Macrofauna assemblage composition and soil moisture interact to affect soil ecosystem functions

Changing climatic conditions and habitat fragmentation are predicted to alter the soil moisture conditions of temperate forests. It is not well understood how the soil macrofauna community will respond to changes in soil moisture, and how changes to species diversity and community composition may affect ecosystem functions, such as litter decomposition and soil fluxes. Moreover, few studies have considered the interactions between the abiotic and biotic factors that regulate soil processes. Here we attempt to disentangle the interactive effects of two of the main factors that regulate soil processes at small scales - moisture and macrofauna assemblage composition. The response of assemblages of three common temperate soil invertebrates (Glomeris marginata Villers, Porcellio scaber Latreille and Philoscia muscorum Scopoli) to two contrasting soil moisture levels was examined in a series of laboratory mesocosm experiments. The contribution of the invertebrates to the leaf litter mass loss of two common temperate tree species of contrasting litter quality (easily decomposing Fraxinus excelsior L. and recalcitrant Quercus robur L.) and to soil CO₂ fluxes were measured. Both moisture conditions and litter type influenced the functioning of the invertebrate assemblages, which was greater in high moisture conditions compared with low moisture conditions and on good quality vs. recalcitrant litter. In high moisture conditions, all macrofauna assemblages functioned at equal rates, whereas in low moisture conditions there were pronounced differences in litter mass loss among the assemblages. This indicates that species identity and assemblage composition are more important when moisture is limited. We suggest that complementarity between macrofauna species may mitigate the reduced functioning of some species, highlighting the importance of maintaining macrofauna species richness.     

五大连池药泉山大型土壤动物对旅游踩踏的响应

以黑龙江省五大连池世界地质公园的药泉山为研究对象,按照距离游道的远近分为重度踩踏区,轻度踩踏区和非踩踏区3种踩踏干扰强度,分析大型土壤动物数量,群落组成,多样性对旅游踩踏干扰的响应。研究结果表明不同干扰区之间大型土壤动物类群数量差异显著(P0.001),重度踩踏区显著低于轻度踩踏区和非踩踏区。不同干扰区大型土壤动物个体数差异明显(P0.001),其中轻度踩踏区个体密度最大(68头/m~2),重度踩踏区个体密度最小(10头/m~2)。不同踩踏强度干扰区H'指数差异明显(P0.05),轻度踩踏区及非踩踏区的多样性显著高于严重踩踏区。典型对应分析表明旅游踩踏主要通过改变土壤理化特性而影响大型土壤动物的组成及其多样性,重度踩踏区、轻度踩踏区和非踩踏区对大型土壤动物影响最显著的因子分别为土壤全氮含量,土壤含水率和土壤全磷含量。     

The contribution of nitrogen deposition to the eutrophication signal in understorey plant communities of European forests

We evaluated effects of atmospheric deposition of nitrogen on the composition of forest understorey vegetation both in space and time, using repeated data from the European wide monitoring program ICP‐Forests, which focuses on normally managed forest. Our aim was to assess whether both spatial and temporal effects of deposition can be detected by a multiple regression approach using data from managed forests over a relatively short time interval, in which changes in the tree layer are limited. To characterize the vegetation, we used indicators derived from cover percentages per species using multivariate statistics and indicators derived from the presence/absence, that is, species numbers and Ellenberg's indicator values. As explanatory variables, we used climate, altitude, tree species, stand age, and soil chemistry, besides deposition of nitrate, ammonia and sulfate. We analyzed the effects of abiotic conditions at a single point in time by canonical correspondence analysis and multiple regression. The relation between the change in vegetation and abiotic conditions was analyzed using redundancy analysis and multiple regression, for a subset of the plots that had both abiotic data and enough species to compute a mean Ellenberg N value per plot using a minimum of three species. Results showed that the spatial variation in the vegetation is mainly due to “traditional” factors such as soil type and climate, but a statistically significant part of the variation could be ascribed to atmospheric deposition of nitrate. The change in the vegetation over the past c. 10 years was also significantly correlated to nitrate deposition. Although the effect of deposition on the individual species could not be clearly defined, the effect on the vegetation as a whole was a shift toward nitrophytic species as witnessed by an increase in mean Ellenberg's indicator value.     

