Abstract Detail


Winkler, Daniel [1], Grossiord, Charlotte [2], Belnap, Jayne [1], Howell, Armin [1], Ferrenberg, Scott [3], Smith, Hilda [1], Reed, Sasha [1].

Phenological advancement and trait plasticity compensates for reduced carbon fixation after 13 years of warming.

Drylands play a dominant role in global carbon cycling and are particularly vulnerable to increasing temperatures that increase evapotranspiration and accelerate drying of terrestrial surfaces. Most warming experiments to date capture only community-level data and fail to track individual plants, potentially leading to divergent patterns that can arise in relation to population dynamics versus predicting a species persistence and survival. In a 13-year ecosystem warming experiment in a southwestern dryland, we investigated the consequences of rising temperature on a widespread, keystone grass species Achnatherum hymenoides. In an effort to make inferences about the likelihood of this species surviving and how dryland ecosystem function may change in the future, we tested for shifts in aboveground biomass, phenology, photosynthesis (i.e., net photosynthesis and photosynthetic acclimation), and for signs of water stress after 13 years of continuous warming. We also evaluated population cover and recruitment in an effort to reveal how changes in population dynamics and individual growth patterns interact. Warming dramatically affected plant growth through large enhancements in aboveground production, However, there were fewer individuals in warmed plots due to lower survival and recruitment over the course of the experiment, reducing overall plant cover. As a result, while measured plants are much larger in the warmed plots, they also represent more of the younger individuals who germinated in our experiment’s warmer world conditions. Plants also responded to warming through large changes in phenological cycles, advancing spring green-up by 8.5 ± 2.9 days, date of first flower by 10.8 ± 1.3 days, and senescence by 2.2 ± 1.1 days, leading to a longer growing season (+6.3 days). No treatment effects were found on photosynthetic optima or temperature optima, but net photosynthesis in the warmed plots was reduced by 30% when soil moisture was not limiting. This suggests individual plants did not acclimate to changes in temperature, likely due to low photosynthetic plasticity. Overall, our study demonstrates a plastic response of A. hymenoides to tolerate 13 years of warming by shifting growth and aboveground allocation strategies and downregulating CO2 fixation to prevent plant damage. Together, these results suggest A. hymenoides may be capable of facing increased temperatures but that the species may not be as abundant nor will the species represent as much of the system’s vegetation cover.

1 - US Geological Survey, 2290 S West Resource Boulevard, Moab, UT, 84532, USA
2 - Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Z├╝rcherstrasse 111, Birmensdorf, Switzerland
3 - New Mexico State University, Department of Biology, Las Cruces, NM, USA

warming experiment
Indian ricegrass
Colorado Plateau.

Presentation Type: Oral Paper
Number: 0007
Abstract ID:193
Candidate for Awards:None

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