Nutrient availability as the key regulator of global forest carbon balance

• Published in: Nature climate change Vol. 4; no. 6; pp. 471 - 476
• Main Authors: Fernández-Martínez, M., Vicca, S., Janssens, I. A., Sardans, J., Luyssaert, S., Campioli, M., Chapin III, F. S., Ciais, P., Malhi, Y., Obersteiner, M., Papale, D., Piao, S. L., Reichstein, M., Rodà, F., Peñuelas, J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2014; Nature Publishing Group
• Subjects: 631/158/2454; 704/158/2454; Biological and medical sciences; Carbon cycle; Carbon dioxide; Carbon sequestration; Climate Change; Climate Change/Climate Change Impacts; Climate models; Climatology. Bioclimatology. Climate change; Continental interfaces, environment; Earth, ocean, space; Ecosystems; Environment; Environmental Law/Policy/Ecojustice; Exact sciences and technology; External geophysics; Forestry; Forests; Fundamental and applied biological sciences. Psychology; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; letter; Meteorology; Nutrient availability; Nutrient balance; Ocean, Atmosphere; Photosynthesis; Primary production; Respiration; Sciences of the Universe; Dynamical climatology; Climate change; Radiation use efficiency; Forests; Primary productivity; Nutrient; Bioavailability; Biomass; Photosynthesis; Carbon sequestration
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/nclimate2177

A synthesis of findings from 92 forests in different climate zones reveals that nutrient availability plays a crucial role in determining forest carbon balance, primarily through its influence on respiration rates. These findings challenge the validity of assumptions used in most global coupled carbon-cycle climate models. Forests strongly affect climate through the exchange of large amounts of atmospheric CO 2 (ref.  1 ). The main drivers of spatial variability in net ecosystem production (NEP) on a global scale are, however, poorly known. As increasing nutrient availability increases the production of biomass per unit of photosynthesis 2 and reduces heterotrophic 3 respiration in forests, we expected nutrients to determine carbon sequestration in forests. Our synthesis study of 92 forests in different climate zones revealed that nutrient availability indeed plays a crucial role in determining NEP and ecosystem carbon-use efficiency (CUEe; that is, the ratio of NEP to gross primary production (GPP)). Forests with high GPP exhibited high NEP only in nutrient-rich forests (CUEe = 33 ± 4%; mean ± s.e.m.). In nutrient-poor forests, a much larger proportion of GPP was released through ecosystem respiration, resulting in lower CUEe (6 ± 4%). Our finding that nutrient availability exerts a stronger control on NEP than on carbon input (GPP) conflicts with assumptions of nearly all global coupled carbon cycle–climate models, which assume that carbon inputs through photosynthesis drive biomass production and carbon sequestration. An improved global understanding of nutrient availability would therefore greatly improve carbon cycle modelling and should become a critical focus for future research.