Alexei V. Uvarov

Respiration activity of Dendrobaena octaedra (Lumbricidae) under constant and diurnally fluctuating temperature regimes in laboratory microcosms

Abstract Adult Dendrobaena octaedra were kept individually in microcosms with leaf litter/sand substrate under constant (15 °C) or fluctuating (10–20 °C or 5–25 °C) diurnal temperature regimes and an optimum moisture content. After 10, 34, 61, 92, 109 or 126 days, the rate of worms CO 2 production was measured at the corresponding acclimation temperatures. A clear pattern of ‘day/night’ change in CO 2 production rate ( V ) was obtained under T 10–20 and T 5–25 regimes. Under T 15 , no evidence of diurnal respiration cycle was observed. The average V values of acclimated animals at 5, 10, 15, 20 and 25 °C were 32.3, 50.3, 73.5, 105.0 and 148.5 mm 3 ·g −1 ·h −1 , respectively. The relationship between V and temperature ( T , °C) in the 5–25 °C interval is close to a straight line on the semi-logarithmic scale and it can be expressed as log 10 V = 1.3610.0337 T . Compared with the T 15 regime, the effect of temperature fluctuations on the average daily respiration rate [( V day V night)/2 ] was hardly pronounced at T 10–20 while being significantly stimulatory at T 5–25 Two trends in the metabolic reactions to the change in constant temperature regimes can be suggested for earthworms: i) a compensatory reaction within the optimal temperature range; and ii) a decrease or lack of compensation in less favourable conditions. The V/T relationships in fluctuating regimes can be markedly different from those observed in constant conditions. This should be regarded as ecological interpretations. The relationship between CO 2 production and body weight in D. octaedra depended on the temperature regime. The display of this effect coincided with the temperature zone optimal for reproduction in the population studied: it was significant at 15 and 20 °C and close to the surface principle reaction ( b = 0.71). A trade-off effect was observed in the distribution of individual resources between respiration, reproduction and survival of D. octaedra in relation to the type of temperature regime.

Effects of diurnal temperature fluctuations on population responses of forest floor mites

Summary Population responses of a forest floor saprotrophic mite, Nothrus silvestris (Oribatei), were studied in litter microcosms for 14 weeks under three temperature regimes. The regimes reflected a range of diurnal fluctuations ( T 10–20 and T 5–25 - daily fluctuations from 10 to 20 °C and 5 to 25 °C, respectively) around a mean of 15 °C (constant regime, T 15 ). The T 5–25 regime was unfavourable, leading to the highest mortality and the lowest reproduction rates in the mite parental population. Moderate fluctuations ( T 10–20 regime) caused the lowest mortality and the highest offspring production and therefore, the highest population growth in N. silvestris . Population responses were intermediate under the T 15 regime. Thus, a trade-off between reproduction and adult mite survival that is regulated by temperature regime seems to exist in N. silvestris . Similar trends of population responses to temperature regime were observed in another litter mite, Schwiebea sp. (Acaroidea), which was also collected from the microcosms.

Soil fauna: key to new carbon models

Soil organic matter (SOM) is key to maintaining soil fertility, mitigating climate change, combatting land degradation, and conserving above- and below-ground biodiversity and associated soil processes and ecosystem services. In order to derive management options for maintaining these essential services provided by soils, policy makers depend on robust, predictive models identifying key drivers of SOM dynamics. Existing SOM models and suggested guidelines for future SOM modelling are defined mostly in terms of plant residue quality and input and microbial decomposition, overlooking the significant regulation provided by soil fauna. The fauna controls almost any aspect of organic matter turnover, foremost by regulating the activity and functional composition of soil microorganisms and their physical-chemical connectivity with soil organic matter. We demonstrate a very strong impact of soil animals on carbon turnover, increasing or decreasing it by several dozen percent, sometimes even turning C sinks into C sources or vice versa. This is demonstrated not only for earthworms and other larger invertebrates but also for smaller fauna such as Collembola. We suggest that inclusion of soil animal activities (plant residue consumption and bioturbation altering the formation, depth, hydraulic properties and physical heterogeneity of soils) can fundamentally affect the predictive outcome of SOM models. Understanding direct and indirect impacts of soil fauna on nutrient availability, carbon sequestration, greenhouse gas emissions and plant growth is key to the understanding of SOM dynamics in the context of global carbon cycling models. We argue that explicit consideration of soil fauna is essential to make realistic modelling predictions on SOM dynamics and to detect expected non-linear responses of SOM dynamics to global change. We present a decision framework, to be further developed through the activities of KEYSOM, a European COST Action, for when mechanistic SOM models include soil fauna. The research activities of KEYSOM, such as field experiments and literature reviews, together with dialogue between empiricists and modellers, will inform how this is to be done.

