Soil life under stress

In this thesis I studied how long-term soil contamination affects microbial populations and processes, ecosystem properties and functional stability. I also investigated which parameters are suitable as indicators of soil quality in long-term contaminated soils. I found that contamination had a negative impact on many examined microbial parameters, e.g. biomasses, respiration and growth rate (Chapter 2). Some parameters like protozoan biomass and metabolic quotient did not show any effect of stress probably due to strong variation. No single parameter indicated effects of both stressors. Thus, a set of indicators is needed to assess the condition of contaminated soils. In chapter 3 I tested information indices as a tool to describe ecological succession in belowground ecosystems. I used data from a primary succession on the island of Schiermonnikoog. I found that the indices that describe both size and organization of ecosystem followed trends predicted by the theory, but at the same time they were strongly correlated with total system biomass. Therefore I could not say whether the observed trends reflect succession or simply the build up of biomass. However, analysis of relative indices that are independent of biomass and describe only the organization of the ecosystem, showed that succession occurred only in soils between 0 and 10 years old. Since other authors clearly have shown that there has been succession in these soils in, I conclude that the relative information indices are not sensitive indicators of succession. In contaminated soils, however, relative information indices were sensitive to stress caused by high concentrations of copper and by low pH (chapter 4). Stress affected the organization of belowground ecosystems as predicted by the theory. Stressed soils were more vulnerable to external perturbations and less efficient in processing energy than unstressed soils. As the relative information indices responded to stress in predictable manner and each of them revealed effects of both stresses I concluded that these indices are useful indicators of environmental stress. In contrary the absolute indices responded in unpredicted manner to stress and therefore are not suitable as indicators of stress. In chapters 5 and 6, I used ¿stress on stress¿ experiments to test the functional stability of soil respiration and bacterial growth rate to additional stress or disturbance in experimentally contaminated soils. The results described in Chapter 5 seemed to confirm the hypothesis that microbial processes in not-stressed soils are more stable to additional stress. The microbial processes showed different responses to disturbances (Chapter 6) than to stress (Chapter 5). In some cases stressed soils appeared to be more stable to additional disturbance than not-stressed soils, in other cases the opposite was found. In chapter 7, I tested the functional stability in a real field situation with zinc and cadmium pollution. In this experiment processes responded differently than in the former experiments. Probably the response of a process depends on whether a co-tolerance towards a given (subsequent) stress was developed during exposure to the first stress

Soil life under stress

In this thesis I studied how long-term soil contamination affects microbial populations and processes, ecosystem properties and functional stability. I also investigated which parameters are suitable as indicators of soil quality in long-term contaminated soils. I found that contamination had a negative impact on many examined microbial parameters, e.g. biomasses, respiration and growth rate (Chapter 2). Some parameters like protozoan biomass and metabolic quotient did not show any effect of stress probably due to strong variation. No single parameter indicated effects of both stressors. Thus, a set of indicators is needed to assess the condition of contaminated soils. In chapter 3 I tested information indices as a tool to describe ecological succession in belowground ecosystems. I used data from a primary succession on the island of Schiermonnikoog. I found that the indices that describe both size and organization of ecosystem followed trends predicted by the theory, but at the same time they were strongly correlated with total system biomass. Therefore I could not say whether the observed trends reflect succession or simply the build up of biomass. However, analysis of relative indices that are independent of biomass and describe only the organization of the ecosystem, showed that succession occurred only in soils between 0 and 10 years old. Since other authors clearly have shown that there has been succession in these soils in, I conclude that the relative information indices are not sensitive indicators of succession. In contaminated soils, however, relative information indices were sensitive to stress caused by high concentrations of copper and by low pH (chapter 4). Stress affected the organization of belowground ecosystems as predicted by the theory. Stressed soils were more vulnerable to external perturbations and less efficient in processing energy than unstressed soils. As the relative information indices responded to stress in predictable manner and each of them revealed effects of both stresses I concluded that these indices are useful indicators of environmental stress. In contrary the absolute indices responded in unpredicted manner to stress and therefore are not suitable as indicators of stress. In chapters 5 and 6, I used ¿stress on stress¿ experiments to test the functional stability of soil respiration and bacterial growth rate to additional stress or disturbance in experimentally contaminated soils. The results described in Chapter 5 seemed to confirm the hypothesis that microbial processes in not-stressed soils are more stable to additional stress. The microbial processes showed different responses to disturbances (Chapter 6) than to stress (Chapter 5). In some cases stressed soils appeared to be more stable to additional disturbance than not-stressed soils, in other cases the opposite was found. In chapter 7, I tested the functional stability in a real field situation with zinc and cadmium pollution. In this experiment processes responded differently than in the former experiments. Probably the response of a process depends on whether a co-tolerance towards a given (subsequent) stress was developed during exposure to the first stress

Information indices as a tool for quantifying development of below-ground terrestrial ecosystems

