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Abstract: The effect of earthworms on humus composition and humic acid (HA) characteristics was studied in a rice–wheat rotation agroecosystem. Experimental plots in the rotation had five treatments, i.e., incorporation or mulching of maize residues with or without added earthworms and a control. Compared with the control, the application of maize residues to soil either alone or in combinations with earthworms strongly affected the humus composition and HA characteristics. In the presence of earthworms, the carbon ratio of HA to fulvic acid (FA), and the alkyl C/O-alkyl C and hydrophobic C/hydrophilic C ratios of HA were slightly higher, while the aliphatic C/aromatic C ratio of HA was slightly lower following maize residue incorporation than the same treatment without earthworms. In contrast, these ratios generally remained almost constant following maize residue mulching. Thus, earthworm activity following maize residue incorporation was more favorable for the HA formation, and was associated with a decrease in aliphaticity of HA, and an increase in its degree of humification and hydrophobicity. [Copyright &y& Elsevier]

Earthworms naturally secrete substantial amounts of mucus (relative to their body size) from the cuticle when moving through the soil. However, how the metabolites in the epidermally derived mucus affect soil microfauna is largely unknown. The objective of this study was to determine how earthworm mucus affected the physiology of the model nematode Caenorhabditis elegans and that of two soil-dwelling bacterial-feeding nematodes: Mesorhabditis sp. and Protorhabditis sp. The traits examined included phobotaxis, reproduction, mortality, body size, feeding inhibition rate, and feeding preference. Two nematode species escaped from the earthworm mucus, whereas earthworm mucus reduced the reproduction of C. elegans and increased the mortality of C. elegans and Mesorhabditis sp. Moreover, earthworm mucus reduced the feeding rate of C. elegans and Protorhabditis sp. and changed the feeding preferences of all three species of nematodes. At 48 h, earthworm mucus increased feeding on Bacillus amyloliquefaciens JX1 for C. elegans and Protorhabditis sp. and reduced feeding on Escherichia coli OP50 for Mesorhabditis sp. These results suggest that earthworm mucus can be detrimental to bacterial-feeding nematodes and provide insights into the non-trophic interactions between earthworms and other soil biota. • Two of the three bacterial-feeding nematodes escaped from earthworm mucus. • Earthworm mucus reduced the reproduction of C. elegans. • Earthworm mucus increased the mortality of the C. elegans and Mesorhabditis sp. • Earthworm mucus inhibited the feeding rate of C. elegans and Protorhabditis sp and changed the feeding preferences of all the bacterial-feeding nematodes. [ABSTRACT FROM AUTHOR]

Bio-fertilizers are thought to be overwhelmingly superior to chemical fertilizers for the improvement of soil quality and productivity. However, the comprehensive effects of bio-fertilizer on the soil ecosystem and the possibility of using multiple soil beneficial biota are still not well understood. A two-year field study was conducted to examine how crop yield, soil biochemical properties, enzyme activities, and functional diversity responded to different bio-fertilizers in the sweet potato phase of a double-cropping system (sweet potato and rapeseed). Six fertilizer treatments, including one chemical treatment (CF), two organic treatments (OM, organic manure; MC, organic manure plus chemical fertilizer) and three bio-fertilizer treatments (MCN containing nematodes, MCE containing earthworms, and MCP containing phosphate-solubilizing bacteria) were compared. The soils under CF had the lowest values for all soil parameters in comparison with the other treatments. Among the organic and bio-fertilizer treatments, OM performed better in improving soil biological properties such as soil respiration and microbial biomass, while soils under all these treatments had similar soil enzyme activities and functionality. Crop yield was positively correlated with soil nutrient levels, microbial biomass and enzyme activity, and most of the biochemical variables were highly intercorrelated. Our results indicated that organic fertilizers and bio-fertilizers were superior to chemical fertilizers and generally improved soil quality and productivity to similar levels in the field. [ABSTRACT FROM AUTHOR]

