Abstract. We present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to the North Atlantic. The Amazon basin dominates the overall phosphorus flux and has the highest phosphorus flux per area. The total nitrogen flux from the Amazon is also lar¥e, contributing 3.3 Tg yr

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The tropical rainforest mesocosm within the Biosphere 2 Laboratory, a model system of some 110 species developed over 12 years under controlled environmental conditions, has been subjected to a series of comparable drought experiments during 2000-2002. In each study, the mesocosm was subjected to a 4-6 week drought, with welldefined rainfall events before and after the treatment. Ecosystem CO 2 uptake rate ( A eco ) declined 32% in response to the drought, with changes occurring within days and being reversible within weeks, even though the deeper soil layers did not become significantly drier and leaf-level water status of most large trees was not greatly affected. The reduced A eco during the drought reflected both morphological and physiological responses. It is estimated that the drought-induced 32% reduction of A eco has three principal components: (1) leaf fall increased two-fold whereas leaf expansion growth of some canopy dominants declined to 60%, leading to a 10% decrease in foliage coverage of the canopy. This might be the main reason for the persistent reduction of A eco after rewatering. (2) The maximum photosynthetic electron transport rate at high light intensities in remaining leaves was reduced to 71% for three of the four species measured, even though no chronic photoinhibition occurred. (3) Stomata closed, leading to a reduced ecosystem water conductance to water vapour (33% of pre-drought values), which not only reduced ecosystem carbon uptake rate, but may also have implications for water and energy budgets of tropical ecosystems. Additionally, individual rainforest trees responded differently, expressing different levels of stress and stress avoiding mechanisms. This functional diversity renders the individual response heterogeneous and has fundamental implications to scale leaf level responses to ecosystem dynamics.Key-words : chlorophyll fluorescence; drought; leaf area; leaf fall; leaf growth; net ecosystem CO 2 exchange; photosynthesis; photosynthetic electron transport; tropical rainforest; tropical trees.Abbreviations : A eco , ecosystem photosynthetic CO 2 uptake rate ( m mol CO 2 m -2 s -1 ); c i , apparent intercellular CO 2 concentration (p.p.m.); ET, ecosystem evapotranspiration (mmol H 2 O m -2 s -1 ); ETR, photosynthetic electron transport rate ( m mol electrons m -2 s -1 ); F 0 , ground fluorescence of the dark-adapted leaf; F m , maximum fluorescence of the dark-adapted leaf; F , fluorescence of the light-adapted leaf; F m ¢ , maximum fluorescence of the light-adapted leaf; F v / F m , pre-dawn potential quantum yield of photosystem (PS) II (

We took advantage of the distinctive system-level measurement capabilities of the Biosphere 2 Laboratory (B2L) to examine the effects of prolonged exposure to elevated [CO 2 ] on carbon flux dynamics, above-and belowground biomass changes, and soil carbon and nutrient capital in plantation forest stands over 4 years. Annually coppiced stands of eastern cottonwoods (Populus deltoides) were grown under ambient (400 ppm) and two levels of elevated (800 and 1200 ppm) atmospheric [CO 2 ] in carbon and N-replete soils of the Intensive Forestry Mesocosm in the B2L. The large semiclosed space of B2L uniquely enabled precise CO 2 exchange measurements at the near ecosystem scale. Highly controllable climatic conditions within B2L also allowed for reproducible examination of CO 2 exchange under different scales in space and time. Elevated [CO 2 ] significantly stimulated whole-system maximum net CO 2 influx by an average of 21% and 83% in years 3 and 4 of the experiment. Over the 4-year experiment, cumulative belowground, foliar, and total aboveground biomass increased in both elevated [CO 2 ] treatments. After 2 years of growth at elevated [CO 2 ], early season stand respiration was decoupled from CO 2 influx aboveground, presumably because of accelerated fine root production from stored carbohydrates in the coppiced system prior to canopy development and to the increased soil carbohydrate status under elevated [CO 2 ] treatments. Soil respiration was stimulated by elevated [CO 2 ] whether measured at the system level in the undisturbed soil block, by soil collars in situ, or by substrate-induced respiration in vitro. Elevated [CO 2 ] accelerated depletion of soil nutrients, phosphorus, calcium and potassium, after 3 years of growth, litter removal, and coppicing, especially in the upper soil profile, although total N showed no change. Enhancement of aboveand belowground biomass production by elevated [CO 2 ] accelerated carbon cycling through the coppiced system and did not sequester additional carbon in the soil.

A B S T R A C TThe land use system in Russia changed considerably after 1990: 30.2 million ha of croplands were abandoned. Based on the own field investigations that were carried out in abandoned lands of different age (Luvic Phaeozems, deciduous forest zone; Moscow region, 54 • 50 N, 37 • 37 E), it has been shown that after 4-5 yr of abandonment, the former croplands acted as a stable sink of CO 2 . The net ecosystem production (NEP) in the post-agrogenic ecosystems averaged 245 ± 73 g C m −2 yr −1 for the first 15 yr after land use change that corresponds to an estimated 74 ± 22 Tg C yr −1 for the total area of abandoned lands in Russian Federation. Currently, the Russian territory acts as an absolute sink of atmospheric CO 2 at a rate about 0.90 Pg C yr −1 . Using three different approaches, it was demonstrated that after 1990, the carbon sequestration in Russian soils (0-20 cm layer) has averaged 34 ± 2.2 Tg C yr −1 . This soil C forms net biome production (NBP) where carbon lifetime is much longer than in 'Kyoto forests'. Thus, the post-agrogenic ecosystems in Russia provide with the additional CO 2 sink in NEP and NBP that could annually compensate about 25% of the current fossil fuel emissions in the Russian Federation.