Drought and small-bodied herbivores modify nutrient cycling in the semi-arid shortgrass steppe.
Lemoine, N. P., & Smith, M. D.. 2019.
Abstract
Climate change will increase the fre-
quency of droughts over the next century, with severe
consequences for ecosystem function in semi-arid
grasslands. The shortgrass steppe (SGS) experi-
ences some of the largest interannual variation in
precipitation among terrestrial biomes and exhibits
extremely high sensitivity to drought. Yet despite
decades of research describing the consequences of
drought for ecosystem function in the SGS, we
currently have little information regarding the impact
of drought on bioavailability of important nutrients
other than nitrogen, the contribution of herbivores to
bioavailable concentrations of these nutrients, and
whether drought alters herbivore-derived nutrient
cycling. To quantify the impacts of long-term drought
and small-bodied herbivores on nutrient cycling and
aboveground net primary production (ANPP), we
factorially manipulated rainfall and herbivore pres-
ence in the SGS of northern Colorado. Specifically, we
measured the impacts of drought and herbivores on
bioavailability of ten important nutrients: aluminum,
calcium, iron, potassium, magnesium, manganese,
nitrate, phosphorus, sulfur, and zinc. We then correlated these nutrients with grass production to
determine whether reduced plant growth under
drought conditions causes a belowground buildup of
nutrients. Drought reduced ANPP as expected, and
also altered concentrations of many nutrients apart
from N, which clustered in their drought response. In
contrast, small-bodied herbivores did not affect ANPP
or soil N. However, they did contribute to the
bioavailable soil concentrations of two important
nutrients: PO4-P and S. Importantly, drought gener-
ally did not modify the contribution of herbivores to
nutrient cycling, suggesting that herbivores might be a
critical component of biogeochemical cycling regard-
less of precipitation in semi-arid grasslands.
Key Words
Biogeochemistry, Ecosystem function, Grasshoppers, Grasslands, Climate change
