Earthworm activity can strongly influence soil structure and organic matter (OM) dynamics of agricultural soils. Several short-term studies (≤90 days) have shown that earthworms can increase ...incorporation of residue carbon (C) into soil aggregates, suggesting reduced decomposition in the longer term. In contrast, another body of short-term studies reported that earthworms can increase carbon dioxide (CO2) emission from soils, thus suggesting increased decomposition in the longer term instead. To solve this controversy, we measured the effect of the epigeic Lumbricus rubellus (Hoffmeister) and the endogeic Aporrectodea caliginosa (Savigny) on the soil C balance in a unique 750-day mesocosm experiment, where loess soil was surface-applied with maize (Zea mays L.) residues every six months. Carbon inputs and outputs were strictly controlled: no soil C input through growing plants and no leaching of soil organic C. Flux measurements of CO2 were taken regularly and aggregate size distribution and total C and residue-derived C in the aggregate fractions (using the natural δ13C signature of maize) were measured after 185, 565 and 750 days. Both earthworm species increased cumulative CO2 emissions by at least 25%, indicating a higher C loss compared to the no-earthworm control. Yet, both earthworm species also increased the amount of soil C associated with the macroaggregate fraction after 750 days. L. rubellus increased the amount of residue-derived C in the macroaggregate fraction after 565 and after 750 days, whereas A. caliginosa increased residue-derived C in all the measured soil fractions after 750 days. Our results show that earthworms can simultaneously enhance CO2 emissions and C incorporation in aggregate fractions. However, over 750 days the presence of earthworms resulted in a lower total C content due to a higher overall OM decomposition rate. We therefore propose that under the most realistic incubation conditions so far (longer term and multiple residue applications), earthworms stimulate the mineralization of freshly added and older OM to a greater extent than that they stabilize residue-derived C inside biogenic aggregates. Future studies should focus on the balance between these processes in the presence of growing plants.
•Earthworms increase cumulative CO2 emissions by at least 25%.•Earthworms increase the amount of soil C associated with the macroaggregate fraction.•Earthworms can thus simultaneously enhance CO2 emission and C incorporation.•Earthworm presence results in lower total C content due to higher OM decomposition.•Earthworms stimulate OM mineralization more than that they stabilize residue C.
BACKGROUND AND AIMS: Intense rains are becoming more frequent. By causing waterlogging, they may increase soil erosion and soil surface compaction, hamper seedling establishment, and reduce plant ...growth. Since anecic earthworms make vertical burrows that improve water infiltration, we hypothesised that they can counteract such disturbance. METHODS: In a field experiment, intact soil mesocosms with ryegrass (Lolium multiflorum), with or without introduced adult Lumbricus terrestris, underwent either a precipitation regime with two intense rain events (36 mm, at beginning and end of spring), or a control regime with the same cumulative rainfall but no intense events. Short-term response of soil moisture and lagged response of plant growth were measured, and soil macroporosity was quantified. RESULTS: Intense rains reduced ryegrass shoot biomass (by 16–21 % on average) only in the absence of earthworms. Waterlogging duration aboveground was not affected, whereas soil moisture contents after intense rainfall tended to drop faster with earthworms present. Continuous vertical macropores were found only in the mesocosms to which earthworms had been added. The number of such macropores was 2.4 times higher under the intense precipitation regime, despite similar earthworm survival. CONCLUSIONS: We found that anecic earthworms can offset negative effects of intense rainfall on plant growth aboveground. Underlying mechanisms, such as macropore formation and enhanced nutrient cycling, are discussed. We also observed that altered precipitation patterns can modify earthworm burrowing behaviour, as earthworms had produced more burrows under the intense regime.
