Climatic limits of temperate rainforest tree species are explained by xylem embolism resistance among angiosperms but not among conifers

Abstract

Summary Hydraulic failure explains much of the increased rates of drought‐induced tree mortality around the world, underlining the importance of understanding how species distributions are shaped by their vulnerability to embolism. Here we determined which physiological traits explain species climatic limits among temperate rainforest trees in a region where chronic water limitation is uncommon. We quantified the variation in stem embolism vulnerability and leaf turgor loss point among 55 temperate rainforest tree species in New Zealand and tested which traits were most strongly related to species climatic limits. Leaf turgor loss point and stem P50 (tension at which hydraulic conductance is at 50% of maximum) were uncorrelated. Stem P50 and hydraulic safety margin were the most strongly related physiological traits to climatic limits among angiosperms, but not among conifers. Morphological traits such as wood density and leaf dry matter content did not explain species climatic limits. Stem embolism resistance and leaf turgor loss point appear to have evolved independently. Embolism resistance is the most useful predictor of the climatic limits of angiosperm trees. High embolism resistance in the curiously overbuilt New Zealand conifers suggests that their xylem properties may be more closely related to growing slowly under nutrient limitation and to resistance to microbial decomposition.

Weak coordination between leaf drought tolerance and proxy traits in herbaceous plants

“…Májeková et al., 2019), water limitation simultaneously results in smaller cell wall expansion, smaller cells and/or relatively thicker and more lignified secondary cell walls, that is, greater LDMC (Poorter et al., 2009). Our results are consistent with previous evidence on coordination between these two leaf‐level traits—on C4 grasses from different habitats (Liu & Osborne, 2015), on prairie species including C3 and C4 graminoids, forbs and shrubs (Blumenthal et al., 2020; Griffin‐Nolan et al., 2019) and on woody temperate rainforest angiosperms (Laughlin et al., 2020).…”

“…However, further research insofar under‐represented PFTs, such as conifers or annual plants, are needed to fully validate this hypothesis. An absence of such a relationship in temperate rainforest conifers (possibly due to smaller sample size— n = 12; Laughlin et al., 2020) could suggest that in certain groups or environmental conditions other factors might drive trait selection, and thus also the trait–trait covariation.…”

“…However, the evidence that the aforementioned traits are coordinated with leaf drought tolerance ( π tlp ) is so far weak and ambiguous. Moreover, most of our knowledge relating simple functional and hydraulic traits stems from woody species (Bartlett et al., 2012b and references therein; Esperón‐Rodríguez et al., 2018; Griffin‐Nolan et al., 2018 and references therein; Laughlin et al., 2020; Maréchaux et al., 2020) and, not surprisingly, from more arid regions of the world (Bartlett et al., 2012b; Griffin‐Nolan et al., 2019; Liu & Osborne, 2015), potentially hindering a clear generalization. Multiple studies have consistently documented either no or just a weak positive relationship between π tlp and SLA on both local and global scales (Bartlett et al., 2012b; Esperón‐Rodríguez et al., 2018; Liu & Osborne, 2015; Májeková et al., 2019; Maréchaux et al., 2015, 2020; Zhu et al., 2018).…”

“…Although it is often considered interchangeable with SLA (e.g. Laughlin et al., 2020; Pierce et al., 2013, but see Garnier et al., 2001; Hodgson et al., 2011), LDMC has been consistently, though with a different strength of the relationship, found to be negatively related to π tlp (higher LDMC related to more negative π tlp ) in different ecosystems and across different functional types (Blumenthal et al., 2020; Griffin‐Nolan et al., 2019; Laughlin et al., 2020; Liu & Osborne, 2015). The scattered and often ambiguous evidence on the coordination between π tlp and simple functional traits calls for further studies that would fill this gap.…”

“…So far, most studies found that π tlp carried a relatively weak phylogenetic signal (e.g. on woody species: Fu et al., 2012; Laughlin et al., 2020; Liu et al., 2015; and C4 grasses: Liu & Osborne, 2015). Potentially, a strong phylogenetic signal in π tlp among species would also enable a better prediction of π tlp than based on other traits alone, as closely related species would have similar π tlp values (Penone et al., 2014).…”