Status report on the key climate variables technical supplement to the
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- Other contributing observations
- Significant data management issues
- Current capability
Variable: Soil respirationMain climate application Soils function as the main terrestrial carbon store; at least twice as much carbon is stored in soils as in the atmosphere (Borken et al., 2002). Respiration (root and microbial) is the second largest carbon flux into the atmosphere after the oceans (Schlesinger & Andrews, 2000) and is probably responsible for the observed variations in net ecosystem carbon exchange (NEE) (Valentini et al. 2000). Thus, it has become increasingly important to improve our understanding of how respiration will be affected by climate change, i.e., by the predicted rise in global mean temperatures. Correctly distinguishing between root and soil microbial respiration has become one of the greatest challenges in soil sciences and it is still not adequately solved; this is reflected in the many different methods used (Kuzyakov, 2002). Temperature sensitivity of soil respiration as determined by the Q10 (the increase in respiration per 10 °C) is a prime driver of carbon circulation (soil – atmosphere) in climate models, yet there is considerable uncertainty about the value and meaning of this term (Bekku et al., 2003). Contributing baseline GCOS observations None.
Other contributing observationsThere are no known global networks that systematically record soil respiration and there is no accepted standard method for measuring root and soil microbial respiration. The closest to a global data set for soil respiration is presented by Raich & Schlesinger (1992) who summarized the results of about 172 publications (prior to 1992) across 11 biomes. However, in producing this compilation, the authors had to make assumptions in many cases, e.g., use of average growing season or deriving data from figures. Furthermore, many different methods had been used and the associated environmental data were often either not well defined or were inadequate (Irvine & Law, 2002). Moreover, the issue of duration of soil respiration monitoring needs to be addressed if data are to be generalised. Soil respiration is an integral component of larger ecosystem scale measurements and there is an increasing body of data from eddy flux sites (c. 220), e.g., CarboEurope, Euro-Flux, Asia-Flux, Ko-Flux, Oz-Flux, Fluxnet-Canada, Ameri-Flux, which are all integrated into the Fluxnet initiative. Another useful, but indirect, approach to assessing changes in soil respiration is to monitor key driving variables, such as soil moisture, soil temperature, timing of litter input, leaf nitrogen status via satellite and airborne technology. However, the output from such measurements is still inadequate. Significant data management issuesThere is no known global historical archive of soil respiration data. However, the above flux network sites may help in creating such a dataset. Analysis productsFirstly, soil respiration is a major input for climate models and will determine the predicted positive feedback that releases even more carbon into the atmosphere if climate becomes warmer (Cox et al. 2000). However, to derive Q10 values (see above) from measured CO2 concentration in soil gas chambers requires improved and standardised techniques. In particular, soil temperature measurements have to reflect the soil depths most responsible for the measured CO2 (Irvine & Law, 2002). Furthermore, combining datasets may help in determining whether soil respiration acclimates (i.e. decreasing Q10 with increasing temperature). Secondly, soil moisture detection from space or airborne pictures needs to be improved to reflect the soil layers relevant for respiration; so far only the top few centimetres of soil moisture can be detected. Although the superficial soil horizons may be most susceptible to water deficit they may contribute little to total soil respiration (Borken et al. 2002). Current capabilityMajor efforts are underway to generate global data on NEE (Fluxnet). However, so far little has been achieved in unifying soil respiration methodologies and the problem of comparing individual measurements even within collaborative initiatives is rarely achieved (e.g. see Subke, 2002). Apart from one publication (op. cit.), no real global data have been summarized. Moreover, there is a clear need to re-address assumptions about soil respiration currently embedded in available climate models, particularly with regard to sensitivity to environmental change. Issues and priorities
References Bekku, Y. S., Nakatsubo, T., Kume, A., Adachi, M., and Koizumi, H. (2003) Effect of warming on the temperature dependence of soil respiration rate in arctic, temperate and tropical soils. Applied Soil Ecology, 22, 205-210. Borken, W., Xu, Y.-J., Davidson, E. A., and Beese, F. (2002) Site and temporal variation of soil respiration in European beech, Norway spruce, and Scots pine forests. Global Change Biology, 8, 1205-1216. Cox, P. M., Betts, R. A., Jones, C. D., Spall, S. A., and Totterdell, I. J. (2000) Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature, 408, 184-187. Irvine, J. and Law, B. E. (2002) Contrasting soil respiration in young and old-growth ponderosa pine forests. Global Change Biology, 8, 1183-1194. Kuzyakov, Y. (2002) Separating microbial respiration of exudates from root respiration in non-sterile soils: a comparison of four methods. Soil Biology and Biochemistry, 34, 1621-1631. Raich J. W. and Schlesinger W. H., (1992) The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate. Tellus, 44B, 81-99. Schlesinger W. H. and Andrews J. A., Soil respiration and the global carbon cycle. Biogeochemistry, 48, 7-20. 2000. Subke, J.-A. (2002) Forest floor CO2 fluxes in temperate forest ecosystems. An investigation of spatial and temporal patterns and abiotic controls. Doctorate Thesis at the Univ. of Bayreuth, Germany. Published in: Bayreuther Forum Oekologie, Band 96 / 2002, ISSN 0944 - 4122. Valentini, R., Matteucci, G., Dolman, A. J., Schulze, E.-D., Rebmann, C., Moors, E. J., Granier, A., Gross, P., Jensen, N. O., Pilegaard, K., Lindroth, A., Grelle, A., Bernhofer, C., Grünwald, T., Aubinet, M., Ceulemans, R., Kowalski, A. s., Vasala, T., Rannik, Ü., Berbigier, P., Loustau, D., Guomundsson, J., Thogeirsson, H., Ibrom, A., Morgenstern, K., Clement, R., Moncrieff, J., Montagnani, L., Minerbi, S., and Jarvis, P. G. (2000) Respiration as the main determinant of carbon balance in European forests. Nature, 404, 861-865. Variable: Soil organic carbon Directory: pages -> prog prog -> Regional Association IV (North America, Central America and the Caribbean) Hurricane Operational Plan prog -> Review of the ra IV hurricane operational plan prog -> Cyclone programme prog -> World meteorological organization prog -> World meteorological organization technical document prog -> Regional Association IV (North America, Central America and the Caribbean) Hurricane Operational Plan prog -> World meteorological organization ra IV hurricane committee thirty-fourth session prog -> World meteorological organization ra IV hurricane committee thirty-third session prog -> Review of the past hurricane season prog -> Ra IV hurricane committee thirty-fourth session ponte vedra beach, fl, usa Download 0.61 Mb. Share with your friends:
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