of maize residue, according to fresh body weight, while commercial speciesEisenia foetida had no significant influence on dry mass loss of maize residue. Liming with CaCO3 or CaOshowed little effect on maize residue breakdown involved by Pheretima carnosal but it inhibited this processinvolved by Drawida gisti. The capability of Pheretima carnosa to the decomposition of five kinds of organicmaterials was thoroughly examined. The dry mass losses in worm treatments were in the order of soybeanresidue > maize residue > pig manure > semi-decayed maize > ryegrass. However, the relative contributionsof the earthworm to dry mass loss were in the order of pig manure (89.8%) > semi-decayed maize residue(49.1%) > maize residue (29.4%) > soybean residue (20.9%) > ryegrass residue (16.5%). Pheretima carnosaconsumed 20~120 mg dry weight of organic material per gram fresh weight of biomass per day.

Subtropical forest macro-decomposers rapidly transfer litter carbon and nitrogen into soil mineral-associated organic matter

Background:Forest soils in tropical and subtropical areas store a significant amount of carbon.Recent framework to assess soil organic matter(SOM)dynamics under evolving global conditions suggest that dividing bulk SOM into particulate and mineral-associated organic matter(POM vs.MAOM)is a promising method for identifying how SOM contributes to reducing global warming.Soil macrofauna,earthworms,and millipedes have been found to play an important role in facilitating SOM processes.However,how these two co-existing macrofaunae impac the litter decomposition process and directly impact the formation of POM and MAOM remains unclear.Methods:Here,we set up a microcosm experiment,which consisted of 20 microcosms with four treatments earthworm and litter addition(E),millipedes and litter addition(M),earthworm,millipedes,and litter addition(E+M),and control(only litter addition)in five replicates.The soil and litter were sterilized prior to beginning the incubation experiment to remove any existing microbes.After incubating the samples for 42 days,the litte properties(mass,C,and N contents),soil physicochemical properties,as well as the C and N contents,and POM and MAOM^(13)C abundance in the 0–5 and 5–10 cm soil layers were measured.Finally,the relative influences o soil physicochemical and microbial properties on the distribution of C and N in the soil fractions were analyzed Results:The litter mass,C,and N associated with all four treatments significantly decreased after incubation especially under treatment E+M(litter mass:-58.8%,litter C:-57.0%,litter N:-75.1%,respectively),while earthworm biomass significantly decreased under treatment E.Earthworm or millipede addition alone showed no significant effects on the organic carbon(OC)and total nitrogen(TN)content in the POM fraction,but join addition of both significantly increased OC and TN regardless of soil depth.Importantly,all three macrofauna treatments increased the OC and TN content and decreased the^(13)C abundance in the MAOM fraction.More than65%of the total variations in the distribution of OC and TN throughout the two fractions can be explained by a combination of soil physicochemical and microbial properties.Changes in the OC distribution in the 0–5 cm soi layer are likely due to a decrease in soil pH and an increase in arbuscular mycorrhizal fungi(AMF),while those in the 5–10 cm layer are probably caused by increases in soil exchangeable Ca and Mg,in addition to fungi and gram-negative(GN)bacteria.The observed TN distribution changes in the 0–5 cm soil likely resulted from a decrease in soil pH and increases in AMF,GN,and gram-negative(GP)bacteria,while TN distribution changes in the 5–10 cm soil could be explained by increases in exchangeable Mg and GN bacteria.Conclusions:The results indicate that the coexistence of earthworms and millipedes can accelerate the litte decomposition process and store more C in the MAOM fractions.This novel finding helps to unlock the processe by which complex SOM systems serve as C sinks in tropical forests and addresses the importance of soil mac rofauna in maintaining C-neutral atmospheric conditions under global climate change.

蚯蚓活动下矿物对凋落物分解及腐殖化的影响

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。