Development of a soil compaction indicator in life cycle assessment

Purpose

Integrating soil quality impacts in life cycle assessment (LCA) requires a global approach to assess impacts on soil quality that can be adapted to individual soil and climate contexts. We have developed a framework for quantifying indicators of impact on soil quality, valid for all soil and climate conditions, and considering both on-site and off-site agricultural soils. Herein, we present one of the framework’s impact indicators, which has not yet been quantified in detail in LCA studies: soil compaction.

Material and methods

The method includes guidelines and tools for estimating midpoint compaction impacts in topsoil and subsoil as a loss of soil pore volume (in cubic metre per functional unit). The life cycle inventory (LCI) and life cycle impact assessment are based on simulation modelling, using models simple enough for use by non-experts, general enough to be parameterised with available data at a global scale and already validated. Data must be as site specific and accurate as possible, but if measured data are missing, the method has a standardised framework of rules and recommendations for estimating or finding them. The main model used, COMPSOIL, predicts compaction due to agricultural traffic. Results are illustrated using a case study involving several crops in different soil and climate conditions: a representative pig feed produced in Brittany, France.

Results and discussion

Predicted compaction impacts result from the combination of site-specific soil, climate and management characteristics. The data necessary to the LCI are readily available from free soil and climate databases and research online. Results are consistent with compaction observed in the field. Within a soil type, predictions are most sensitive to initial bulk density and soil water content.

Conclusions

The method lays the foundation for possible improvement by refining estimates of initial soil conditions or adding models that are simple and robust enough to increase the method’s capacity and accuracy. The soil compaction indicator can be used in LCAs of bio-based materials and of waste management stages that consider composting. The framework includes other operational indicators (i.e. water erosion, soil organic matter change) to assess impact on soil quality. They complement other impact categories, providing increased ability to identify “impact swapping”.     

Fungal functional diversity inferred along Ellenberg's abiotic gradients: Palynological evidence from different soil microbiota

The aim of this paper is to analyse whether the functional diversity of the fungal community follows the environmental gradients as much as vascular plants. After determination of the Ellenberg's indicator values on the basis of 602 cormophyte species occurring in 110 permanent plots across Central Europe, the relation between soil fungi and the abiotic factors as defined by Ellenberg's indicators has been evaluated. The palynological assessment proves that not the fungal occurrence, but the concentration of fungal remains is the most appropriate tool to unravel causal links between the belowground microflora and the soil abiotic factors. The analyses show a striking dichotomy within the fungal community. First, the logarithms of fungal diversity and hyphal density show close but opposite relationships with light, moisture, soil reaction and nitrogen availability. Second, fungal functional groups show parallel, decreasing trends for soil reaction and nitrogen availability. Aside from the mycorrhizal network as a whole (ericoid, EM and AM), we demonstrate that the degree of ecological information supplied by the different trophic levels (litter-related fungi, fimicolous fungi, wood-related fungi and strictly ericoid mycorrhizal fungi) is much greater than expected from previous studies.     

Cloud forests of the Orinoco River Basin (Colombia): Variation in vegetation and soil macrofauna composition along the hydrometeorological gradient

Tropical montane cloud forests (TMCF) in the Orinoco River Basin are vulnerable to climate and regional land-use changes. These changes will force TMCF to migrate upwards, affecting biodiversity conservation and water flow regulation. Here, we evaluate how vegetation and soil macrofauna composition vary along the hydrometeorological gradient driven by an increase in fog incidence with elevation. Vegetation data were collected for all individuals with a diameter at breast height (DBH) > 5 cm in four vegetation plots (5 × 50 m; total: 0.1 ha) every 100 m in altitude between 1700 and 2200 m a.s.l. From each plot, we obtained three soil monoliths from the organic layer and three from the mineral horizon, and manually extracted their soil macrofauna. For these groups, we describe: (1) their compositional changes along the hydrometeorological gradient employing ordination analyses techniques and (2) the relation of the composition changes between vegetation and soil macrofauna communities using a symmetrical co-correspondence analysis. Our results show that the vegetation morphospecies composition and soil macrofauna-order composition vary significantly with the hydrometeorological gradient along elevation. The co-correspondence between vegetation and soil macrofauna reveals a shared breakpoint above the 2000 m a.s.l., where fog is more persistent. Furthermore, we identified eight indicator vegetation species and two soil macrofauna orders associated with specific elevations. These results suggest that under a climate-change-driven fog lift, the TMCF of the Orinoco River Basin will be displaced. Moreover, this study provides a baseline to monitor such displacement.     