Biological nitrification inhibition (BNI) has been considered a plant strategy to increase N use efficiency by reducing N losses via N
2
O emissions or nitrate leaching. However, recent studies have ...revealed no difference in gross nitrate production among
Urochloa humidicola
genotypes with previously described high- and low-BNI capacity and pointed towards a crucial role for microbial N immobilization. In the current greenhouse study, we compared the
15
N acquisition by two
U. humidicola
genotypes (with high- and low-BNI capacity) and their soil-associated microorganisms at four points in time after fertilization (50 kg N ha
−1
). Soil microorganisms slightly out-competed both genotypes during the first 24 h after fertilization, and microorganisms associated with high-BNI genotype immobilized more N than microbes associated with low-BNI plants. Nevertheless, by the end of the experiment, low-BNI plant genotype had acquired more
15
N, despite higher to N
2
O emissions. Furthermore, higher
15
N root-to-shoot transfer was observed in low-BNI plants, potentially indicating higher contribution of nitrate to plant N uptake. In conclusion, our results confirm higher importance of microbial N immobilization in high-BNI genotypes, at least in the short-term. However, this did not result in higher N uptake by the high BNI genotype during the first 3 weeks after fertilization as could be expected. Long-term field studies are required to better understand the implications of direct (BNI sensu stricto) and indirect mechanisms (including differences in rhizosphere microbial biomass, activity and composition between high- and low-BNI genotypes), processes on plant N use efficiency, N storage in soil, and N losses to the environment.
► Sustainable management of soils requires monitoring of biological indicators. ► No such indicator is universal; different indicators suit different soil functions and environments. ► Biological ...soil indicator sets should reflect the hierarchical organization of soil organisms. ► Indicators require validation across soil and land use types using standardized methods. ► Integrated datasets support the development of ecological theory and communication tools.
Soil biota are essential for many soil processes and functions, yet there are increasing pressures on soil biodiversity and soil degradation remains a pertinent issue. The sustainable management of soils requires soil monitoring, including biological indicators, to be able to relate land use and management to soil functioning and ecosystem services. Since the 1990s, biological soil parameters have been assessed in an increasing number of field trials and monitoring programmes across Europe. The development and effective use of meaningful and widely applicable bio-indicators, however, continue to be challenging tasks. This paper aims to provide an overview of current knowledge on the characterization and assessment of soil biodiversity. Examples of biological soil indicators and monitoring approaches are presented. Furthermore the value of databases for developing a better understanding of the relationship between soil management, soil functions and ecosystem services is discussed. We conclude that integration of monitoring approaches and data sets offers good opportunities for advancing ecological theory as well as application of such knowledge by land managers and other decision makers.
The capacity of several plant species or landraces to inhibit nitrification in soil (biological nitrification inhibition, BNI) has been assessed in certain tropical pastures. These assessments are ...commonly based on potential net nitrification rates, which do not differentiate between gross nitrification and other processes that may reduce the amount of nitrate in soil. In a greenhouse experiment using two genotypes of
Urochloa humidicola
with contrasting BNI capacity in vitro, we evaluated gross N transformation rates before and after (7 and 21 days) N fertilization, while periodically measuring N
2
O emissions. Gross nitrification rates (in fact gross nitrate production assessed by pool dilution technique) were comparable in both genotypes and were low in comparison to strong microbial NH
4
+
immobilization. The N
2
O emissions were higher in pots with low-BNI plants. The discrepancy between the potential net nitrification rates assessed in laboratory assays (higher in low-BNI plants) and gross nitrification in pot or field experiments (no differences between genotypes) can be attributed to the out-competition of ammonia oxidizers by plant N uptake and ammonia immobilizing heterotrophic microbes, resulting in low nitrification under conditions where growing plants are present. This study confirmed the capacity of certain
U. humidicola
genotypes to reduce N
2
O emissions but warrants further investigation of the underlying mechanisms. It also questions the relevance of BNI in the rhizosphere of this plant species as other mechanisms (rather than the inhibition of gross nitrification) seem to be more important in maintaining low-nitrate soil environments in soil–plant systems of
U. humidicola
.
