Thomas Bolger

Functional traits as indicators of biodiversity response to land use changes across ecosystems and organisms.

Rigorous and widely applicable indicators of biodiversity are needed to monitor the responses of ecosystems to global change and design effective conservation schemes. Among the potential indicators of biodiversity, those based on the functional traits of species and communities are interesting because they can be generalized to similar habitats and can be assessed by relatively rapid field assessment across eco-regions. Functional traits, however, have as yet been rarely considered in current common monitoring schemes. Moreover, standardized procedures of trait measurement and analyses have almost exclusively been developed for plants but different approaches have been used for different groups of organisms. Here we review approaches using functional traits as biodiversity indicators focussing not on plants as usual but particularly on animal groups that are commonly considered in different biodiversity monitoring schemes (benthic invertebrates, collembolans, above ground insects and birds). Further, we introduce a new framework based on functional traits indices and illustrate it using case studies where the traits of these organisms can help monitoring the response of biodiversity to different land use change drivers. We propose and test standard procedures to integrate different components of functional traits into biodiversity monitoring schemes across trophic levels and disciplines. We suggest that the development of indicators using functional traits could complement, rather than replace, the existent biodiversity monitoring. In this way, the comparison of the effect of land use changes on biodiversity is facilitated and is expected to positively influence conservation management practices.

Temperature, wetting cycles and soil texture effects on carbon and nitrogen dynamics in stabilized earthworm casts.

Abstract Two soils, one a silty loam soil (Kilkea) and the other a clayey soil (Leitrim), and stabilized earthworm cast derived from both soils, were subjected to two wet-drying regimes (4 d and 16 d wetting intervals) at two temperatures (10°C and 20°C). Each treatment was sampled regularly for CO2 emissions and dissolved organic carbon, ammonium and nitrate were measured in leachate. Production of CO2 from the clayey soil was 20–40% less than from the silty loam at both temperatures and under both cycles, while production was 40% less at the lower temperature. Amounts of dissolved organic carbon (DOC) in leachate from the silty loam soil were greater than from the clayey soil, while, in general, greater amounts of DOC leached from uningested soil than from earthworm cast. Treatments with the silty loam soil lost approximately 30–40 times more total N than corresponding clayey soils under the 4 d cycle, and 12–16 times more under the 16 d cycle, thus illustrating the extent of nutrient protection in clay soils, but also the reduction of this effect with super-saturation and prolonged drying (16 d cycle). Nutrient losses suggest greater protection of nutrients in cast at first, followed by a reduction in protection (weakening of aggregate structure) in later cycles. These results have important implications for nutrient losses in the field, since significant and complex interactions were evident between the experimental factors. To improve our understanding of soil organic matter (SOM) dynamics, interactions between climatic, soil and cast-mediated changes (i.e. increased organic–inorganic interaction and burial) need to be incorporated into future models of soil decomposition.

Decomposition of 13C-labelled plant material in a European 65–40° latitudinal transect of coniferous forest soils: simulation of climate change by translocation of soils

Standard 13 C-labelled plant material was exposed over 2‐3 yr at 8 sites in a north‐south climatic gradient of coniferous forest soils, developed on acid and calcareous parent materials in Western Europe. In addition to soils exposed in their sites of origin, replicate units containing labelled material were translocated in a cascade sequence southwards along the transect, to simulate the eAects of climate warming on decomposition processes. The current Atlantic climate represented the most favourable soil temperature and moisture conditions for decomposition. Northward this climatic zone, where the soil processes are essentially temperature-limited, the prediction for a temperature increase of 38C estimated a probable increase of C mineralisation by 20‐ 25% for the boreal zone and 10% for the cool temperate zone. Southward the cool Atlantic climate zone, (the Mediterranean climate), where the processes are seasonally moisture-limited, the predicted increase of temperature by 1‐28C little aAected the soil organic matter dynamics, because of the higher water deficit. A significant decrease of C mineralisation rates was observed only in the superficial layers recognised in Mediterranean forest soils as ‘xeromoder’ and subject to frequent dry conditions. In the deeper Mediterranean soil organic horizons (the mull humus types), representing the major C storage in this zone, C mineralisation was not aAected by a simulated 28C temperature increase. The temperature eAect is probably counteracted by a higher water deficit. 7 2000 Elsevier Science Ltd. All rights reserved.

