How tree roots respond to drought

Abstract

The ongoing climate change is characterized by increased temperatures and altered precipitation patterns. In addition, there has been an increase in both the frequency and intensity of extreme climatic events such as drought. Episodes of drought induce a series of interconnected effects, all of which have the potential to alter the carbon balance of forest ecosystems profoundly at different scales of plant organization and ecosystem functioning. During recent years, considerable progress has been made in the understanding of how aboveground parts of trees respond to drought and how these responses affect carbon assimilation. In contrast, processes of belowground parts are relatively underrepresented in research on climate change. In this review, we describe current knowledge about responses of tree roots to drought. Tree roots are capable of responding to drought through a variety of strategies that enable them to avoid and tolerate stress. Responses include root biomass adjustments, anatomical alterations, and physiological acclimations. The molecular mechanisms underlying these responses are characterized to some extent, and involve stress signaling and the induction of numerous genes, leading to the activation of tolerance pathways. In addition, mycorrhizas seem to play important protective roles. The current knowledge compiled in this review supports the view that tree roots are well equipped to withstand drought situations and maintain morphological and physiological functions as long as possible. Further, the reviewed literature demonstrates the important role of tree roots in the functioning of forest ecosystems and highlights the need for more research in this emerging field.

Phenotypic Plasticity Explains Response Patterns of European Beech (Fagus sylvatica L.) Saplings to Nitrogen Fertilization and Drought Events

“…This supports our second hypothesis that one-year-old plants would react more sensitively to treatments than two-year-old plants, particularly with regard to drought events. We hypothesize that differences in drought sensitivity were mainly related to the plants' shoot:root ratios [22], which significantly differed for one-year-old and two-year-old beech saplings (i.e., two-year-old plants showed relatively higher belowground investments than one-year-old plants). As a consequence of these age-related shifts in biomass allocation patterns (i.e., apparent plasticity; according to Weiner [15]), two-year-old plants may be less drought sensitive and may experience less constraints in their water supply, particularly in periods of drought [42,43].…”

“…As a consequence, a sapling's drought sensitivity may decrease with an age-related increase of belowground investments ("apparent plasticity" [15]). Thus, a tree's phenotypic plasticity (in terms of both plastic allometry and apparent plasticity) may influence its growth responses to environmental change [22].…”

Response of the leaf phenology and tree-ring width of European beech to climate variability

“…The fine roots of European beech are mostly distributed in the uppermost soil layers (to 40 cm), whereas the root density decreases with the soil depth (Meier and Leuschner 2008;Leuschner et al 2004). During a drought, the fine root biomass decreases because of reductions in the transpiration and respiration rates (Brunner et al 2015). A drought spell in the top soil layer (0-0.4 m) can influence forest productivity.…”

Maintaining connectivity: understanding the role of root order and mycelial networks in fine root decomposition of woody plants

“…Water stress can lead to changes in root cell wall constituents, as plants increase concentrations of suberin (a biopolymer composed of aliphatic and aromatic compounds) and lignin, to mediate water loss from cells (Brunner et al 2015). Increased amounts of suberin in root cell walls enhances the hydrophobic protection of tissues, slowing decomposition (Dignac and Rumpel 2013).…”