The effect of topsoil removal in restored heathland on soil fauna, topsoil microstructure, and cellulose decomposition: implications for ecosystem restoration

Communities of soil macrofauna, oribatid mites, and nematodes as well as vegetation and soil chemistry were studied on twelve plots representing three replicates of the following treatments: agricultural meadow, heathland, and heathland restored either by partial or complete topsoil removal 15 years earlier. We also studied the effect of soil macrofauna on decomposition and the microstructure of the soil surface layer with litterbags in combination with the analysis of thin soil sections. The communities of soil macrofauna and oribatid mites significantly differed between agricultural meadows and heathlands. The partial and complete topsoil removal plots were more similar to heathlands with respect to macrofauna and to agricultural meadows with respect to oribatid mites. The density and diversity of soil macrofauna was higher in agricultural meadows than in heathlands; in particular, earthworms, litter transformers, root feeders, and microsaprophags were more abundant on meadows. Heathlands, in contrast, contained a much higher diversity of oribatid mites. The community structure of nematodes did not significantly differ among the treatments. Analysis of thin soil sections revealed a thick organic fermentation layer in heathlands, which was absent in agricultural meadows and only weakly developed in the topsoil removal plots. In agricultural meadows, litterbags and thin soil sections indicated that abundant macrofauna, including endogeic earthworms, were very effective in removing the litter from the soil surface and mixing it into the mineral soil. Possible effects of this soil mixing on restoration success are discussed.     

Litter elemental stoichiometry and biomass densities of forest soil invertebrates

To maintain constant chemical composition, i.e. elemental homeostasis, organisms have to consume resources of sufficient quality to meet their own specific stoichiometric demand. Therefore, concentrations of elements indicate resource quality, and rare elements in the environment may act as limiting factors for individual organisms scaling up to constrain population densities. We investigated how the biomass densities of invertebrate populations of temperate forest soil communities depend on 1) the stoichiometry of the basal litter according to ecological stoichiometry concepts and 2) the population average body mass as predicted by metabolic theory. We used a large data set on biomass densities of 4959 populations across 48 forests in three regions of Germany. Following various ecological stoichiometry hypotheses, we tested for effects of the carbon‐to‐element ratios of 10 elements. Additionally, we included the abiotic litter characteristics habitat size (represented by litter depth), litter diversity and pH, as well as forest type as an indicator for human management. Across 12 species groups, we found that the biomass densities scaled significantly with population‐averaged body masses thus supporting metabolic theory. Additionally, 10 of these allometric scaling relationships exhibited interactions with stoichiometric and abiotic co‐variables. The four most frequent co‐variables were 1) forest type, 2) the carbon‐to‐phosphorus ratio (C:P), 3) the carbon‐to‐sodium ratio (C:Na), and the carbon‐to‐nitrogen ratio (C:N). Hence, our analyses support the sodium shortage hypothesis for microbi‐detritivores, the structural elements hypothesis for some predator groups (concerning N), and the secondary productivity hypothesis (concerning P) across all trophic groups in our data. In contrast, the ecosystem size hypothesis was only supported for some meso‐ and macrofauna detritivores. Our study is thus providing a comprehensive analysis how the elemental stoichiometry of the litter as the basal resource constrain population densities across multiple trophic levels of soil communities.     