Growth, reproduction and litter and soil consumption by Lumbricus terrestris L. in reclaimed peat

Abstract Ninety-one percent of Salix aquatica cv. gigantea litter disappeared within 6 months from experimental cages containing Lumbricus terrestris L. in reclaimed peat, compared with only 28% when L. terrestris was absent. Litter consumption rate was 6–9 mg dry wt g −1 fresh wt day −1 in the field and 10–15 mg g −1 fresh wt day −1 in the laboratory at 15°C. Maximum growth rate in the field was 4mg fresh wt g − day − and 4.55 mg in the laboratory. Cocoon production in the field was 1.3worm −1 month −1 and 2.1 in the laboratory. Mean gut contents were 48-23 mg dry wt g −1 fresh wt over the size range 1–6 g fresh wt and gut transit time was 10h. It was estimated that a Lumbricus biomass of 100gm −2 could consume 1.34 kg soil m −2 yr −1 .

Trophic level modulates carabid beetle responses to habitat and landscape structure : a pan-European study

1. Anthropogenic pressures have produced heterogeneous landscapes expected to influence diversity differently across trophic levels and spatial scales.

Interactions between atmospheric CO2 enrichment and soil fauna.

We have reviewed the responses of soil fauna to increased concentrations of atmospheric CO2 and the consequent climate change. These will affect several attributes of animal populations and communities including their density, biomass, diversity, activity, rates of consumption, life history parameters and migration ability. Changes in the quality and quantity of litter and global warming are the main factors which are expected to modify soil fauna. Although changes have been observed in several attributes of the soil fauna as a consequence of increased concentrations of atmospheric CO2, no general trend which might allow to the prediction of a general pattern of response has been identified. Because of the complexity of the biological mechanisms and the synergetic action of several factors, the few resulting responses reported in the literature are inconclusive. However, some aspects of the situation deserve more attention. These include the consequences of (1) changes in the food resources for soil fauna in the litter layer and in the rhizosphere, (2) the consumption of low quality litter by the macrofauna, (3) the change in life span in response to temperature elevation, (4) the enhancement of earthworm burrowing activity and (5) the changes in community composition arising because of specific differential resistance to adverse conditions.

An improved model to predict the effects of changing biodiversity levels on ecosystem function

Summary 1. The development of models of the relationship between biodiversity and ecosystem function (BEF) has advanced rapidly over the last 20 years, incorporating insights gained through extensive experimental work. We propose Generalised Diversity-Interactions models that include many of the features of existing models and have several novel features. Generalised Diversity-Interactions models characterise the contribution of two species to ecosystem function as being proportional to the product of their relative abundances raised to the power of a coefficient h. 2. A value of h < 1 corresponds to a stronger than expected contribution of species’ pairs to ecosystem functioning, particularly at low relative abundance of species. 3. Varying the value of h has profound consequences for community-level properties of BEF relationships, including: (i) saturation properties of the BEF relationship; (ii) the stability of ecosystem function across communities; (iii) the likelihood of transgressive overyielding. 4. For low values of h, loss of species can have a much greater impact on ecosystem functioning than loss of community evenness. 5. Generalised Diversity-Interactions models serve to unify the modelling of BEF relationships as they include several other current models as special cases. 6. Generalised Diversity-Interactions models were applied to seven data sets and three functions: total biomass (five grassland experiments), community respiration (one bacterial experiment) and nitrate leaching (one earthworm experiment). They described all the nonrandom structure in the data in six experiments, and most of it in the seventh experiment and so fit as well or better than competing BEF models for these data. They were significantly better than Diversity-Interactions models in five experiments. 7. Synthesis. We show that Generalized Diversity-Interactions models quantitatively integrate several methods that separately address effects of species richness, evenness and composition on ecosystem function. They describe empirical data at least as well as alternative models and improve the ability to quantitatively test among several theoretical and practical hypotheses about the effects of

Soil microarthropod contribution to forest ecosystem processes: the importance of observational scale

