• Energy Research

AbstractThe FLUXNET2015 dataset provides ecosystem-scale data on CO2, 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.

Tropical forests may be vulnerable to climate change1-3 if photosynthetic carbon uptake currently operates near a high temperature limit4-6. Predicting tropical forest function requires understanding the relative contributions of two mechanisms of high-temperature photosynthetic declines: stomatal limitation (H1), an indirect response due to temperature-associated changes in atmospheric vapour pressure deficit (VPD)7, and biochemical restrictions (H2), a direct temperature response8,9. Their relative control predicts different outcomes-H1 is expected to diminish with stomatal responses to future co-occurring elevated atmospheric [CO2], whereas H2 portends declining photosynthesis with increasing temperatures. Distinguishing the two mechanisms at high temperatures is therefore critical, but difficult because VPD is highly correlated with temperature in natural settings. We used a forest mesocosm to quantify the sensitivity of tropical gross ecosystem productivity (GEP) to future temperature regimes while constraining VPD by controlling humidity. We then analytically decoupled temperature and VPD effects under current climate with flux-tower-derived GEP trends in situ from four tropical forest sites. Both approaches showed consistent, negative sensitivity of GEP to VPD but little direct response to temperature. Importantly, in the mesocosm at low VPD, GEP persisted up to 38 °C, a temperature exceeding projections for tropical forests in 2100 (ref. 10). If elevated [CO2] mitigates VPD-induced stomatal limitation through enhanced water-use efficiency as hypothesized9,11, tropical forest photosynthesis may have a margin of resilience to future warming.

Projet C de Talent, Université de Hainan ; Fondation nationale des sciences naturelles de Chine [31660142] ; projet LBA-DMIP de la NASA [NNX09AL52G] ; enquête LBA de la NASA [CD-32] ; Partenariats de la Fondation nationale des sciences pour la recherche et l'éducation internationales (PIRE) C-project of Talent, Hainan University; National Natural Science Foundation of China [31660142]; NASA LBA-DMIP project [NNX09AL52G]; NASA LBA investigation [CD-32]; National Science Foundation's Partnerships for International Research and Education (PIRE) C-project of Talent, Hainan University; National Natural Science Foundation of China [31660142]; NASA LBA-DMIP project [NNX09AL52G]; NASA LBA research [CD-32]; National Science Foundation 's Partnerships for International Research and Education (PIRE) C - مشروع المواهب، جامعة هاينان ؛ المؤسسة الوطنية للعلوم الطبيعية في الصين [31660142 ]؛ مشروع LBA - DMIP التابع لناسا [NNX09AL52G ]؛ تحقيق LBA التابع لناسا [CD -32 ]؛ شراكات المؤسسة الوطنية للعلوم للبحث والتعليم الدوليين (PIRE)