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The end-Permian mass extinction has been envisaged as the nadir of biodiversity decline due to increasing volcanic gas emissions over some 9 million years. We propose a different tempo and mechanism of extinction because we recognize two separate but geologically abrupt mass extinctions on land, one terminating the Middle Permian (Guadalupian) at 260.4 Ma and a later one ending the Permian Period at 251 Ma. Our evidence comes from new paleobotanical, paleopedoiogical, and carbon isotopic studies of Portal Mountain, Antarctica, and comparable studies in the Karoo Basin, South Africa. Extinctions have long been apparent among marine invertebrates at both the end of the Guadalupian and end of the Permian, which were also times of warm-wet greenhouse climatic transients, marked soil erosion, transition from high- to low-sinuosity and braided streams, soil stagnation in wetlands, and profound negative carbon isotope anomalies. Both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts, such as the end-Guadalupian Emeishan Basalt and end-Permian Siberian Traps. Keywords: Permian, Triassic, extinction, paleosol, palynology, vertebrates

Soil and vegetative groundcovers reflect light heterogeneously in habitats lacking a continuous overhead canopy, however the effects of reflected light on vegetation in these habitats has received little attention. We test the hypothesis that reflected light flux affects leaf optical properties, anatomy, and photosynthesis of Ipomoea pes-caprae (Convolvulacae), a common sand dune vine with functionally symmetric leaves, by comparing leaves growing over patches of high and low reflected light flux. Patches of high reflected light were found directly over sand and reflected 26.0 [+ or -] 0.9% (mean [+ or -] 1 SE) of incident photosynthetically active radiation (PAR) while patches of low reflected light were found over vegetation and reflected 6.1 [+ or -] 0.7% of incident PAR. Using a novel in situ method to simultaneously illuminate and measure gas exchange of one leaf surface at a time, we show that abaxial surface photosynthetic maxima and palisade parenchyma in sand patches were, respectively, 2.6 times greater and 20% thicker than those found over vegetation patches. Our results suggest that reflected light strongly influences leaf anatomy and gas exchange of L pes-caprae, demonstrating that reflected light can be an important component of the light environment for vegetation of habitats characterized by high-albedo substrates. Key words: Convolvulaceae; gas exchange methodology; Ipomoea pes-caprae; subtropical beaches; vine.

Anthropogenic nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application, alters biogeochemical cycling of ecosystems in a way that leads to altered flux of biogenic greenhouse gases (GHGs). Our meta-analysis of 313 observations across 109 studies evaluated the effect of N addition on the flux of three major GHGs: CO2, CH4 and N2O. The objective was to quantitatively synthesize data from agricultural and non-agricultural terrestrial ecosystems across the globe and examine whether factors, such as ecosystem type, N addition level and chemical form of N addition influence the direction and magnitude of GHG fluxes. Results indicate that N addition increased ecosystem carbon content of forests by 6%, marginally increased soil organic carbon of agricultural systems by 2%, but had no significant effect on net ecosystem CO2 exchange for non-forest natural ecosystems. Across all ecosystems, N addition increased CH4 emission by 97%, reduced CH4 uptake by 38% and increased N2O emission by 216%. The net effect of N on the global GHG budget is calculated and this topic is reviewed. Most often N addition is considered to increase forest C sequestration without consideration of N stimulation of GHG production in other ecosystems. However, our study indicated that although N addition increased the global terrestrial C sink, the CO2 reduction could be largely offset (53–76%) by N stimulation of global CH4 and N2O emission from multiple ecosystems. [ABSTRACT FROM AUTHOR]

Sea-level rise will alter the hydrology of terrestrial coastal ecosystems. As such, it becomes increasingly important to decipher the present role of ocean water in coastal ecosystems in order to assess the coming effects of sea-level rise scenarios. Sand dunes occur at the interface of land and sea. Traditionally, they are conceived as freshwater environments with rain and ground water as the only water sources available to vegetation. This study investigates the possibility of ocean water influx to dune soils and its effect on the physiology of sand dune vegetation. Stable isotopes are used to trace the path of ocean water from the soil to the vegetation. Soil salinity, water content and δ18O values are measured concurrently with stem water and leaf tissue of eight species during the wet and dry season and from areas proximal and distal to the ocean. Our results indicate the dune ecosystem is a mixed freshwater and marine water system characterized by oceanic influence on dune hydrology that is spatially heterogeneous and fluctuates temporally. Ocean water influx to soil occurs via salt spray in areas 5–12 m from the ocean during dry season. Accordingly, vegetation nearest to the sea demonstrate a plastic response to ocean water deposition including elevated integrated water use efficiency ( δ13Cleaf) and uptake of ocean water that comprised up to 52% of xylem water. We suggest physiological plasticity in response to periodic ocean water influx may be a functional characteristic common to species on the leading edge of diverse coastal habitats and an important feature that should be included in modeling coastal ecosystems. Rising sea level would likely cause a repercussive landward shift of dune species in response to encroaching maritime influences. However, human development would restrict this process, potentially causing the demise of dune systems and the protection from land erosion they provide. [ABSTRACT FROM AUTHOR]

Abstract: An empirical method to measure respiratory CO2 recycling using a fast growing agricultural cover crop as a model system was tested and compared with a theoretical method which uses a variation of the Keeling plot. Both methods gave values which were high and similar to each other. The theoretical method gave a value of respiratory based CO2 recycling of 0.41, while the empirical method gave a value of 0.49. Therefore close to half of the respired CO2 is refixed during daytime photosynthesis in this densely planted cover crop. Refixation of respired CO2 during the day should lead to an isotopic enrichment of the remaining respired CO2 leaving the canopy of the cover crop. Therefore, calculations of gross respiration and photosynthesis using isotopic mass balance equations that do not take this isotopic fractionation into account could be in error. We tested this premise by using isotopic mass balance equations to estimate average gross photosynthesis and respiration in this cover crop under two scenarios: (1) no recycling and (2) recycling of respired CO2. Values of gross photosynthesis and respiration were unrealistically low when it was assumed that no recycling occurs. On the other hand, realistic values similar to previous publications were observed when recycling was taken into account. [Copyright &y& Elsevier]