Investigations of the role of microarthropods (Acari and Collembola) in organic matter decomposition and nutrient cycling have shown that they may contribute to primary productivity in nutrient poor conditions. The potential of microarthropods to affect other ecosystem properties, such as above ground plant diversity or succession, lags somewhat. In this contribution we demonstrate: (1) that the effect on the mobilization of nutrients promoted by microarthropods must be measured at the microhabitat scale appropriate to the scale of the faunal activity, and (2) that small changes in the structure of microarthropod assemblages can have significant effects on the local mobilization of nutrients. In the first of two experiments we measured the nutrients leaching from field mesocosms containing litter and mineral soil, with and without fauna. After eight months, the C:N ratios of the litter differed significantly indicating that the fauna were effective in altering the decomposition rate. However, the patterns of release over time and the concentration of the measured nutrients differed little between the two sets of mesocosms. In a second experiment microarthropod assemblages, which differed only slightly, were introduced into laboratory microcosms and the nutrient fluxes were measured over a ten week period. Significant differences were detected in the concentration of nitrogen, K and Mg leached and in CO2 evolved. We suggest that when the potential influence of microarthropods on ecosystem properties is being assessed, specific knowledge of the relevant details of interactions at the smallest scale must be considered. These details can be incorporated or dismissed when interactions on the next level of the ecological hierarchy are examined. Using such analysis we suggest that the creation of soil nutrient hot-spots by microarthropods may have implications for maintaining plant species of lowered competitive ability in a given system.

Decomposition of Quercus petraea litter : influence of burial, comminution and earthworms

Abstract Litter bags containing one of the following: earthworm cast, intact oak litter (Quercus petraea Matt., Liebl.) plus soil and shredded oak litter ( Earthworm casts (surface and buried) had reduced moisture fluctuations relative to non-cast (intact or shredded) treatments. Casts maintained higher levels of organic matter and carbon than non-cast treatments (surface or buried) after 2 years of decomposition. However, while both surface and buried casts maintained higher levels of organic matter, bacterial counts in buried cast remained higher than all other treatments (including surface cast) on five of the seven final sampling dates. Shredding and burial of organic matter did not affect total, cumulative loss of organic matter/carbon from the non-cast treatments. Potential mineralization rates (loss of CO2 at 20°C) from non-cast treatments was influenced by their placement. When temperature and/or moisture became limiting surface non-cast treatments showed reduced losses of CO2 by comparison with buried non-cast treatments. The reverse occurs when the moisture and temperature are not limiting, i.e. surface treatments have greater losses of CO2 than the buried treatments. Thus, both the micro-climatic and soil aggregate effects (and their interactions) were observed to influence the decay dynamics and are discussed in relation to nutrient stabilization/mobilization and microbial populations.

Effects of air pollutant-temperature interactions on mineral-N dynamics and cation leaching in reciplicate forest soil transplantation experiments

Increased emissions of nitrogen compounds have led to atmosphericdeposition to forest soils exceeding critical loads of N overlarge parts of Europe. To determine whether the chemistry offorest soils responds to changes in throughfall chemistry, intactsoil columns were reciprocally transplanted between sites, withdifferent physical conditions, across a gradient of N and Sdeposition in Europe.The transfer of a single soil to the various sites affected itsnet nitrification. This was not simply due to the nitrificationof different levels of N deposition but was explained bydifferences in physical climates which influenced mineralizationrates. Variation in the amount of net nitrification between soiltypes at a specific site were explained largely by soil pH.Within a site all soil types showed similar trends in netnitrification over time. Seasonal changes in net nitrificationcorresponds to oscillations in temperature but variable time lagshad to be introduced to explain the relationships. WithArrhenius‘ law it was possible to approximate gross nitrificationas a function of temperature. Gross nitrification equalled netnitrification after adaptation of the microbial community oftransplanted soils to the new conditions. Time lags, andunderestimates of gross nitrification in autumn, were assumed tobe the result of increased NH4+ availability due either tochanges in the relative rates of gross and net N transformationsor to altered soil fauna-microbial interactions combined withimproved moisture conditions.Losses of NO3- were associated with Ca2+and Mg2+ in non-acidified soil types and with losses ofAl3+ in the acidified soils. For single soils the ionequilibrium equation of Gaines-Thomas provided a useful approximationof Al3+ concentrations in the soil solution as a functionof the concentration of Ca2+. The between site deviationsfrom this predicted equilibrium, which existed for single soils, couldbe explained by differences in throughfall chemistry which affectedthe total ionic strength of the soil solution.The approach of reciprocally transferring soil columnshighlighted the importance of throughfall chemistry, interactingwith the effect of changes in physical climate on forest soilacidification through internal proton production, in determiningsoil solution chemistry. A framework outlining the etiology offorest die-back induced by nitrogen saturation is proposed.