地埂植物篱对大型土壤动物多样性的影响

为了解地埂植物篱作为农田边界对于大型土壤动物多样性的影响,2006年冬季和2007年春季对桑园、桑埂、橘园、橘埂和农田大型土壤动物群落结构进行了调查,共获得大型土壤动物 4533只,隶属于3门、9纲、24类.结果表明,不同土地利用方式大型土壤动物群落的个体密度、类群数和DG多样性指数均存在显著差异.无论在冬季还是在春季,地埂植物篱桑埂和橘埂的个体密度、类群数和DG多样性指数均显著高于农田;冬季桑园和橘园的个体密度、类群数和DG多样性指数也显著高于农田.大型土壤动物群落的个体密度和类群数在垂直分布上与土壤含水量、全N和有机质含量的垂直分布规律一致,均随着土层深度的增加而递减.主成分分析表明,桑埂、橘埂和橘园的大型土壤动物群落组成与桑园和农田存在显著差异,桑园与农田也存在显著差异.地埂植物篱的存在对于大型土壤动物多样性保护具有重要意义.     

Biological indicators of soil quality and soil organic matter characteristics in an agricultural management continuum

Relationships among biological indicators of soil quality and organic matter characteristics were evaluated across a continuum of long-term agricultural practices in Missouri, USA. In addition to chemical and physical soil quality indicators, dehydrogenase and phenol oxidase activity were measured, ¹³C nuclear magnetic resonance (¹³C NMR) and diffuse reflectance Fourier transform (DRIFT) spectra of soil organic matter were collected, and visible, near-infrared reflectance (VNIR) spectra of whole soil were collected. Enzyme activities were positively correlated with several soil quality indicators and labile fractions of soil organic matter (r = 0.58–0.92), and were negatively correlated with DRIFT indices of decomposition stage and recalcitrance (r = ?0.62 to ?0.76). A comparison of vegetative and land management practices was scored using the soil management assessment framework (SMAF)—a soil quality index. Perennial vegetation (i.e., native prairie, restored prairie, and timothy) plots exhibited the greatest soil quality (SMAF scores 93.6–98.6 out of 100), followed by no-till and conventionally cultivated plots, with wheat outranking corn. Among fertilization practices, soil quality followed the order: manure > inorganic fertilizer > unamended soil. Finally, in the estimation of soil properties, VNIR spectra generally outperformed DRIFT spectra using partial least squares regression (PLSR) and multiple, linear regression (MLR). The strongest estimates of dehydrogenase and phenol oxidase activity were found using MLR models of VNIR spectra (R² > 0.78, RPD > 2.20). Overall, this study demonstrates the potential utility and versatility of enzymes in modeling and assessing changes in soil organic carbon fractions and soil quality, and emphasizes the benefits of maintaining long-term agricultural experiments.     

Microbiome resilience of Amazonian forests: Agroforest divergence to bacteria and secondary forest succession convergence to fungi

An alarming and increasing deforestation rate threatens Amazon tropical ecosystems and subsequent degradation due to frequent fires. Agroforestry systems (AFS) may offer a sustainable alternative, reportedly mimicking the plant–soil interactions of the natural mature forest (MF). However, the role of microbial community in tropical AFS remains largely unknown. This knowledge is crucial for evaluating the sustainability of AFS and practices given the key role of microbes in the aboveground–belowground interactions. The current study, by comparing different AFS and successions of secondary and MFs, showed that AFS fostered distinct groups of bacterial community, diverging from the MFs, likely a result of management practices while secondary forests converged to the same soil microbiome found in the MF, by favoring the same groups of fungi. Model simulations reveal that AFS would require profound changes in aboveground biomass and in soil factors to reach the same microbiome found in MFs. In summary, AFS practices did not result in ecosystems mimicking natural forest plant–soil interactions but rather reshaped the ecosystem to a completely different relation between aboveground biomass, soil abiotic properties, and the soil microbiome.     

