Diel and seasonal patterns of tropical forest CO2 exchange

We used eddy covariance to measure the net exchange of CO2between theatmosphere and an old-growth tropical forest in Para ́, Brazil from 1 July 2000 to 1 July2001. The mean air temperature and daily temperature range varied little year-round; therainy season lasted from late December to around July. Daytime CO2uptake under highirradiance averaged 16–19mmol·m22·s21. Light was the main controller of CO2exchange,accounting for 48% of the half-hour-to-half-hour variance. The rate of canopy photosyn-thesis at a given irradiance was lower in the afternoon than the morning. This photosyntheticinhibition was probably caused by high evaporative demand, high temperature, an intrinsiccircadian rhythm, or a combination of the three. Wood increment increased from Januaryto May, suggesting greater rates of carbon sequestration during the wet season. However,the daily net CO2exchange measured by eddy covariance revealed the opposite trend, withgreater carbon accumulation during the dry season. A reduction in respiration during thedry season was an important cause of this seasonal pattern. The surface litter was desiccatedin the dry season, and the seasonal pattern of respiration appears to be a direct result ofreduced forest floor decomposition during drought. In contrast, canopy photosynthesis wasnot directly reduced by the dry season, probably because deep rooting allows the forest toavoid drought stres

Carbon in Amazon forests: unexpected seasonal fluxes and disturbance-induced losses.

The net ecosystem exchange of carbon dioxide was measured by eddy covariance methods for 3 years in two old-growth forest sites near Santarém, Brazil. Carbon was lost in the wet season and gained in the dry season, which was opposite to the seasonal cycles of both tree growth and model predictions. The 3-year average carbon loss was 1.3 (confidence interval: 0.0 to 2.0) megagrams of carbon per hectare per year. Biometric observations confirmed the net loss but imply that it is a transient effect of recent disturbance superimposed on long-term balance. Given that episodic disturbances are characteristic of old-growth forests, it is likely that carbon sequestration is lower than has been inferred from recent eddy covariance studies at undisturbed sites

Mutations in ENPP1 are associated with 'idiopathic' infantile arterial calcification34.

Idiopathic infantile arterial calcification (IIAC; OMIM 208000) is characterized by calcification of the internal elastic lamina of muscular arteries and stenosis due to myointimal proliferation. We analyzed affected individuals from 11 unrelated kindreds and found that IIAC was associated with mutations that inactivated ecto-nucleotide pyrophosphatase/phosphodiesterase I (ENPP1). This cell surface enzyme generates inorganic pyrophosphate (PPi), a solute that regulates cell differentiation and serves as an essential physiologic inhibitor of calcification