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ARS Home » Plains Area » Lubbock, Texas » Cropping Systems Research Laboratory » Plant Stress and Germplasm Development Research » Research » Publications at this Location » Publication #327901

Title: Maintenance of C sinks sustains enhanced C assimilation during long-term exposure to elevated [CO2] in Mojave Desert shrubs

item ARANJUELO, IKER - Public University Of Navarra
item EBBETS, ALLISON - University Of Nevada Las Vegas, Las Vegas, Nv
item EVANS, R - Washington State University
item TISSUE, DAVID - University Of Sydney
item NOGUES, SALVADOR - University Of Barcelona
item VAN GESTEL, NATASJA - Texas Tech University
item Payton, Paxton
item EBBERT, VOLKER - University Of Colorado
item ADAMS III, WILLIAMS - University Of Colorado
item NOWAK, ROBERT - University Of Nevada
item SMITH, STANLEY - University Of Nevada Las Vegas, Las Vegas, Nv

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2011
Publication Date: 4/23/2011
Citation: Aranjuelo, I., Ebbets, A.L., Evans, R., Tissue, D.T., Nogues, S., Van Gestel, N., Payton, P.R., Ebbert, V., Adams III, W.W., Nowak, R.S., Smith, S.D. 2011. Maintenance of C sinks sustains enhanced C assimilation during long-term exposure to elevated [CO2] in Mojave Desert shrubs. Oecologia. 167:339-354.

Interpretive Summary: In this study, a comprehensive suite of physiological process and C balance data were collected from plants during the eighth full growing season of continuous exposure to elevated [CO2] and used to examine the regulation of photosynthetic performance during long-termexposure to elevated [CO2] at the NDFF. Photosynthetic responses and carbon allocation/partitioning patterns were measured for the two dominant shrub species of the Mojave Desert, the evergreen Larrea tridentata and the drought deciduous Ambrosia dumosa. Measurements were made throughout the growing season: from cooler, wetter periods of peak growth in spring to hotter, drier periods of pronounced water stress in summer. Specifically, we examined leaf gas exchange, leaf pigments, leaf N, and leaf soluble sugars and starch to determine the extent that photosynthetic performance was enhanced during longterm exposure to elevated [CO2], and to test specific mechanisms that may cause reduced photosynthetic performance. Because photosynthetic performance is affected by leaf-level and plant-level C allocation, photoassimilate allocation and partitioning also were studied through the use of 13C/12C labeling. We hypothesized that these desert species would downregulate photosynthesis under elevated [CO2] during the moist, early portions of the growing season, and that downregulation would be accompanied by altered leaf pigmentation, decreased leaf N, and increased leaf starch and soluble sugars. Furthermore, we hypothesized that the reduced capacity of plants to allocate C away from leaves would also limit photosynthetic performance under elevated [CO2].

Technical Abstract: During the first few years of elevated atmospheric [CO2] treatment at the Nevada Desert FACE Facility, photosynthetic downregulation was observed in desert shrubs grown under elevated [CO2], especially under relatively wet environmental conditions. Nonetheless, those plants maintained increased Asat (photosynthetic performance at saturating light and treatment [CO2]) under wet conditions, but to a much lesser extent under dry conditions. To determine if plants continued to downregulate during long-term exposure to elevated [CO2], responses of photosynthesis to elevated [CO2] were examined in two dominant Mojave Desert shrubs, the evergreen Larrea tridentata and the drought-deciduous Ambrosia dumosa, during the eighth full growing season of elevated [CO2] treatment at the NDFF. A comprehensive suite of physiological processes were collected. Furthermore, we used C labeling of air to assess carbon allocation and partitioning as measures of C sink activity. Results show that elevated [CO2] enhanced photosynthetic performance and plant water status in Larrea, especially during periods of environmental stress, but not in Ambrosia. d13C analyses indicate that Larrea under elevated [CO2] allocated a greater proportion of newly assimilated C to C sinks than Ambrosia. Maintenance by Larrea of C sinks during the dry season partially explained the reduced [CO2] effect on leaf carbohydrate content during summer, which in turn lessened carbohydrate build-up and feedback inhibition of photosynthesis. d13C results also showed that in a year when plant growth reached the highest rates in 5 years, 4% (Larrea) and 7% (Ambrosia) of C in newly emerging organs were remobilized from C that was assimilated and stored for at least 2 years prior to the current study. Thus, after 8 years of continuous exposure to elevated [CO2], both desert perennials maintained th photosynthetic capacities under elevated [CO2]. We conclude that C storage, remobilization, and partitioning influence the responsiveness of these desert shrubs during long-term exposure to elevated [CO2].