Net ecosystem production

B. (1995). Monitoring seasonal and interannual variations of gross primary productivity, net primary productivity and net ecosystem productivity using a diagnostic model and remotely-sensed data, Tellus, Ser. B, 47,178-190. 

Longer ice-core records show that methane concentrations have varied on a variety of time scales over the past 220 000 years (Fig. 18-15) Qouzel et al, 1993 Brook et al, 1996). Wetlands in tropical (30° S to 30° N) and boreal (50° N to 70° N) regions are the dominant natural methane source. As a result, ice-core records for preanthropogenic times have been interpreted as records of changes in methane emissions from wetlands. Studies of modem wetlands indicate that methane emissions are positively correlated with temperature, precipitation, and net ecosystem productivity (Schlesinger, 1996). 

Net primary production (NPP) is the total carbon fixed minus the amount respired only by the primary producers (Ra). Net ecosystem production (NEP) is derived from the difference between GPP and ecosystem respiration (R), which includes both heterotrophic and autotrophic processes. 

Net ecosystem production the difference between GPP and ecosystem respiration (R), which includes both heterotrophic and autotrophic processes. 

Figure 18.15 Comparative analysis of net ecosystem production for estuaries in relation to loading ratio for DIN TOG Data sources are for MERL mesocosms (Oviatt et al., 1986), for Narragansett Bay (Nixon eta/., 1995), forXomales Bay (Smith andHollibaugh, 1997), for San Francisco Bay (Jassby et al, 1993), for Chesapeake Bay (Kemp et al, 1997), and for Patuxent River estuary in 1985—1994 (Kemp et al, 1999). Figure was adapted from Kemp et al (1997). The DlN TOC load ratio was based on external inputs of DIN (NO3 + NO2 + NH4) andTotal Organic Carbon (TOC) to each site.

The quantity of litter input provides the second critical link between NPP and decomposition because NPP governs the quantity of organic matter inputs to decomposers. When biomes are compared at steady state, heterotrophic respiration (i.e., the carbon released by processing of dead plant material by decomposer organisms and animals) is approximately equal to NPP. In other words, net ecosystem production (NEP), the rate of net carbon sequestration, is approximately zero at steady state, regardless of climate or ecosystem type. This indicates that the quantity and quality of organic matter inputs to soils, as determined by... 

Figure 6 The relationship between wetland CH4 emissions and various measures of primary productivity (a) emissions versus net ecosystem production (NEP) in North-American ecosystems ranging from the subtropics to the subarctic (b) emissions versus GPP in fen peatland mesocosms with high or low water table depths and (c) emissions versus whole-plant net photosynthesis in marsh microcosms exposed to elevated and ambient concentrations of atmospheric CO2. (after Whiting and Chanton, (1993) Updergraff et al., (2001) and Vann and Megonigal (2003), respectively).

Net-Ecosystem-Exchange-NEE Net-Ecosystem-Productivity-NEP (= change in litter organic layer)... 

Increased gross C fixation was found early in the growing season in tussock tundra after 3.5 years of warming, but the net ecosystem production still was negative because of a higher growing season respiratory C loss (Hobbie and Chapin, 1998). Also, measurements in the Swedish treeline heath after seven years of treatment showed a mid-season C loss in warmed plots relative to... 

FIGURE 3 Comparison between the observed seasonal cycle of COi and the simulated seasonal cycle produced by coupling the monthly estimates of net ecosystem production estimated by the Century model and fossil fuel emissions with the Hamburg ocean and atmospheric transport models for each of the seven high-latitude monitoring stations. The first six months of each cycle are displayed twice to reveal the annual variation more clearly. Mean and standard deviation are shown for the observed data (McGuire et iiL, 2000). 

FIG U RE 5.2 Relationship between net ecosystem productivity and net methane flux, (Redrawn from Whiting and Chanton, 1993). 

The fate of NPP is heterotrophic respiration (R ) by herbivores (animals) who consume 10-20% of NPP, and respiration of decomposers (microfauna, bacteria, fungi) in soils. The largest fraction of NPP is delivered to the soil as dead organic matter (litter), which is decomposed by microorganisms under release of CO2, H2O, nutrients and a final resistant organic product, humus. Hence, a net ecosystem production (NEP) is defined ... 

It was previously noted that the net ecosystem production (NEP) nowadays is small or even negligible but it had a strong influence in the period when colonization of... 

O Connell, K.E.B., S.T. Gower and J.M. Norman. 2003. Net ecosystem production of two contrasting boreal black spruce forest communities. Ecosystems 6 248-260. 

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