Drought effects on root and shoot traits and their decomposability

Drought can induce phenotypic plasticity in a range of plant root and shoot traits. These traits have been shown to explain differences in root and shoot litter decomposability between species. However, it is unknown how drought-induced plasticity of root and shoot traits alters their decomposability.To investigate this issue across a range of species, we grew a grass Lolium perenne, a forb Plantago lanceolata and a legume Trifolium repens common to European temperate grasslands and subjected them to a 5-week moderate drought treatment. We compared morphological and chemical root and shoot traits of the droughted plants to well-watered controls. We then conducted a decomposition assay of the senesced root and shoot material over 16 weeks, with mass loss measurements at five timepoints.Drought had significant and sometimes strong effects on morphological and chemical root and shoot traits of all three species, sometimes similar to differences between species and generally in line with a shift to a more resource-conservative strategy. Drought also increased the labile litter fraction in roots of Lolium perenne, which was associated with a substantial increase in non-structural carbohydrates. Drought decreased the labile litter fraction in shoots of Plantago lanceolata, but this could not be explained by the traits we measured. Drought effects on litter decomposability were weaker than on plant traits.Our results suggest that plant trait-mediated effects of drought on litter decomposability can either increase or decrease vegetation feedbacks to climate change. They also show that drought-induced plasticity in root and shoot traits does not automatically translate into equivalent changes in litter decomposability.