Carbon exchange responses of a mesic grassland to an extreme gradient of precipitation
Growing evidence indicates that ecosystem processes may be differentially sensitive to dry versus wet years, and that current understanding of how precipitation affects ecosystem processes may not be predictive of responses to extremes. In an experiment within a mesic grassland, we addressed this uncertainty by assessing responses of two key carbon exchange processes—aboveground net primary production (ANPP) and soil respiration (Rs)—to an extensive gradient of growing season precipitation. This gradient comprised 11 levels that specifically included extreme values in precipitation; defined as the 1st, 5th, 95th, and 99th percentiles of the 112-year climate record. Across treatments, our experimental precipitation gradient linearly increased soil moisture availability in the rooting zone (upper 20 cm). Relative to ANPP under nominal precipitation amounts (defined as between the 15th and 85th percentiles), the magnitude of ANPP responses were greatest to extreme increases in precipitation, with an underlying linear response to both precipitation and soil moisture gradients. By contrast, Rs exhibited marginally greater responses to dry versus wet extremes, with a saturating relationship best explaining responses of Rs to both precipitation and soil moisture. Our findings indicate a linear relationship between ANPP and precipitation after incorporating responses to precipitation extremes in the ANPP–precipitation relationship, yet in contrast saturating responses of Rs. As a result, current linear ANPP–precipitation relationships (up to ~ 1000 mm) within mesic grasslands appear to hold as appropriate benchmarks for ecosystems models, yet such models should incorporate nonlinearities in responses of Rs amid increased frequencies and magnitudes of precipitation extremes.
KeywordsClimate extremes Drought Primary production Rainfall Soil respiration
The authors would like to first and foremost thank the Konza Prairie Biological Station (KPBS) and those affiliated for allowing this project to be possible. In particular, we would like to thank P. O’Neal and J. Larkins of the KPBS for technical support during the project. We would like to thank J. Dietrich, M. Johnston, M. Shields, A. Hoffman, L. Baur, L. Vilonen, M. Clark, M. Updike, R. Griffin-Nolan, A. Post, Q. Yu and W. Mau for assistance in the field. We are grateful for partial financial support to AJF from The Nature Conservancy J.E. Weaver Competitive Grant, The Colorado State University Graduate Degree Program in Ecology, and Western Agricultural Innovations. Support was provided to MDS and AKK by the Konza Prairie Long-term Ecological Research Program, the Drought-Net Research Coordination Network funded by the US National Science Foundation (DEB-1354732) and by the Macrosystems Biology/Emerging Frontiers Programs (EF-1239559, EF-1137378).
Author contribution statement
AJF, AKK, and MDS conceived and designed the study. AJF performed the field research, statistical analyses, and wrote the first draft. All authors contributed to subsequent revisions.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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