Seasonal variation of belowground respired carbon dioxide from Wyoming ecosystems and disturbed minelands.

摘要

Terrestrial ecosystems exchange carbon with the atmosphere as a result of photosynthesis and respiration. Fluxes for these processes are large, and the difference between them is small in most ecosystems. For example, on the global scale the terrestrial photosynthetic flux is approximately 120 Gt. carbon per year and the recent annual storage (net of photosynthesis-respiration) is approximately 1-2 Gt. carbon per year (Lavigne and Robitaille, 1999). Because the balance between photosynthesis and respiration is small in comparison to the rates of these processes, minor changes in the rates of respiration can have a large impact on net primary production. When individual ecosystems are considered, some are substantial sinks of carbon while others can be substantial sources. The differences among ecosystems arise in a large part because of the differences in temperature and vegetation in a specific ecosystem. Temperature is known to be able to determine most of the major processes in the carbon cycle, including the initial fixation of carbon in photosynthesis (Mooney and Ehleringer, 1997), the allocation of carbon between roots and shoots (Farrar, 1988) and root growth (Kaspar and Bland, 1992, respiratory losses of carbon by plants (Ryan, 1991) and the decomposition of organic matter by soil microorganisms (Swift et. al., 1979).; Grassland ecosystems store most of their carbon in soils, where turnover rates are relatively long, and so changes, though they may occur slowly, will be of significant duration. Changes in ecosystem carbon storage will have a significant and long lived effect on global carbon cycles (Parton et. al., 1995).; The objectives of the first study, were: (1) to compare annual and seasonal rates of soil respiration across a range of ecosystems differing in abiotic conditions, and (2) to evaluate the extent to which soil respiration is correlated with soil surface temperature and monthly precipitation levels. The hypothesis is, that (1) rates of respiration would be least in alpine soils and higher in grassland soils due to climate and elevation differences (2) there would be strong intra-annual variation in soil respiration among seasons and (3) that soil respiration, soil temperature and precipitation would be directly related since soil microbial activity is temperature and moisture dependent (Sylvia et. al., 1998).; Land management practices have change in the last 200 years resulting in more areas of disturbed lands. Soil organic matter is reduced for many years following disturbance (Houghton et. al., 1983) affecting soil physical, chemical and biological parameters. Amounts of biomass C from soil organic matter are significantly lower in disturbed soils than in undisturbed soils (Williamson and Johnson, 1990). The lower amounts of carbon in reclaimed disturbed ecosystems would result in lower amounts of CO2 flux from reclaimed areas. Over time CO2 levels from reclaimed ecosystems would return to the approximately the same levels as adjacent undisturbed ecosystems.; The objective of the second study was to examine carbon and nitrogen mineralization rates as well as microbial biomass in reclaimed surface mine soils compared to nearby undisturbed soils to determine if there is a reduced capacity for nutrient cycling in the disturbed soil.