Earthworms and the soil greenhouse gas balance

Earthworms play an essential part in determining the greenhouse gas (GHG) balance of soils worldwide. Their activity affects both biotic and abiotic soil properties, which in turn influence soil GHG emissions, carbon (C) sequestration and plant growth. Yet, the balance of earthworms stimulating C sequestration on the one hand and increasing GHG emissions on the other has not been investigated. Indeed, much is still unclear about how earthworms interact with agricultural land use and soil management practices, making predictions on their effects in agro-ecosystems difficult. In this thesis, I aimed to determine to what extent GHG mitigation by soil C sequestration as affected by earthworms is offset by earthworm-induced GHG emissions from agro-ecosystems under different types of management. To reach this aim, I combined mesocosm and field studies, as well as meta-analytic methods to quantitatively synthesize the literature. Using meta-analysis, I showed that, on average, earthworm activity leads to a 24% increase in aboveground biomass, a 33% increase in carbon dioxide (CO2) emissions and a 42% increase in nitrous oxide (N2O) emissions. The magnitude of these effects depends on soil factors (e.g., soil organic matter content), experimental factors (e.g., crop residue addition or fertilizer type and rate) and earthworm factors (e.g., earthworm ecological category and -density). Conducting both a mesocosm and a field study, I showed that earthworm activity results in increased N2O emissions from fertilized grasslands. Under field conditions I found an increase in earthworm-induced N2O emissions in autumn but not in spring, suggesting that earthworm effects in the field depend on soil physicochemical parameters influenced by meteorological and seasonal dynamics. In a unique two-year experiment with a simulated no-tillage (NT) system and a simulated conventional tillage (CT) system, I found that earthworm presence increases GHG emissions in an NT system to the same level as in a CT system. This suggests that the GHG mitigation potential of NT agro-ecosystems is limited. When considering the C budget in the simulated NT system, I demonstrated that over the course of the experiment earthworms increase cumulative CO2 emissions by at least 25%, indicating a higher C loss compared to the situation without earthworms. Yet, in the presence of earthworms the incorporation of residue-derived C into all measured soil aggregate fractions also increased, indicating that earthworm activity can simultaneously enhance CO2 emissions and C incorporation into aggregate fractions. In conclusion, the revealed dominance of GHG emissions over C sequestration as affected by earthworms implies that their presence in agro-ecosystems results in a negative impact on the soil greenhouse gas balance.</p

Earthworms increase plant production: a meta- analysis

To meet the challenge of feeding a growing world population with minimal environmental impact, we need comprehensive and quantitative knowledge of ecological factors affecting crop production. Earthworms are among the most important soil dwelling invertebrates. Their activity affects both biotic and abiotic soil properties, in turn affecting plant growth. Yet, studies on the effect of earthworm presence on crop yields have not been quantitatively synthesized. Here we show, using meta-analysis, that on average earthworm presence in agroecosystems leads to a 25% increase in crop yield and a 23% increase in aboveground biomass. The magnitude of these effects depends on presence of crop residue, earthworm density and type and rate of fertilization. The positive effects of earthworms become larger when more residue is returned to the soil, but disappear when soil nitrogen availability is high. This suggests that earthworms stimulate plant growth predominantly through releasing nitrogen locked away in residue and soil organic matter. Our results therefore imply that earthworms are of crucial importance to decrease the yield gap of farmers who can't -or won't- use nitrogen fertilizer

The soil N cycle: new insights and key challenges

The study of soil N cycling processes has been, is, and will be at the centre of attention in soil science research. The importance of N as a nutrient for all biota; the ever-increasing rates of its anthropogenic input in terrestrial (agro)ecosystems; its resultant losses to the environment; and the complexity of the biological, physical, and chemical factors that regulate N cycling processes all contribute to the necessity of further understanding, measuring, and altering the soil N cycle. Here, we review important insights with respect to the soil N cycle that have been made over the last decade, and present a personal view on the key challenges of future research. We identify three key challenges with respect to basic N cycling processes producing gaseous emissions: 1. quantifying the importance of nitrifier denitrification and its main controlling factors; 2. characterizing the greenhouse gas mitigation potential and microbiological basis for N2O consumption; 3. characterizing hotspots and hot moments of denitrification Furthermore, we identified a key challenge with respect to modelling: 1. disentangling gross N transformation rates using advanced 15N / 18O tracing models Finally, we propose four key challenges related to how ecological interactions control N cycling processes: 1. linking functional diversity of soil fauna to N cycling processes beyond mineralization; 2. determining the functional relationship between root traits and soil N cycling; 3. characterizing the control that different types of mycorrhizal symbioses exert on N cycling; 4. quantifying the contribution of non-symbiotic pathways to total N fixation fluxes in natural systems We postulate that addressing these challenges will constitute a comprehensive research agenda with respect to the N cycle for the next decade. Such an agenda would help us to meet future challenges on food and energy security, biodiversity conservation, water and air quality, and climate stability

