| 1. |
- Pfeifer-Meister, Laurel, et al.
(författare)
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Pushing the limit : experimental evidence of climate effects on plant range distributions
- 2013
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 94:10, s. 2131-2137
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Tidskriftsartikel (refereegranskat)abstract
- Whether species will be extirpated in their current geographic ranges due to rapidly changing climate, and if so, whether they can avoid extinction by shifting their distributions are pressing questions for biodiversity conservation. However, forecasts of climate change impacts on species' geographic distributions rarely incorporate a demographic understanding of species' responses to climate. Because many biotic and abiotic factors at multiple scales control species' range limits, experimentation is essential to establish underlying mechanisms. We used a manipulative climate change experiment embedded within a natural climate gradient to examine demographic responses of 12 prairie species with northern range limits within the Pacific Northwest, USA. During the first year, warming decreased recruitment of species even at the coolest edge of their current ranges, but this effect disappeared when they were moved poleward beyond their current ranges. This response was largely driven by differences in germination rates. Other vital rates responded in unique and sometimes opposing ways (survivorship vs. fitness) to species' current ranges and climate change, and were mediated by indirect effects of climate on competition and nutrient availability. Our results demonstrate the importance of using regional-scale climate manipulations and the need for longer-term experiments on the demographic responses that control species' distributions.
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| 2. |
- Wilson, Rachel M., et al.
(författare)
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Hydrogenation of organic matter as a terminal electron sink sustains high CO2 : CH4 production ratios during anaerobic decomposition
- 2017
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Ingår i: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 112, s. 22-32
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Tidskriftsartikel (refereegranskat)abstract
- Once inorganic electron acceptors are depleted, organic matter in anoxic environments decomposes by hydrolysis, fermentation, and methanogenesis, requiring syntrophic interactions between microorganisms to achieve energetic favorability. In this classic anaerobic food chain, methanogenesis represents the terminal electron accepting (TEA) process, ultimately producing equimolar CO2 and CH4 for each molecule of organic matter degraded. However, CO2:CH4 production in Sphagnum-derived, mineral-poor, cellulosic peat often substantially exceeds this 1:1 ratio, even in the absence of measureable inorganic TEAs. Since the oxidation state of C in both cellulose-derived organic matter and acetate is 0, and CO2 has an oxidation state of +4, if CH4 (oxidation state -4) is not produced in equal ratio, then some other compound(s) must balance CO2 production by receiving 4 electrons. Here we present evidence for ubiquitous hydrogenation of diverse unsaturated compounds that appear to serve as organic TEAs in peat, thereby providing the necessary electron balance to sustain CO2:CH4 > 1. While organic electron acceptors have previously been proposed to drive microbial respiration of organic matter through the reversible reduction of quinone moieties, the hydrogenation mechanism that we propose, by contrast, reduces CAC double bonds in organic matter thereby serving as (1) a terminal electron sink, (2) a mechanism for degrading complex unsaturated organic molecules, (3) a potential mechanism to regenerate electron-accepting quinones, and, in some cases, (4) a means to alleviate the toxicity of unsaturated aromatic acids. This mechanism for CO2 generation without concomitant CH4 production has the potential to regulate the global warming potential of peatlands by elevating CO2:CH4 production ratios.
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