There is mounting evidence that plant responses to environmental stress are mediated by epigenetic factors, including DNA methylation. Understanding relationships between DNA methylation, plant development and individual fitness in contrasting environments is key to uncover potential impacts of epigenetic regulation on plant adaptation. Here, we used an experimental approach combining controlled alteration of epigenetic features with exposure to stress. Two provenances of Erodium cicutarium were exposed to a demethylating agent (5-azacytidine) and recurrent drought, and effects on above- and belowground phenotypic traits related to early development, phenology and fitness assessed. Application of 5-azacytidine significantly reduced DNA methylation in leaf and root tissues. This slowed plant development, delayed flowering, and reduced the number of inflorescences produced, independent of water regime. Recurrent drought reduced final above- and belowground biomass and inflorescence production, regardless of the 5-azacytidine exposure. Increased fruit and seed-set were the only adaptations to drought in E. cicutarium, together with an increased number of flowers per inflorescence in water-stressed plants previously treated with 5-azacytidine. Epigenetic effects can desynchronize plant growth, flowering and senescence in both favourable and adverse environments. Future studies should focus on understanding intraspecific variation in ability to change the plant methylome in response to stress, and transgenerational transmission of such responses.
The axial co-variation of xylem anatomical traits is well documented, but lacks a deeper understanding of the tip-to-base dynamics of wood capacitance and resistance to embolism formation for assessing the performance of forest trees under drought stress. For the first time, relative water loss (RWL) curves were generated from wood sampled along the entire length of two mature conifer trees, spanning from the tip of the canopy to the base of the trunk. These measurements were conducted alongside hydraulic vulnerability curves. Parameters related to wood water retention capacity and safety/efficiency of the hydraulic system were extracted. The results revealed significant changes in wood capacitance, resistance to embolism formation and maximum hydraulic conductivity along the gradient from the tree tip to the base, with the most pronounced variation occurring within the first 200 apical centimetres. Resistance to embolism formation and wood capacitance were notably greater at the crown periphery compared to the stem base, with lower water potentials (Ψ) driving 20%, 50%, and 80% loss of hydraulic conductivity, accompanied by a higher release of wood capacitive water volume at the P50 threshold. The strong correlation between relative water loss and conductivity loss highlights the promising potential of traits derived from RWL curves as efficient and rapid indicators for assessing drought sensitivity. This research sheds light on the potential link between axial variation in xylem anatomical traits, drought-induced embolism vulnerability, and wood capacitance, with important implications for investigating plant responses to climate change.
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