Free-air CO2 enrichment (FACE) reduces the inhibitory effect of soil nitrate on N2 fixation of Pisum sativum.
OBJECTIVE
Additional carbohydrate supply resulting from enhanced photosynthesis under predicted future elevated CO2 is likely to increase symbiotic nitrogen (N) fixation in legumes. This study examined the interactive effects of atmospheric CO2 and nitrate (NO3(-)) concentration on the growth, nodulation and N fixation of field pea (Pisum sativum) in a semi-arid cropping system.


METHODS
Field pea was grown for 15 weeks in a Vertosol containing 5, 25, 50 or 90 mg NO3(-)-N kg(-1) under either ambient CO2 (aCO2; 390 ppm) or elevated CO2 (eCO2; 550 ppm) using free-air CO2 enrichment (SoilFACE).


RESULTS
Under aCO2, field pea biomass was significantly lower at 5 mg NO3(-)-N kg(-1) than at 90 mg NO3(-)-N kg(-1) soil. However, increasing the soil N level significantly reduced nodulation of lateral roots but not the primary root, and nodules were significantly smaller, with 85% less nodule mass in the 90 NO3(-)-N kg(-1) than in the 5 mg NO3(-)-N kg(-1) treatment, highlighting the inhibitory effects of NO3(-). Field pea grown under eCO2 had greater biomass (approx. 30%) than those grown under aCO2, and was not affected by N level. Overall, the inhibitory effects of NO3(-) on nodulation and nodule mass appeared to be reduced under eCO2 compared with aCO2, although the effects of CO2 on root growth were not significant.


CONCLUSIONS
Elevated CO2 alleviated the inhibitory effect of soil NO3(-) on nodulation and N2 fixation and is likely to lead to greater total N content of field pea growing under future elevated CO2 environments.
Department of Animal, Plant & Soil Sciences, Centre for AgriBioscience, La Trobe University, Melbourne, Vic, 3086, Australia, C.Butterly@latrobe.edu.au C.Tang@latrobe.edu.au.
Clayton R
CR
Butterly
Department of Animal, Plant & Soil Sciences, Centre for AgriBioscience, La Trobe University, Melbourne, Vic, 3086, Australia, Department of Economic Development, Jobs, Transport and Resources, Horsham, Vic, 3401, Australia and.
Roger
R
Armstrong
Faculty of Veterinary and Agricultural Science, The University of Melbourne, Melbourne, Vic, 3010, Australia.
Deli
D
Chen
Department of Animal, Plant & Soil Sciences, Centre for AgriBioscience, La Trobe University, Melbourne, Vic, 3086, Australia, C.Butterly@latrobe.edu.au C.Tang@latrobe.edu.au.
Caixian
C
Tang
D000388:Air; D018533:Biomass; D002245:Carbon Dioxide / Q000494:pharmacology*; D005308:Fertilizers; D007874:Leghemoglobin / Q000378:metabolism; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation / Q000187:drug effects*; D009587:Nitrogen Isotopes; D018532:Pisum sativum / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology; D053204:Root Nodules, Plant / Q000187:drug effects / Q000502:physiology; D012987:Soil / Q000737:chemistry*
D005308:Fertilizers; D007874:Leghemoglobin; D009566:Nitrates; D009587:Nitrogen Isotopes; D012987:Soil; D002245:Carbon Dioxide; D050901:Nitrate Reductase; D009584:Nitrogen
15N; FACE; Nitrogen fixation; Pisum sativum; carbon cycling; climate change; free-air CO2 enrichment; high atmospheric CO2; nitrate; nitrogen cycling