New Phytologist and the ‘fate’ of carbon in terrestrial ecosystems

‘Fate’ is not a word typically associated with the rigors of science; rather, it is a word that evokes thoughts of destiny, perhaps under the control of a supernatural being. Yet, in the context of the ‘fate of carbon’, the word has particular importance for readers of New Phytologist, particularly those seeking to understand how past, current and future climates impact on carbon allocation and storage in terrestrial ecosystems. Indeed, the ‘fate of carbon’ is central in determining responses to environmental gradients (both in terms of plant performance and survival), ecosystem net productivity and respiration, deposition of plant detritus in soils (and thus the extent of soil carbon storage) and the magnitude of negative feedbacks between terrestrial ecosystems and atmospheric [CO2], to mention a few. As such, it not surprising that many papers in New Phytologist address questions about the many ‘fates’ of carbon in plants; these include earlier papers by John Farrar and others exploring the patterns of carbon partitioning within leaves and between shoots and roots, and the underlying factors likely to control carbon allocation to different organs (Farrar, 1985; Farrar & Farrar, 1985; Farrar & Jones, 2000). Since then, the focus on this topic has grown, with New Phytologist publishing approx. 50 papers over the past 2 yr that touch on carbon allocation/cycling in plants. This reflects a wider trend across the vegetation–soil–climate field of research, with a search of the ISI database revealing an c. three-fold increase over the past 20 yr in the number of papers published each year that address issues related to carbon allocation/cycling in plants. The increasing focus on carbon allocation/cycling has occurred independent of concomitant increases in papers focusing on effects of elevated atmospheric [CO2] on plants, which at New Phytologist have not increased in recent years (reflecting, in part, the cessation of major Free Air CO2 enrichment studies in recent years). Rather, the increased focus on ‘fate of carbon’ reflects the fundamental nature of this issue for the functioning of terrestrial biomes across the globe, as well as how future climates will impact on crop yields. When considering how carbon is allocated and stored in terrestrial ecosystems, focus is often first placed on the fate of carbon that had recently been assimilated by photosynthesis. Here, isotopic studies (carbon-13 (13C) and carbon-14 (14C)) have provided new insights into the fate of newly fixed carbon with respect to: (1) carbon accumulation in nonstructural vs structural pools (Streit et al., 2013); (2) incorporation of carbon into short- and long-lived plant tissues; (3) the speed with which recently fixed carbon reaches locations remote from the source tissues (i.e. developing shoots/stems/roots (Kagawa et al., 2006; Högberg et al., 2008), mycorrhizal symbionts (Högberg et al., 2010) and/or soils (Högberg et al., 2008)); and, (4) the mean residency time (MRT) of carbon in each of these pools/tissues/locations (Carbone & Trumbore, 2007; Keel et al., 2012; Carbone et al., 2013; Lynch et al., 2013; Richardson et al., 2013). Such studies show that a large fraction of recently-fixed carbon is translocated from leaves-to-roots-to-soils in the hours–days after assimilation (Högberg et al., 2008; Carbone et al., 2013), with labelling and mass-balance studies showing that ≈ 50% of photosynthate being respired by plant tissues and soils within days of fixation (Atkin et al., 2007; Carbone & Trumbore, 2007; Streit et al., 2013). Importantly, however, not all carbon is allocated to growth or respired over such short-time frames; rather, MRTs of nonstructural carbon compounds (i.e. starch/sugars) vary six-fold in fine roots of boreal forests (Keel et al., 2012), with 14C-based estimates indicating that MRT of starch and sugars exceeding a decade in some hardwood forest species (Richardson et al., 2013). By storing carbon reserves, trees are better able to buffer transient imbalances in carbon supply/use (Klein & Hoch, 2014). Moreover, that nonstructural carbohydrates are stored for very long periods in some species raises important questions about whether climate–vegetation models can assume near immediate allocation of photosynthate to formation of new tissues and/or respiratory carbon-release (Cox et al., 1998; Galbraith et al., 2010; Lynch et al., 2013; De Kauwe et al., 2014; Fatichi et al., 2014), and the role carbon starvation will play in declines of forest ecosystems subjected to biotic and abiotic stresses (Fajardo et al., 2012; Sala et al., 2012; Adams et al., 2013; Galvez et al., 2013; Hartmann et al., 2013; McDowell et al., 2013a,b; O'Grady et al., 2013; Palacio et al., 2014). Collectively, such studies highlight the multitude of ways in which the ‘fate of carbon’ has relevance for our understanding of how plants function in variable environments, and the importance of accounting for carbon allocation/use in models that predict the impacts of future climates on plant performance and survival. The earlier mentioned studies also showcase the importance of isotope studies for advancing our understanding of carbon allocation/use in plants. Importantly, isotopic approaches are increasing being used by studies that seek to understand aspects of plant–water relations and associated tissue chemistry (Dubbert et al., 2014; Treydte et al., 2014), as well as help elucidate the complex interactions between metabolic processes in plants (Boex-Fontvieille et al., 2013; Tcherkez & Tea, 2013). Given this increasing utilization of isotopic approaches in submissions to the Environment Section, New Phytologist is pleased to announce the appointment of Margaret Barbour (Faculty of Agriculture and Environment, University of Sydney) to the Editorial Board. Margaret has split her scientific career between Australia and New Zealand, having previously worked at Landcare Research in New Zealand (2001–2009). During her PhD at the Australian National University (under the supervision of Graham Farquhar), Margaret established herself as a leading authority on variability in oxygen isotopes in plant tissues, and how such studies can be used to understand the evaporative environment in which leaves develop and function. Her work has been applied in a diverse range of studies, ranging from selection of crops differing in water use and yield through to those that seek to reconstruct past climates from tree ring stable isotopes. Margaret has also established herself as a leader in studies using stable isotopes and novel, laser-based techniques to quantify terrestrial carbon and water exchange at the atmosphere–vegetation–soil interface. An example of Margaret's expertise in stable isotopes is her 2011 paper using 13C-based techniques to elucidate aspects of ecosystem carbon cycling (Barbour et al., 2011). Margaret's interests complement those of the other Environment Section Editors – David Ackerly, Owen Atkin, Amy Austin, Nate McDowell, Andrea Polle and Richard Norby. While it may not have been fate that led to Margaret joining New Phytologist as an Editor, what is clear is that her expertise will ensure that authors working in the area of stable isotopes (including studies investigating the fate of carbon) will receive input from a leader in the field when they submit their best to the journal.