Precipitation Controls on Carbon and Nitrogen Cycles in Arid-Semiarid Ecosystems
Ecosystem ecologists typically agree that water availability is the most frequently
limiting factor in arid and semiarid ecosystems. However, the relationship between
annual precipitation (PPT) and key ecosystem processes is often not clear. For example,
PPT does not account for more than 20-40% of the interannual variability of
aboveground net primary production (ANPP) in these systems. Is it incorrect that water
availability is the most important limiting factor in these ecosystems? Another possibility
is that plant meristem density interacting with precipitation can constrain the response of
ANPP to changes in water availability. Osvaldo Sala and Lara Reichmann (photo below;
Brown University), and Deb Peters (Jornada Experimental Range) are experimentally
testing the meristem-limitation hypothesis within a grass-dominated (Bouteloua
eriopoda) community at the Jornada. We are using rainout shelters (photo at bottom) to
reproduce a precipitation gradient with five levels of precipitation: 50% and 80% reduced
precipitation, control (incoming precipitation), and 50% and 80% increased precipitation.
After the second year, the precipitation treatments will be reversed to simulate high
interannual precipitation variability typical of arid ecosystems. In addition, the PPT
treatment will be combined with two levels of nitrogen: ambient N and increased N. We
expect that meristem density will respond proportionally to precipitation input: highest in
the watered plots, lowest in the dry plots, and intermediate in control plots. In addition,
we expect that plant production following a wet year will be less constrained by meristem
density than productivity in a year that follows a drought. Understanding these
mechanisms will improve ANPP forecasts, and may be useful to project ecosystem
responses under different climate scenarios.
Installing rainout shelter |
Increased precipitation simulation |
Rainout shelter |
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