2 results
4 - Determination of soil carbon stocks and changes
- Edited by Werner L. Kutsch, Max-Planck-Institut für Biogeochemie, Jena, Michael Bahn, Leopold-Franzens-Universität Innsbruck, Austria, Andreas Heinemeyer
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- Book:
- Soil Carbon Dynamics
- Published online:
- 11 May 2010
- Print publication:
- 07 January 2010, pp 49-75
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Summary
INTRODUCTION
Soil carbon pools and the global carbon cycle
In terrestrial ecosystems soils represent the major reservoir of organic carbon (Table 4.1), but with large and yet unquantified uncertainties in their estimates (mainly due to low soil sample numbers used for global up-scaling and assumptions on mean soil depths). At the global level, the soil organic matter (SOM) pool (estimated to 1 m depth) contains about 1580 Pg of carbon (Pg = 1015 g), about 610 Pg are stored in the vegetation and about 750 Pg are present in the atmosphere (Schimel, 1995). Carbon is found in soils both in organic and inorganic forms (Table 4.2). Organic carbon is commonly classified into three ‘arbitrary’ pools, mostly for modelling purposes (such as in CENTURY), i.e. fast, slow and passive reflecting the rate of turnover. However, it is difficult to relate these pools to soil carbon fractions (see Section 4.1.5). The total amount of carbonate carbon to 1 m depth is estimated at 695–748 Pg carbon (Batjes, 1996). About one third of organic soil carbon occurs in forests and another third in grasslands and savannas, the rest in wetlands, croplands and other biomes (Janzen, 2004). The global soil organic carbon map (Fig. 4.1, ISLSCP II; ORNL DAAC, http://daac.ornl.gov/) shows the areas of high soil organic carbon predominantly in cold boreal (e.g. Northern Canada) and warm and humid tropical regions (e.g. South-East Asia), reflecting areas of deep organic soils (i.e. peatlands).
Biogeochemistry of an afrotropical montane rain forest on Mt. Kilimanjaro, Tanzania
- Marion Schrumpf, Wolfgang Zech, Jan C. Axmacher, Herbert V. M. Lyaruu
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- Journal:
- Journal of Tropical Ecology / Volume 22 / Issue 1 / January 2006
- Published online by Cambridge University Press:
- 21 December 2005, pp. 77-89
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In contrast to their well-studied counterparts in the Neotropics and in Asia, East African montane rain forests are surrounded by semi-arid savanna plains. These plains have a high erosion potential for salt crusts accumulated at the soil surface. Hence it may be hypothesized that East African montane forest ecosystems experience strongly enhanced nutrient inputs via dry deposition, which alters their overall biogeochemistry. The aim of our study was to test this hypothesis by investigating K, Mg, Ca, Na and N-forms in rainfall, throughfall, fine litter, litter percolate and soil solution of a montane rain forest at Mt. Kilimanjaro. Four forest plots situated at elevations between 2250 and 2350 m asl on the south-western slopes of Mt. Kilimanjaro were studied for 2 y. In contradiction to our hypothesis, inputs of K, Mg, Ca and Na via rainfall (7.5, 0.9, 2.3 and 6.2kg ha−1y−1) and throughfall (35, 2.0, 3.5 and 11kg ha−1−1) were low on Mt. Kilimanjaro. Fluxes of NH4-N and NO3-N were within the range observed at other montane rain forests, with NO3-N being the only nutrient partly absorbed in the forest canopies (2.9kg ha−1y−1 in rainfall, 0.9kg ha−1y−1 in throughfall). The highest overall nutrient concentrations in water samples occurred in litter percolate (1.4mg l−1 K, 0.3mg l−1 Mg, 0.8mg l−1 Ca, 0.3mg l−1 NH4-N, 0.9mg l−1 NO3-N), with values still being low compared to other sites. Nutrient concentrations in seepage water strongly declined with increasing soil depth. Thus, both inputs and losses of base cations from the forest by water pathways are assumed to be low. N or P limitation of growth is not expected since high fluxes of N and P in fine litter (119 and 5.9kg ha−1y−1 for N and P respectively) indicate low within-stand efficiency.