Sustainable agriculture aims to manage soil and plant health while relying less on chemical inputs. The individual effect of organic amendments or resistant crop cultivars on the suppression of root pests through modulating soil and plant performance is being well documented. However, the interactions between organic amendments and crop cultivars are less well studied. A pot experiment was conducted across two tomato cultivars of distinct resistance to root-knot nematodes (RKNs, Meloidogyne incognita ) with three amendments including inorganic fertilizer (IF), conventional compost (CC) and vermicompost (VC). All treatments were inoculated with second-stage juveniles of M. incognita to simulate the root-knot nematode disease in field condition and to focus on the comparison among different soil amendment effects. Plant growth (shoot height, shoot biomass, root biomass and root C:N ratio), root defense metabolites (phenolics) and their related genes expression, and soil properties including pH, electrical conductivity, available nutrients, 3-indoleacetic acid (IAA), microbial biomass and activity were analyzed at 14 and 30 days post inoculation (dpi). Compared with inorganic fertilizer, vermicompost significantly decreased the numbers of nematode-induced galls on susceptible (Sus) and resistant (Res) cultivar roots by 77% and 42% respectively at 14 dpi, and by 59% and 46% respectively at 30 dpi. Vermicompost also significantly increased root defense metabolite concentrations, defense related gene expression, and improved soil properties ( p < 0.05) except for mineral nitrogen. Multivariate analyses further indicated that soil properties particularly pH, root primary and secondary defense metabolites were negatively associated with root gall. Moreover, soil microbial activity, pH and IAA concentration were the main soil properties positively associated with plant defense metabolites production and biomass for both susceptible and resistant cultivars. Overall, vermicompost could significantly suppress root pests via modulating soil properties as well as plant defenses, particularly for the susceptible plant. [ABSTRACT FROM AUTHOR]

Organic amendments not only promote soil quality and plant performance directly but also facilitate the establishment of introduced microbial agents. A field experiment with a fully factorial design was conducted using three levels of vermicompost (without vermicompost, low dose of 15 Mg ha −1 and high dose of 30 Mg ha −1 ), with and without plant growth-promoting rhizobacteria (PGPR) to investigate their effects in a tomato – by spinach rotation system. Our results demonstrated that applying PGPR alone had no effect on soil properties and crop performance. Vermicompost enhanced the beneficial effects of PGPR on both soil and crop, with the extent of promotion depending on the dose of vermicompost and crop types. In the presence of vermicompost, PGPR significantly ( P < 0.05) reduced soil carbon and nitrogen but increased soil microbial biomass carbon and nitrogen. PGPR also significantly increased the yield of tomato and spinach under the low dose of vermicompost, but only significantly increased tomato yield under the high dose of vermicompost. There were strongly synergistic effects between vermicompost and PGPR on crop quality, with crop nitrate concentration being significantly decreased, while the vitamin C in tomato and soluble protein in spinach was significantly increased. Our results revealed the high potential of integrating vermicompost and microbial agents to substitute for regular chemical fertilization practices. [ABSTRACT FROM AUTHOR]

Abstract: Microcosm experiments were carried out to study the effects of bacterial-feeding nematodes and prometryne on soil bacterial communities in contaminated soil. Prometryne (5 or 10mgkg−1 dry soil, that is, P5 or P10) and bacterial-feeding nematodes (5 or 10 individuals g−1 dry soil, that is, N5 or N10), singly and in combination (P5N5, P5N10, P10N5, P10N10), were added to a nematode-free soil. An uncontaminated nematode-free soil was studied for comparison (Control). Bacterial-feeding nematode grazing boosted soil enzyme activities in contaminated soils, thus speeding up prometryne degradation. In the initial stage of the experiment, prometryne enhanced the soil enzyme activities too, but served the opposite purpose later. Denaturing gradient gel electrophoresis (DGGE) analysis indicated that prometryne contamination and nematode grazing over the incubation period exerted an obvious impact on Species richness (S), Shannon–Wiener index (H′) and Evenness (E H ) of soil bacteria, which increased initially, then decreased and increased again later. The cluster analysis of DGGE profiles showed that the similarity of soil bacterial communities in all treatments with indigenous microbes, P5, P5N5, P5N10, P10, P10N5, and P10N10 and the Control was 75%, 44%, 78% and 49% at Day 0, Day 8, Day 18 and Day 30, respectively. Compared to the Control, DGGE profiles displayed a varying characteristic bands pattern in all treatments over the incubation period with certain bands present in the treatments while not in the Control and vice versa, suggesting that bacterial-feeding nematode grazing and prometryne contamination affected soil bacterial communities evidently. Consequently, when added to contaminated soil, bacterial-feeding nematodes can contribute to restoration of contaminated sites by degrading toxic compounds like prometryne through enhanced microbial activity. [Copyright &y& Elsevier]

