Photosynthesis forests, temperate

The availability of reactive nitrogen limits photosynthesis in a wide variety of terrestrial and marine ecosystems. Nitrogen limitation is particularly common in temperate and boreal forests, temperate grasslands, and Arctic and subalpine tundra, and in estuaries and coastal marine ecosystems in temperate zones.Introduction of relatively large external inputs of the nutrient must be expected to change the productivity of affected ecosystems, as well as the modes of their nitrogen storage and composition of their species. 

As NEP is often small relative to the gross fluxes of photosynthesis and ecosystem respiration, the net flux is sometimes less than the error of measurement. More important than error is bias, and the approach is vulnerable to bias because both the fluxes of CO2 and the micro-meteorological conditions are systematically different day and night. Wind speeds below 17 cm s in a temperate zone forest, e.g., resulted in an underestimate of nighttime respiration (Barford et al., 2001). A similar relationship between nighttime wind speed and respiration in forests in the Brazilian Amazon suggests that the assumption that lateral transport is unimportant may have been invalid (Miller et al., in press). 

Lloyd,. (1999), The CO, dependence of photosynthesis, plant growth responses to elevated CO2 concentrations and their interaction with. soil nutrient status. II. Temperate and boreal forest productivity and the combined effects of increasing CO, concentrations and increa.sed nitrogen deposition at a global scale. Functional Ecol. 13,439-459. 

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