Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.

Within-species and among-species differences in growth responses to a changing climate have been well documented, yet the relative magnitude of within-species vs. among-species variation has remained largely unexplored. This missing comparison impedes our ability to make general predictions of biodiversity change and to project future species distributions using models. We present a direct comparison of among- versus within-species variation in response to three of the main stresses anticipated with climate change: drought, warming, and frost. Two earlier experiments had experimentally induced (i) summer drought and (ii) spring frost for four common European grass species and their ecotypes from across Europe. To supplement existing data, a third experiment was carried out, to compare variation among species from different functional groups to within-species variation. Here, we simulated (iii) winter warming plus frost for four grasses, two nonleguminous, and two leguminous forbs, in addition to eleven European ecotypes of the widespread grass Arrhenatherum elatius. For each experiment, we measured: (i) C/N ratio and biomass, (ii) chlorophyll content and biomass, and (iii) plant greenness, root (15) N uptake, and live and dead tissue mass. Using coefficients of variation (CVs) for each experiment and response parameter, a total of 156 within- vs. among-species comparisons were conducted, comparing within-species variation in each of four species with among-species variation for each seed origin (five countries). Of the six significant differences, within-species CVs were higher than among-species CVs in four cases. Partitioning of variance within each treatment in two of the three experiments showed that within-species variability (ecotypes) could explain an additional 9% of response variation after accounting for the among-species variation. Our observation that within-species variation was generally as high as among-species variation emphasizes the importance of including both within- and among-species variability in ecological theory (e.g., the insurance hypothesis) and for practical applications (e.g., biodiversity conservation).

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Climate change affects all seasons, but warming is more pronounced in winter than summer at mid- and high latitudes. Winter warming can have profound ecological effects, which are rarely compared to the effects of summer warming, and causal explanations are not well established. We compared mild aboveground infrared warming in winter to warming in summer in a semi-natural, cool-temperate grassland in Germany for four years. Aboveground plant biomass increased following winter warming (+18%) and was unaffected by summer warming. Winter warming affected the composition of the plant community more than summer warming, favoring productive species. Winter warming increased soil respiration more than summer warming. Prolonged growing seasons and changes in plant-community composition accounted for the increased aboveground biomass production. Winter warming stimulated ecological processes, despite causing frost damage to plant roots and microorganisms during an extremely cold period when warming reduced the thermal insulation provided by snow. Future warming beyond such intermittent frosts may therefore further increase the accelerating effects of winter warming on ecological processes.

Malyshev, A., and Quijón, P. A. 2011. Disruption of essential habitat by a coastal invader: new evidence of the effects of green crabs on eelgrass beds. – ICES Journal of Marine Science, 68: 1852–1856. Eelgrass (Zostera marina) beds have been declining in Atlantic Canada and elsewhere, partly as a result of sediment disruption and direct feeding/cutting of basal meristems by the green crab (Carcinus maenas). Green crabs are detrimental to eelgrass beds, and field and laboratory experiments have confirmed that the deleterious role of this invasive species is mediated by at least two mechanisms, depending on the size/age of the crabs: uprooting by adults and grazing by juveniles. Eelgrass uprooting and grazing by green crabs are likely to contribute to further declines or a lack of recovery of eelgrass beds.