Information indices from ecosystem network analysis (ENA) describe the size and organization of an ecosystem and are claimed to quantify ecosystem development [Ulanowicz, R.E., 1986, Growth and Development, Springler-Verslag, New York, 203 pp.]. To date, these indices were not used to describe a gradient of ecosystem development for a field situation. Here we used information indices to quantify soil succession with soils of different age on the island Schiermonnikoog, The Netherlands. We evaluated whether information indices describe ecosystem development as predicted by ENA. For the Island of Schiermonnikoog the biomasses of soil organisms and roots were measured on four stages of succession (0, 10, 25 and 100 years old soils). Organisms were grouped based on their feeding characteristics. With these data consumption, respiration, excretion, external input and output flows to, from and between groups were calculated. These flows, in turn, were used to calculate the information indices. Relative information indices describe the organization of an ecosystem; i.e. level of organisation (specialization of flows), diversity and evenness of flows, and disorganisation. Absolute indices describe both size (in terms of energy flow) and organisation of the system. System size is used to scale the absolute indices and will be analysed separately as well. We found that the absolute indices increased when succession processed, as predicted by theory. This pattern could have been due to the build-up of biomass, which apparently did not level off. Because the succession gradient deals mostly with young soils (0, 10 and 25 years old) and only one older field (100 years old), the gradient should include more soils of around 100 years old and older to exclude this possibility. Relative indices, on the other hand, increased initially, but then levelled off. We think that this was due to the strong aggregation of functional groups, especially at lower trophic levels, because information in some functional groups showed (expected) trends. Our results suggest that the absolute indices are able to describe ecological succession of terrestrial below-ground ecosystems. The relative indices, in contrast, appeared to be insensitive to subtle succesional change

Functional stability of microbial communities from long-term stressed soils to additional disturbance

Functional stability, measured in terms of resistance and resilience of soil respiration rate and bacterial growth rate, was studied in soils from field plots that have been exposed to copper contamination and low pH for more than two decades. We tested whether functional stability follows patterns predicted by either the "low stress-high stability" or the "high stress-high stability" theory. Treatments consisting of soils with no or high copper load (0 or 750 kg/ha) and with low or neutral pH (4.0 or 6.1) were used. Stability was examined by applying an additional disturbance by heat (50 degrees C for 18 h) or drying-rewetting cycles. After heating, the respiration rate indicated that the soils without copper were less stable (more affected) than the soils with 750 kg/ha. Bacterial growth rate was more stable (resistant) to heat in the pH 6.1 than in the pH 4.0 soils. Growth rate was stimulated rather than inhibited by heating and was highly resilient in all soils. The respiration rate was less affected by drying-rewetting cycles in the pH 4.0 soils than in the pH 6.1 soils. Bacterial growth rate after drying-rewetting disturbance showed no distinct pattern of stability. We found that the stability of a particular process could vary significantly, depending on the kind of disturbance; therefore, neither of the two theories could adequately predict the response of the microbial community to disturbance

Functional stability of microbial communities from long-term stressed soils to additional disturbance

Functional stability, measured in terms of resistance and resilience of soil respiration rate and bacterial growth rate, was studied in soils from field plots that have been exposed to copper contamination and low pH for more than two decades. We tested whether functional stability follows patterns predicted by either the "low stress-high stability" or the "high stress-high stability" theory. Treatments consisting of soils with no or high copper load (0 or 750 kg/ha) and with low or neutral pH (4.0 or 6.1) were used. Stability was examined by applying an additional disturbance by heat (50 degrees C for 18 h) or drying-rewetting cycles. After heating, the respiration rate indicated that the soils without copper were less stable (more affected) than the soils with 750 kg/ha. Bacterial growth rate was more stable (resistant) to heat in the pH 6.1 than in the pH 4.0 soils. Growth rate was stimulated rather than inhibited by heating and was highly resilient in all soils. The respiration rate was less affected by drying-rewetting cycles in the pH 4.0 soils than in the pH 6.1 soils. Bacterial growth rate after drying-rewetting disturbance showed no distinct pattern of stability. We found that the stability of a particular process could vary significantly, depending on the kind of disturbance; therefore, neither of the two theories could adequately predict the response of the microbial community to disturbance

Functional stability of microbial communities in contaminated soils near a zinc smelter (Budel, the Netherlands)

Environmental pollution causes adverse effects on many levels of ecosystem organization; it might affect the use efficiency of available resources which will make the system more sensitive to subsequent stress. Alternatively the development of community tolerance may make the system more resistant to additional stresses. In this study we investigate the functional stability, measured in the terms of resistance and resilience, of microbial populations inhabiting contaminated soils near a zinc smelter. With functional stability we mean that we look at processes rather than at population dynamics. We measure changes in respiration and bacterial growth rate in response to addition of stress (lead, salt) or disturbance (heat). We used soils that differ in the level of pollution with zinc and cadmium originating from an adjacent smelter. Our results showed, with regard to respiration, that the most polluted soils have the lowest stability to salt (stress) and heat (disturbance). This confirms the hypothesis that more stressed systems have less energy to cope with additional stress or disturbance. However, bacterial growth rates were affected in a different way than respiration. There was no difference between the soils in resistance and resilience to addition of lead. In case of salt treatment, the least polluted soils showed highest stability. In contrast, the least polluted soils were the least stable to increased temperature, which supports the hypothesis that more stressed soils are more stable to additional stress/disturbance due to properties they gained when exposed to the first stress (pollution by the smelter). Thus, the responses of microbial processes to stress, their nature and size, depend on the kinds of stress factors, especially whether a subsequent stress is similar to the first stress, in terms of the mechanism with which the organisms deal with the stress

