Earthworms Modulate Impacts of Soil Heterogeneity on Plant Growth at Different Spatial Scales

Soil heterogeneity (uneven distribution of soil nutrients and/or other properties) is ubiquitous in nature and can greatly affect plant growth. As earthworm activity can influence nutrient redistribution in the soil, we hypothesize that earthworms may alter the effect of soil heterogeneity on plant growth and this effect may depend on the scale of soil heterogeneity. To test these hypotheses, we grew the clonal grass Leymus chinensis in three soil treatments (heterogeneous large vs. heterogeneous small patch vs. homogeneous soil treatment) with or without earthworms [i.e., Eisenia fetida Savigny (Lumbricidae, epigeic redworm)]. In the heterogeneous treatments, the soil consisted of patches with and without 15N-labeled litter (referred to as high- and low-quality patches, respectively), and in the homogeneous treatment, the soil was an even mixture of the two types of soil patches. Biomass of L. chinensis was significantly higher in the high- than in the low-quality patches, showing the foraging response; this foraging response occurred at both scales and under both earthworm treatments. Compared to the homogeneous treatment, the heterogeneous large patch treatment increased biomass of L. chinensis without earthworms, but decreased it with earthworms. In contrast, biomass of L. chinensis in the heterogeneous small patch treatment did not differ from that in the homogeneous treatment, irrespective of earthworms. Belowground biomass was much greater in the heterogeneous small than in the heterogeneous large patch treatment without earthworms, but it did not differ between these two scale treatments with earthworms. In the heterogeneous treatments, soil 15N was greater in the high- than in the low-quality patches, but this effect became much weaker with than without earthworms, suggesting that earthworm activity homogenized the soil. We conclude that earthworms can change the impact of soil heterogeneity on plant growth via homogenizing the soil, and that this effect of earthworms varies with patch scale. Such scale-dependent interactive effects of soil heterogeneity and earthworms could be a potential mechanism modulating plant community structure and productivity.

Global earthworm distribution and activity windows based on soil hydromechanical constraints

Earthworm activity modifies soil structure and promotes important hydrological ecosystem functions for agricultural systems. Earthworms use their flexible hydroskeleton to burrow and expand biopores. Hence, their activity is constrained by soil hydromechanical conditions that permit deformation at earthworm’s maximal hydroskeletal pressure (≈200kPa). A mechanistic biophysical model is developed here to link the biomechanical limits of earthworm burrowing with soil moisture and texture to predict soil conditions that permit bioturbation across biomes. We include additional constraints that exclude earthworm activity such as freezing temperatures, low soil pH, and high sand content to develop the first predictive global map of earthworm habitats in good agreement with observed earthworm occurrence patterns. Earthworm activity is strongly constrained by seasonal dynamics that vary across latitudes largely due to soil hydromechanical status. The mechanistic model delineates the potential for earthworm migration via connectivity of hospitable sites and highlights regions sensitive to climate.

Effects of glyphosate-based herbicides and their active ingredients on earthworms, water infiltration and glyphosate leaching are influenced by soil properties

Background Glyphosate-based herbicides (GBHs) are among the most often used pesticides. The hundreds of GBHs used worldwide consist of the active ingredient (AI) glyphosate in form of different salts, possibly other AIs, and various mostly undisclosed co-formulants. Pesticide risk assessments are commonly performed using single AIs or GBHs at standard soil conditions without vegetation. In a greenhouse experiment, we established a weed population with common amaranth (Amaranthus retroflexus) to examine the effects of three GBHs (Roundup LB Plus, Roundup PowerFlex, Touchdown Quattro) and their corresponding AIs (salts of glyphosate isopropylammonium, potassium, diammonium) on the activity and physiological biomarkers (glutathione S-transferase, GST; acetylcholine esterase, AChE) of an ecologically relevant earthworm species (Lumbricus terrestris). GBHs and AIs were applied at recommended doses; hand weeding served as control. Experiments were established with two soil types differing in organic matter content (SOM; 3.0% vs. 4.1%) and other properties. Results Earthworm activity (casting and movement activity) decreased after application of glyphosate formulations or active ingredients compared to hand weeding. We found no consistent pattern that formulations had either higher or lower effects on earthworm activity than their active ingredients; rather, differences were substance-specific. Earthworm activity was little affected by soil organic matter levels. Biomarkers remained unaffected by weed control types; GST but not AChE was decreased under high SOM. Water infiltration after a simulated heavy rainfall was interactively affected by weed control types and SOM. Leachate amount was higher after application of formulations than active ingredients and was higher under low SOM. Glyphosate concentrations in soil and leachate were strongly affected by application of formulations or active ingredients and varied with SOM (significant weed control type x SOM interaction). Conclusions We found that both commercial formulations and pure active ingredients can influence earthworms with consequences on important soil functions. Glyphosate products showed increased, reduced or similar effects than pure glyphosate on particular soil functions; soil properties can substantially alter this. Especially at lower SOM, heavy rainfalls could lead to more glyphosate leaching into water bodies. A full disclosure of co-formulants would be necessary to further decipher their specific contributions to these inconsistent effects.

