Summary 1.Peatland soils are estimated to store a third of all terrestrial carbon stocks and are very sensitive to climate change. In these systems, one group of soil mesofauna, enchytraeid worms (Annelida, Oligochaeta), represent up to 70% of total soil fauna biomass and previous studies have highlighted their potential use as 'biological indicators' for functionally important changes in the C cycle. 2. To examine the link between temperature, enchytraeids and carbon fluxes we performed a microcosm experiment in which we assessed the influence of temperature on enchytraeid populations and soil CO 2 and DOC release from a Galician peatland soil over 90 days. Additionally, to unravel the potential underlying mechanisms responsible for DOC production, we also tested the effects of increasing temperatures and enchytraeid activities on the presence of organic chelating metals (iron and aluminium) and hydrogen ions (i.e. acidity) in the soil solution. 3. Enchytraeid population numbers and biomass increased over time at both temperature treatments (14 and 19 ° C), with the greatest increase produced at the highest temperature (to over five and seven times higher initial values, respectively, by day 88). Results also showed that, under warmer conditions, enchytraeid activities increased both CO 2 fluxes and DOC release by twofold ( Q 10 values of 3·9 and 3·6, respectively). 4. The combined effect of temperature and enchytraeids promoted the breakdown of organic substances and consequently, more DOC and iron were leached. An important decline in H + release was observed when enchytraeids were present and possibly eliminating one of the critical mechanisms restricting DOC release. These leachate pH values were also responsible for aluminium immobilisation and hence for its insignificant role in the export of DOC from the peat soil. 5. We conclude that temperature change alone does not explain all the observed increases in soil respiration and DOC production but rather soil invertebrate responses to warming are crucial in controlling C fluxes in peatland soils. This is the result of temperature induced changes of enchytraeid populations and activities which have the potential of speeding up the decomposition of organic matter and altering soil aeration, metal mobilization and acidity of the soil solution, with important implications for the global carbon cycle. 6. There is an urgent need for incorporating the response of soil biology in climate change modelling to make better predictions of future changes in terrestrial carbon pools.

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Prescribed burning is a tool that is frequently used for various land management objectives, mainly related to reduction of hazardous forest fuels, habitat management and ecological restoration. Given the crucial role of soil in forest ecosystem processes and functions, assessing the effects of prescribed burning on soil is particularly relevant. This study reviews research on the impacts of repeated prescribed burning on the physical, chemical and biological properties of soil. The available information shows that the effects are highly variable, rather inconsistent and generally minor for most of the soil characteristics studied, while a number of soil properties show contrasting responses. On the other hand, ecosystem characteristics, differences in fire severity, frequency of application and the cumulative effect of treatment repetition over time, have possibly made it more difficult to find a more common response in soil attributes. Our study has also revealed some limitations of previous research that may have contributed to this result, including a limited number of long-term studies, conducted at a few experimental sites, and in a limited number of forest ecosystems. Research issues concerning the effects of prescribed fire on soil are presented. The need to integrate such research into a broader interdisciplinary framework, encompassing the role of the fire regime on ecosystem functions and processes, is also highlighted.

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1. Peatlands are important carbon (C) stores as a result of acidity, waterlogging conditions and low temperatures slowing decomposition rates. However, climate change is predicted to bring not only changes in abiotic conditions but also the replacement of peat-forming vegetation, such as Sphagnum mosses, with vascular plants. In these systems, enchytraeid worms represent the dominant mesofaunal group, and previous climate change manipulations have shown that their abundances and vertical distribution are strongly influenced by temperature and moisture gradients, with important implications for C cycling. Therefore, determining their behavioural responses to changes in both abiotic and biotic factors is crucial to quantify their contribution to decomposition processes.2. We investigated the importance of vertical edaphic gradients (soil moisture and labile C) on enchytraeids total numbers, vertical distribution and feeding activities by inverting intact soil cores and hence, reversing both substrate quality but leaving the microclimatic gradients intact. This manipulative experiment was set up in two different peatland areas, one dominated by heather (Erica mackaiana) and another by mosses (Sphagnum sp.) to determine the influence of different plant functional growth forms on these responses.3. Our results showed that most enchytraeid species were 'stayers' (i.e. in the 'Upturned cores', they remained in the same layer where they are 'Normally' located), and hence, their vertical distribution was more dependent on substrate quality than a change in microclimate. This response was more evident under drier conditions (i.e. the highest locations of the height gradient at the heather site) than at the wettest locations (i.e. the bottom of the slope and under mosses) due to more pronounced vertical gradients in substrate quality. Furthermore, radiocarbon measurements on enchytraeid tissues showed that to avoid competition among the growing populations for the limited labile resources present in the top layers, enchytraeids selected older C sources. 4. These findings indicate that future climate change scenarios will not only bring important changes in the abiotic conditions (temperature and moisture) and biotic properties of peatlands (both vegetation composition and below-ground soil biota | Additional supporting information may be found online in the Supporting Information section. How to cite this article: Briones MJI, Carrera N, Huang J, Barreal ME, Schmelz RM, Garnett MH. Substrate quality and not dominant plant community determines the vertical distribution and C assimilation of enchytraeids in peatlands.