Complement Component C1q as Serum Biomarker to Detect Active Tuberculosis

Transplantation and autoimmunit

A simple and effective method to keep earthworms confined to open-top mesocosms

Earthworms can have a profound effect on a myriad of soil physical, chemical and microbial parameters. To better understand their role in the soil, they are often studied under controlled conditions. However, a persistent problem in such controlled experiments is the ability of earthworms to escape from experimental units with open tops (e.g. for plant growth). Here, we tested whether adhesive hook tape applied to the inside of mesocosms is effective in confining them to their experimental units. A mesocosm study was set up with hook tape treatments (control, one layer, two layers), mesocosm material (polyvinylchloride – PVC, polypropylene – PP) and earthworm species (Lumbricus rubellus (Hoffmeister), Aporrectodea caliginosa (Savigny), Lumbricus terrestris (L.) + Aporrectodea longa (Ude)) as different factors to study the escape of earthworms during 24 h. In the treatments without hook tape, individuals of L. rubellus and A. caliginosa escaped, with highest escape rates (80%) for L. rubellus from the PP mesocosms, and lowest escape rates (20%) for A. caliginosa from the PVC mesocosms. When hook tape was applied, in either one or two layers, no individuals of those species escaped. The two anecic earthworm species, L. terrestris and A. longa did not escape from any mesocosms, irrespective of the presence of hook tape. As not a single earthworm escaped from the hook tape treatments, we conclude that applying hook tape is a simple, inexpensive and effective method to keep earthworms confined to experimental units

Residue incorporation depth is a controlling factor of earthworm-induced nitrous oxide emissions

Earthworms can increase nitrous oxide (N2O) emissions, particularly in no-tillage systems where earthworms are abundant. Here, we study the effect of residue incorporation depth on earthworm-induced N2O emissions. We hypothesized that cumulative N2O emissions decrease with residue incorporation depth, because (i) increased water filled pore space (WFPS) in deeper soil layers leads to higher denitrification rates as well as more complete denitrification; and (ii) the longer upward diffusion path increases N2O reduction to N2. Two 84-day laboratory mesocosm experiments were conducted. First, we manually incorporated maize (Zea maysL.) residue at different soil depths (incorporation experiment). Second, 13C-enriched maize residue was applied to the soil surface and anecic species Lumbricus terrestris (L.) and epigeic species Lumbricus rubellus (Hoffmeister) were confined to different soil depths (earthworm experiment). Residue incorporation depth affected cumulative N2O emissions in both experiments (P <0.001). In the incorporation experiment, N2O emissions decreased from 4.91 mg N2O–N kg-1 soil (surface application) to 2.71 mg N2O–N kg-1 soil (40–50 cm incorporation). In the earthworm experiment, N2O emissions from L. terrestris decreased from 3.87 mg N2O–N kg-1 soil (confined to 0–10 cm) to 2.01 mg N2O–N kg-1 soil (confined to 0–30 cm). Both experimental setups resulted in dissimilar WFPS profiles that affected N2O dynamics. We also found significant differences in residue C recovery in soil organic matter between L. terrestris (28–41%) and L. rubellus (56%). We conclude that (i) N2O emissions decrease with residue incorporation depth, although this effect was complicated by dissimilar WFPS profiles; and (ii) larger residue C incorporation by L. rubellus than L. terrestris indicates that earthworm species differ in their C stabilization potential. Our findings underline the importance of studying earthworm diversity in the context of greenhouse gas emissions from agro-ecosystems

Earthworm-induced N mineralization in fertilized grassland increases both N2O emission and crop-N uptake

