Abstract. This paper describes patterns of below‐ground components in grassland ecosystems. It provides estimates of the contribution of below‐ground organs to the total phytomass of the community and of different species to the below‐ground phytomass; it describes the distribution of above‐ and below‐ ground organs of different species and the spatial and temporal correlation between above‐ground and below‐ground phyto‐mass – both total standing crop and net primary production. 10 Siberian grasslands (meadows and steppes) were investigated during 15 yr. Ca. 70 % of the living phytomass is located in the soil and no less than 70 % of the net primary production is allocated in below‐ground organs. Phytomass distribution in the soil layer is more homogeneous than above‐ground. For some species the spatial distribution within 1‐m2 plots of the green and below‐ground phytomass is similar, for others it is quantitatively or qualitatively different. According to the dominance‐diversity curve, the above‐ground size hierarchy is much stronger than the below‐ground one. The active growth of above‐ and below‐ground organs of a species may occur at different times of the season and it varies from year to year. Allocation of organic substances to rhizomes and roots occurs simultaneously and with proportional intensity.

Abstract. Grassland management type (grazed or mown) and intensity (intensive or extensive) play a crucial role in the greenhouse gas balance and surface energy budget of this biome, both at field scale and at large spatial scale. However, global gridded historical information on grassland management intensity is not available. Combining modelled grass-biomass productivity with statistics of the grassbiomass demand by livestock, we reconstruct gridded maps of grassland management intensity from 1901 to 2012. These maps include the minimum area of managed vs. maximum area of unmanaged grasslands and the fraction of mown vs. grazed area at a resolution of 0.5 • by 0.5 • . The grassbiomass demand is derived from a livestock dataset for 2000, extended to cover the period 1901-2012. The grassbiomass supply (i.e. forage grass from mown grassland and biomass grazed) is simulated by the process-based model ORCHIDEE-GM driven by historical climate change, rising CO 2 concentration, and changes in nitrogen fertilization. The global area of managed grassland obtained in this study increases from 6

We used available field survey and literature data to produce inventory maps of wetland biomass and net primary production (NPP) for western Siberia. Field survey data were obtained for major types of wetland microlandscapes within the boreal (taiga) region. We developed a multiscale approach based on using a regional wetland typology map (1:2,500,000 scale), further refined by satellite image classifications (LANDSAT‐7, SPOT, RESURS, 1:200,000 scale). Satellite images on test areas designated in the boreal region of western Siberia were classified by 30 landscape classes. We used aerial photography (1:25,000 scale) to evaluate the fraction of the area occupied by microlandscape elements within patterned wetlands. As a result, we were able to produce a GIS map‐based inventory of ecosystem phytomass and NPP in west Siberian wetlands. Using the GIS map, the average and total net primary production and biomass were estimated by ecosystem type, the number of vegetation layers, and climatic gradient. The annual NPP to live biomass ratio increases southward from 0.27 in the tundra to 0.65 in the steppe region. Live biomass of wetlands amounts to only 10–30% of the average biomass of upland forests in the same climatic region, although wetland NPP was found to be equal or higher then that of upland forests. Mosses and the belowground fraction of grasses are the major contributors to NPP. Average live biomass and NPP in wetlands were estimated to be 1600 g/m2 and 790 g/m2/yr, respectively. Total wetland NPP amounts to 530 Tg/yr, and live biomass amounts to 1070 Tg.

No abstract

No abstract

We would like to dedicate this paper to co-author Richard Payne. Richard was a member of a group of 8 climbers caught in an avalanche in the Himalayas at the end of May. Correspondence AbstractRecent studies show that soil eukaryotic diversity is immense and dominated by micro-organisms. However, it is unclear to what extent the processes that shape the distribution of diversity in plants and animals also apply to micro-organisms. Major diversification events in multicellular organisms have often been attributed to longterm climatic and geological processes, but the impact of such processes on protist diversity has received much less attention as their distribution has often been H I I I J J J J J J J J J K K K

Abstract. Natural and anthropogenic mercury (Hg) emissions are sequestered in terrestrial soils over short, annual to long, millennial timescales before Hg mobilization and run-off impact wetland and coastal ocean ecosystems. Recent studies have used Hg-to-carbon (C) ratios (RHgC's) measured in Alaskan permafrost mineral and peat soils together with a northern circumpolar permafrost soil carbon inventory to estimate that these soils contain large amounts of Hg (between 184 and 755 Gg) in the upper 1 m. However, measurements of RHgC on Siberian permafrost peatlands are largely missing, leaving the size of the estimated northern soil Hg budget and its fate under Arctic warming scenarios uncertain. Here we present Hg and carbon data for six peat cores down to mineral horizons at 1.5–4 m depth, across a 1700 km latitudinal (56 to 67∘ N) permafrost gradient in the Western Siberian Lowland (WSL). Mercury concentrations increase from south to north in all soil horizons, reflecting a higher stability of sequestered Hg with respect to re-emission. The RHgC in the WSL peat horizons decreases with depth, from 0.38 Gg Pg−1 in the active layer to 0.23 Gg Pg−1 in continuously frozen peat of the WSL. We estimate the Hg pool (0–1 m) in the permafrost-affected part of the WSL peatlands to be 9.3±2.7 Gg. We review and estimate pan-Arctic organic and mineral soil RHgC to be 0.19 and 0.63 Gg Pg−1, respectively, and use a soil carbon budget to revise the pan-Arctic permafrost soil Hg pool to be 72 Gg (39–91 Gg; interquartile range, IQR) in the upper 30 cm, 240 Gg (110–336 Gg) in the upper 1 m, and 597 Gg (384–750 Gg) in the upper 3 m. Using the same RHgC approach, we revise the upper 30 cm of the global soil Hg pool to contain 1086 Gg of Hg (852–1265 Gg, IQR), of which 7 % (72 Gg) resides in northern permafrost soils. Additional soil and river studies in eastern and northern Siberia are needed to lower the uncertainty on these estimates and assess the timing of Hg release to the atmosphere and rivers.

Abstract. To improve the simulation of vegetation-climate feedbacks in the high latitudes, three new circumpolar Plant Functional Types (PFTs) were added in the ORCHIDEE land surface model, namely non-vascular plants (NVPs) representing bryophytes and lichens, arctic shrubs, and arctic C3 grasses. Non-vascular plants are assigned no stomatal conductance, very shallow roots, and can desiccate during dry episodes and become active again during wet periods, which gives them a larger phenological plasticity compared to grasses and shrubs. Shrubs have a specific carbon allocation scheme, and differ from trees by their larger survival rates in winter, due to protection by snow. Arctic C3 grasses have the same equations than in the original ORCHIDEE version, but different parameter values, optimized from in-situ observations of biomass and NPP in Siberia. In situ observations of living biomass and productivity from Siberia were used to calibrate the parameters of the new PFTs using a Bayesian optimization procedure. With the new PFTs, we obtain a lower Net Primary Productivity (NPP) by 31 % (from 55° N), as well as a lower roughness length (−41 %), transpiration (+33 %) and a higher winter albedo (by 3.6 %) due to a larger snow cover. A simulation of the water balance and runoff and drainage in the high northern latitudes using the new PFTs results in an increase of fresh water discharge in the Arctic ocean by 11 % (+140 km−3 y−1), owing to less evapotranspiration. Future developments should focus on the competition between these three PFTs and boreal trees PFTs, in order to simulate their area changes in response to climate change, and the effect of carbon-nitrogen interactions.