Drying climate may strongly affect plant productivity and standing biomass and, thus,
ecosystem carbon cycling. While drought effects on grassland aboveground plant biomass
(AGB) have been widely studied and are generally negative, reports on belowground
plant biomass (BGB) are much fewer, and results are more variable. In a full factorial
experiment in a temperate grassland, we studied the legacy effect of an initial extreme
drought, conducted in 2014, and the effect of four levels of chronic precipitation
change, water addition, ambient precipitation, moderate drought, and severe drought
between 2015 and 2018, on AGB, BGB, and BGB/AGB, in 2019. AGB was negatively affected
by chronic drought, and also by extreme drought within each level of chronic precipitation
change except severe drought. Total BGB was not influenced by extreme drought but
was negatively impacted by chronic severe drought. Responses were the strongest in
the shallow soil layer (0-10 cm), where both extreme and chronic droughts decreased
belowground biomass, and weak in the deep soil layer (10-20 cm). BGB/AGB was not altered
by extreme drought, but increased in chronic drought plots, because the decrease of
AGB was much greater than the decrease in BGB. Our results indicate that lagged effects
of previous extreme drought and chronic change in precipitation are both important
in shaping biomass pools and allocation in grasslands, sometimes with interactive
effects.
