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Abstract The effects of land use change on soil carbon stocks are of concern in the context of international policy agendas on greenhouse gas emissions mitigation. This paper reviews the literature for the influence of land use changes on soil C stocks and reports the results of a meta analysis of these data from 74 publications. The meta analysis indicates that soil C stocks decline after land use changes from pasture to plantation (-10%), native forest to plantation (-13%), native forest to crop (-42%), and pasture to crop (-59%). Soil C stocks increase after land use changes from native forest to pasture (+ 8%), crop to pasture (+ 19%), crop to plantation (+ 18%), and crop to secondary forest (+ 53%). Wherever one of the land use changes decreased soil C, the reverse process usually increased soil carbon and vice versa . As the quantity of available data is not large and the methodologies used are diverse, the conclusions drawn must be regarded as working hypotheses from which to design future targeted investigations that broaden the database. Within some land use changes there were, however, sufficient examples to explore the role of other factors contributing to the above conclusions. One outcome of the meta analysis, especially worthy of further investigation in the context of carbon sink strategies for greenhouse gas mitigation, is that broadleaf tree plantations placed onto prior native forest or pastures did not affect soil C stocks whereas pine plantations reduced soil C stocks by 12–15%. [ABSTRACT FROM AUTHOR]

Passive open-top devices have been proposed as a method to experimentally increase temperature in high-latitude ecosystems. There is, however, little documentation on the efficacy of these devices. This paper examines the performance of four open-top chambers for altering temperature at six sites in the Arctic and Antarctica. Most of the heating effect was due to daytime warming above ambient; occasional night-time cooling below ambient, especially of air temperatures, depressed mean daily temperature. The mean daily temperatures at four arctic sites were generally increased by 1.2--1.8 deg.C; but occasionally, temperature depressions also occurred. Under optimal conditions at theantarctic site (dry soils, no vegetation, high radiation) mean dailysoil temperatures were increased by + 2.2 deg.C (-10 cm) to + 5.2 deg.C (0 cm). Protection from wind may play a more important role than temperature per se in providing a favourable environment for plant growth within opentop devices. Wind speed had a generally negative impact on mean daily temperature. Daily global radiation was both positively and negatively related to chamber temperature response. The effect of chambers on snow accumulation was variable with the Alexandra Fjord site showing an increased accumulation in chambers but no difference in the date of snowmelt, while at Latnjajaure in a deep snowfall site, snowmelt occurred 1--2 weeks earlier in chambers, potentially increasing the growing season. Selection of a passive temperature-enhancing system requires balancing the temperature enhancement desired against potential unwanted ecological effects such as chamber overheating and altered light, moisture, and wind. In general, the more closed the temperature-enhancing system, the higher is the temperature enhancement, but the larger are the unwanted ecological effects. Open-top chambers alter temperature significantly and minimize most unwantedecological effects; as a consequence, these chambers are a useful tool [ABSTRACT FROM AUTHOR]

The objectives of this paper are broadly to examine arctic soils andspecifically to examine soil properties at ITEX sites. The Arctic isdominated by cold, wet, shallow soils often characterized by surficial organic horizons. Seven of 11 soil orders in Soil Taxonomy are present in the circumarctic and alpine zones of the ITEX Project. Soil organic matter is highly correlated to soil carbon (sink or source of atmospheric CO2), soil moisture (surficial energy balance), and soil nitrogen (plant limiting nutrient). Because of these vitalroles, soil organic matter is a keystone that will influence the future response of arctic ecosystems to climate change. Saxifraga oppositifolia, a widespread circum-arctic and alpine plant species, was exposed to increased temperature at three ITEX sites of different latitudes: Val Bercla in the Swiss Alps (46 deg.N), Latnjajaure in mid-alpine Northern Sweden (68 deg.N), and Alexandra Fjord, Ellesmere Island (79 deg.N) in the Canadian High Arctic. Phenology, growth, and reproduction were monitored for 2 or 3 consecutive years. Increased temperature had little influence on the phenology of S. oppositifolia, although flowering period was somewhat longer and pollination earlier in the experimental plots. A decrease in the density of flowers on each plant was noted at two sites over 3 years, with a slightly larger decrease in the warmed plots. The few changes observed in reproductive variables (e.g. fruit: flower ratio) are mostly assigned to increased shading by taller growing neighbouring plants of other species, thus limiting performance of the shade-intolerant S. oppositifolia. It is assumed that survival of this species, especially at the lower limits of its altitudinal and latitudinal distribution, will depend on seed dispersal to new, open habitats. [ABSTRACT FROM AUTHOR]

