The effects of a temperature increase on the carbon budget of an ecosystem provides an example of this complexity (Figure 1). Net ecosystem production (NEP), defined as the overall carbon balance of an ecosystem over some time period (Woodwell and Whittaker 1968, Mooney et al. 1999), has two major components, net primary production (NPP) and heterotrophic respiration (Rh). NPP, the principal input of carbon to the ecosystem, is the net result of CO2 fixation by photosynthesis and CO2 loss by plant respiration. The product of NPP is new organic matter, which accumulates first in plants as living biomass and is eventually transferred to soils as litter and to animals and decomposer organisms as food. Rh represents the loss of carbon from the ecosystem by respiration of animals and decomposers; the products of Rh include CO2 and other inorganic carbon products (e.g., CH4). Both NPP and Rh are affected directly by temperature change. Both are usually increased by warming, although Rh often increases more rapidly in the short term (Woodwell 1995). In addition, warming can affect NPP and Rh indirectly by altering the ecosystem's moisture regime, nitrogen availability, length of its growing season, or species composition (Figure 1). Warming-driven changes in moisture, nitrogen, or species composition may also have intermediate effects on other ecosystem processes or states (e.g litter quality and quantity, which affect both Rh and nitrogen mineralization), leading to multistep indirect effects including losses of carbon through fire or leaching and changes in the balance of NPP and Rh (Melillo et al. 1990, Chapin et al. 1997).
The effects of a temperature increase on the carbon budget of an ecosystem provides an example of this complexity (Figure 1). Net ecosystem production (NEP), defined as the overall carbon balance of an ecosystem over some time period (Woodwell and Whittaker 1968, Mooney et al. 1999), has two major components, net primary production (NPP) and heterotrophic respiration (Rh). NPP, the principal input of carbon to the ecosystem, is the net result of CO2 fixation by photosynthesis and CO2 loss by plant respiration. The product of NPP is new organic matter, which accumulates first in plants as living biomass and is eventually transferred to soils as litter and to animals and decomposer organisms as food. Rh represents the loss of carbon from the ecosystem by respiration of animals and decomposers; the products of Rh include CO2 and other inorganic carbon products (e.g., CH4). Both NPP and Rh are affected directly by temperature change. Both are usually increased by warming, although Rh often increases more rapidly in the short term (Woodwell 1995). In addition, warming can affect NPP and Rh indirectly by altering the ecosystem's moisture regime, nitrogen availability, length of its growing season, or species composition (Figure 1). Warming-driven changes in moisture, nitrogen, or species composition may also have intermediate effects on other ecosystem processes or states (e.g litter quality and quantity, which affect both Rh and nitrogen mineralization), leading to multistep indirect effects including losses of carbon through fire or leaching and changes in the balance of NPP and Rh (Melillo et al. 1990, Chapin et al. 1997).
การแปล กรุณารอสักครู่..
