Drought resistance of Pinus sylvestris seedlings conferred by plastic root architecture rather than ectomycorrhizal colonisation

Abstract

International audienceAbstract ContextIncreased summer drought is considered as a threat to the regeneration of Pinus sylvestris in the Central Alps. To a certain degree, seedlings are able to mitigate negative effects of drought by altering root/shoot ratios. But, seedlings may also enhance access to water and nutrients by cooperation with ectomycorrhizal fungi. AimsWe tested the importance of both mechanisms for drought resistance of P. sylvestris seedlings during early establishment and assessed whether differences occur between topsoil and deeper soil layers. MethodsBiomass allocation and colonisation of fine roots by ectomycorrhizal fungi were assessed in seedlings grown for 6 months in a common garden under different precipitation scenarios: constant drought (March–September), summer drought (June–September), and wet conditions. ResultsRoot/shoot ratios increased from 0.6 under wet conditions to 0.8 under drought conditions, irrespective of the onset of the drought (March vs. June). In both drought scenarios, seedlings had shorter roots in the topsoil, increased the number of root tips per root length in both soil layers, but did not alter the colonisation rate of root tips by ectomycorrhizal fungi. ConclusionWe conclude that plasticity in root architecture is an important mechanism for drought resistance of P. sylvestris during early seedling establishment

Root architecture might account for contrasting establishment success of Pseudotsuga menziesii var. menziesii and Pinus sylvestris in Central Europe under dry conditions

“…The rooting behaviour of Pinus sylvestris, by contrast, with a distinct taproot that develops early during the seedling stage (Fig. 3), enables the species to quickly reach deeper soil layers (Lyr and Hoffmann 1967;Moser et al 2015). Likewise, high phenotypic plasticity facilitates the establishment of Pinus sylvestris in disturbed environments despite their heterogeneity and low predictability (Chevin and Lande 2011).…”

“…Consequently, the morphology and plasticity of the root system are crucial parameters to assess a species' ability to successfully establish and compete under current and future climatic conditions. Like most pines species, Pinus sylvestris produces a taproot already during the earliest seedling stages (Wilcox 1968), reaching up to 40-cm soil depth within 6 months after germination (Moser et al 2015) and allowing it to acquire water from deeper soil layers that are less rapidly depleted during drought events (Ryel et al 2008). By contrast, little is known about the root architecture of Pseudotsuga menziesii seedlings during early establishment (but see Preisig et al 1979 for 5-8-year-old seedlings), while 10-80-year-old Pseudotsuga menziesii were shown to have a superficial root system (Mauer and Palatova 2012), which only slowly advances to deeper soil layers (Domec et al 2004).…”

Biomass partitioning in a future dry andCO2enriched climate: Shading aggravates drought effects in Scots pine but not European black pine seedlings

“…Larger investments in root biomass of more drought adapted tree populations have been observed for long (e.g. Hertel et al, 2013;Moser, Kipfer, Richter, Egli, & Wohlgemuth, 2014;Taeger et al, 2015;Zimmer & Grose, 1958), but could not be directly related to climatic variables of the seed origin (see e.g. Taeger et al, 2015).…”

Fine roots and ectomycorrhizal colonization in black spruce subjected to reductions in soil moisture

“…No information was available on potential modifications of biomass allocation towards deeper soil layers or outside the area covered by the plastic roofs for improving the access of roots to other water resources that were not excluded by the treatment. Such adaptation mechanisms are described for other conifer species (Moser et al 2015;Pregitzer et al 2002), so may also reasonably occur in black spruce.…”