What do ecologists miss by not digging deep enough? Insights and methodological guidelines for assessing soil fertility status in ecological studies

Soil fertility is one of the major drivers of ecological processes and is therefore frequently investigated in ecological research. Although often referred to in studies, soil fertility is not well quantified. Consequently some studies have resorted to classifying site soil fertility according to the potential fertility associated with underlying geology, ignoring the soil nutrient status of the rootzone. A common protocol is for ecologists to sample the upper soil layers only (<20 cm). Unfortunately these surface layers are those most likely to be altered by the vegetation itself and may not necessarily reflect the influence of the geological substrate. Using examples, we attempt to provide some practical guidelines on how to determine the intrinsic nutrient status of soils. Soil data from five sites in southern African savannas were used to demonstrate: a) when deeper soil sampling may not be needed, b) how to determine which nutrients may be limiting at a site, c) the importance of bulk density measurements and d) the effect of three different sampling methods. Our data illustrate that the effects of fine scale landscape variability on soil nutrients were evident to variable soil depths. Frequent fires affected soils only to depths of <5 cm, the presence of tree canopies affected soils up to 50 cm, while topographic position affected soil nutrients to a depth of 90 cm. Bulk density did not differ between depths nor between treatments within sites, but differed amongst sites. None of the alternative methods used to collect soil samples (i.e. augering vs. digging soil pits and sampling by depth or horizon) resulted in significant differences in nutrient measures. Standardised sampling from at least three depths together with bulk density measurements allow for calculation of nutrient stocks as a measure of intrinsic soil nutrient status, while also providing insights into nutrient distributions with depth, thereby allowing meaningful cross-site comparisons.     

A Striking Profile: Soil Ecological Knowledge in Restoration Management and Science

Available evidence suggests that research in terrestrial restoration ecology has been dominated by the engineering and botanical sciences. Because restoration science is a relatively young discipline in ecology, the theoretical framework for this discipline is under development and new theoretical offerings appear regularly in the literature. In reviewing this literature, we observed an absence of in‐depth discussion of how soils, and in particular the ecology of soils, can be integrated into the developing theory of restoration science. These observations prompted us to assess the current role of soil ecological knowledge in restoration research and restoration practice. Although soils are universally regarded as critical to restoration success, and much research has included manipulations of soil variables, we found that better integration of soil ecological principles could still contribute much to the practice of ecosystem restoration. Here we offer four potential points of departure for increased dialog between restoration ecologists and soil ecologists. We hope to encourage the view that soil is a complex, heterogeneous, and vital entity and that adoption of this point of view can positively affect restoration efforts worldwide.     

Ecological theory meets soil ecotoxicology: Challenge and chance

The degradation of soils due to various anthropogenic stress factors is alarming. Although chemicals are a major reason for soil degradation, most ecologists are not interested in studying such effects. We try to wake their interest by addressing a number of unsolved soil ecotoxicological problems that are related to disturbance ecology, biodiversity, ecosystem functioning and modelling. Features distinguishing chemical from natural stress render promising new aspects in disturbance ecology. Ecotoxicological studies are ideal models of disturbance, particularly regarding frequency, intensity or multitude of stress. Patterns of secondary succession after a major chemical damage can directly be related to the intermediate disturbance hypothesis. More knowledge on altered life history patterns following stress could support both evolutionary ecology and risk assessment. We raise the question if inherent resource competition makes communities more vulnerable to stress. Three aspects of ecotoxicological risk assessment are introduced: (1) exposure and bioavailability, which is directly connected to environmental heterogeneity; (2) tests on ecosystem functioning, suffering from major drawbacks; and (3) modelling. Here, promising approaches exist but need substantial input for being applicable to soils. Ecological modelling should put more emphasis on simulating both natural and chemical disturbances, including behavioural aspects and environmental variability. Finally, research needs for ecological risk assessment in soils are derived such as a simple system to assess the impact of chemicals on soil biodiversity, the inclusion of behavioural changes of keystone species or the consideration of density-dependent effects. Common research efforts of basic ecologists and soil ecotoxicologists could render a lot of mutual benefits.     