Abstract: The effects of bacterial-feeding nematodes on nitrification and the ammonia-oxidizing bacteria (AOB) community composition were studied in soil microcosms. Sterilized soils were inoculated with mixed soil bacteria (obtained by filtering) or with bacteria and bacterial-feeding nematodes, after which the dynamic inorganic nitrogen concentration was measured weekly. After 28 days of incubation, denaturing gradient gel electrophoresis (DGGE) based on PCR amplification of the amoA gene was used to analyze the AOB community composition. In addition, a clone library from the amoA gene fragments was established using clones randomly selected and sequenced from the two treatments. The results showed that the presence of bacterial-feeding nematodes led to significantly greater NH4 + and NO3 − contents over the entire incubation period, indicating that bacterial-feeding nematodes promoted both N mineralization and nitrification. The results of DGGE showed that the AOB community composition was significantly changed in the presence of bacterial-feeding nematodes. Furthermore, the sequencing results suggested that Nitrosospira sp. was the dominant species in the treatment without nematodes, while Nitrosomonas sp. and Nitrosospira sp. were the dominant species in the treatment with nematodes. Such changes in the AOB community may be one of explanation of the important role that nematodes play in promoting nitrification. [Copyright &y& Elsevier]

Abstract: The effect of earthworms on soil hydrolases (protease, urease, invertase, and alkaline phosphatase) and dehydrogenase activities was investigated in maize residue amended rice–wheat rotation agro-ecosystem. Experimental plots in the rotation had five treatments, i.e. incorporation or mulching of maize residues with or without added earthworms and an untreated control. The application of maize residues to soil without earthworms significantly enhanced the five soil enzyme activities compared with the control treatment during rice and wheat cultivation. The presence of earthworms further significantly enhanced protease activity in the soils with both incorporated and mulched maize residues during two cultivation seasons, but only significantly increased alkaline phosphatase activity in the soil with incorporated maize residue during the rice cultivation season. Invertase activity was significantly enhanced by the presence of earthworms in the soil with maize residue incorporation during two cultivation seasons. There were no changes in dehydrogenase activity when earthworms were present. Additionally, the five enzyme activities in earthworm casts were significant higher than those in the surrounding soil, especially dehydrogenase and invertase activities. Whatever the treatment, the values obtained for the enzyme activities in both soil and casts, except for dehydrogenase activity in earthworm casts, were significantly higher under wheat than those in rice-cultivated soil. These results indicate that the presence of earthworms strongly affected soil enzyme activities, depending on the method of organic residue application, and the enhanced enzyme activities of earthworm casts probably contributed to the surrounding soil enzyme activities. [Copyright &y& Elsevier]

Abstract: Understanding the effects of alternative farming on soil quality parameters, such as microbial communities, size, activity and soil nutrient content, is of central importance to concepts of sustainability. Combining organic amendments with chemical fertilizer is a promising approach to develop more sustainable fertilization strategies. We investigated the impacts of quantity, type and application time of organic amendments on temporal dynamics of paddy soil microbial biomass, activity, carbon fractions and nutrient status under a long-term field experiment in a rice–rice cropping system. We established treatments with seven fertilization practices characterized by different quantities and application times of green manure (GM), farmyard manure (FYM) and rice straw (RS) in combination with low amount of chemical fertilizers. We further established one treatment with only recommended amount of chemical fertilizer and an unfertilized control. At all sampling times, organic amendments with low amount of chemical fertilizer enhanced microbial biomass, activity and nutrient availability more than recommended amount of chemical fertilization only and an unfertilized control, with higher quantities of FYM resulting in stronger effects than all other organic amendments. The strongest increase of microbial biomass, activity, carbon and nutrient availability was generally found in the treatment with the most diverse resources and highest amount of organic amendments. Principle component analysis indicated that most soil variables measured were correlated to total soil organic C. Regression analysis indicated that the integrated paddy soil properties were closely related to yearly C input and rice yield. Strong temporal dynamics were demonstrated for all soil variables, indicating that we need multiple time sampling strategies to explore the overall influences of fertilization practices on paddy soil. Our results indicate that the development of effective fertilization practices, especially by manipulating the quantity and type of organic amendments, may improve long-term sustainability of paddy soil ecosystems. [Copyright &y& Elsevier]

