Drought Treated Seedlings of Quercus petraea (Matt.) Liebl., Q. robur L. and Their Morphological Intermediates Show Differential Radial Growth and Wood Anatomical Traits

Abstract

Background and Objectives: Studying responses in woody plants upon water limitation is gaining importance due to the predicted increase in frequency and intensity of droughts in Europe. We studied the variation in radial growth and in wood anatomical traits caused by water limited growth conditions in offspring from Quercus petraea (Matt.) Liebl., Q. robur L. and their morphological intermediates grown in the same environment. Materials and Methods: Cross sections were prepared from the stems of 210 three-year-old potted seedlings, comprising control plants and seedlings that experienced from late spring until early autumn of the first growing season two sequential periods of water with-holding each followed by plentiful re-watering. Pith radius, ring width of the three growing seasons and latewood vessel diameter in second and third growing season were measured. Presence of intra-annual density fluctuations, dendritic patterns of latewood vessels and the level of ring closure of earlywood vessels were observed. The traits were modelled to examine the explanatory power of the taxon of the mother tree and the drought treatment. Results: Most of the traits displayed significant differences between offspring from Q. petraea and Q. robur and offspring from the morphological intermediates behaved inconsistent among the traits. Most of the traits were significantly affected by the drought stress in the first growing season. Apart from radial growth, also latewood vessel size was reduced in the two growing seasons following the year in which drought was imposed on the seedlings, suggesting an adaptation to improve the tolerance to drought stress. We also found an indication for a compensation growth mechanism, counteracting the lost growing time during the drought stress, as the level of ring closure of the earlywood vessels in the year following the drought treatment was further advanced in the treated seedlings, an effect that disappeared in the subsequent year. Conclusion: Oaks exposed to drought adapt their growth and xylem structure to improve drought resistance. While youth growth of Q. robur is more competition-oriented, with a faster juvenile growth, Q. petraea seems to invest more in a precautious growth, being more prepared for stressful conditions. It is therefore possible that Q. robur seedlings may suffer more from intensified droughts than Q. petraea seedlings.

Adaptability responses to drought stress in the oak species Quercus petraea growing on dry sites

“…In terms of the root to shoot ratios based on the below-and aboveground dry biomass, all of the plants exposed to reduced irrigation had higher values than the optimally treated seedlings, except for those in Forest Botanic Garden 1. The root to shoot ratio of plants usually increases under the influence of drought because they reduce the leaf growth to increase their water-absorbing area, thereby decreasing their transpiration area, as confirmed in oaks by Dickson and Tomlinson (1996), Thomas and Gausling (2000), Arend et al (2011) and Vander Mijnsbrugge et al (2017, 2020. This is widely considered to be an adaptive mechanism by which the plant can restore the balance between absorption of soil water by the roots and water loss by the leaves (Arend et al 2011).…”

Drought effects of annual and long-term temperature and precipitation on mortality risk for 9 common European tree species

“…Species tolerating warmer conditions possess mechanisms to withstand heat and drought to a certain degree. Oak seedlings, for example, exposed to drought have been shown to have adapted their growth and xylem structure to improve drought resistance, for example, via reduction of latewood vessel size (Vander Mijnsbrugge et al 2020). Grouping according to distribution was also performed for North American species into plant functional traits with subsequent mortality patterns analyzed by Dietze and Moorcroft (2011), who distinguished between angiosperms and gymnosperms.…”

“…Whereas xylem hydraulic failure seems to be ubiquitous across multiple tree taxa at drought induced mortality, evidence supporting carbon starvation is not universal and more common for gymnosperms than angiosperms (Adams et al 2017). Species differ in their degree to adapt wood anatomical traits (Vander Mijnsbrugge et al 2020) or e.g. the degree in which they can compensate for leaf damage caused by insects during the spring (e.g.…”

Effects of Suillus Luteus on the root morphology and endogenous hormones of Pinus massoniana seedlings under drought stress

“…Drought stress can restrict the survival and growth of plants, while changing their structure and function (Vander Mijnsbrugge et al 2020). In arid areas, water scarcity is one of the most critical factors causing plant mortality (Allen et al 2010).…”