Numerous papers on nitric oxide have been published covering variousaspects ranging from its solution and gas-phase chemistry, biochemical and physiological functions and atmospheric processes. This reviewemphasizes recent developments in the literature relating to NO/NOx production in agricultural soils. We have tried to minimize overlap with other recent and relevant review articles. Emission measurements that have been made since 1992 are tabulated and discussed in terms of variability, fertilization effects, and advances made in monitoringfluxes. We describe attempts made by a number of authors to utilize ecological markers such as aeration, water, ammonium, nitrate content, etc. in order to distinguish between nitrification and denitrification as the primary source of production and/or consumption in naturalfield situations. This may allow a rational accounting for the high spatial and temporal variability observed, and the formulation of reliable predictive models. Factors such as diffusion, oxygen, water, and carbon (content and quality) that regulate or significantly influence production, consumption and emission are discussed. Finally some important implications of recent research relating to nitrification and denitrification is presented showing the chemical oxidation of NO which could occur when the acetylene inhibition technique is used. [ABSTRACT FROM AUTHOR]

One of the main options for carbon mitigation identified by the IPCCis the sequestration of carbon in soils. In this paper we use statistical relationships derived from European long-term experiments to explore the potential for carbon sequestration in soils in the EuropeanUnion. We examine five scenarios, namely (a) the amendment of arablesoils with animal manure, (b) the amendment of arable soils with sewage sludge, (c) the incorporation of cereal straw into the soils in which it was grown, (d) the afforestation of surplus arable land through natural woodland regeneration, and (e) extensification of agriculture through ley-arable farming. Our calculations suggest only limitedpotential to increase soil carbon stocks over the next century by addition of animal manure, sewage sludge or straw (less than 15 Tg C y{sup}-1{end}), but greater potential through extensification of agriculture (~~ 40 Tg C y{sup}-1{end}) or through the afforestation of surplus arable land (~~ 50 Tg C y{sup}-1{end}). We estimate that extensification could increase the total soil carbon stock of the European Union by 17%. Afforestation of 30% of present arable land would increase soil carbon stocks by about 8% over a century and would substitute up to 30 Tg C y{sup}-1{end} of fossil fuel carbon if the wood were used as biofuel. However, even the afforestation scenario, with the greatest potential for carbon mitigation, can sequester only 0.8% of annual global anthropogenic CO{sub}2{end}-carbon. Our figures suggest that, although efforts in temperate agriculture can contribute to global carbon mitigation, the potential is small compared to that available through reducing anthropogenic CO{sub}2{end} emissions by halting tropical and sub-tropical deforestation or by reducing fossil fuel burning. [ABSTRACT FROM AUTHOR]

Tree growth at northern treelines is generally temperature‐limited due to cold and short growing seasons. However, temperature‐induced drought stress was repeatedly reported for certain regions of the boreal forest in northwestern North America, provoked by a significant increase in temperature and possibly reinforced by a regime shift of the pacific decadal oscillation (PDO). The aim of this study is to better understand physiological growth reactions of white spruce, a dominant species of the North American boreal forest, to PDO regime shifts using quantitative wood anatomy and traditional tree‐ring width (TRW) analysis. We investigated white spruce growth at latitudinal treeline across a >1,000 km gradient in northwestern North America. Functionally important xylem anatomical traits (lumen area, cell‐wall thickness, cell number) and TRW were correlated with the drought‐sensitive standardized precipitation–evapotranspiration index of the growing season. Correlations were computed separately for complete phases of the PDO in the 20th century, representing alternating warm/dry (1925–1946), cool/wet (1947–1976) and again warm/dry (1977–1998) climate regimes. Xylem anatomical traits revealed water‐limiting conditions in both warm/dry PDO regimes, while no or spatially contrasting associations were found for the cool/wet regime, indicating a moisture‐driven shift in growth‐limiting factors between PDO periods. TRW reflected only the last shift of 1976/1977, suggesting different climate thresholds and a higher sensitivity to moisture availability of xylem anatomical traits compared to TRW. This high sensitivity of xylem anatomical traits permits to identify first signs of moisture‐driven growth in treeline white spruce at an early stage, suggesting quantitative wood anatomy being a powerful tool to study climate change effects in the northwestern North American treeline ecotone. Projected temperature increase might challenge growth performance of white spruce as a key component of the North American boreal forest biome in the future, when drier conditions are likely to occur with higher frequency and intensity. [ABSTRACT FROM AUTHOR]