Earthworms Effect on Microbial Population and Soil Fertility as Well as Their Interaction with Agriculture Practices (original) (raw)

Microbial Dynamics of Endemic Earthworms on Soil Health and Sustainable Agriculture

ABSTRACT Earthworms harness the microorganisms which are beneficial to the agro-ecosystem, as they synergistically decompose soil organic matter and help in nutrients cycling. Lampito mauritii and Perionyx excavatus are endemic earthworms which dominate the Indian soils, especially in south India. However, the exotic earthworm Eudrilus eugeniae has been harnessed for the formation of compost and organic matter decomposition. Endemic earthworms do not coexist with exotics as they eliminate the former due to competition for food and space. The present study aims to reveal the physical, chemical and biological differences between the different products of the endemic earthworms L. mauritii and P. excavatus and the exotic earthworm E. eugeniae to better understand their contributions to agricultural soil and nutrient management. The three major earthworm products include cast, compost and drilosphere soil of earthworms. Different groups of microorganisms present in earthworm products include major microbial groups, biofertilisers, carbon, and nitrogen mineralizers. The results reveal that the products of endemic earthworms show significant increase in biofertilisers such as nitrogen fixers and phosphate solubilizers, heterotrophic bacteria, fungi and actinomycetes compared to the products from the exotic earthworm. Among the three products studied, vermicompost, especially of the endemic species, shows a balanced C/ N ratio and increased microbial density including biofertilisers.

Significance of earthworms in stimulating soil microbial activity

Biology and Fertility of Soils, 1998

The stimulatory effect of earthworms (Lumbricus terrestris L.) on soil microbial activity was studied under microcosm-controlled conditions. The hypothesis was tested that microbial stimulation observed in the presence of a soil invertebrate would be due to the utilization of additional nutritive substances (secretion and excretion products) that it provides. Changes in microbial activity were monitored by measuring simultaneously CO 2 release and protozoan population density. The increase in CO 2 released in the presence of earthworms was found to result from both earthworm respiration and enhanced microbial respiration. The stimulation of microbial activity was confirmed by a significant increase in protozoan population density, which was 3-19 times greater in the presence of earthworms. The respiratory rate of L. terrestris was estimated to be 53 ml O 2 g P1 h P1. Earthworm respiration significantly correlated with individual earthworm weight, but there was no correlation between the increase in microbial respiration and earthworm weight. This finding does not support the hypothesis given above that enhanced microbial respiration is due to utilization of earthworm excreta. A new hypothesis that relationships between microbial activity and earthworms are not based on trophic links alone but also on catalytic mechanisms is proposed and discussed.

Impacts of earthworms on soil components and dynamics. A review

Earthworm populations are important decomposers contributing to aggregate formation and nutrient cycling processes involving nitrogen cycles, phosphorus and carbon. They are known to influence soil fertility by participating to important processes in soil such as soil structure regulation and organic matter dynamics. Earthworms also modify the microbial communities through digestion, stimulation and dispersion in casts. Consequently, changes in the activities of earthworm communities, as a result of soil management practices, can also be used as indicators of soil fertility and quality. It is therefore important to understand how earthworm communities affect soil dynamics. This review adresses the current state of knowledge on earthworm's impacts on soil structure and soil organic matter (carbon, nitrogen, and phosphorus) dynamics, with special emphasis on the effects of land management practices on earthworm communities.

Role of Earthworms in Soil Fertility and Factors Affecting Their Population Dynamics: A Review

2015

Earthworms mix soil layers and incorporate organic matter into the soil. This mixing allows the dispersion of the organic matter through the soil and makes the nutrients held in it available to plants and improves the fertility of the soil. Earthworms when present improve the soil physical, chemical and biological properties and acts as soil conditioner. They do so by fragmentation, aeration, breakdown of organic matter in soil and release plant available nutrients and also due to secretion of plant growth hormones, their role in nitrogen fixation, carbon dynamics, and phosphorous dynamics. But their population in soil is threatened by a number of soil and environmental factors. Agricultural practices like heavy tillage operation and application of chemical fertilizers also contribute in the reduction of earthworms in soil. Change in land use due to increase in human population brings change in the system and make it unsuitable for the growth and development of earthworms. This revi...

EARTHWORM AS SOIL ECOSYSTEM ENGINEERS: A REVIEW

Earthworm and microorganisms are interdependent on each other. The interactions between them help to regulate the biogeochemical cycle of terrestrial life. A large diversity of fungi, bacteria, yeast, actinomycetes and protozoa are found to be present in the gut and cast of earthworms. Their number and species depend on their feed substrates obtained in soil. It has been studied that the microbial proliferation is more in the casts, due to the environment prevailing-rich nutrient supply and large surface area available for growth and reproduction of the microbes that lead to the enhanced microbial activity and humic acid contents in casts. Diversity of microorganisms is also found in vermicompost and vermiwash. This in turn depended on the raw material used for compost. A significant increase was noted in flora after composting. Within an ecological group, habitat was found to be a more important determinant of the gut wall associated community composition than the host species.