Selecting biological indicators for monitoring soils: A framework for balancing scientific and technical opinion to assist policy development

Soils are one of the most important features of the natural capital of terrestrial ecosystems. There is a strong and increasing policy requirement for effective monitoring of soils at local, regional and national-scales. However, it remains unclear which properties of soils are most appropriately monitored. This is partly due to the wide range of goods and services that soils provide, but also their inherent chemical, physical and biological complexity. Given that the biota plays such fundamental roles in the majority of ecosystem services provided by soils, biological properties are logical candidates as effective indicators, to complement soil physico-chemical properties. A plethora of biological methods have been suggested as indicators for monitoring soils but few are used in national-scale monitoring or are published as international standards. A framework for selecting ecologically relevant biological indicators of soil quality, for national-scale soil monitoring, that cover the range of functions and services of soil was devised. The literature was surveyed to identify 183 candidate biological indicators which were then scored by experts and stakeholders against a wide range of scientific and technical criteria. The framework used the scores and weightings to then rank, prioritise and select the indicators. This semi-objective approach using a “logical sieve” allowed repeated iterations to take account of end-user requirements and expert opinion. A ranked list of 21 indicators was produced that covered a range of genotypic-, phenotypic- and functional-based indicators for different trophic groups. Four of these were not deemed sufficiently robust for ready deployment in a national-scale monitoring scheme without further methodological development. The suite of indicators identified offers the strongest potential candidates for deployment in national-scale soil monitoring schemes. However, standard operating procedures, their inherent sensitivity, ability to discriminate between soil:land use combinations, ecological interpretation all need to be confirmed. The power of the approach adopted here is that it provides a clear record and audit trail on the decision-making process, enables different priorities to be set contingent on the nature of the desired monitoring, and can direct and allow the inclusion of further methods or indicators into the framework.     

非饱和土壤水力参数的模型及确定方法

土壤水力参数的选取和确定是土壤中水分运动和污染物迁移预测的基础,本文在国内外研究成果的基础上,综述了土壤水力参数的模型(土壤水分特征曲线模型、土壤导水率模型)及其直接测定法和间接推求法,并比较了土壤水力参数的模型及确定方法的适用性与局限性,以便为生态环境建设和农业可持续发展研究中土壤水力参数的选取提供依据。     

Ecological amplitude in Silene nutans in relation to allozyme variation at the western margin of its distribution

Abstract. At the western border of its geographical range, Silene nutans (Caryophyllaceae) has evolved two groups of parapatric populations showing distinct allozyme patterns and apparently occurring on different bedrock types. This study tests the hypothesis that these groups represent edaphic ecotypes. With this in view, the ecological amplitude of 36 populations of Silene nutans from Belgium was investigated and their synecology specified using vegetation composition and soil parameters; Ellenberg indicator values were used for ecological interpretation of the vegetation analyses. The results provide evidence that allozyme and habitat variations are correlated, the two groups occurring on contrasting soil with distinct vegetation types. One group is restricted to alkaline soils and typically occurs in open calcareous grasslands, fringes and scrub. The other group is characterized by wider autecological and synecological ranges with a bimodal pH- distribution, occurring on two kinds of siliceous soils: (1) neutral soils, supporting vegetation with a high species richness comprising many mesophilous species, and (2) CaCO₃ -free bedrocks characterized by acidophilous, species-poor, open dry grasslands and woodlands. It also appears that factors not related to soil chemistry, such as microclimate, are involved in the ecological specialization of the two ecotypes. It is argued that these ecotypes exemplify adaptive radiation and parapatric speciation at the margin of a species distribution area.     

Silicate weathering in temperate forest soils: insights from a field experiment

Few studies of silicate mineral weathering have been conducted in carbonate-bearing temperate forest soils. With climate and vegetation held constant, we compared soil mineralogy and major element chemistry of soil waters from a carbonate-free temperate aspen forest site in the Cheboygan watershed, northern Michigan, with that from carbonate-containing soils from experimental tree-growth chambers (low- vs. high- fertility). All soils were well-drained sands (quartz, Na-rich plagioclase, and K-feldspar) with minor amounts of carbonate present only in the experimentally manipulated soils. The Na⁺ concentrations in soil waters corrected for atmospheric deposition (Na*) were used to compare relative rates of plagioclase feldspar weathering across sites. In natural soil water profiles, maximum concentrations of Na*, Si, and dissolved organic carbon (DOC) were observed by a depth of 15 cm, a soil zone free of carbonate minerals. Mean Na* and DOC concentrations were different in the three soils, and increased in the order natural soil < low-fertility chambers < high-fertility chambers. While low pH environments are generally viewed as enhancing weathering rates, here higher Na* appears to be related to high DOC, which is consistent with observed increases in active organic functional groups as pH increases. Our results suggest that under a specific vegetative cover, the soil carbon environment affects the weathering flux observed. Our study also suggests that disturbed soils provide an enhanced physical and chemical environment for weathering. Generalized silicate weathering models may benefit from including the enhancing effects of organic anions at moderate pH in addition to precipitation and temperature.     

