Soil invertebrates control peatland C fluxes in response to warming

Abstract

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.

Vegetation exerts a greater control on litter decomposition than climate warming in peatlands

“…We also found that enchytraeids, which are the most dominant fauna in terms of biomass and function in peatland systems (Briones et al 2007), increased weakly in response to shrub removal. Given the importance of enchytraeids in promoting DOC and DON production, and accelerating rates of C and N mineralization (Briones et al 1998, Cole et al 2002, Carrera et al 2009), their positive response to shrub removal is likely to have contributed to the observed increases in litter decomposition. Taken together, our results point to a cascade of effects of shrub removal on the soil system that promote rates of litter decomposition (Bragazza et al 2013), illustrating the importance of live plant effects on decomposition through soil processes.…”

“…Such understanding is particularly important for peatlands because of their vulnerability to changes in climate and vegetation, and because of the vast stocks of organic carbon that they contain, estimated to equate to half of the total atmospheric carbon as CO 2 (Gorham 1991, Dise 2009). Although previous studies in peatland have shown that warming generally increases rates of decomposition (Bragazza et al 2009, Carrera et al 2009, Dorrepaal et al 2009), and that litter from different plant species decomposes at different rates (Dorrepaal et al 2007, Ward et al 2010, we have little understanding of how live vegetation affects decomposition in these carbonrich ecosystems.…”

The implications of climate change for positive contributions of invertebrates to world agriculture.

“…Harte et al (1996) showed that experimental heating of 551 field plots in a subalpine meadow in Colorado reduced biomass of soil mesofauna and 552 macrofauna in dry zones but enhanced biomass in moist zones. Soil invertebrate responses to 553 warming are crucial in controlling carbon fluxes in peat soils (Carrera et al, 2009) and have 554 the potential to speed up the decomposition of organic matter with important implications for 555 the global carbon cycle. Expected increases in temperature will also favour humivorous 556 (humus-feeding) termites and endogeic earthworm species that feed in the soil (Lavelle et al, 557 1997).…”

A Survey of Roadside Soil Arthropod Communities from Three Elevations in Mauritius

“…An increase in plant diversity can lower the soil temperature by 3˚C [15]. Biones et al [16] and Carrera et al [17] state that temperature reduction by vegetation has positive impact on soil fauna through stress reduction and higher feeding rates [18]. The high abundance of the Nitidulidae and Formicidae during the hotter months (January, February and March) at Flic en Flac (public beach) was probably a result of increased human activity such as camping and picnics which gave rise to more litter at the site.…”