Attention to soil biodiversity and its importance for sustainable food production has markedly increased in recent years. In particular, the loss of soil biodiversity as a consequence of intensive ...agriculture, land degradation and climate change has raised concerns due to the expected negative impacts on ecosystem services, food security and human health. The result is a strong demand for ‘nature-based’ practices that stimulate soil biodiversity or beneficial soil organisms and enhance soil health. Here, we examine the origin of popular ideas on the role of soil biology in sustainable soil management, as well as their potential to address key global challenges related to agriculture. Three examples of such ideas are discussed: 1) a higher fungal:bacterial (F:B) biomass ratio favours soil carbon storage and nutrient conservation; (2) intensive agricultural practices lead to a decline in soil biodiversity with detrimental consequences for sustainable food production; (3) inoculation with arbuscular mycorrhizal fungi reduces agriculture's dependency on synthetic fertilizers. Our analysis demonstrates how ecological theories, especially E.P. Odum's (
1969) hypotheses on ecological succession, have inspired the promotion of agricultural practices and commercial products that are based on the mimicry of (soil biology in) natural ecosystems. Yet our reading of the scientific literature shows that popular claims on the importance of high F:B ratios, soil biodiversity and the inoculation with beneficial microbes for soil health and sustainable agricultural production cannot be generalized and require careful consideration of limitations and possible trade-offs. We argue that dichotomies and pitfalls associated with the normative use of nature as a metaphor for sustainability can be counterproductive given the urgency to achieve real solutions that sustain food production and natural resources. Finally, implications for soil ecology research and sustainable soil management in agriculture are discussed.
In Latin America, the cultivation of Arabica coffee (
Coffea arabica
) plays a critical role in rural livelihoods, biodiversity conservation, and sustainable development. Over the last 20 years, ...coffee farms and landscapes across the region have undergone rapid and profound biophysical changes in response to low coffee prices, changing climatic conditions, severe plant pathogen outbreaks, and other drivers. Although these biophysical transformations are pervasive and affect millions of rural livelihoods, there is limited information on the types, location, and extent of landscape changes and their socioeconomic and ecological consequences. Here we review the state of knowledge on the ongoing biophysical changes in coffee-growing regions, explore the potential socioeconomic and ecological impacts of these changes, and highlight key research gaps. We identify seven major land-use trends which are affecting the sustainability of coffee-growing regions across Latin America in different ways. These trends include (1) the widespread shift to disease-resistant cultivars, (2) the conventional intensification of coffee management with greater planting densities, greater use of agrochemicals and less shade, (3) the conversion of coffee to other agricultural land uses, (4) the introduction of Robusta coffee (
Coffea canephora
) into areas not previously cultivated with coffee, (5) the expansion of coffee into forested areas, (6) the urbanization of coffee landscapes, and (7) the increase in the area of coffee produced under voluntary sustainability standards. Our review highlights the incomplete and scattered information on the drivers, patterns, and outcomes of biophysical changes in coffee landscapes, and lays out a detailed research agenda to address these research gaps and elucidate the effects of different landscape trajectories on rural livelihoods, biodiversity conservation, and other aspects of sustainable development. A better understanding of the drivers, patterns, and consequences of changes in coffee landscapes is vital for informing the design of policies, programs, and incentives for sustainable coffee production.
Previous laboratory studies using epigeic and anecic earthworms have shown that earthworm activity can considerably increase nitrous oxide (N2O) emissions from crop residues in soils. However, the ...universality of this effect across earthworm functional groups and its underlying mechanisms remain unclear. The aims of this study were (i) to determine whether earthworms with an endogeic strategy also affect N2O emissions; (ii) to quantify possible interactions with epigeic earthworms; and (iii) to link these effects to earthworm-induced differences in selected soil properties. We initiated a 90-day 15N-tracer mesocosm study with the endogeic earthworm species Aporrectodea caliginosa (Savigny) and the epigeic species Lumbricus rubellus (Hoffmeister). 15N-labeled radish (Raphanus sativus cv. Adagio L.) residue was placed on top or incorporated into the loamy (Fluvaquent) soil. When residue was incorporated, only A. caliginosa significantly (p < 0.01) increased cumulative N2O emissions from 1350 to 2223 μg N2O–N kg−1 soil, with a corresponding increase in the turnover rate of macroaggregates. When residue was applied on top, L. rubellus significantly (p < 0.001) increased emissions from 524 to 929 μg N2O–N kg−1, and a significant (p < 0.05) interaction between the two earthworm species increased emissions to 1397 μg N2O–N kg−1. These effects coincided with an 84% increase in incorporation of residue 15N into the microaggregate fraction by A. caliginosa (p = 0.003) and an 85% increase in incorporation into the macroaggregate fraction by L. rubellus (p = 0.018). Cumulative CO2 fluxes were only significantly increased by earthworm activity (from 473.9 to 593.6 mg CO2–C kg−1 soil; p = 0.037) in the presence of L. rubellus when residue was applied on top. We conclude that earthworm-induced N2O emissions reflect earthworm feeding strategies: epigeic earthworms can increase N2O emissions when residue is applied on top; endogeic earthworms when residue is incorporated into the soil by humans (tillage) or by other earthworm species. The effects of residue placement and earthworm addition are accompanied by changes in aggregate and SOM turnover, possibly controlling carbon, nitrogen and oxygen availability and therefore denitrification. Our results contribute to understanding the important but intricate relations between (functional) soil biodiversity and the soil greenhouse gas balance. Further research should focus on elucidating the links between the observed changes in soil aggregation and controls on denitrification, including the microbial community.
