Limited legacy effects of extreme multi-year drought on carbon and nitrogen cycling in a mesic grassland

The intensification of drought throughout the US Great Plains has the
potential to have large impacts on grassland functioning, as has been
shown with dramatic losses of plant productivity annually. Yet, we have a
poor understanding of how grassland functioning responds after drought
ends. This study examined how belowground nutrient cycling responds after
drought and whether legacy effects persist post-drought. We assessed the
two-year recovery of nutrient cycling processes following a four-year
experimental drought in a mesic grassland by comparing two different
growing season drought treatments - chronic (each rainfall event reduced
by 66%) and intense (all rain eliminated until 45% of annual rainfall was
achieved) – to the control (ambient precipitation) treatment. At the
beginning of the first growing season post-drought, we found that in situ
soil CO2 efflux and laboratory-based soil microbial respiration were
reduced by 42% and 22% respectively in the intense drought treatment
compared to the control, but both measures had recovered by mid-season
(July) and remained similar to the control treatment in the second
post-drought year. We also found that extractable soil ammonium and total
inorganic N were elevated throughout the growing season in the first year
after drought in the intense treatment. However, these differences in
inorganic N pools did not persist during the growing season of the second
year post-drought. The remaining measures of C and N cycling in both
drought treatments showed no post-drought treatment effects. Thus,
although we observed short-term legacy effects following the intense
drought, C and N cycling returned to levels comparable to non-droughted
grassland within a single growing season regardless of whether the drought
was intense or chronic in nature. Overall, these results suggest that key
aspects of C and N cycling in mesic tallgrass prairie do not exhibit
persistent legacies from four years of experimentally-induced drought.