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New Phytologist: bridging the ‘plant function – climate modelling divide’

2016; Wiley; Volume: 209; Issue: 4 Linguagem: Inglês

10.1111/nph.13876

1469-8137

Owen K. Atkin,

Tree-ring climate responses

In December 2015, the 21st session of the Conference of the Parties (COP) to the 1992 United Nations Framework Convention on Climate Change (UNFCCC) took place in Paris, France. The ‘Paris Agreement’ (UNFCCC, 2015) set out plans to limit emissions of greenhouse gases such as CO2, and in doing so, hold the increase in global average temperatures to < 2°C above pre-industrial levels (Cornwall, 2015). Whether this ambitious target is met will depend on numerous factors, not-the-least being the commitment of member-states to ratify and implement the Agreement; here, political and economic considerations will be paramount. Yet, factors not in the control of member states – such as environment-mediated changes in the functioning of forest ecosystems – will also be pivotal in determining the extent of atmospheric CO2 accumulation in the coming decades. Because of this, a well-developed understanding of how abiotic stresses affect CO2/water fluxes in plants will be central for accurate prediction of future atmospheric CO2 concentrations, and how much carbon can be stored in terrestrial landscapes. The manner via which plant processes are represented in terrestrial biosphere models (TBMs), and associated land-surface components of Earth System Models (ESMs), will also be crucial in improving their predictive ability. Ideally, there should be open dialogue between plant biologists and climate modellers, facilitated where possible by both communities publishing their papers in common journals. Yet, most scientific journals typically focus on only one of these two areas (i.e. plant function or model evaluation). By contrast, New Phytologist publishes papers that explore the mechanistic basis of environment-mediated changes in plant function alongside papers that model ecosystem and Earth system functioning (Atkin, 2013). One area that has direct relevance to the goals of the Paris Agreement is how drought and related climate extremes contribute to tree mortality; at New Phytologist, an increasing number of papers have addressed questions in this area, including influential reviews, modelling papers and theoretical viewpoints (e.g. McDowell et al., 2008; Meir et al., 2015; Mencuccini et al., 2015). Several papers have addressed the role of hydraulic traits in mediating water movement within individual plants and whole ecosystems (Martinez-Vilalta et al., 2014; Anderegg, 2015), while others have assessed the extent to which plant taxa differ in their susceptibility to hydraulic failure (McDowell et al., 2013a,b; Mitchell et al., 2013; Poyatos et al., 2013). Moreover, some studies have focussed on genetic variants differing in hydraulic conductance and associated assimilation rates of individual species (e.g. Zsogon et al., 2015). Others have highlighted the dynamic response of hydraulic traits to changes in the abiotic and biotic environment such as water availability (Mitchell et al., 2013; Poyatos et al., 2013), atmospheric CO2 concentration (Rico et al., 2013) and insect infestation (Domec et al., 2013). Moreover, in many papers published in New Phytologist, the importance of ‘thirst’ and ‘carbon starvation’ for drought-induced mortality has been debated (Adams et al., 2013; Galvez et al., 2013; Mitchell et al., 2013; O'Grady et al., 2013; Hartmann et al., 2015; Meir et al., 2015). Underpinning the role of ‘carbon starvation’ as a factor contributing to drought-induced mortality is the extent to which carbon accumulates/is depleted in above- and below-ground plant tissues (Adams et al., 2013; Galvez et al., 2013; Hartmann et al., 2013; Zhao et al., 2013), the duration over which carbon is stored (Lynch et al., 2013; Richardson et al., 2013, 2015), and whether carbon supply limits plant growth in a range of environments (Cheesman & Winter, 2013; Streit et al., 2013; Fatichi et al., 2014). In addition to these empirically-based studies, an increasing number of papers in New Phytologist also employ in silico analyses to evaluate TBM performance for forest trees experiencing variations in drought (e.g. Powell et al., 2013) and elevated atmospheric CO2 (e.g. De Kauwe et al., 2014; Zaehle et al., 2014). Collectively, such papers provide a rich resource for improving how plant function under drought is represented in TBMs and ESMs, which in turn should improve the predictive ability of such models. In addition to accounting for drought-mediated changes in plant function in vegetation–climate models, there is also a pressing need to better represent the diversity and variation of plant traits in the next generation of models; here, the availability of global databases (e.g. Kattge et al., 2011; Dryad Digital