Mycorrhizal association as a primary control of the CO ₂ fertilization effect

Abstract

Plants buffer increasing atmospheric CO 2 concentrations through enhanced growth, but the question whether nitrogen availability constrains the magnitude of this ecosystem service remains unresolved. Synthesizing experiments from around the world, we show that CO 2 fertilization is best explained by a simple interaction between nitrogen availability and mycorrhizal association. Plant species that associate with ectomycorrhizal fungi show a strong biomass increase (30 ± 3%, P<0.001) in response to elevated CO 2 regardless of nitrogen availability, whereas low nitrogen availability limits CO 2 fertilization (0 ± 5%, P=0.946) in plants that associate with arbuscular mycorrhizal fungi. The incorporation of mycorrhizae in global carbon cycle models is feasible, and crucial if we are to accurately project ecosystem responses and feedbacks to climate change.One Sentence Summary: Only plants that associate with ectomycorrhizal fungi can overcome nitrogen limitation, and thus take full advantage of the CO 2 fertilization effect. Main Text:Terrestrial ecosystems sequester annually about a quarter of anthropogenic CO 2 emissions (1), slowing climate change. Will this effect persist? Two contradictory hypotheses have been offered: the first is that CO 2 will continue to enhance plant growth, partially mitigating anthropogenic CO 2 emissions (1, 2), while the second is that nitrogen (N) availability will limit the CO 2 fertilization effect (3, 4), reducing future CO 2 uptake by the terrestrial biosphere (5-7). Plants experimentally exposed to elevated levels of CO 2 (eCO 2 ) show a range of responses in biomass, from large and persistent (8, 9) to transient (6), to non-existent (10), leaving the question of CO 2 fertilization open. Differences might be driven by different levels of plant N availability across experiments (11), but N availability alone cannot explain contrasting results based on available evidence (7,12). For instance, among two of the most studied free-air CO 2 This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Terrer, C. et al. "Mycorrhizal association as a primary

Maintaining connectivity: understanding the role of root order and mycelial networks in fine root decomposition of woody plants

“…This idea gained recent support by Terrer et al (2016) who found that plant species colonized by ECM fungi were able to sustain increased growth under elevated concentrations of carbon dioxide despite low soil N availability a phenomenon that has also been reported by others (Drake et al 2011). One possible mechanism for this sustained growth response is that ECM fungi, supplied with additional C from host plants, are able to mine recalcitrant compounds for N thereby increasing plant N uptake (Phillips et al 2012;Terrer et al 2016). To gain a more complete picture of the organisms and conditions driving the decomposition of the most distal root orders, there are a number of questions that require answers (Table 1).…”

Short-term carbon input increases microbial nitrogen demand, but not microbial nitrogen mining, in a set of boreal forest soils

“…However, a stimulation of enzyme synthesis by N was not observed in this study (Table 2), and (4) finally, microbial N mining might depend on the association of plants with mycorrhizal fungi, an effect that we would have underestimated in our laboratory experiment. Ectomycorrhiza-the dominant mycorrhiza in boreal forests-have been linked to the release of available N from SOM polymers (Lindahl et al 2007;Talbot et al 2013), and to increased N mining under elevated CO 2 (Drake et al 2011;Terrer et al 2016). Microbial N mining might thus depend not on plantsoil C allocation in general, but specifically on the allocation of C to certain mycorrhiza.…”

The influence of soil properties and nutrients on conifer forest growth in Sweden, and the first steps in developing a nutrient availability metric

“…Janssens et al, 2010;Vicca et al, 2012;Fernández-Martínez et al, 2014). Moreover, nutrient availability can modify ecosystem responses to global atmospheric and climatic changes, such as nitrogen (N) deposition (From et al, 2016), increasing CO2 levels (Norby et al, 2010;Terrer et al, 2016), warming (Dieleman et al, 2012) and drought (Friedrich et al, Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-372 Manuscript under review for journal Biogeosciences Discussion started: 2 November 2017 c Author(s) 2017. CC BY 4.0 License.…”