•Two widely used earthworm sampling methods were compared.•The methods detected similar ecological responses to agricultural intensification.•One method detected more earthworms than the other ...method.•More earthworms found with smaller total sampling area but larger hand-sorting area.•Agricultural intensification resulted in communities dominated by small earthworms.
To assess whether different sampling protocols provide similar results on earthworm community responses to land use, comparisons across different environments are required. Using an ongoing experiment in France, we assessed whether two protocols, widely used in international projects and global databases, provide similar estimates of earthworm abundance, and detect the same community responses to agricultural intensification. Method A consisted of hand-sorting composite samples of three soil monoliths 35×35×20cm each, and applying formalin in the resulting holes. Method B consisted of applying formalin over a 1m2 contiguous area and subsequently hand-sorting a 25×25×25cm soil monolith within it. Higher abundance was obtained from Method A than from Method B, but the two methods led to the same ecological conclusions. Firstly, they both showed that earthworm biomass and density decreased with agricultural intensification. Secondly, they showed similar land use effects on earthworm ecological group proportions, age structure, and body size distribution, pointing to a relative loss of large-bodied earthworms with agricultural intensification. These findings suggest that data from the two methods are both suitable to investigate the community response of earthworms, whereas assessments of earthworm abundance per se are more sensitive to the sampling protocol. Merits and drawbacks of the methods in terms of time and labour needed and of statistical variation are discussed.
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•OC was reliably quantified in calcareous POM/MAOM fractions with 4 methods.•Sodium hexametaphosphate (SHMP) dispersion did not affect quantification of OC.•Guidance on the selection ...of the most optimal OC method is provided.
Accurate quantification of soil organic carbon (OC) pools is essential to study the dynamics of OC in soils. Therefore, organic matter is often separated into physical fractions with distinct turnover times, e.g. particulate (POM) and mineral-associated organic matter (MAOM), after which their OC content is measured. Calcareous soils are under-represented in such fractionation studies, because the required analytical differentiation between OC and inorganic carbon (IC) is not straightforward and implies more processing time, sample mass and equipment. Here, we review the performance of four methods to quantify OC in POM and MAOM fractions of soils containing 3–16 g IC kg−1 and 10–25 g OC kg−1 (n = 16). We assessed the similarity and consistency of the data obtained with the different methods. Furthermore, we checked how their ability to distinguish OC from IC was influenced by the fractionation and in particular by the dispersion with sodium hexametaphosphate (SHMP). The four methods were: 1) Elemental carbon analysis after removal of IC by acid fumigation (OCfum); 2) Elemental carbon analysis after removal of IC with aqueous acid (OCaq); 3) Elemental carbon as determined by Rock-Eval 6 thermal analysis (OCRE6); and 4) Elemental carbon analysis after removal of OC by loss on ignition and subsequent quantification of OC by difference between total carbon and IC (OCLOI). We found that the OCfum, OCaq, and OCLOI methods produced similar OC contents for bulk soils, whereas OCRE6 results were slightly but significantly lower. Total recovered OCRE6 contents of the summed POM and MAOM fractions were similar to the bulk soil OCRE6 contents. In contrast, the recovered OCfum, OCaq and OCLOI contents were slightly higher than respective bulk soil OC contents (108–112%), especially in soils with high IC/OC ratios. We show that this was not caused by operational artefacts or chemical changes that occurred during OC fractionation, but rather likely indicated error propagation. We conclude that all 4 methods can reliably quantify OC in POM and MAOM fractions in calcareous soils and that the optimal choice depends on the required accuracy of the results and the available sample mass, lab equipment and processing time. Based on our findings and practical considerations, we provide guidance for the selection of the most optimal OC quantification method to study OC dynamics in calcareous soils.
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