Future shifts in precipitation and temperature are expected to dramatically affect plant traits. To date, many studies have explored the effects of acute stresses, but few have investigated the consequences of chronic exposure (> 5 years) to distinct climatic conditions. We used naturally occurring Plantago lanceolata growing under different precipitation regimes (ambient, 50% less than ambient = drought) and temperatures (ambient, +~0.8, +~2.4, +~4.0 oC above ambient) at the Boston Area Climate Experiment (BACE, constructed in 2007) to elucidate the consequences to growth and chemistry of chronic exposure to drought and temperature. We hypothesized that the combination of drought and warming would have stronger effects on plant size and the leaf metabolome than chronic exposure to only one stress, and expected that the effects of drought would be more pronounced than those of warming given the species' shallow rooting system and wide latitudinal distribution. To test this we measured plant size and profiled diverse plant metabolites including foliar nitrogen, amino acids, sugars, the sugar alcohol sorbitol, di- and tricarboxylic acids, the cyclic polyol myo-inositol and iridoid glycosides). Plant traits were assessed in early June 2016 prior to the onset of severe drought.
Results/Conclusions
Precipitation and drought had little effect on plant size at the time of sampling but large effects on the leaf metabolome. The analysis of several primary and secondary metabolites revealed striking effects of drought and lesser effects of warming on leaf chemistry. Moreover, as hypothesized, the effects of the drought treatment were strong and most pronounced under warming. Compared to the ambient condition, plants in the drought treatment had lower concentrations of foliar nitrogen, amino acids and most sugars and higher concentrations of sorbitol, a common stress-induced metabolite. Moreover, drought-exposed plants showed lower leaf concentrations of catalpol, an iridoid glycoside well known to affect the performance of herbivores. While the effects of warming were less pronounced, the temperature extremes (i.e., the highest temperatures) resulted in most distinct plant responses to drought. We discuss how these changes in chemistry might impact herbivores.