COS 182-3 - Drought and long-term nutrient availability treatment effects on plant diversity and productivity in restored prairie

Background/Question/Methods

Multiple global change drivers interact to affect grassland diversity and productivity, but less is known about their interactive effects in restored grassland. We tested the interactive effects of multi-year-imposed drought and long-term nutrient availability treatments on plant community structure and productivity of restored prairie by leveraging a field experiment established in 1997 that contains long-term nutrient treatments. Starting in 2020 and continuing into 2021, we installed rainout shelters over half of each plot to create a split block design with a fully factorial combination of precipitation and nutrient availability (ambient N, enriched N, and reduced N). We hypothesized that multi-year-imposed drought would reduce differences in both productivity and community structure among ambient, enriched, and reduced-N soil relative to levels under ambient rainfall. We visually measured plant composition and cover to calculate plant community diversity, richness, evenness, grass cover, and forb cover. We estimated aboveground net primary productivity (ANPP) by harvesting peak plant biomass. We measured gravimetric soil moisture every 2-3 weeks to verify rainout shelters reduced precipitation compared to the ambient precipitation treatment. We tested the effects and interactions of nutrient and precipitation on plant community metrics and ANPP using mixed models.

Results/Conclusions

Gravimetric moisture was lower under rainfall shelters compared to ambient conditions, especially when rainfall amounts between measurement periods were low. Plant community responses were affected by an interaction of the manipulated drivers, whereas only a main effect of nutrient affected ANPP. Diversity and richness were lower or remained unchanged in under rainout shelters in the ambient-N and enriched-N soil compared to ambient precipitation, but diversity and richness in the reduced-N soil was higher under experimental drought compared to ambient precipitation. Grass cover was lower under reduced precipitation compared to ambient precipitation regardless of nutrient availability. Forb cover was higher in soil with reduced-N and reduced precipitation relative to all other treatments. Total and grass ANPP were higher under enriched-N compared to ambient-N and reduced-N treatments over all levels of precipitation. Forb ANPP, however, did not differ among nutrient or precipitation treatments. Short-term drought has greater potential to negatively affect diversity in restored prairie, particularly prairies restored on deep, fertile soils and those receiving exogenous sources of N. Extreme N limitation may promote forb cover and ANPP under ambient and drought conditions.