The genetics of drought tolerance in conifers

Abstract

Contents 1034I.1034II.1035III.1037IV.1038V.1042VI.1043VII.1045References1045 Summary As temperatures warm and precipitation patterns shift as a result of climate change, interest in the identification of tree genotypes that will thrive under more arid conditions has grown. In this review, we discuss the multiple definitions of ‘drought tolerance’ and the biological processes involved in drought responses. We describe the three major approaches taken in the study of genetic variation in drought responses, the advantages and shortcomings of each, and what each of these approaches has revealed about the genetic basis of adaptation to drought in conifers. Finally, we discuss how a greater knowledge of the genetics of drought tolerance may aid forest management, and provide recommendations for how future studies may overcome the limitations of past approaches. In particular, we urge a more direct focus on survival, growth and the traits that directly predict them (rather than on proxies, such as water use efficiency), combining research approaches with complementary strengths and weaknesses, and the inclusion of a wider range of taxa and life stages.

Resist, recover or both? Growth plasticity in response to drought is geographically structured and linked to intraspecific variability in Pinus pinaster

“…Our approach can be useful for the conservation and sustainable use of forest genetic resources because it allows the ecogeographical zonation of forest resilience to be defined based on spatially explicit information (Figure ). For instance, these results highlight that distinct provenances may be better adapted to recovery after drought and therefore could be used in assisted migration programmes (Moran, Lauder, Musser, Stathos, & Shu, ). Finally, we advocate that species distribution models (e.g.…”

Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying

“…However, producing more needles during the seedling stage also increases transpiration demands (Moran et al. ) and prioritizing height growth appears to come at the expense of root length, both of which may disadvantage lodgepole pine seedlings as drought increases within their current distribution.…”

“…As fires become more frequent at higher elevations in Yellowstone, these traits may confer advantage to lodgepole pine over other high-elevation conifer species because lodgepole pine could rapidly colonize burns and dominate early succession (Loehle 1998, Ettinger andHilleRisLambers 2017). However, producing more needles during the seedling stage also increases transpiration demands (Moran et al 2017) and prioritizing height growth appears to come at the expense of root length, both of which may disadvantage lodgepole pine seedlings as drought increases within their current distribution. In contrast, Douglas-fir seedlings allocated resources to root length at the expense of height growth.…”

The “isohydric trap”: A proposed feedback between water shortage, stomatal regulation, and nutrient acquisition drives differential growth and survival of European pines under climatic dryness

“…Therefore, in a global scenario of climate warming combined with increasing rates of anthropogenic N deposition (Güsewell, ; Jonard et al., ) we should expect plant P status (along with K and micronutrients like Cu or Zn) to be particularly vulnerable to decreases in transpiration fluxes during prolonged periods of climatic dryness, whereas plant N status may be less responsive. In addition, the reduced carbon assimilation exhibited by drought‐sensitive mountain pine species at the common garden site (Salazar‐Tortosa et al., ) could lead to low carbon availability to support the growth and activity of fine roots and ectomycorrhizal (EMF) fungi (Gessler et al., ; Matías et al., ; Moran et al., ). This could hamper even more the assimilation of low mobility nutrients, whose absorption has high energy and carbon costs such as the production of extramatrical EMF mycelium, the secretion of phosphatases and organic acids by roots and mycorrhizae for solubilization and mineralization of inorganic and organic P, or rhizosphere priming effects (Achat, Augusto, Gallet‐Budynek, & Loustau, ; Kreuzwieser & Gessler, ).…”

“…The responses of plant species and individuals to water shortage span a variety of mechanisms that either tend to increase water uptake (e.g., enhanced root growth) or reduce water loss (e.g., stomatal closure). Stomatal regulation is the quickest mechanism to cope with drought, leading to two contrasting strategies termed anisohydry and isohydry, characterized by relaxed versus tight stomatal control of transpiration in response to decreases in plant water potential (Moran, Lauder, Musser, Stathos, & Shu, ; Tardieu & Simonneau, ; but see Martínez‐Vilalta & Garcia‐Forner, ). These strategies are clearly the opposite extremes of a continuous ecophysiological gradient (Klein, ) but, overall, the degree of stomatal regulation of transpiration is currently considered a key functional trait that explains not only individual plant response to drought, but also forest persistence under current and future climatic conditions (McDowell et al., ).…”