土壤中水溶性有机质及其对重金属化学与生物行为的影响

土壤水溶性有机质是陆地生态系统和水生生态系统中一种重要的、很活跃的化学组分,已成为环境科学、土壤学和生态学等学科的研究热点．土壤DOM对重金属化学与生物行为有重要影响。但其机理尚不清楚．文中从土壤性质、环境条件、人为因素等方面阐述了土壤DOM产生及影响因素,总结评述了DOM对重金属化学行为和生物有效性的影响,将DOM对重金属的影响机制归纳为络合机制、竞争吸附机制、酸碱缓冲机制．在此基础上,提出了DOM研究存在的问题及其展望．     

Conducting robust ecological analyses with climate data

Although the number of studies discerning the impact of climate change on ecological systems continues to increase, there has been relatively little sharing of the lessons learnt when accumulating this evidence. At a recent workshop entitled ‘Using climate data in ecological research’ held at the UK Met Office, ecologists and climate scientists came together to discuss the robust analysis of climate data in ecology. The discussions identified three common pitfalls encountered by ecologists: 1) selection of inappropriate spatial resolutions for analysis; 2) improper use of publically available data or code; and 3) insufficient representation of the uncertainties behind the adopted approach. Here, we discuss how these pitfalls can be avoided, before suggesting ways that both ecology and climate science can move forward. Our main recommendation is that ecologists and climate scientists collaborate more closely, on grant proposals and scientific publications, and informally through online media and workshops. More sharing of data and code (e.g. via online repositories), lessons and guidance would help to reconcile differing approaches to the robust handling of data. We call on ecologists to think critically about which aspects of the climate are relevant to their study system, and to acknowledge and actively explore uncertainty in all types of climate data. And we call on climate scientists to make simple estimates of uncertainty available to the wider research community. Through steps such as these, we will improve our ability to robustly attribute observed ecological changes to climate or other factors, while providing the sort of influential, comprehensive analyses that efforts to mitigate and adapt to climate change so urgently require.     

Soil organic carbon budget and fertility variation of black soils in Northeast China

Black soils in Northeast China are characteristic of high soil organic carbon (SOC) density and were strongly influenced by human activities. Therefore, any change in SOC pool of these soils would not only impact the regional and global carbon cycle, but also affect the release and immobilization of nutrients. In this study, we reviewed the research progress on SOC storage, budget, variation, and fertility under different scenarios. The results showed that the organic carbon storage of black soils was 646.2 TgC and the most potential sequestration was 2887.8 g m⁻². According to the SOC budget, the net carbon emission of black soils was 1.3 TgC year⁻¹ under present soil management system. The simulation of CENTURY model showed that future climate change and elevated CO₂ concentration, especially the increase of precipitation, would increase SOC content. Furthermore, fertilization and cropping sequence obviously influenced SOC content, composition, and allocation among different soil particles. Long-term input of organic materials such as manure and straw renewed original SOC, improved soil structure and increased SOC accumulation. Besides, soil erosion preferred to transport soil particles with low density and fine size, decreased recalcitrant SOC fractions at erosion sites and increased activities of soil microorganism at deposition sites. After natural grasslands were converted into croplands, obvious variation of soil chemical nutrients, physical structure, and microbial activities had taken place in surface and subsurface soils, and represented a degrading trend to a certain degree. Our studies suggested that adopting optimal management such as conservation tillage in black soil region is an important approach to sequester atmospheric CO₂ and to slow greenhouse effects.     