Suitability of Molluscs as Bioindicators for Meadow‐ and Flood‐Channels of the Elbe‐Floodplains

The goals of the subproject “molluscs” within the inter‐disciplinary research project “Indicator systems for the characterisation and prediction of ecological changes in floodplain systems” were: – develop further existing mollusc‐based indicator systems of site quality and to test their transferability, – characterise grassland sites within the recent floodplains of three study areas along the Elbe River, – analyse the relationships between indicator species‐/groups and abiotic parameters, – compile and use selected species traits in the analytical process. The results clearly show several characteristic species groups related to the hydrology of the sites (i.e. inundation and desiccation regime) and on to the degree of agricultural use. These dependencies can be interpreted by the simultaneous analysis of the species traits. “Models” are proposed, that are applicable to nature protection measures at the landscape scale. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The soil quality concept as a framework to assess management practices in vulnerable agroecosystems: A case study in Mediterranean vineyards

Land management aiming to sustain ecosystem services is an important issue, especially in biodiversity hot spots such as found in Mediterranean areas. In Mediterranean areas, viticulture is an important land use. Vineyards are frequently found on inherently poor soils and are submitted to intensive management practices, which threaten soil functioning and associated ecosystem services. To encourage winegrowers and stakeholders to be reflective and adapt their vineyard practices, we evaluated the effects of three soil management practices (inter row plant cover duration, weeding and fertilization strategies) on soil functioning in 146 commercial plots distributed in Southern France, by a complementary set of biological and physico-chemical indicators. We used the concept of soil dynamic quality to evaluate some soil management practices on soil functioning. The influence of inherent soil properties derived from pedogenesis on soil dynamic indicator response was accounted for by considering the response of soil indicators for three soil groups differing in their stoniness and Ca carbonate content. The three soil management practices systematically influenced some nematode-based indicators, whereas other indicators were ascribable to a specific soil type or practice. We demonstrated that the potential of soil management practices to enhance soil functioning is restricted by soil type. In particular for calcareous soils, the soil functioning is very stable limiting effects of soil management practices. The presence of a cover crop, even temporary, in the inter row, is the only practice which benefits soil functioning whatever the soil type whereas organic fertilization and chemical weeding exhibit contrasting results on soil functioning.     

Sustainability indicator development—Science or political negotiation?

The efforts to develop sustainability indicators have strongly increased since the beginning of the 1990s, often led by intergovernmental processes. More recently, a number of sustainability indicator development processes have been initiated within large research projects that aim to design tools for sustainability assessments, funded by the European Union. The development of sustainability indicators provides a particular challenge to scientists, given the essentially normative dimension of the concept of “sustainability”. Thus, we argue, the development of sustainability indicators is a process of both scientific “knowledge production” and of political “norm creation”, and both components need to be properly acknowledged. Based on a respective theoretical framework and comparing five cases of sustainability indicator development processes (three science-led and two led by intergovernmental processes), we find that the political norm creation dimension is not fully and explicitly recognized in science-led processes. The paper concludes by discussing a number of implications for the design of sustainability indicator development processes, in particular with regard to participation and representation as well as adjustment of indicators over time.     

戈壁生态系统蚁穴微生境对大型土壤动物多样性的影响

收获蚁蚁穴是戈壁生态系统中重要的微生境, 它通过汇集凋落物和改善土壤环境强烈影响动植物的分布及多样性。鉴于此, 本文选择戈壁荒漠收获蚁(Messor desertus)蚁穴为研究对象, 于2020年5月、6月和10月利用陷阱法调查了蚁穴及毗邻裸地大型土壤动物的种类组成及数量变化, 并分析其影响要素。结果表明: (1) 10月, 蚁穴和裸地间大型土壤动物群落组成存在显著差异, 而5月和6月二者间相差较小, 10月(62.9%)蚁穴和裸地大型土壤动物的平均相异性高于5月(34.8%)和6月(39.3%); (2) 5月, 蚁穴大型土壤动物均匀度指数显著低于裸地, 6月, 蚁穴大型土壤动物活动密度和类群丰富度均显著高于裸地, 10月, 蚁穴大型土壤动物类群丰富度和多样性指数均显著高于裸地; (3)荒漠收获蚁蚁穴显著提高了其他食性土壤动物的活动密度及类群丰富度, 还增强了捕食性和非捕食性土壤动物的相互作用关系并改变了荒漠收获蚁与蚁穴大型土壤动物类群的种间相互作用关系; (4) pRDA排序结果表明, 土壤电导率、全氮和粉粒含量是影响蚁穴和裸地大型土壤动物分布的主要土壤因子。总之, 戈壁生态系统荒漠收获蚁蚁穴微生境提高了大型土壤动物多样性, 改变了大型土壤动物类群间的营养和非营养关系, 这会影响大型土壤动物的营养结构及其功能。     

