Abstract
Key messageLocal adaptation largely segregates between traits affecting light responses and water relations, but population-level differences in stomatal conductance when growth is unconstrained converge among populations under water stress.Warming temperatures and altered precipitation patterns threaten plant populations worldwide. European beech (Fagus sylvatica) is a species that expresses both high phenotypic plasticity and local adaptation among populations. Beech seedlings’ susceptibility to prolonged drought may be dictated by their immediate light environment. We tested whether seedlings of four beech provenances, from contrasting edaphoclimatic environments, expressed differences in trait responses to imposed water stress under sun and shade treatments. Populations from the southern range margin were expected to display greater water-stress tolerance and core populations’ faster growth rates in the absence of abiotic limitations. Both high light and water stress induced differences in trait responses among provenances, but traits that failed to respond to our experimental treatments likewise did not segregate at the provenance level. Hence, those traits responding to light, e.g., increasing leaf flavonol index and leaf mass area, also tended to differ among provenances. Similarly, there was evidence of local adaptation among provenances in traits, like midday leaf water potential, responding to water stress. Exceptionally, there was a three way interaction water- × -light- × -provenance for stomatal conductance which converged among provenances under water stress. Leaf chlorophyll content also varied both with light and water in a provenance-specific manner. We found core provenances’ growth traits to outperform others under favourable conditions, whereas southern and high-elevation populations displayed traits adapted to tolerate high irradiance. Only stomatal conductance produced a complementary interactive response between light- × -water across provenances, whereas other traits responded less to combined water stress and high irradiance than to either treatment alone.
Highlights
Climate change across Europe is expected to drive the northwards range shift of tree species, due largely to warmer and drier conditions, facilitating better growth of populations at1 3 Vol.:(0123456789)Trees (2021) 35:53–67 the leading range-edge but increasing the likelihood of mortality at the trailing range-edge (Pulido et al 2019; Archambeau et al 2020; Fréjaville et al 2020)
It is worth noting here that the absence of shading provoked fluctuations in temperature and relative humidity in the Sun treatments that is likely, when combined with the imposed water-stress, to have increased the intensity of drought compared with Shade plots (Fig. S3), with likely consequences for the traits of seedlings therein
The significant two-way interactions we report corroborate previous studies that found physiological traits responding to sun-shade transitions to differ among beech provenances (e.g., Tognetti et al 1998) and likewise those traits affecting water relations in response to drought (Robson et al 2012; Sánchez-Gómez et al 2013; Baudis et al 2014; Pšidová et al 2015), but hardly any light- × -waterstress interactions affecting water relations or other measured traits (Robson et al 2009)
Summary
Climate change across Europe is expected to drive the northwards range shift of tree species, due largely to warmer and drier conditions, facilitating better growth of populations at1 3 Vol.:(0123456789)Trees (2021) 35:53–67 the leading range-edge but increasing the likelihood of mortality at the trailing range-edge (Pulido et al 2019; Archambeau et al 2020; Fréjaville et al 2020). Shade-tolerance in beech at the species level confers crosstolerance, allowing trees to survive better under some environmental stresses (Valladares et al 2007), this does not always apply to shade and drought which can interact to produce an antagonistic effect on the morphological and physiological acclimation responses of tree seedlings (Niinemets 2010). Potential antagonism in these functionaltrait responses to combined water-and-light limitation can impede the recruitment of beech seedlings (Aranda et al 2005; Robson et al 2009). In arid environments, shade can sometimes benefit woody saplings (e.g., Pistacia and Quercus) by reducing leaf temperatures and photoinhibition, and promoting shade phenotypes that are typically better adapted to survive drought than sun phenotypes, despite the larger initial decreases in photochemical efficiency they suffer under equivalent drought stress (Valladares et al 2005)
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