土壤中抗性基因的产生,扩散传播以及消减的研究进展

近年来,土壤中残留的大量抗生素不可避免的导致耐药微生物和抗性基因的增加和扩散,引起一系列土壤污染和生态风险。作为一类新兴污染物,抗性基因的污染水平已经远远超出我们的预想,因此对土壤中抗性基因的分布水平、扩散传播及消减技术的研究刻不容缓。本文对国内外土壤中抗生素和抗性基因残留水平进行了总结分析,探讨了土壤中抗性基因的产生、扩散的内在动力和机制。同时,分析了土壤中抗性基因分布和扩散的影响因素,如:抗生素残留水平,土壤理化性质和环境条件等。在此基础上,探讨了土壤抗性基因阻隔和消减技术,包括传统降解方法:高温,光照催化、微波-H2O2-微生物联合处理技术等,并提出新型消解技术:取代活性基团、靶位修饰以及改变外排泵的通透性等。讨论未来在控制抗性基因生态风险,降低其在土壤中的丰度,有效阻截技术的发展趋势。     

Relationships between soil parameters and vegetation in abandoned terrace fields vs. non-terraced fields in arid lands (Lanzarote,Spain): An opportunity for restoration

Over 90% of terraced fields have been abandoned on the island of Lanzarote in the last 40 years. The present work analyses the effects of abandonment on the soil and vegetation recovery of terraced field agroecosystems by comparing them with adjacent non-terraced fields in Lanzarote, Canary Islands (Spain). This information is necessary to take the appropriate management actions to achieve goals such as soil protection and biodiversity conservation. Results indicate that terraced fields display better soil quality than non-terraced ones, as shown by the significant differences found in parameters such as SAR, exchangeable Na, CaCO₃, B content, moisture content or soil depth. Moreover, the terraced fields' plant community has more species similarities with the native plant community when compared with non-terraced areas. Owing to characteristics such as deeper soils, more water capacity, lower salinity and less sodic soils, terraced soils provide better conditions for passive restoration of both soil and vegetation. Therefore, the recovery and maintenance of wall structures and revegetation with native/endemic species are proposed to promote the restoration of native systems and preserve a landscape with cultural and aesthetic value.     

恢复及演替过程中的土壤生态学考虑

 人类社会的日益扩张,导致人类加速占据地球表面景观,并胁迫地球上生态系统提供不断增长的资源需求和废物吸收能力。所以保护尚未“开放”的自然生态系统及恢复退化的生态系统成为人类长期生存的重要保证。该文着重讨论了恢复过程中的土壤生态学问题。土壤是所有陆地生态系统的结构与功能基础。土壤微生物与动物的种群变化,土壤有机质的积累,及主要元素地球化学循环的改变是恢复生态的重要环节。生态恢复与演替有许多共性,所以演替理论对于认识生态系统恢复中的结构与功能变化有着很大帮助。与自然演替不同的是,人的积极参与在生态恢复中占有中心位置。从最初样地的确立与物种的选择,到后续的灌溉与施肥管理,人的选择影响着土壤的演化,生态系统的发展方向,和最终恢复生态的结果。为保障恢复生态系统的可持续性,短期的工作目标,如提供养分促进植物生长,务必与长期的工作目标,如土壤的恢复相结合。植物与土壤的相互反馈是生态恢复成功的重要标志。成功的生态恢复不仅是对现有生态学理论的“试金检验”,也是推动生态学学科发展的重要原动力。     

Des ressources végétales endémiques pour optimiser durablement les opérations de réhabilitation du couvert forestier en milieu méditerranéen et tropical : exemple des plantes facilitatrices vectrices de propagation des champignons mycorhiziens

