• Energy Research

Aims Recent studies revealed convergent temperature sensitivity of ecosystem respiration (Re) within aquatic ecosystems and between terrestrial and aquatic ecosystems. We do not know yet whether various terrestrial ecosystems have consistent or divergent temperature sensitivity. Here, we synthesized 163 eddy covariance flux sites across the world and examined the global variation of the apparent activation energy (Ea), which characterizes the apparent temperature sensitivity of and its interannual variability (IAV) as well as their controlling factors. Methods We used carbon fluxes and meteorological data across FLUXNET sites to calculate mean annual temperature, temperature range, precipitation, global radiation, potential radiation, gross primary productivity and Re by averaging the daily values over the years in each site. Furthermore, we analyzed the sites with >8 years data to examine the IAV of Ea and calculated the standard deviation of Ea across years at each site to characterize IAV. Important Findings The results showed a widely global variation of Ea, with significantly lower values in the tropical and subtropical areas than in temperate and boreal areas, and significantly higher values in grasslands and wetlands than that in deciduous broadleaf forests and evergreen forests. Globally, spatial variations of Ea were explained by changes in temperature and an index of water availability with differing contribution of each explaining variable among climate zones and biomes. IAV and the corresponding coefficient of variation of Ea decreased with increasing latitude, but increased with radiation and corresponding mean annual temperature. The revealed patterns in the spatial and temporal variations of Ea and its controlling factors indicate divergent temperature sensitivity of R-e, which could help to improve our predictive understanding of R-e in response to climate change.

Aims Recent studies revealed convergent temperature sensitivity of ecosystem respiration (Re) within aquatic ecosystems and between terrestrial and aquatic ecosystems. We do not know yet whether various terrestrial ecosystems have consistent or divergent temperature sensitivity. Here, we synthesized 163 eddy covariance flux sites across the world and examined the global variation of the apparent activation energy (Ea), which characterizes the apparent temperature sensitivity of and its interannual variability (IAV) as well as their controlling factors. Methods We used carbon fluxes and meteorological data across FLUXNET sites to calculate mean annual temperature, temperature range, precipitation, global radiation, potential radiation, gross primary productivity and Re by averaging the daily values over the years in each site. Furthermore, we analyzed the sites with >8 years data to examine the IAV of Ea and calculated the standard deviation of Ea across years at each site to characterize IAV. Important Findings The results showed a widely global variation of Ea, with significantly lower values in the tropical and subtropical areas than in temperate and boreal areas, and significantly higher values in grasslands and wetlands than that in deciduous broadleaf forests and evergreen forests. Globally, spatial variations of Ea were explained by changes in temperature and an index of water availability with differing contribution of each explaining variable among climate zones and biomes. IAV and the corresponding coefficient of variation of Ea decreased with increasing latitude, but increased with radiation and corresponding mean annual temperature. The revealed patterns in the spatial and temporal variations of Ea and its controlling factors indicate divergent temperature sensitivity of R-e, which could help to improve our predictive understanding of R-e in response to climate change.

Su una coltura di soia, sono stati misurati i flussi dievapotraspirazione e di fotosintesi apparente mediante la tecnicamicrometereologica del rapporto di Bowen, integrata con lamisurazione dei gradienti della concentrazione di CO2. La coltura,che ha sviluppato una densa vegetazione (LAI massimo = 6.7), hadissipato sotto forma di calore latente la maggior partedell'energia disponibile. A tre mesi dalla semina, il valore mediodiurno del rapporto di Bowen risultato ancora relativamentebasso, e pari a 0.23. I valori di fotosintesi apparente sonorisultati minori di quelli riportati, per la stessa specie, daaltri Autori. Gli andamenti giornalieri dei flussi assimilativisono stati caratterizzati da fenomeni di isteresi, probabilmenteper effetto della maggiore attivit respiratoria nelle orepomeridiane. Il fenomeno si accentuato nel corso della stagionecolturale con l' intensificarsi dei processi di traslocazione degliassimilati above a soybean canopy, evapotranspiration and apparent canopy photosynthesis were monitored by the micrometeorologicaltechnique of the Bowen ratio energy balance (BREB), integrated withthe measurement of the CO2 concentration gradient. The dense canopy(maximum LAI = 6.7) managed to dissipate most of the availableenergy under the form of latent heat and even three months aftersowing, mean daytime Bowen ratio averaged 0.23. Apparent canopy photosynthesis rates were lower than reported elsewhere for soybean; daily trends showed typical hysteretic loops likely due tothe higher afternoon respiration rates. The loops were increasinglymore pronounced as the sink size increased along the season.

Su una coltura di soia, sono stati misurati i flussi dievapotraspirazione e di fotosintesi apparente mediante la tecnicamicrometereologica del rapporto di Bowen, integrata con lamisurazione dei gradienti della concentrazione di CO2. La coltura,che ha sviluppato una densa vegetazione (LAI massimo = 6.7), hadissipato sotto forma di calore latente la maggior partedell'energia disponibile. A tre mesi dalla semina, il valore mediodiurno del rapporto di Bowen risultato ancora relativamentebasso, e pari a 0.23. I valori di fotosintesi apparente sonorisultati minori di quelli riportati, per la stessa specie, daaltri Autori. Gli andamenti giornalieri dei flussi assimilativisono stati caratterizzati da fenomeni di isteresi, probabilmenteper effetto della maggiore attivit respiratoria nelle orepomeridiane. Il fenomeno si accentuato nel corso della stagionecolturale con l' intensificarsi dei processi di traslocazione degliassimilati above a soybean canopy, evapotranspiration and apparent canopy photosynthesis were monitored by the micrometeorologicaltechnique of the Bowen ratio energy balance (BREB), integrated withthe measurement of the CO2 concentration gradient. The dense canopy(maximum LAI = 6.7) managed to dissipate most of the availableenergy under the form of latent heat and even three months aftersowing, mean daytime Bowen ratio averaged 0.23. Apparent canopy photosynthesis rates were lower than reported elsewhere for soybean; daily trends showed typical hysteretic loops likely due tothe higher afternoon respiration rates. The loops were increasinglymore pronounced as the sink size increased along the season.

In this chapter the Eddy Covariance network of Italy is presented, with a short introduction to each of the 29 sites that were active during the CarboItaly project. These sites provided a unique dataset for a better study and understanding of the carbon cycle of terrestrial ecosystems and the links between carbon sink capacity and the main environmental factors. After a number of examples of Eddy Covariance time series where it is possible to see the effect of interannual climate variability and disturbances and managements practices, an analysis of the role of the Carbon Uptake Period in the total Net Ecosystem Exchange (NEE) definition and a study of the effect of temperature and precipitation on the interannual variability of NEE are presented in order to show the way these data can contribute to a better understanding of the role and response of ecosystems to climate change.