Earthworm species composition affects the soil bacterial community and net nitrogen mineralization

Pedobiologia, 2006

Knowledge of the effects of species diversity within taxonomic groups on nutrient cycling is important for understanding the role of soil biota in sustainable agriculture. We hypothesized that earthworm species specifically affect nitrogen mineralization, characteristically for their ecological group classifications, and that earthworm species interactions would affect mineralization through competition and facilitation effects. A mesocosm experiment was conducted to investigate the effect of three earthworm species, representative of different ecological groups (epigeic: Lumbricus rubellus; endogeic: Aporrectodea caliginosa tuberculata; and anecic: Lumbricus terrestris), and their interactions on the bacterial community, and on nitrogen mineralization from 15 N-labelled crop residue and from soil organic matter.

Exotic earthworms alter soil microbial community composition and function

Soil Biology and Biochemistry, 2013

Exotic earthworms can profoundly alter soil carbon (C) and nitrogen (N) dynamics in northern temperate forests, but the mechanisms explaining these responses are not well understood. We compared the soil microbial community (SMC) composition (measured as PLFAs) and enzyme activity between paired earthworm-invaded and earthworm-free plots in northern hardwood forests of New York, USA. We hypothesized that differences in SMCs and enzyme activity between plots would correspond with differences in soil C content and C:N ratios. Relative abundance of several bacterial (mostly gram-positive) PLFAs was higher and that of two fungal PLFAs was lower in earthworm compared to reference plots, largely because of earthworm incorporation of the organic horizon into mineral soil. In surface mineral soil earthworms increased arbuscular mycorrhizal fungi (AMF) and gram-positive bacterial PLFAs, and decreased fungal (mostly saprotrophic) and several bacterial (gram-negative and non-specific) PLFAs. Earthworms also increased the activities of cellulolytic relative to lignolytic enzymes in surface mineral soil, and the relationships between enzyme activities and components of the SMC suggest a substratemediated effect on the SMC and its metabolism of C. A highly significant relationship between components of the SMC and soil C:N also suggests that earthworms reduce soil C:N through functional and compositional shifts in the SMC. Finally, changes in AMF abundances were linked to phosphatase activity, suggesting that earthworms do not necessarily inhibit P-acquisition by AMF-associated plants in our study system. We conclude that the combined influence of earthworm-related changes in physical structure, accessibility and chemistry of organic matter, and relative abundance of certain groups of fungi and bacteria promote C metabolism, in particular by increasing the activities of cellulolytic vs. lignolytic enzymes.

Bacteria and protozoa in soil microhabitats as affected by earthworms

Biology and Fertility of Soils, 1997

The effects of incorporation of elm leaves (Ulmus glabra) into an agricultural sandy loam soil by earthworms (Lumbricus festivus) on the bacterial and protozoan populations were investigated. Three model systems consisting of soil, soil with leaves, and soil with leaves and earthworms, respectively, were compared. The total, viable, and culturable number of bacteria, the metabolic potentials of bacterial populations, and the number of protozoa and nematodes were determined in soil size fractions. Significant differences between soil fractions were shown by all assays. The highest number of microorganisms was found in microaggregates of 2±53 lm and the lowest in the <0.2 lm fraction. A major part of the bacteria in the latter fraction was viable, but non-culturable, while a relatively higher number of culturable bacteria was found in the macroaggregates. The number of colony-forming units and 5-cyano-2,3-ditolyl tetrazolim chloride (CTC)-reducing bacteria explained a major part of the variation in the number of protozoa. High protozoan activity and predation thus coincided with high bacterial activity. In soil with elm leaves, fungal growth is assumed to inhibit bacterial and protozoan activity. In soil with elm leaves and earthworms, earthworm activity led to increased culturability of bacteria, activity of protozoa, number of nematodes, changed metabolic potentials of the bacteria, and decreased differences in metabolic potentials between bacterial populations in the soil fractions. The effects of earthworms can be mediated by mechanical mixing of the soil constituents and incorporation of organic matter into the soil, but as the earthworms have only consumed a minor part of the soil, priming effects are believed partly to explain the increased microbial activity.

The wave towards a new steady state: effects of earthworm invasion on soil microbial functions

Biological …, 2011

Earthworms are ecosystem engineers that cause a long cascade of ecological effects when they invade previously earthworm-free forests. However, the consequences of earthworm invasion for soil microbial functions are poorly understood. Here, we used two well-studied invasion fronts of European earthworms in northern North American hardwood forests previously devoid of earthworms in order to investigate three stages of earthworm invasion: uninvaded, the front of the leading edge of earthworm invasion and locations invaded at least 10 years previously. Soil microbial biomass, respiration and metabolic quotient were measured. Earthworms had marked effects on soil microbial biomass (-42%) and respiration (-32%). At both sites, impacts were most pronounced at the leading edge of the invasion front, significantly decreasing soil microbial C use efficiency. This was most likely due to the disturbance of the soil microbial community caused by water stress. Based on these results, we hypothesize that effects of earthworm invasion on native soil ecosystem functioning are most pronounced at the peak of the invasion wave. After experiencing this wave, ecosystems possibly enter a new steady state with altered biotic compositions and functions.