The overexploitation of natural resources, resulting in an increased need for arable lands by local populations, causes a serious dysfunction in the soil's biological functioning (mineral deficiency, salt stress, etc.). This dysfunction, worsened by the climatic conditions (drought), requires the implementation of ecological engineering strategies allowing the rehabilitation of degraded areas through the restoration of essential ecological services. The first symptoms of weathering processes of soil quality in tropical and Mediterranean environments result in an alteration of the plant cover structure with, in particular, the pauperization of plant species diversity and abundance. This degradation is accompanied by a weakening of soils and an increase of the impact of erosion on the surface layer resulting in reduced fertility of soils in terms of their physicochemical characteristics as well as their biological ones (e.g., soil microbes). Among the microbial components particularly sensitive to erosion, symbiotic microorganisms (rhizobia, Frankia, mycorrhizal fungi) are known to be key components in the main terrestrial biogeochemical cycles (C, N and P). Many studies have shown the importance of the management of these symbiotic microorganisms in rehabilitation and revegetation strategies of degraded environments, but also in improving the productivity of agrosystems. In particular, the selection of symbionts and their inoculation into the soil were strongly encouraged in recent decades. These inoculants were selected not only for their impact on the plant, but also for their ability to persist in the soil at the expense of the residual native microflora. The performance of this technique was thus evaluated on the plant cover, but its impact on soil microbial characteristics was totally ignored. The role of microbial diversity on productivity and stability (resistance, resilience, etc.) of eco- and agrosystems has been identified relatively recently and has led to a questioning of the conceptual bases of controlled inoculation in sustainable land management. It has been suggested that the environmental characteristics of the area to rehabilitate should be taken into account, and more particularly its degradation level in relation to the threshold of ecological resilience. This consideration should lead to the optimization of the cultural practices to either (i) restore the original properties of an ecosystem in case of slightly degraded environments or (ii) transform an ecosystem in case of highly degraded soils (e.g., mine soils). In this chapter, we discuss, through various examples of experiments conducted in tropical and Mediterranean areas, the performance of different strategies to manage the microbial potential in soils (inoculation of exotic vs. native species, inoculation or controlled management potential microbial stratum via aboveground vegetation, etc.) based on the level of environmental degradation.     

The big ecological questions inhibiting effective environmental management in Australia

The need to improve environmental management in Australia is urgent because human health, well‐being and social stability all depend ultimately on maintenance of life‐supporting ecological processes. Ecological science can inform this effort, but when issues are socially and economically complex the inclination is to wait for science to provide answers before acting. Increasingly, managers and policy‐makers will be called on to use the present state of scientific knowledge to supply reasonable inferences for action based on imperfect knowledge. Hence, one challenge is to use existing ecological knowledge more effectively; a second is to tackle the critical unanswered ecological questions. This paper identifies areas of environmental management that are profoundly hindered by an inability of science to answer basic questions, in contrast to those areas where knowledge is not the major barrier to policy development and management. Of the 22 big questions identified herein, more than half are directly related to climate change. Several of the questions concern our limited understanding of the dynamics of marine systems. There is enough information already available to develop effective policy and management to address several significant ecological issues. We urge ecologists to make better use of existing knowledge in dialogue with policy‐makers and land managers. Because the challenges are enormous, ecologists will increasingly be engaging a wide range of other disciplines to help identify pathways towards a sustainable future.     

Accumulating evidence in ecology: Once is not enough

Many published studies in ecological science are viewed as stand‐alone investigations that purport to provide new insights into how ecological systems behave based on single analyses. But it is rare for results of single studies to provide definitive results, as evidenced in current discussions of the “reproducibility crisis” in science. The key step in science is the comparison of hypothesis‐based predictions with observations, where the predictions are typically generated by hypothesis‐specific models. Repeating this step allows us to gain confidence in the predictive ability of a model, and its corresponding hypothesis, and thus to accumulate evidence and eventually knowledge. This accumulation may occur via an ad hoc approach, via meta‐analyses, or via a more systematic approach based on the anticipated evolution of an information state. We argue the merits of this latter approach, provide an example, and discuss implications for designing sequences of studies focused on a particular question. We conclude by discussing current data collection programs that are preadapted to use this approach and argue that expanded use would increase the rate of learning in ecology, as well as our confidence in what is learned.     

C:N:P stoichiometry in soil: is there a “Redfield ratio” for the microbial biomass?

Well-constrained carbon:nitrogen:phosphorus (C:N:P) ratios in planktonic biomass, and their importance in advancing our understanding of biological processes and nutrient cycling in marine ecosystems, has motivated ecologists to search for similar patterns in terrestrial ecosystems. Recent analyses indicate the existence of “Redfield-like” ratios in plants, and such data may provide insight into the nature of nutrient limitation in terrestrial ecosystems. We searched for analogous patterns in the soil and the soil microbial biomass by conducting a review of the literature. Although soil is characterized by high biological diversity, structural complexity and spatial heterogeneity, we found remarkably consistent C:N:P ratios in both total soil pools and the soil microbial biomass. Our analysis indicates that, similar to marine phytoplankton, element concentrations of individual phylogenetic groups within the soil microbial community may vary, but on average, atomic C:N:P ratios in both the soil (186:13:1) and the soil microbial biomass (60:7:1) are well-constrained at the global scale. We did see significant variation in soil and microbial element ratios between vegetation types (i.e., forest versus grassland), but in most cases, the similarities in soil and microbial element ratios among sites and across large scales were more apparent than the differences. Consistent microbial biomass element ratios, combined with data linking specific patterns of microbial element stoichiometry with direct evidence of microbial nutrient limitation, suggest that measuring the proportions of C, N and P in the microbial biomass may represent another useful tool for assessing nutrient limitation of ecosystem processes in terrestrial ecosystems.     