Functional stability of microbial communities in contaminated soils

Functional stability, measured in terms of resistance and resilience of respiration and growth rate of bacteria and fungi, was studied in soils that have been exposed to copper and low pH for more than twenty years. We used treatments, consisting of soil with no or high copper load (0 or 750 kg ha(-1)) and low or neutral pH (4.0 or 6.1). Stability was examined by applying an additional stress in the form of lead or salt. After addition of lead, respiration (decomposition of freshly added lucerne meal) showed lower resistance at low than at neutral pH and at high copper than at low copper. The most acid and contaminated soil was the least resistant. Respiration showed no resilience after addition of lead. Bacterial growth rate (thymidine incorporation) also showed resistance at low pH but only in soils that were not contaminated with copper. After addition of salt, respiration showed no differences in resistance but the soils without copper contamination showed higher resilience. Bacterial growth rate showed lower resistance at low pH than at neutral pH, the latter in which the growth rate increased by on average 123%. This increase at high pH was faster in soil without copper than in soil with copper contamination in which the growth rate initially decreased and then increased. The effects of secondary stress depended on the nature of the stress (lead or salt) and on the parameter measured (respiration or bacterial growth rate). In general the highest resistance and/or resilience were found in the least contaminated soils with neutral pH and/or no copper contamination. Thus, the microbial communities in the cleaner soils showed the highest functional stability. The results seem to confirm the notion that environmental stress alters ecosystems such that supplementary stress will have stronger impacts than in an unstressed system. The results may also confirm the insurance-hypothesis that reduced biodiversity due to the first stress negatively affected community stability. As an alternative, we discuss the observed effects in terms of altered energy budget

Evaluation of information indices as indicators of environmental stress in terrestrial soils

Information indices from Ecosystem Network Analysis (ENA) can be used to quantify the development of an ecosystem in terms of its size and organization. There are two types of indices, i.e. absolute indices that describe both the size and organization of ecosystem (Total System Throughput (TST)¿system size, Ascendancy (A)¿size of organized flows and Development Capacity (C)¿upper limit for A, Overhead (L)¿size of unorganized flows) and relative indices that describe only the organization (Average Mutual Information (AMI = A:TST), Flow Diversity (H = C:TST), Relative Overhead (RL = L:TST)). It is theorized that environmental stress impair the ecosystem development and that the effect of stress can be quantified with the ENA information indices. Here we applied ENA on a case of environmental stress in a terrestrial ecosystem, i.e. soils that have endured long-term exposure to elevated copper concentration and altered pH. The absolute indices showed an unexpected pattern of response to pollution, suggesting that ecosystems in polluted soils are more active and better organized than these in unpolluted soils. The relative indices, alternatively, responded to pollution as predicted by theory, i.e. with decrease of stress (pollution level) the level of specialization increased (increase of AMI) and losses of energy, e.g. due to respiration, decreased (decrease of Overhead). The diversity and evenness of flows showed hump-backed relationship with stress. Less polluted soils appeared to be less vulnerable to external disturbances and more efficient in processing energy (higher Relative Ascendancy (RA = A:C)) than polluted soils. The relative information indices were rigid to changes in values of assumed parameters. The relative indices, opposite to absolute indices, appeared to be useful as indicators of environmental stress on the ecosystem level

A European perspective on alternatives to animal testing for environmental hazard identification and risk assessment

Tests with vertebrates are an integral part of environmental hazard identification and risk assessment of chemicals, plant protection products, pharmaceuticals, biocides, feed additives and effluents. These tests raise ethical and economic concerns and are considered as inappropriate for assessing all of the substances and effluents that require regulatory testing. Hence, there is a strong demand for replacement, reduction and refinement strategies and methods. However, until now alternative approaches have only rarely been used in regulatory settings. This review provides an overview on current regulations of chemicals and the requirements for animal tests in environmental hazard and risk assessment. It aims to highlight the potential areas for alternative approaches in environmental hazard identification and risk assessment. Perspectives and limitations of alternative approaches to animal tests using vertebrates in environmental toxicology, i.e. mainly fish and amphibians, are discussed. Free access to existing (proprietary) animal test data, availability of validated alternative methods and a practical implementation of conceptual approaches such as the Adverse Outcome Pathways and Integrated Testing Strategies were identified as major requirements towards the successful development and implementation of alternative approaches. Although this article focusses on European regulations, its considerations and conclusions are of global relevanc