Comparisons of macrofaunal assemblages on restored and non-restored oyster reefs in mesohaline regions of Chesapeake Bay in Maryland

Maryland's recently created oyster restored reefs provide us with a unique opportunity to observe the abundance and species composition of macrofauna assemblages on unexploited reefs with high concentrations of mature oysters and undisturbed reef architecture. They might thus be used to better understand the magnitude of losses to reef dwelling macrofauna communities, and the associated loss of ecological functions resulting from reef destruction. We sampled reef macrofaunal assemblages on restored plots at four restored oyster reefs and adjacent non-restored plots located outside restored boundaries. We then compared the effects of study site location, and habitat quality (restored versus non-restored) on macrofaunal density using thirteen response variables. Density of macrofauna was an order of magnitude higher on restored reefs, epifaunal density was more than twice as high on restored reefs and sessile macrofaunal density was two orders of magnitude higher on restored reefs. Three out of the five dominant taxonomic groups were much more abundant on restored plots. Mean amphipod density was 20 times higher on restored plots and densities of xanthid crabs and demersal fish were both four times greater on restored plots. Two out of four functional feeding groups: suspension feeders and carnivore/omnivores, were more abundant on restored plots. Since reef macrofauna include many important fish prey species, oyster reef restoration may have the potential to augment fish production by increasing fish prey densities and fish foraging efficiency.     

Familiar soil conditions help Pinus ponderosa seedlings cope with warming and drying climate

Changes in temperature and moisture as a result of climate forcing can impact performance of planted trees. Tree performance may also be sensitive to new soil conditions, for example, brought about by seeds germinating in soils different from those colonized by ancestral populations. Such “edaphic constraint” may occur with natural migration or human‐assisted movement. Pinus ponderosa seedlings, sourced from one location (“home” site), were grown across a field environmental gradient in either their original home soil or in soils from two different “away” sites. Seedlings were inoculated with site‐specific soil organisms by germinating seeds in living soil. After 6 months, the inoculated seedlings were transplanted into sterilized soils from the home or away sites. This experimental design allowed us to uncouple the importance of abiotic and biotic soil properties and test (1) how biotic and abiotic soil properties interact with climate to influence plant growth and stress tolerance, and (2) the role of soil biota in facilitating growth in novel environments. Seedlings grew least in hotter and drier away sites with away soil biota. Home soil biota ameliorated negative impacts on growth of hotter and drier away sites. Measurements of photosynthetic rate, stomatal conductance, and chlorophyll florescence (Fv/Fm) suggest that edaphic constraint reduced growth by increasing tree water stress. Results suggest that success of Ponderosa pine plantings into warming environments will be enhanced by pre‐inoculation with native soil biota of the seed source.     

Vegetation and soil responses to livestock grazing in Central Asian grasslands: a review of Chinese literature

Grasslands in northern China and the Qinghai-Tibetan plateau are particularly important to both ecosystem functioning and pastoral livelihoods. Although there are numerous degradation studies on the effect of livestock grazing across the region, they are largely only published in Chinese, and most focus on single sites. Based on case studies from 100 sites, covering a mean annual precipitation gradient of 95–744 mm, we present a comprehensive, internationally accessible review on the impact of livestock grazing on vegetation and soils. We compared ungrazed or slightly grazed sites with moderately and heavily grazed sites by evaluating changes in two indicator groups: vegetation (plant species richness, vegetation cover, aboveground biomass, belowground biomass and root/shoot ratio) and soil (pH, bulk density, organic C, total N, total P and available P). Most indicators declined with intensified grazing, while soil pH, bulk density and belowground biomass increased. Available P showed no clear response. Variables within indicator groups were mostly linearly correlated at a given grazing intensity. Relative grazing effects on different indicators varied along specific abiotic gradients. Grazing responses of plant species richness, aboveground biomass, soil bulk density, total N and available P interacted with precipitation patterns, while grazing effects on belowground biomass were influenced by temperature. Elevation had impact on grazing responses of aboveground biomass and soil organic carbon. Complex grazing effects reflect both methodological inconsistency and ecological complexity. Further assessments should consider specific characteristics of different indicators in the context of the local environment.     