Talking Frogs: The Role of Communication in Ecological Research on Private Land

This paper argues that improving the communication between landholders and ecologists will result in better conservation outcomes for ecosystem management on private land. It examines a case study of ecological research on frogs undertaken on private, agricultural land in south-eastern Australia. The paper questions the traditional separation of ecological science from landholders specifically and the public in general. In addressing this issue the authors wish to improve the relevance of ecology for landholders, raise the profile of social science for ecologists working on private land and examine the implications of improving ecologist – landholder relationships. For landholders, an improved understanding of the ecological context of their agricultural activities may lead to sustainability gains. For ecologists, a deeper appreciation for the social context of their ecological research provides an opportunity to see how their work is perceived and/or acted upon in practice. For both parties, a communicative relationship may minimise future need for ecosystem repair. Such an approach (for both landholders and ecologists) can lead to the break down of stereotypes and/or a greater appreciation of the others’ perspectives, constraints and values with respect to conservation on private land. In the productive discussions arising from conversations between landholders and ecologists, new approaches to sustainable land management and nature conservation may emerge.     

Palaeolimnological insights for biodiversity science: an emerging field

1. Decreases in biodiversity are so widespread that they are now considered a form of global change in their own right. Given the grave nature of this issue, rapid advances in understanding are needed to mitigate further impacts. In this Opinion paper, we argue that palaeolimnological studies have important contributions to make to biodiversity science. 2. Given that long‐term community data are sparse in their geographic coverage and tend to span no more than 5 years, greater insight into biodiversity dynamics can be obtained from palaeoecological analyses. One such approach is palaeolimnology, which is a field that can provide long‐term data on changes in both physico‐chemical and biological components of lake ecosystems. 3. To date, a handful of quantitative palaeolimnological studies have addressed biodiversity questions, focussing primarily on defining the drivers of change in species richness or identifying functional traits that best capture ecosystem processes. Several studies have also quantified the role of spatial variables in determining assemblage structure, a necessary first step in addressing how metacommunity interactions influence biodiversity–ecosystem processes. Overall, these early studies show that palaeolimnological approaches can address both similar and novel questions compared with contemporary ecological studies. However, palaeolimnology allows for a great expansion of the temporal scale of investigation, the quantification of rates of change to stressors and the possibility of conducting experiments by applying resurrection techniques. 4. As an emerging field, there are numerous exciting applications of palaeolimnology to biodiversity science. It is an opportune time to create synergy between contemporary aquatic ecologists and palaeolimnologists.     

Assessment of Heavy Metals Contamination in Agricultural Soil of Southwestern Nile Delta,Egypt

The spatial and vertical distributions of heavy metals were quantitatively determined for organic-rich agricultural soils in the Southwestern Nile Delta. This study aims to undertake an assessment of heavy metals contamination in the soils of Quessna district using the inductively coupled plasma-optical emission spectroscopy, remote sensing, and geographic information system techniques. In this study, 24 soil samples were collected at 12 sites representing the main suburbs in the Quessna district. The concentrations of the studied metals decreased in the order of Zn > Cr > Pb > Cu > Ni > Co. The contamination degree and ecological risk assessment for metals in soil samples were evaluated using the enrichment factor, geoaccumulation index, improved Nemerow's pollution index, Pollution load index, and potential ecological risk index. The spatial and vertical distribution of heavy metals concentrations were affected by soil properties such as clay and organic matter content and scavenger metals (Fe and Mn). The intensive urbanization, industrial activity, and agricultural practices are thought to be the main anthropogenic sources of heavy metals contamination. Further studies especially human health risk assessment are recommended to investigate possible risks for humans from heavy metals in this area.