The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

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The root systems of forest trees are composed of different diameters and heterogeneous physiological traits. However, the pattern of root respiration rates from finer and coarser roots across various tropical species remains unknown. To clarify how respiration is related to the morphological traits of roots, we evaluated specific root respiration and its relationships to mean root diameter (D) of various diameter and root tissue density (RTD; root mass per unit root volume; gcm(-3)) and specific root length (SRL; root length per unit root mass; mg(-1)) of the fine roots among and within 14 trees of 13 species from a primary tropical rainforest in the Pasoh Forest Reserve in Peninsular Malaysia. Coarse root (2-269mm) respiration rates increased with decreasing D, resulting in significant relationships between root respiration and diameter across species. A model based on a radial gradient of respiration rates of coarse roots simulated the exponential decrease in respiration with diameter. The respiration rate of fine roots (<2mm) was much higher and more variable than those of larger diameter roots. For fine roots, the mean respiration rates for each species increased with decreasing D. The respiration rates of fine roots declined markedly with increasing RTD and increased with increasing SRL, which explained a significant portion of the variation in the respiration among the 14 trees from 13 species examined. Our results indicate that coarse root respiration in tree species follows a basic relationship with D across species and that most of the variation in fine root respiration among species is explained by D, RTD and SRL. We found that the relationship between root respiration and morphological traits provides a quantitative basis for separating fine roots from coarse roots and that the pattern holds across different species.

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We investigated inter-annual variation of canopy CO 2 exchange (NEE) and evapotranspiration during a 7-year period over a lowland Dipterocarp forest in Pasoh, Peninsular Malaysia, using the eddy covariance method. Annual rainfall fluctuated between 1,451 and 2,235 mm during this period. Annual evapotranspiration estimated by energy budget correction and gap filling using the relationship between latent heat and available energy was 1,287 ± 52 mm. Despite inter-annual variation in rainfall, annual evapotranspiration was stable, except for a slight decrease in the driest year (2009). Evapotranspiration was roughly related to the amount of available energy, but was regulated by stomatal closure to prevent excessive water loss at high vapour pressure deficit. Even during dry periods, no significant decrease in evapotranspiration occurred, as water was supplied from soil layers deeper than 0.5 m. Ecosystem respiration (RE) increased with soil water content. Daytime NEE was also stable during the 7 years, despite climate variability. Afternoon inhibition of canopy photosynthesis was seen every month. Daytime NEE did not become more negative with increasing solar radiation, or with increasing soil water content. During dry periods, gross primary production (GPP) and thus canopy gross photosynthesis decreased slightly, coupled with decreased daytime RE. In this forest, variability in rainfall pattern resulted in seasonal and inter-annual variability in micrometeorology; evapotranspiration, photosynthesis, and RE responded to these changes, and compensated for each other and/or other components of micrometeorology, resulting in rather stable annual evapotranspiration and NEE, even during a very dry year associated with an El Nino Southern Oscillation (ENSO) event.

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