Assessment of soil microbial diversity measurements as indicators of soil functioning in organic and conventional horticulture systems

Soil quality assessment is necessary to detect changes on soil properties among different management practices. Some microbial properties could be useful to predict changes in soil providing an integrated and relevant vision of soil functioning. The aim of this work was to evaluate and compare different methods to assess microbial diversity, such as methyl ester fatty acids (PLFA) and catabolic response profiles (CRP) to act as indicators of soil functioning. The study was carried out in an intensive horticulture production system. Undisturbed soil, 5 years plots, and more than 20 years plots under organic and conventional production were studied. Principal component analysis followed by multivariate discriminate analysis showed that d-glucose, d-glucosamine, α-ketobutyric, α-ketoglutaric and uric acids were the substrates with the highest sensitivity to separate situations. The same analysis was performed for PLFA, showing that C18:1w9, C13:0, C16:1w9, C14:0, i15:0 and cy19:0 methyl ester fatty acids were the most sensitive. Multivariate analysis of variance of selected substrates and fatty acids showed that CRP and PLFA techniques were both capable to characterize the studied systems. Saturated/monounsaturated (S/M), iso/anteiso (i/a) and cyclopropyl/precursors (cy/pre) microbial stress indicators were higher in plots under conventional management, presenting also these situations the lowest microbial biomass and fungi/bacteria ratio (F/B), especially in plots under conventional management for more than 20 years. Microbial functional diversity, calculated as evenness (E) from CRP was capable to distinguish between all situations and management systems showing the potential of this measurement to act as an integrative indicator of soil functioning.     

Soil macrofauna as indicators of soil quality and land use impacts in smallholder agroecosystems of western Nicaragua

The tropical dry forest region along the western slope of Central America represents a biodiverse and fragile area that is under increasing pressure from agricultural production, thus threatening the provision of ecosystem services, the integrity of these landscapes, and the rural communities who depend on them. To address this issue, we evaluated the influence of common agricultural management practices (cropping and livestock systems) vs. the Quesungual slash-and-mulch agroforestry system (QSMAS) on diverse parameters of soil quality and function. We then used this information to identify soil invertebrate bioindicators that represent key aspects of soil quality (chemical fertility, physical properties, aggregate morphology, and biological functioning). In February of 2011 soil sampling was conducted on six hillside farms near the town of Somotillo in western Nicaragua to assess soil properties and the abundance and diversity of soil macrofauna within four management systems: (1) QSMAS, based on maize production, (2) traditional maize cropping system with few trees (TC), (3) silvopastoral system with low tree density (SP), and (4) secondary forest (SF), used as a reference. The conversion of forest to agriculture demonstrated the greatest impact of management in this study. For example, SF presented significantly higher diversity of soil invertebrate taxonomic groups than either TC or SP (P < 0.03), and demonstrated the lowest level of soil compaction, significantly less than SP (P < 0.05). Additionally, SF demonstrated the highest value of soil quality according to a synthetic indicator that integrates chemical, physical and biological aspects of soil quality. Although overall soil quality under QSMAS was lower than SF, this system demonstrated the highest abundance (number of individuals) of soil macrofauna, and appeared to at least partially mitigate the negative consequences of forest conversion on soil functioning. Using the Indicator Value Index, which ranks species according to their specificity and fidelity across sites, along with farmer consultation we found seven indicator taxa of soil quality that could greatly facilitate future evaluation of land management impacts by farmers and technicians in the region. We suggest that the methodology applied is robust and adaptable to diverse agroecological contexts and would allow for more rapid responses to evolving land use issues as they arise.