Anthropogenic and natural CO2 emission sources in an arid urban environment.

Recent research has shown the Phoenix, AZ metropolitan region to be characterized by a CO2 dome that peaks near the urban center. The CO2 levels, 50% greater than the surrounding non-urban areas, have been attributed to anthropogenic sources and the physical geography of the area. We quantified sources of CO2 emissions across the metropolitan region.

Belowground carbon pools and processes in different age stands of Douglas-fir.

Forest floor material and soil organic matter may act as both a source and a sink in global CO2 cycles. Thus, the ecosystem processes controlling these pools are central to understanding the transfers of carbon (C) between the atmosphere and terrestrial systems. To examine these ecosystem processes, the effect of stand age on temporal carbon source-sink relationships was examined in 20-year-old, 40-year-old and old-growth stands of Douglas-fir (Pseudotsuga menziesii (Mirb.

CO fluxes of cryptogamic crusts: II. Response to dehydration.

The carbon dioxide exchange of Microcoleus- and Scytonema-dominated cryptogamic crusts as related to dehydration was measured in the laboratory with a modified discrete sampling technique and infrared gas analysis. The dehydration curves predicted that carboxylation and dark respiration rates for both crust types would become zero at from 4 to 5% water content (W) (approximately 16-23% soil saturation), with the water contents at which the rates became zero significantly lower in the second treatment cycle than the first. The dehydration curves predicted that net photosynthesis rates would become zero at 6.

CO fluxes of cryptogamic crusts: I. Response to resaturation.

The relationship between carbon dioxide exchange of Microcoleus- and Scytonema-dominated cryptogamic crusts and resaturation time was measured in the laboratory with a modified discrete sampling technique and infrared gas analysis. Maximum net photosynthetic rate of Microcoleus was 187 nmol CO m s and of Scytonema was 111 nmol CO m s for rehydration to 100% soil saturation. Both crust types demonstrated a slow rise in resaturation respiration and took 2 days to become fully active after the (first rehydration to 100% soil saturation after long-term dryness, and only one day to become active after the second rehydration cycle.