Plants manage water stress through various mechanisms, including increasing concentrations of compounds such as abscisic acid (ABA) to signal stomatal closure and reduce water loss, changing plant secondary metabolite concentrations, and altering morphological traits such as growth and leaf mass per area. During a drought period, plant growth often slows down earlier than carbon uptake through photosynthesis, and the ‘excess’ carbon may be partitioned to greater production of secondary compounds. Yet, this theoretical prediction has been difficult to test empirically. In a greenhouse, McKiernan et al. (2015) investigated variation in physiological, morphological, and chemical traits of two juvenile Eucalyptus species from four locations along a precipitation gradient, examining locality-specific responses to water deficit and rewatering.
Surprisingly, McKiernan et al. (2015) found that responses to mild water deficit were conserved across the four localities. This means that individuals that originated from drier environments, and thus were expected to exhibit traits to better manage drought stress, responded similarly to those from more humid locations. Water deficit decreased leaf water potential, increased foliar ABA levels, and decreased aboveground biomass and leaf water content, while secondary compounds with similar biosynthetic pathways exhibited common responses to water deficit. Depending on the pathway, the concentrations either increased or decreased, thus suggesting that simple carbon-balance theories alone cannot explain the dynamics of secondary compounds. Future studies should investigate the effects of more severe drought on concentrations of secondary compounds to determine if drought severity influences the expression of locality-specific responses.
Adam B. McKiernan, Brad M. Potts, Timothy J. Brodribb, Mark J. Hovenden, Noel W. Davies, Scott A.M. McAdam, John J. Ross, Thomas Rodemann, Julianne M. O’Reilly-Wapstra, 2015, ‘ Responses to mild water deficit and rewatering differ among secondary metabolites but are similar among provenances within Eucalyptus species ‘, Tree Physiology, p. tpv106 http://dx.doi.org/10.1093/treephys/tpv106
Ülo Niinemets, 2015, ‘Uncovering the hidden facets of drought stress: secondary metabolites make the difference’, Tree Physiology, p. tpv128 http://dx.doi.org/10.1093/treephys/tpv128