Contrasting above‐ and belowground sensitivity of three Great Plains grasslands to altered rainfall regimes

Abstract

Intensification of the global hydrological cycle with atmospheric warming is expected to increase interannual variation in precipitation amount and the frequency of extreme precipitation events. Although studies in grasslands have shown sensitivity of aboveground net primary productivity (ANPP) to both precipitation amount and event size, we lack equivalent knowledge for responses of belowground net primary productivity (BNPP) and NPP. We conducted a 2-year experiment in three US Great Plains grasslands--the C4-dominated shortgrass prairie (SGP; low ANPP) and tallgrass prairie (TGP; high ANPP), and the C3-dominated northern mixed grass prairie (NMP; intermediate ANPP)--to test three predictions: (i) both ANPP and BNPP responses to increased precipitation amount would vary inversely with mean annual precipitation (MAP) and site productivity; (ii) increased numbers of extreme rainfall events during high-rainfall years would affect high and low MAP sites differently; and (iii) responses belowground would mirror those aboveground. We increased growing season precipitation by as much as 50% by augmenting natural rainfall via (i) many (11-13) small or (ii) fewer (3-5) large watering events, with the latter coinciding with naturally occurring large storms. Both ANPP and BNPP increased with water addition in the two C4 grasslands, with greater ANPP sensitivity in TGP, but greater BNPP and NPP sensitivity in SGP. ANPP and BNPP did not respond to any rainfall manipulations in the C3 -dominated NMP. Consistent with previous studies, fewer larger (extreme) rainfall events increased ANPP relative to many small events in SGP, but event size had no effect in TGP. Neither system responded consistently above- and belowground to event size; consequently, total NPP was insensitive to event size. The diversity of responses observed in these three grassland types underscores the challenge of predicting responses relevant to C cycling to forecast changes in precipitation regimes even within relatively homogeneous biomes such as grasslands.

Plants alter their vertical root distribution rather than biomass allocation in response to changing precipitation

“…Second, this future increased precipitation is likely to shift community structure to include a greater proportion of shallow‐rooted species, which will further influence ecosystem functioning and stability (Wilcox et al. , Jones et al. ).…”

Contrasting effects of precipitation manipulations in two Great Plains plant communities

“…; Wilcox et al. ). While these studies provide predictions for future provisioning of ecosystem goods and services (Chapin et al.…”

Contrasting responses of steppeStipassp. to warming and precipitation variability

“…Studies have revealed a greater frequency of droughts in the semiarid areas of northern China (Wu, Dijkstra, Koch, Peñuelas, & Hungate, 2011), which will become even more common in the future as a result of climate change (Battisti & Naylor, 2009;Ma, Zhou, Angélil, & Shiogama, 2017). Decreases in water availability have led to the migration of steppe vegetation and a reduction in steppe area, with additional changes to the structure and productivity of steppe plant communities (Wertin, Reed, & Belnap, 2015;Wilcox, Fischer, Muscha, Petersen, & Knapp, 2015). Steppes in Inner Mongolia account for nearly 67% of the total area of temperate steppe in China (Kang, Han, Zhang, & Sun, 2007) and are highly affected by climate change (Sui, Zhou, & Zhuang, 2013).…”