Rising CO ₂ drives divergence in water use efficiency of evergreen and deciduous plants

Abstract

Intrinsic water use efficiency (iWUE), defined as the ratio of photosynthesis to stomatal conductance, is a key variable in plant physiology and ecology. Yet, how rising atmospheric CO2 concentration affects iWUE at broad species and ecosystem scales is poorly understood. In a field-based study of 244 woody angiosperm species across eight biomes over the past 25 years of increasing atmospheric CO2 (~45 ppm), we show that iWUE in evergreen species has increased more rapidly than in deciduous species. Specifically, the difference in iWUE gain between evergreen and deciduous taxa diverges along a mean annual temperature gradient from tropical to boreal forests and follows similar observed trends in leaf functional traits such as leaf mass per area. Synthesis of multiple lines of evidence supports our findings. This study provides timely insights into the impact of Anthropocene climate change on forest ecosystems and will aid the development of next-generation trait-based vegetation models.

Elevated CO<sub>2</sub>, increased leaf-level productivity and water-use efficiency during the early Miocene

“…5a). The difference between reconstructed Miocene iWUE and that of modern deciduous trees is greater still (deciduous iWUE Q1-Q3 = 27-52), consistent with the expectation that increased Ca favors evergreen trees (Niinemets et al, 2011;Soh et al, https://doi.org/10.5194/cp-2020-30 Preprint. Discussion started: 10 March 2020 c Author(s) 2020.…”

Elevated CO<sub>2</sub>, increased leaf-level productivity, and water-use efficiency during the early Miocene

“…Here, t g is the length of the growing season in months, which we can derive from the fossil plant assemblage using the method of Spicer et al (2009). G w , A tot , and iWUE values for Litsea calicarioides, Cryptocarya taieriensis, C. maarensis, cf.…”

“…The ESS envelope was determined using deep-sea δ 18 O of benthic foraminifera (Zachos et al, 2001) and the transform function approach from Hansen et al (2013) (Supplement). Proxy-based Neogene C a reconstructions are derived from a previously published compilation (Foster et al, 2017) and are supplemented with more recently published data (Ji et al, 2018;Londoño et al, 2018;Super et al, 2018;Greenop et al, 2019;Moraweck et al, 2019;Steinthorsdottir et al, 2019). Error bars on gas-exchange-based proxy estimates represent ±1σ .…”

Revisiting the carbon isotope discrimination and water use efficiency relation: the influence of mesophyll conductance

“…Quantitative prediction of iWUE is essential to anticipate plant responses to climate change factors like CO2 and precipitation regime (Adams et al, 2019;Soh et al, 2019). Recent studies have shown an increased need to quantify the rate at which iWUE has been changing in different geographical regions (Adams et al, 2019).…”

“…The iWUEsim model (Eqn 2) has been widely used to infer iWUE from δ 13 C values in climate archives like herbage (Koehler et al, 2012), tree rings (Frank et al, 2013;van der Sleen et al, 2015), or animal tissues (Barbosa et al, 2010). Compared to instantaneous iWUE derived from gas exchange measurements, biomass-based Δ provides a time-integrated iWUE and enables time-series analysis spanning from days to millennia (Soh et al, 2019;Adams et al, 2020).…”