Cow dung and tea waste amendments enhance the biotransformation of textile mill sludge into vermicomposts using Eisenia fetida

Vermicomposting of textile mill sludge (TMS) with cow dung (CD) and tea waste (TW) as amendments was done in seven different combinations using Eisenia fetida for 90 days. Results revealed that pH decreased from 7.68–8.63 to 7.09–7.59. TOC content and C/N ratio reductions were in range of 15.71–20.08% and 39.33–50.05% respectively (P < 0.05). The macronutrients in the form of TN, TP and TK increased 0.38–0.64 folds, 1.07–2.27 folds and 0.56–1.98 folds respectively after the end of bioconversion process (P < 0.05), among increases in ash content and EC. The biomass and cocoon production of E.fetida increased significantly (P < 0.05), while increasing mortality rate of earthworms was observed in treatments containing 50% or more TMS content. The bacterial population beneficial for degradation of organic matter increased significantly over initial substrates (P < 0.05). Increased humification index in the end product indicated better maturity of vermicompost as observed in treatments containing higher proportions of amendments. The addition of amendments favored earthworm activity which significantly decreased the heavy metal concentration (Fe, Cu, Pb, Zn) in the end product. The study concluded that sustainable utilization of TMS could be achieved for the cleaner and enriched vermicompost production by addition of amendments CD and TW in proportions of 50% and above.

Dynamics of spatial and temporal outflow from a soil column influenced by earthworm activity

&lt;p&gt;Earthworms are known as ecosystem engineers, which influence the chemical and physical properties in their own environment and thereby strongly modify soil processes. Soil structure (soil aggregates and macropores) formed by earthworms during burrowing activity may influence the soil moisture retention and water flow, enhancing infiltration into deep soil layers.&lt;/p&gt;&lt;p&gt;We studied the influence of anecic earthworms (&lt;em&gt;Lumbricus terrestris&lt;/em&gt; fed on poplar leaves) on the spatial and temporal variability in water outflow and storage through a soil column. Therefore, we established a cylinder (30cm diameter, 50cm high) with silty loamy soil. At the bottom boundary, 15 fiberglass wicks drain the water from the soil column. With these wicks the water outflow is measured with a spatial and temporal resolution.&amp;#160; After an initial wetting of the soil, irrigation of the soil cylinder was done twice per week with a full cone nozzle, with an intensity of 36 mm/h and a duration of 20 minutes After 17 weeks 10 adult earthworms were added to the column. The research design consists of three phases (i) soil-filled column ( 14 &amp;#160;weeks, with a gap of 4 weeks in the middle due to the corona lockdown) (ii) transition phase: initial earthworm activity (3 days) (iii) soil column with earthworm created structure (7 weeks).&lt;/p&gt;&lt;p&gt;After the experiment, the column was excavated carefully by layers of 4cm at a time. All of the earthworms were found back alive in the column. There was evidence of earthworm burrows down to 26 cm depth in the soil column, earthworm created aggregates were seen only in the top few centimeters.&lt;/p&gt;&lt;p&gt;We expected the outflow of water from the soil column to change due to the earthworm activity: on the one hand, the creation of macroaggregates was expected to increase the water retention in the soil, and on the other hand, the macropores were expected to create a stronger spatial variability in outflow and a more rapid reaction of outflow to the irrigation events.&amp;#160;&lt;/p&gt;&lt;p&gt;We observed mainly an earlier and slightly higher peak in the total outflow of the column coinciding with an earlier and higher peak in the spatial variability in the outflow of the wicks.&lt;/p&gt;

Stability of Aggregates Made by Earthworms in Soils with Organic Additives

Earthworm activity is a key factor in creating soil aggregates, but introduced organic matter and abiotic factors are also equally important. The purpose of this study was to investigate the stability of aggregates made by earthworms in soils with organic additives. Additionally, the two aggregate stability measurement methods were compared: (i) the wet-sieve method and (ii) the laser diffraction method. A six-month container experiment containing sixteen treatments and controls were made. Each treatment included one of four types of soil texture: sand, loam, silty loam and clay, and one of four additives: straw, peat, compost and compost with added microorganisms. To each treatment, six earthworms were added, two each of species commonly occurring in Polish soils: Dendrodrilus rubidus, Aporrectodea caliginosa and A. rosea. This study confirmed that earthworm activity was the factor favoring aggregate formation. In terms of the investigated organic additives, the efficiency of aggregate creation was as follows: compost with active bacteria, compost, peat and straw. Nevertheless, earthworms alone, without the addition of an organic additive, did not form permanent aggregates. The wet sieving and laser diffractometry methods of measuring aggregate stability were comparable for silty, clayey and loamy soils.

Earthworm Inoculation Improves Upland Rice Crop Yield and Other Agrosystem Services in Madagascar

The effects of earthworm inoculation and cropping systems on upland rice systems were examined over a four-year period in the Highlands of Madagascar. Each year, endogeic earthworms Pontoscolex corethrurus (Rhinodrilidae) were inoculated (EW+) at a density of 75 ind m−2 or were not inoculated (EW0). Inoculation was tested in three cropping systems: conservation agriculture (CA) and traditional tillage with or without residues restitution. Soil and plant properties were measured during the first three years while soil biological properties were assessed at the fourth year. At the end of the experiment, earthworm density was three-fold higher in EW+ than in EW0, demonstrating the success of the inoculation. Earthworm density was more important in CA than in tillage systems. Earthworm inoculation had higher significant effects on soil and plant properties than cropping systems. Earthworm inoculation had positive effects on soil macroaggregation (+43%), aboveground biomass (+27%), rice grain yield (+45%), and N grain amount (+43%). Intensifying earthworm activity in field conditions to meet the challenge of ecological transition is supported by our study.