HR: 16:30h
AN: B54B-03 INVITED    [Abstracts]
TI: Linking the Response of Annual Grasslands to Warming and Altered Rainfall Across Scales of Gene Expression, Species, and Ecosystem
AU: * Torn, M S
EM: mstorn@lbl.gov
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: * Torn, M S
EM: mstorn@lbl.gov
AF: UC Berkeley, Valley Life Sciences Bldg, Berkeley, CA 94720, United States
AU: Bernard, S M
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: Castanha, C
EM: castanha@nature.berkeley.edu
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: Fischer, M L
EM: mlfischer@lbl.gov
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: Hopkins, F M
EM: FMHopkins@lbl.gov
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: Placella, S A
EM: placella@nature.berkeley.edu
AF: UC Berkeley, Valley Life Sciences Bldg, Berkeley, CA 94720, United States
AU: St.Clair, S B
EM: samuel_stclair@byu.edu
AF: UC Berkeley, Valley Life Sciences Bldg, Berkeley, CA 94720, United States
AU: Salve, R
EM: R_Salve@lbl.gov
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: Sudderth, E
EM: sudderth@calmail.berkeley.edu
AF: UC Berkeley, Valley Life Sciences Bldg, Berkeley, CA 94720, United States
AU: Herman, D
EM: skyhawk@nature.berkeley.edu
AF: UC Berkeley, Valley Life Sciences Bldg, Berkeley, CA 94720, United States
AU: Ackerly, D
EM: dackerly@sbcglobal.net
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: Ackerly, D
EM: dackerly@sbcglobal.net
AF: UC Berkeley, Valley Life Sciences Bldg, Berkeley, CA 94720, United States
AU: Firestone, M K
EM: mkfstone@nature.berkeley.edu
AF: Lawrence Berkeley Lab, One Cyclotron Rd, Berkeley, CA 94720, United States
AU: Firestone, M K
EM: mkfstone@nature.berkeley.edu
AF: UC Berkeley, Valley Life Sciences Bldg, Berkeley, CA 94720, United States
AB: Climate change can influence terrestrial ecosystems at multiple biological levels: gene expression, species, and ecosystem. We are studying California grassland mesocosms with seven annual species (five grasses, two forbs) that were started in 2005. In the 2006-2007 growing season, they were exposed to three rainfall treatments (297, 552, and 867 mm y-1) and soil and air temperature (ambient and elevated +4oC) in replicated greenhouses. This presentation will combine plant and ecosystem level results with transcript level analyses associated with key enzymes, such as rubisco and glutamine synthetase (GS). Because rainfall is the dominant climate variable for most processes in this Mediterranean ecosystem, the effect of warming was strongly mediated by rainfall. In fact, we saw significant interactions between temperature and rainfall treatments at all three biological levels. For example, at the ecosystem level, warming led to a decrease in aboveground and total NPP under low rainfall, and an increase under high rainfall. For the dominant species, Avena barbata, warming had no effect under high rainfall, but suppressed Avena NPP in low rainfall. At the same time, warmer, wetter conditions accelerated Avena flowering by almost 15 days. This shift in phenology was presaged by observations at the transcript level. Specifically, in the high temperature, high rainfall treatment, the levels of mRNAs for RbcS and GS2 (encoding the small subunit of rubisco and the chloroplastic isoform of GS, respectively) declined while GS1 (encoding the cytosolic isoform of GS) was upregulated several weeks before heading. The transcript level response (along with soil and plant nitrogen data) indicated the leaf had switched from a carbon and nitrogen sink to a source - consistent with more mature plant function and earlier flowering. Soil CO2 respiration also showed strong rain-by-temperature interactions that were due mainly to changes in root response (respiration and/or exudates) rather than in microbial respiration. Overall, the pervasive rain-by-temperature interactions mean that it may be very difficult to predict the effect of warming alone, without accounting for changes in precipitation (in our Mediterranean system). While predictions of warming of 3-6°C in the next 100 years are fairly certain, changes in precipitation are much more uncertain, with some forecasts drier and others wetter for a given location. We suggest that uncertainty about future precipitation and the interacting influences of temperature and moisture on ecosystems are currently key limitations in predicting ecosystem response to climate change, particularly in Mediterranean ecosystems such as the one studied here.
DE: 0410 Biodiversity
SC: Biogeosciences [B]
MN: 2007 Fall Meeting