PS 43-161 - Changes in precipitation and aboveground net primary production, but not the relationship between precipitation and aboveground net primary production, on the US Plains over the last 40 years
Postdoctoral Scholar National Center for Ecological Analysis and Synthesis, United States
Abstract: Aboveground net primary production (ANPP) is a key component of ecosystem C cycling and an integrated measure of ecosystem function. Much of the inter-annual variation in grassland ANPP can be explained by variation in precipitation amount and pattern. Increasing atmospheric [CO2] is changing the climate in numerous ways, which might alter ANPP and/or the underlying relationship between precipitation and ANPP. Different types of grasslands and different topographic positions within a grassland might respond differently to these changes, as they have previously been shown to respond differently to precipitation manipulation. We analyzed long-term (~40 year) records of precipitation, temperature, atmospheric [CO2], and ANPP at two topographic positions (upland and lowland) from two ecosystems (tallgrass prairie and shortgrass steppe) on opposite ends of the US Central Great Plains, in order to address the questions: How have climate and ANPP changed over the past several decades at the eastern (wet) and western (dry) ends of the US Central Great Plains? Which aspects of climate best explain interannual variation in ANPP of uplands and lowlands at each grassland? And has the relationship between climate and ANPP changed over time at either topographic position at either grassland? We found strong evidence that total precipitation, average precipitation event size, the number of large precipitation events, and the daily minimum temperature during the growing season have all increased (p< 0.05) at the tallgrass prairie, while the number of precipitation events during the growing season decreased (p< 0.05) at the shortgrass steppe. Over the same time, ANPP increased in tallgrass prairie lowlands (by ~40%) and shortgrass steppe uplands (by ~80%), meaning that ANPP is diverging between topographic positions at the tallgrass prairie and converging between topographic positions at the shortgrass steppe. Model selection indicated that total precipitation amount and the average length of dry periods during the growing season best explained inter-annual variation in ANPP at most locations, but suggest that additional factors not considered in our analysis also influence ANPP. Importantly, we found no evidence that the relationship between precipitation amount and ANPP has changed over time at either topographic position at either grassland. These results improve our understanding of how the climate has changed over the past several decades, and how those changes have impacted grassland ecosystem function. They also suggest that current models estimating ANPP based on precipitation remain useful at these sites even as the climate changes.