The application of organic fertilizers affects soil aggregates, nutrient situations and bacterial communities. However, the direct and indirect effect of different resource-derived organic fertilizers on soil bacterial communities and their links to soil aggregate is poorly understood. Here, we carried out a field experiment for three years to investigate the linkages between soil aggregates and bacterial diversity in a dryland red soil. Six treatments were compared: (no fertilizer (CK), chemical fertilizer (CF), 60% chemical fertilizer + straw at 4500 kg ha−1 (RFS), 60% CF + biochar at 1500 kg ha−1 (RFB), 60% CF + pig manure at 15000 kg ha−1 (RFP), and 60% CF + vermicompost at 15000 kg ha−1 (RFV)). The application of pig manure or vermicompost (animal-derived organic fertilizer) enhanced the soil pH, the content of large macroaggregate (>2 mm), organic matter, available phosphorous and available nitrogen, while decreased the content of small macroaggregate (0.25–2 mm) and microaggregate (<0.25 mm) compared with other treatment. Relative abundances of the dominant bacterial phyla varied across chemical and organic fertilizer treatments, primarily by increasing Bacteroidetes, Gemmatimonadetes, and decreasing Chloroflexi, Acidobacteria and Planctomycetes. Organic fertilizers particularly animal-derived organic fertilizer enhanced the Richness, Shannon and Pielou indices of soil bacteria compared with chemical fertilizer treatment. The regulation of animal-derived organic fertilizers on bacterial community structure (accounting for 53.04% of the variance) was greater than that of plant-derived organic fertilizers (straw and biochar, accounting for 7.69% of the variance). The bacterial alpha diversity showed positive correlation with large macroaggregate, but a negative correlation with small macroaggregate. Further, structural equation models indicated that animal-derived organic fertilizers impacted bacterial diversity positively by regulating resource availability through soil aggregates. However, for the plant-derived organic fertilizers, bacterial diversity was negatively affected by soil aggregates alone, but this was not regulated by fertilization. In addition, animal-derived organic fertilizer also positively affected soil bacteria diversity indirectly via changing soil pH and resource availability. Overall, the different impacts of animal- and plant-derived organic fertilizers on soil bacterial community highlighting the pivotal role of soil habitat architecture and resource chemistry changed by organic fertilizers in the regulation of soil bacteria, which may influence soil quality and agricultural sustainable development. • Animal-derived organic fertilizer (AOF) decreased 0.25–2 and <0.25 mm soil aggregates. • AOF increased >2 mm soil aggregates, pH, organic matter, available P and N. • AOF affect soil bacterial community structure than plant-derived (POF). • AOF affect bacterial community mainly via changing aggregates, pH and resource availability. • Aggregates affect bacterial diversity alone under POF, but not regulated by fertilization. [ABSTRACT FROM AUTHOR]

To clarify the 'auxin-driven' effect of bacterial-feeding nematodes on plant growth, the influence of an indole-3-acetic acid (IAA)-producing bacteria, Bacillus amyloliquefaciens , non-IAA-producing bacteria Variovorax sp., and two bacterial-feeding nematodes (Cephalobus sp. and Mesorhabditis sp.) on the growth of Arabidopsis thaliana after various exposure durations was investigated using a gnotobiotic microcosm incubation system. The nematodes, responses of soil chemistry (IAA and mineral nitrogen), plant growth (root architecture, shoot dry weight, and plant nitrogen), and the expression of two IAA-responsive genes, IAA3 and IAA13 , were measured. Bacterial-feeding nematodes stimulated the activity of IAA-producing bacteria by grazing, and promoted the mineralization of nitrogen in the soil, thus increasing the soil IAA and nitrogen content and promoting shoot dry weight and plant nitrogen content. The A. thaliana root architecture consisted of a highly branched root system, with bigger surface area. The IAA3 and IAA13 genes in A. thaliana roots significantly increased and there were significant correlations with the soil IAA content. This study further confirms the existence of an auxin-driven effect that promotes A. thaliana growth by bacterial-feeding nematodes through changes in the expression of root genes. Unlabelled Image • Bacterial-feeding nematodes stimulated the activity of IAA-producing bacteria. • The addition of nematodes and bacteria increased mineral nitrogen and IAA content. • The addition of nematodes promoted A. thaliana roots with bigger surface area. • The IAA3 and IAA13 genes in A. thaliana root significantly increased. • The existence of 'auxin-driven' effect on plant growth was further revealed. [ABSTRACT FROM AUTHOR]