Browsing by Author "Hirano, Takashi"

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The surface-atmosphere exchange of carbon dioxide in tropical rainforests: Sensitivity to environmental drivers and flux measurement methodology
(2018-12) Fu, Zheng; Gerken, Tobias; Bromley, Gabriel T.; Araújo, Alessandro; Bonal, Damien; Burban, Benoit; Ficklin, Darren L.; Fuentes, Jose D.; Goulden, Michael L.; Hirano, Takashi; Kosugi, Yoshiko; Liddell, Michael; Nicolini, Giacomo; Niu, Shuli; Roupsard, Olivier; Stefani, Paolo; Mi, Chunrong; Tofte, Zaddy; Xiao, Jingfeng; Valentini, Riccardo; Wolf, Sebastian; Stoy, Paul C.
Tropical rainforests play a central role in the Earth system by regulating climate, maintaining biodiversity, and sequestering carbon. They are under threat by direct anthropogenic impacts like deforestation and the indirect anthropogenic impacts of climate change. A synthesis of the factors that determine the net ecosystem exchange of carbon dioxide (NEE) at the site scale across different forests in the tropical rainforest biome has not been undertaken to date. Here, we study NEE and its components, gross ecosystem productivity (GEP) and ecosystem respiration (RE), across thirteen natural and managed forests within the tropical rainforest biome with 63 total site-years of eddy covariance data. Our results reveal that the five ecosystems with the largest annual gross carbon uptake by photosynthesis (i.e. GEP > 3000 g C m(-2) y(-1)) have the lowest net carbon uptake - or even carbon losses versus other study ecosystems because RE is of a similar magnitude. Sites that provided sub canopy CO2 storage observations had higher average magnitudes of GEP and RE and lower average magnitudes of NEE, highlighting the importance of measurement methodology for understanding carbon dynamics in ecosystems with characteristically tall and dense vegetation. A path analysis revealed that vapor pressure deficit (VPD) played a greater role than soil moisture or air temperature in constraining GEP under light saturated conditions across most study sites, but to differing degrees from -0.31 to -0.87 mu mol CO2 m(-2) s(-1) hPa(-1). Climate projections from 13 general circulation models (CMIP5) under the representative concentration pathway that generates 8.5 W m(-2) of radiative forcing suggest that many current tropical rainforest sites on the lower end of the current temperature range are likely to reach a climate space similar to present-day warmer sites by the year 2050, warmer sites will reach a climate not currently experienced, and all forests are likely to experience higher VPD. Results demonstrate the need to quantify if and how mature tropical trees acclimate to heat and water stress, and to further develop flux-partitioning and gap-filling algorithms for defensible estimates of carbon exchange in tropical rainforests.
Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms
(2012-03-07) Niu, Shuli; Luo, Yiqi; Fei, Shenfeng; Yuan, Wenping; Schimel, David; Law, Beverly E.; Ammann, Christof; Arain, M. Altaf; Arneth, Almut; Aubinet, Marc; Barr, Alan G.; Beringer, Jason; Bernhofer, Christian; Black, T. Andrew; Buchmann, Nina; Cescatti, Alessandro; Chen, Jiquan; Davis, Kenneth J.; Dellwik, Ebba; Desai, Ankur R.; Etzold, Sophia; Francois, Louis; Gianelle, Damiano; Gielen, Bert; Goldstein, Allen; Groenendijk, Margriet; Gu, Lianhong; Hanan, Niall; Helfter, Carole; Hirano, Takashi; Hollinger, David Y.; Jones, Mike B.; Kiely, Gerard; Kolb, Thomas E.; Kutsch, Werner L.; Lafleur, Peter; Lawrence, David M.; Li, Linghao; Lindroth, Anders; Litvak, Marcy; Loustau, Denis; Lund, Magnus; Marek, Michal; Martin, Timothy A.; Matteucci, Giorgio; Migliavacca, Mirco; Montagnani, Leonardo; Moors, Eddy; Munger, J. William; Noormets, Asko; Oechel, Walter C.; Olejnik, Janusz; Pilegaard, Kim; Paw U, Kyaw Tha; Pilegaard, Kim; Rambal, Serge; Raschi, Antonio; Scott, Russell L.; Seufert, Günther; Spano, Donatella; Stoy, Paul C.; Sutton, Mark A.; Varlagin, Andrej; Vesala, Timo; Weng, Ensheng; Wohlfahrt, Georg; Yang, Bai; Zhang, Zhongda; Zhou, Xuhui
It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystemclimate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models.