Contrasting trait syndromes in angiosperms and conifers are associated with different responses of tree growth to temperature on a large scale

Abstract

Recent large-scale studies of tree growth in the Iberian Peninsula reported contrasting positive and negative effects of temperature in Mediterranean angiosperms and conifers. Here we review the different hypotheses that may explain these trends and propose that the observed contrasting responses of tree growth to temperature in this region could be associated with a continuum of trait differences between angiosperms and conifers. Angiosperm and conifer trees differ in the effects of phenology in their productivity, in their growth allometry, and in their sensitivity to competition. Moreover, angiosperms and conifers significantly differ in hydraulic safety margins, sensitivity of stomatal conductance to vapor-pressure deficit (VPD), xylem recovery capacity or the rate of carbon transfer. These differences could be explained by key features of the xylem such as non-structural carbohydrate content (NSC), wood parenchymal fraction or wood capacitance. We suggest that the reviewed trait differences define two contrasting ecophysiological strategies that may determine qualitatively different growth responses to increased temperature and drought. Improved reciprocal common garden experiments along altitudinal or latitudinal gradients would be key to quantify the relative importance of the different hypotheses reviewed. Finally, we show that warming impacts in this area occur in an ecological context characterized by the advance of forest succession and increased dominance of angiosperm trees over extensive areas. In this context, we examined the empirical relationships between the responses of tree growth to temperature and hydraulic safety margins in angiosperm and coniferous trees. Our findings suggest a future scenario in Mediterranean forests characterized by contrasting demographic responses in conifer and angiosperm trees to both temperature and forest succession, with increased dominance of angiosperm trees, and particularly negative impacts in pines.

Improved representation of plant functional types and physiology in the Joint UK Land Environment Simulator (JULES v4.2) using plant trait information

“…Needle-leaf species in JULES have a lower D crit than other trees, grasses, and shrubs. The lower D crit increases the likelihood of the stomata being closed -similar to Mediterranean conifers that tend to close their stomata earlier than angiosperms (Carnicer et al, 2013) -and it tightly regulates the stomatal aperture, making plants more sensitive to increasing D. This is analogous to plants conserving water at the expense of assimilation. We use updated f 0 and D crit from a synthesis of water use efficiency at the FLUXNET sites (Dekker et al, 2016).…”

Regulation of Water Use in the Southernmost European Fir (Abies pinsapo Boiss.): Drought Avoidance Matters

“…In conifers, water uptake may be expressed as the product of leaf-specific conductivity (LSC) and the water potential gradient (ΔΨ; that is, the difference between xylem water potential at midday and at predawn). On the other hand, water losses may be approximated by the product of stomatal conductance (gs) and atmospheric vapour pressure deficit (VPD) [41]: LSC* ΔΨ =gs* VPD (4) In this study, VPD and ΔΨ values were not very different between the low and high elevations, whereas gs was significantly lower at low elevation. Thus, according to Equation (4), a similar value in ΔΨ between the two populations suggests a reduction in the whole-plant hydraulic conductance at low elevation, likely due to decreased leaf-specific conductivity [42,43].…”

“…Considerable literature on recent forest decline draws attention to a direct link between climate change and the water relations of trees. Extreme climatic events, such as drought, are among the main drivers of forest dynamics and are usually related to forest decline of drought-sensitive tree species [1][2][3][4]. Understanding contrasting drought sensitivity among tree species and how these differences will affect their water and carbon balances is therefore an important topic to forecast likely responses to global warming and increasing drought stress in forests [5].…”

“…The physiological responses of trees to drought range from declining leaf water potential as soil water availability decreases (anisohydric response) to the maintenance of leaf water potential above a threshold (isohydric response) [6]. Drought-induced tree decline has been reported for several ecosystems and is usually focused on isohydric tree species, such as relict Mediterranean mountain conifers [4]. This tree die-off is mainly characterized by declining growth patterns, increases in defoliation and extensive death [1][2][3].…”

Heavy Metal Contamination of Soils

“…Furthermore, the efficiency of phytoextraction depends on a good choice of plant species, not only for the type of soil and MTE to remove but also for climatic conditions. If poplars and willows can adapt to many soils, they are however more sensitive than conifers to low temperatures and freeze-thaw embolism (Carnicer et al 2013). Conifers may therefore appear as models of interest for pollutions localized in cold regions.…”