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ARS Home » Southeast Area » Raleigh, North Carolina » Plant Science Research » Research » Publications at this Location » Publication #201335
Title: Elevated atmospheric CO2 and O3 differentially alter nitrogen acquisition in peanut

Author
item TU, CONG - NCSU
item Booker, Fitzgerald
item Burkey, Kent
item HU, SHUIJIN - NCSU

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2009
Publication Date: 8/12/2009
Citation: Tu, C., Booker, F.L., Burkey, K.O., Hu, S. 2009. Elevated atmospheric CO2 and O3 differentially alter nitrogen acquisition in peanut. Crop Science. 49:1827-1836.

Interpretive Summary: Carbon dioxide (CO2) and ozone (O3) concentrations in the atmosphere have rapidly increased over the past 50 years mainly due to the burning of fossil fuels. These trends are expected to continue throughout this century. Elevated CO2 usually stimulates photosynthesis and plant productivity, while elevated O3 inhibits them. Whether these gases also alter the plant’s ability to acquire mineral nutrients such as nitrogen (N) is unclear. Using open-top field chambers, we examined the separate and combined effects of CO2 and O3 on N acquisition in peanut (Arachis hypogaea L.). Peanut, a legume, obtains N from the soil as well as from the air through a process called symbiotic N fixation, which occurs in bacteria-filled nodules on the roots. The bacteria capture gaseous N and pass it along to the plant in exchange for carbohydrates supplied by the plant. The amount of N supplied to the plant by N fixation can be estimated by measuring a natural stable isotope, 15N, in plant tissues. In our experiment, peanut was treated with a range of CO2 concentrations (ambient to more than twice-ambient) in combination with charcoal-filtered air (clean air control), non-filtered air, and non-filtered air plus added O3. Plant N acquisition was examined by measuring N concentrations and 15N natural abundance in leaf, stem and seed materials. Early in the growing season, elevated CO2 significantly reduced N concentrations in plant leaves, but had no effects on the 15N abundance. By the final harvest, however, elevated CO2 did not affect the N concentration in plant materials, but reduced their 15N abundance by up to 50%, suggesting that CO2 enrichment significantly increased the contribution of air-derived N to the plant. In contrast, elevated O3 affected neither the N concentrations nor the 15N values early in the growing season. By the final harvest, however, elevated O3 significantly reduced total biomass N. Also, the 15N abundance in plant materials was significantly higher under elevated O3 than in the control, indicating that symbiotic N2 fixation was critically inhibited. Our results showed that elevated atmospheric CO2 and O3 affected peanut N acquisition differently. Atmospheric CO2 enrichment enhanced N acquisition via uptake from soil during the early growing stage but through symbiotic N fixation during reproductive growth. Increasing O3 concentrations reduced plant N acquisition, mainly by inhibiting symbiotic N2 fixation late in the growing season. Inhibitory effects of O3 on N acquisition were generally ameliorated by elevated CO2. In addition, our results suggest that, unlike non-N fixing crops such as wheat, seed N content in peanut and other legumes may not decline at elevated CO2 because of enhanced N2 fixation.

Technical Abstract: Both CO2 and ozone (O3) concentrations in the atmosphere have increased over the past 50 years and are predicted to rise continually during this century. Elevated CO2 usually stimulates while elevated O3 often inhibits plant photosynthesis and primary production. Whether these changes are partly related to effects on nitrogen (N) acquisition has, however, received little attention. Using open-top field chambers, we examined the effects of reciprocal combinations of CO2 and O3 on N acquisition in peanut (Arachis hypogaea L.) grown in a sandy loam soil. Treatments were ambient CO2 and CO2-enrichment of approximately 175, 350 and 630 ppm in combination with charcoal-filtered air (21 ppb, control), non-filtered air (49 ppb), and non-filtered air plus O3 (79 ppb). Plant N acquisition was examined by measuring N concentrations and 15N natural abundance in leaf, stem and seed tissues. Early in the growing season, elevated CO2 significantly reduced N concentrations in leaves by 23–39%, but had no effect on 15N abundance. By the final harvest, there was no effect of elevated CO2 on N concentration in plant tissue samples, but 15N abundance was lower by up to 50%. This suggests that CO2 enrichment significantly increased the contribution of air-derived N to the plant. Elevated O3 affected neither the N concentrations nor the delta 15N values early in the growing season. By the final harvest, however, added O3 significantly reduced total biomass N. Also, the 15N abundance in plant materials was significantly higher (10–44%) under elevated O3 than in the control, indicating that symbiotic N2 fixation was critically inhibited. These findings indicate that elevated CO2 enhances N acquisition from the soil and the air in peanut while elevated O3 inhibits it, mainly by inhibiting symbiotic N2 fixation. Inhibitory effects of O3 on N acquisition were generally ameliorated by elevated CO2. In addition, our results suggest that, unlike non-N fixing crops such as wheat, seed N content in peanut and other legumes may not decline at elevated CO2.