|Sala, Osvaldo -|
|Gherardi, Laureano -|
|Reichmann, Lara -|
|Jobbagy, Esteban04 -|
Submitted to: Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 25, 2012
Publication Date: N/A
Interpretive Summary: Our objective was to test four hypotheses about mechanisms explaining controls on aboveground net primary production (ANPP) through time and space in grasslands. We used 16 long-term series of ANPP from different rsearch sites to test these hypotheses. Our results show that legacies of previous conditions were important for all grassland types from deserts to tallgrass prairie. We developed general models of this relationship to show that legacies of previous year's rainfall decrease in importance as mean annual rainfall increases across a gradient from arid to mesic grasslands. Our results suggest that different grassland types will respond differently to climate change drive alterations in water availability, and that the magnitude of the response will increase with time.
Technical Abstract: Variability of aboveground net primary production (ANPP) of arid to sub-humid ecosystems displays a closer association with precipitation when considered across space, based on multiyear averages for different locations, than through time, based on year to year change at single locations. Here, we propose a theory of controls of ANPP based on four hypotheses about legacies of wet and dry years that explains space vs. time differences in ANPP-precipitation relationships. We tested the hypotheses using 16 longterm series of ANPP. We found that legacies, revealed by the association of current- vs. previous-year conditions through the temporal series occur across all ecosystem types from deserts to mesic grasslands. Therefore, previous-year precipitation and ANPP control a significant fraction of current-year production. We developed unified models for the controls of ANPP through space and time. The relative importance of current- versus previous-year precipitation changes along a gradient of mean annual precipitation with the importance of current-year PPT decreasing whereas the importance of previous-year PPT remains constant as mean annual precipitation increases. Finally, our results suggest that ANPP will respond to climate-change driven alterations in water availability and, more importantly, that the magnitude of the response will increase with time.