Environmental changes, such as climate warming and higher herbivory pressure, are altering the carbon balance of Arctic ecosystems; yet, how these drivers modify the carbon balance among different habitats remains uncertain. This hampers our ability to predict changes in the carbon sink strength of tundra ecosystems. We investigated how spring goose grubbing and summer warming-two key environmental-change drivers in the Arctic-alter CO2 fluxes in three tundra habitats varying in soil moisture and plant-community composition. In a full-factorial experiment in high-Arctic Svalbard, we simulated grubbing and warming over two years and determined summer net ecosystem exchange (NEE) alongside its components: gross ecosystem productivity (GEP) and ecosystem respiration (ER). After two years, we found net CO2 uptake to be suppressed by both drivers depending on habitat. CO2 uptake was reduced by warming in mesic habitats, by warming and grubbing in moist habitats, and by grubbing in wet habitats. In mesic habitats, warming stimulated ER (+75%) more than GEP (+30%), leading to a 7.5-fold increase in their CO2 source strength. In moist habitats, grubbing decreased GEP and ER by similar to 55%, while warming increased them by similar to 35%, with no changes in summer-long NEE. Nevertheless, grubbing offset peak summer CO2 uptake and warming led to a twofold increase in late summer CO2 source strength. In wet habitats, grubbing reduced GEP (-40%) more than ER (-30%), weakening their CO2 sink strength by 70%. One-year CO2-flux responses were similar to two-year responses, and the effect of simulated grubbing was consistent with that of natural grubbing. CO2-flux rates were positively related to aboveground net primary productivity and temperature. Net ecosystem CO2 uptake started occurring above similar to 70% soil moisture content, primarily due to a decline in ER. Herein, we reveal that key environmental-change drivers-goose grubbing by decreasing GEP more than ER and warming by enhancing ER more than GEP-consistently suppress net tundra CO2 uptake, although their relative strength differs among habitats. By identifying how and where grubbing and higher temperatures alter CO2 fluxes across the heterogeneous Arctic landscape, our results have implications for predicting the tundra carbon balance under increasing numbers of geese in a warmer Arctic.

Carbon dioxide fluxes between ecosystems of the Earth are presented. It was shown that intensifying its absorption of terrestrial ecosystems by 3.2% would prove sufficient to neutralize carbon dioxide emissions from the combustion of fossil fuels and cement production. It was shown that Polish forests absorb 84.6 million tons of CO2/year, that is 26% of emissions from fossil fuel combustion and cement production, while agricultural crops absorb 103 million tons of CO2/year. Total carbon dioxide sequestration by forests and agricultural crops amounts to 187.5 million tons of CO2/year, which is tantamount to 59% of emissions from fossil fuel combustion and cement production. Forestation of marginal soils would further increase carbon dioxide absorption in Poland by 20.6 million tons of CO2/year. Moreover, if plants were sown in order to produce green manure - instead of leaving soil fallow - sequestration could still be boosted by another 6.2 million tons of CO2/year.

The Antarctic Peninsula has experienced a strong climate warming trend of +0.53 degrees C (mean annual air temperature) over the last 50 years. In the Polar Regions, changes in vegetation and permafrost due to a warming climate are expected to produce strong feedbacks to climate and, despite their relatively small areal extent, ice-free areas in Antarctica provide unique natural environments for studying these effects. Off the Antarctic Peninsula, close to Rothera Research Station on Adelaide Island, we used in situ measurements to assess whether spatial variation of CO2 fluxes exists a) among three important and typical vegetation types at Rothera Point during the daylight period; b) across four different ecosystem types (from Antarctic vascular tundra to barren soil) on neighbouring Anchorage Island during the peak of the growing season (January-February 2009). We aimed to assess whether Net Ecosystem Exchange (NEE), Ecosystem Respiration (ER) and Gross Ecosystem Photosynthesis (GEP) change among the selected ecosystem types and determine which environmental factors (soil moisture, soil temperature and PAR) influence NEE and ER. The data obtained at Rothera Point confirmed the presence of spatial variation of CO2 fluxes related to vegetation type, and temporal variation of the CO2 cycle during the daylight period for moss and barren soil ecosystems. At Anchorage Island the spatial variation of CO2 fluxes was mainly influenced by vegetation type at inter-community level. Deschampsia and Sanionia showed higher NEE and ER values (-0.03/0.43 mu mol CO2 m(-2) s(-1) for Deschampsia NEE; 0/0.62 mu mol CO2 m(-2) s(-1) Sanionia NEE; 0.27/2.03 mu mol CO2 m(-2) s(-1) Deschampsia ER; 0.31/1.7 mu mol CO2 m(-2) s(-1) Sanionia ER) than the other vegetation types studied. We measured generally positive NEE values probably due to high soil respiration. Our data suggest that ecosystems such as those studied may act as a source for CO2 release to the atmosphere and that this source effect is likely to continue and/or to increase until the legacy of organic matter and nutrients stored in the soils is largely decomposed. (C) 2012 Elsevier B.V. All rights reserved.