Earthworms can increase plant nitrogen (N) availability by stimulating mineralization of organic matter. However, recent studies show that they can also cause elevated emission of the greenhouse gas nitrous oxide (N2O). It is unclear to what extent these two effects occur in fertilized grasslands, where earthworm densities are typically greatest. The aims of this study were therefore to (i) quantify the effects of earthworm activity on N uptake and N2O emissions in fertilized grasslands and (ii) link these effects to earthworm functional groups. In a 73-day factorial mesocosm experiment, combinations of Lumbricus rubellus (Lr, epigeic), Aporrectodea longa (Al, anecic) and Aporrectodea caliginosa (Ac, endogeic) individuals were introduced into columns with grass growing on a fertilized (250 kg N ha-1) loamy soil. Introduction of Lr resulted in 50.8% (P <0.001) larger N2O emissions and 5.4% (P = 0.032) larger grass biomass. Grass-N uptake increased from 172 to 188 kg N ha-1 in the presence of Lr (P <0.001), from 176 to 183 kg N ha-1 in the presence of Ac (P = 0.001), and from 168 to 199 kg N ha-1 when all three earthworm species were present (P = 0.006). Lr increased soil NH4+-N concentrations (P = 0.010), further indicating enhanced mineralization of N caused by earthworm activity. We conclude that the previously observed beneficial effect of earthworm presence on plant-N availability has a negative side-effect: increased emissions of the mineralized N as N2

Duurzaamheidsanalyse van bodemgebruik in natuurgebieden

In deze studie is een inventarisatie, beschrijving en beoordeling van het bodemgebruik in natuurgebieden gemaakt. Het bevat overwegingen om de effecten van maatregelen op bepaalde bodemfuncties positief of negatief te beoordelen. Effectgerichte maatregelen zijn zeer divers. Binnen OBN is het van belang de kennisontwikkeling bij maatregelen en inrichting te stimuleren. Dit rapport dient als basis om het begrip duurzaam bodemgebruik in natuurterreinen concreet te maken plus de rol van de overheid daarbij

Earthworms can increase nitrous oxide emissions from managed grassland: a field study

Earthworms are important in determining the greenhouse gas (GHG) balance of soils. In laboratory studies they have been shown to increase emissions of the potent GHG nitrous oxide (N2O). Here we test whether these earthworm-induced N2O emissions also occur in the field. We quantified N2O emissions in managed grassland in two different seasons (spring and autumn), applying two different types of fertilizer (organic and artificial fertilizer) and under two earthworm densities (175 individuals and 350 individuals m(-2)) of the species Lumbricus rubellus (Hoffmeister). We found an increase in earthworm-induced N2O emissions of 286 and 394% in autumn for low and high earthworm densities (P = 0.044 and P = 0.007, respectively). There were no effects of earthworms on N2O emissions in spring. Fertilizer additions significantly increased cumulative N2O emissions and grass N content in spring and autumn. For grass N content interactions between earthworm addition and fertilizer type existed in both seasons. Our results suggest that the pathways through which earthworms affect N cycling (and thereby N2O emission) differ with weather conditions. We postulate that in spring the dry weather conditions overruled any earthworm effects, whereas in autumn earthworms mainly improved soil aeration and thereby increased both plant N uptake and diffusion of N2O to the atmosphere. While we showed the presence of earthworm-induced N2O emissions in managed grassland under field conditions for the first time, the nature and intensity of the earthworm effect in the field is conditional on soil physicochemical parameters and thereby on meteorological and seasonal dynamics. (C) 2013 Elsevier B.V. All rights reserved

Earthworm-induced N mineralization in fertilized grassland increases both N2O emission and crop-N uptake

Earthworms can increase plant nitrogen (N) availability by stimulating mineralization of organic matter. However, recent studies show that they can also cause elevated emission of the greenhouse gas nitrous oxide (N2O). It is unclear to what extent these two effects occur in fertilized grasslands, where earthworm densities are typically greatest. The aims of this study were therefore to (i) quantify the effects of earthworm activity on N uptake and N2O emissions in fertilized grasslands and (ii) link these effects to earthworm functional groups. In a 73-day factorial mesocosm experiment, combinations of Lumbricus rubellus (Lr, epigeic), Aporrectodea longa (Al, anecic) and Aporrectodea caliginosa (Ac, endogeic) individuals were introduced into columns with grass growing on a fertilized (250 kg N ha-1) loamy soil. Introduction of Lr resulted in 50.8% (P <0.001) larger N2O emissions and 5.4% (P = 0.032) larger grass biomass. Grass-N uptake increased from 172 to 188 kg N ha-1 in the presence of Lr (P <0.001), from 176 to 183 kg N ha-1 in the presence of Ac (P = 0.001), and from 168 to 199 kg N ha-1 when all three earthworm species were present (P = 0.006). Lr increased soil NH4+-N concentrations (P = 0.010), further indicating enhanced mineralization of N caused by earthworm activity. We conclude that the previously observed beneficial effect of earthworm presence on plant-N availability has a negative side-effect: increased emissions of the mineralized N as N2