Data from: Drought history affects grassland plant and microbial carbon turnover during and after a subsequent drought event

Drought periods are projected to become more severe and more frequent in
many European regions. While effects of single strong droughts on plant
and microbial carbon (C) dynamics have been studied in some detail,
impacts of recurrent drought events are still little understood. We tested
whether the legacy of extreme experimental drought affects responses of
plant and microbial C and nitrogen (N) turnover to further drought and
rewetting. In a mountain grassland we conducted a 13C pulse-chase
experiment during a naturally occurring drought and rewetting event in
plots previously exposed to experimental droughts, and in ambient
controls. After labelling we traced 13C below-ground allocation and
incorporation into soil microbes using phospholipid fatty acid (PLFAs)
biomarkers. Drought history had no effects on the standing shoot and fine
root plant biomass. However, plants with experimental drought history
displayed decreased shoot N concentrations, and increased fine root N
concentrations relative to those in ambient controls. During the natural
drought plants with drought history assimilated and allocated less 13C
below-ground; moreover, fine root respiration was reduced and not fuelled
by fresh C compared to plants in ambient controls. Regardless of drought
history microbial biomass remained stable during natural drought and
rewetting. Although microbial communities initially differed in their
composition between soils with and without drought history, they responded
to the natural drought and rewetting in a similar way: gram-positive
bacteria increased, while fungal and gram-negative bacteria remained
stable. In soils with drought history a strongly reduced uptake of recent
plant-derived 13C in microbial biomarkers was observed during the natural
drought, pointing to a smaller fraction of active microbes or to a
microbial community that is less dependent on plant C. Synthesis: Drought
history can induce changes in above- versus below-ground plant N
concentrations and affect the response of plant C turnover to further
droughts and rewetting by decreasing plant C uptake and below-ground
allocation. Drought history does not affect the responses of the microbial
community to further droughts and rewetting, but alters microbial
functioning, particularly the turnover of recent plant-derived carbon,
during and after further drought periods.