CO2 enhancement of forest productivity constrained by limited nitrogen availability

By Richard J. Norby, Jeffrey M. Warren, Colleen M. Iversen, B. Medlyn, Ross McMurtrie. Proceedings of the National Academy of Sciences of the United States of America, 2009

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Stimulation of terrestrial plant production by rising CO2 concentration is projected to reduce the airborne fraction of anthropogenic CO2 emissions. Coupled climate–carbon cycle models are sensitive to this negative feedback on atmospheric CO2, but model projections are uncertain because of the expectation that feedbacks through the nitrogen (N) cycle will reduce this so-called CO2 fertilization effect. We assessed whether N limitation caused a reduced stimulation of net primary productivity (NPP) by elevated atmospheric CO2 concentration over 11 y in a free-air CO2 enrichment (FACE) experiment in a deciduous Liquidambar styraciflua (sweetgum) forest stand in Tennessee. During the first 6 y of the experiment, NPP was significantly enhanced in forest plots exposed to 550 ppm CO2 compared with NPP in plots in current ambient CO2, and this was a consistent and sustained response. However, the enhancement of NPP under elevated CO2 declined from 24% in 2001–2003 to 9% in 2008. Global analyses that assume a sustained CO2 fertilization effect are no longer supported by this FACE experiment. N budget analysis supports the premise that N availability was limiting to tree growth and declining over time —an expected consequence of stand development, which was exacerbated by elevated CO2. Leaf- and stand-level observations provide mechanistic evidence that declining N availability constrained the tree response to elevated CO2; these observations are consistent with stand-level model projections. This FACE experiment provides strong rationale and process understanding for incorporating N limitation and N feedback effects in ecosystem and global models used in climate change assessments.

Subfields: Global and Planetary Change, Plant Science

View Paper: https://www.semanticscholar.org/paper/af93f746f6bd78e86672545028e6aadef0e16a18

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Citations in the corpus

Global change effects on humid tropical forests: Evidence for biogeochemical and biodiversity shifts at an ecosystem scale (2016, background): “For example, NPP increased 24% during years 3–5 of 1.5 times ambient CO2 but was only 9% above background by year 10 at a forest FACE site in Oak Ridge, TN [Norby et al., 2010].”
Land-use and climate change risks in the Amazon and the need of a novel sustainable development paradigm (2016, background): “Although these locations may potentially stock larger carbon pools in the long term, the responses to CO2 fertilization may be limited due to relative low nutrient availability (137).”
Climate change effects on biodiversity, ecosystems, ecosystem services, and natural resource management in the United States. (2020, background): “It is also unclear if fertilization effects will continue as forests age (Norby et al., 2010).”
Traits to stay, traits to move: a review of functional traits to assess sensitivity and adaptive capacity of temperate and boreal trees to climate change (2016, background): “However, questions remain concerning our capacity to accurately predict long-term tree response to elevated CO2 (Norby et al. 2010; Norby and Zak 2011; Walker et al. 2015).”
Diverse Mycorrhizal Associations Enhance Terrestrial C Storage in a Global Model (2019, background): “Limitation of plant C accumulation by N availability has been supported by stoichiometric arguments (Hungate et al., 2003; Zaehle, Friedlingstein, et al., 2010), global model simulations (e.g., Wieder et al., 2015), and ecosystem‐scale observations (Norby et al., 2010).”
Patterns and Mechanisms of Nutrient Resorption in Plants (2015, background): “Northern environments, which tend to be N-limited, are particularly susceptible to further N restrictions under elevated CO2, since enhanced plant growth increases mineral nutrient requirements (Norby et al., 2010).”
Attributing forest responses to global‐change drivers: limited evidence of a CO2‐fertilization effect in Iberian pine growth (2015, background): “Nevertheless, radial growth could respond nonlinearly to rising Ca (Norby et al., 2010) but also to warmer temperatures (Way & Oren, 2010; De Grandpr e et al., 2011).”
Conservation from the bottom up: forecasting effects of global change on dynamics of organic matter and management needs for river networks (2011, background): “Elevated atmospheric CO2 can stimulate terrestrial productivity and increase detrital inputs to aquatic systems when plant growth is not nutrient limited (Norby et al. 2010).”
Estimating autotrophic respiration in streams using daily metabolism data (2013, background): “Measurements of GPP and ER allow budgeting of C in ecosystems (Lovett et al. 2006) and provide insight into the coupling of C cycling with other elements such as N and P (Hoellein et al. 2007, Hall et al. 2009, Norby et al. 2010).”
Metagenomic reconstruction of nitrogen cycling pathways in a CO2-enriched grassland ecosystem (2017, background): “Under eCO2, increased organic C input to the soil and intensified N limitation are two major ecological impacts affecting belowground microbial communities (Hu et al., 2001; Luo et al., 2004, 2006b; Norby et al., 2010; Reich and Hobbie, 2013; Reich et al., 2006).”
The mycorrhizal-associated nutrient economy: a new framework for predicting carbon-nutrient couplings in temperate forests. (2013, methodology): “…MANE framework builds on previous classifications for forests such as 'mull' vs 'mor' (Mueller, 1878; Handley, 1954), 'open' vs 'closed' ecosystems (Odum, 1969), 'fungal' vs 'bacterial' energy channels (Wardle et al., 2004) and ecosystems with 'extravagant' vs 'conservative' traits (Chapman et…”