Drought effects on root and shoot traits and their decomposability

1. 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. 2. 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. 3. 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. 4. 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.