Repository: http://datadryad.org) provide opportunities to analyse and account for the complexities of morphological, physiological and chemical-composition traits that occur within natural ecosystems (Comas & Eissenstat, 2009; Fisher et al., 2010b; Asner & Martin, 2011; Scheiter et al., 2013; Wullschleger et al., 2015). Recently, three papers were published in New Phytologist that illustrate the utility of assembling global trait databases. Niinemets et al. (2015) constructed an impressive database quantifying the impact of 831 within-canopy light gradients on leaf traits of 304 species; their analysis revealed marked differences in the ability of contrasting species to acclimate to changes in light availability. Similarly, a leaf respiration database (899 species, 100 sites) showed that respiratory fluxes at a common measuring temperature vary among species and global gradients in temperature and aridity (Atkin et al., 2015), with the results providing a framework for improving representation of respiration in TBMs. Finally, Moles et al. (2013) assembled an unprecedented dataset on 261 species spanning 80 families and 75 globally distributed sites to assess whether there are trade-offs among chemical and physical traits that enable defence against herbivores. Their results point to plants displaying a range of combinations of defence traits, and that there is little evidence of trade-offs among traits. Collectively, such studies highlight the value of aggregating traits into a global database, and how such databases – published in New Phytologist – can help improve TBM/ESM performance and provide new insights into ecological phenomena. Given the growing number of submissions that evaluate the role of plants in determining vegetation–climate model performance, New Phytologist is pleased to announce the appointment of Rosie A. Fisher (Staff Scientist at the National Centre for Atmospheric Research (NCAR), Boulder, CO, USA) to the Editorial Board. During her PhD and subsequent posts, Rosie investigated the impact of drought on the Amazon rainforest, with her PhD and other projects combining detailed in situ plant physiology observations with ecosystem models (Fisher et al., 2006, 2007, 2008; Metcalfe et al., 2010) as well as integrating ecological theory into large-scale land-surface schemes (Huntingford et al., 2008; Meir et al., 2008; da Costa et al., 2010; Metcalfe et al., 2010; Marthews et al., 2012; Fu et al., 2013; Joetzjer et al., 2014). After leaving the University of Edinburgh (UK), Rosie worked with Ian Woodward (past Editor-in-Chief of New Phytologist) at the University of Sheffield (UK) on understanding ecosystem processes in Dynamic Global Vegetation Models (DGVMs), including that contained within the JULES (Joint UK Land Environmental Simulator) land surface model (Atkin et al., 2008; Ostle et al., 2009; Fisher et al., 2010b; Huntingford et al., 2010). In 2009, Rosie moved to the United States to take up a post-doctoral position integrating mechanisms of plant death into land surface models (Fisher et al., 2010b) at Los Alamos National Laboratory in New Mexico; thereafter, she moved to Boulder, Colorado to take up a Project Scientist post at NCAR, where she has continued working on developing new methods for simulating the future of natural ecosystems and their responses to climate change. Her work has primarily focused on the integration of Ecosystem Demography processes into the Community Land Model (CLM) (Fisher et al., 2010b, 2015) to further facilitate direct linkages between field observations and climate model dynamics. Rosie also continues to pursue her interests in plant hydraulics (McDowell et al., 2011, 2013a; Bonan et al., 2012) and in the representation of plant nutrient cycling in land surface models (Fisher et al., 2010a; Xu et al., 2012) and in many other aspects of how vegetation phenology, physiology and gas exchange are represented in the CLM (McDowell et al., 2011, 2013a; Bonan et al., 2012; Marthews et al., 2012; Xu et al., 2012; Malhi et al., 2014; Ali et al., 2015; Dahlin et al., 2015; Lombardozzi et al., 2015). She is particularly motivated by the opportunity to facilitate the inclusion of ideas from observational and theoretical plant sciences into ESMs, and to that end is engaged in numerous model-inspired experiments and working groups that attempt to find common ground between communities. Thus, while we can only speculate on whether Rosie's move to Boulder, Colorado was motivated by her love of running and skiing in the mountains, it seems safe to assume that the opportunity to play an ongoing role in bridging the plant function–climate modelling divide played a major role in her decision to remain in the United States. Her expertise in this area will ensure that authors working at the plant function–climate modelling interface receive expert input when they submit their best work to New Phytologist.