A microcosmic approach to compare effects of constant and varying temperature conditions on soil structure/soil biota interrelationships

Abstract A microcosm laboratory experiment was performed, modelling patterns of soil structure/biota interrelationships in a simple litter/sand ecosystem. The microcosms were populated by 3 different kinds of litter saprotrophic communities (microbiota; microbiota + Nothrus silvestris mites; microbiota + Dendrobaena octaedra worms) and kept at constant (15°C) and varying (10–20°C and 5–25°C) diurnal temperature regimes. After 4 months, organic matter loss due to respiration was similar in all treatments. However, the part of litter organic matter translocated by earthworms into a newly-formed “soil” horizon tended to correlate positively with a decrease in the range of temperature fluctuations. Earthworms were highly sensitive to the type of temperature regime, their mortality and cocoon production being maximal at constant temperature.

Spatial Distribution and Species Co-Occurrence in Soil Invertebrate and Plant Communities on Northern Taiga Islands

Geographical gradients of patterns of species associations in ecological communities are largely unknown. Previous evidence indicated nested community assembly — caused mainly by unequal colonization probabilities and habitat capacity — and a tendency towards negative species associations in arid and tropical plant and animal communities. Patterns of community assembly in arctic environments are poorly studied. Here we use a data set on arctic plant and animal species obtained from arctic islands of the Kandalaksha Bay (White Sea), to infer patterns of species association across taxa and trophic groups. We performed co-occurrence and nestedness analyses to study patterns of community assembly and diversity of 1109 plant and animal species grouped according to taxa, dispersal ability, and ecological guild membership. Twelve out of 50 (24%) sufficiently species-rich families and orders on the environmentally relatively stable forested islands showed significantly negative species associations (segregation), while this proportion decreased to less than 13% on less stable heath, rocky, and sea-shore islands. Segregation was not linked to spatial species turnover across islands. Species richness of plants and animals decreased at higher levels of disturbance. We detected evidence for a gradient in species richness and ecological interactions from the most disturbed sea-shore and rocky islands to more stable forested islands. Species spatial distributions appeared to be largely random, in contrast to previous meta-analyses that used mainly communities at lower latitudes. We speculate that in arctic environments spatial turnover of species (vicariant segregation) is of less importance than turnover-independent (checkerboard) segregation. Our data support the view that ecological assemblages in high-latitude environments are less structured by ecological interactions than comparable assemblages in lower latitudes. We also add to the evidence that environmental disturbance regimes work against stable community structures. We notice the need for a formal meta-analysis on latitudinal trends in community structure.

Do alterations in mesofauna community affect earthworms

Abstract Interactions between the saprotrophic animal groups that strongly control soil microbial activities and the functioning of detrital food webs, such as earthworms and mesofauna, are not well understood. Earthworm trophic and engineering activities strongly affect mesofauna abundance and diversity through various direct and indirect pathways. In contrast, mesofauna effects on earthworm populations are less evident; however, their importance may be high, considering the keystone significance of earthworms for the functioning of the soil system. We studied effects of a diverse mesofauna community of a deciduous forest on two earthworm species representing epigeic (Lumbricus rubellus) and endogeic (Aporrectodea caliginosa) ecological groups. In microcosms, the density of total mesofauna or its separate groups (enchytraeids, collembolans, gamasid mites) was manipulated (increased) and responses of earthworms and soil systems were recorded. A rise in mesofauna density resulted in a decrease of biomass and an increased mortality in L. rubellus, presumably due to competition with mesofauna for litter resources. In contrast, similar mesofauna manipulations promoted reproduction of A. caliginosa, suggesting a facilitated exploitation of litter resources due to increased mesofauna activities. Changes of microcosm respiration rates, litter organic matter content and microbial activities across the manipulation treatments indicate that mesofauna modify responses of soil systems in the presence of earthworms. However, similar mesofauna manipulations could induce different responses in soil systems with either epigeic or endogeic lumbricids, which suggests that earthworm/mesofauna interactions are species-specific. Thus, mesofauna impacts should be treated as a factor affecting the engineering activities of epigeic and endogeic earthworms in the soil.