Nitrogen dynamics and growth of seedlings of an N-fixing tree (Gliricidia sepium (Jacq.) Walp.) exposed to elevated atmospheric carbon dioxide

• Published in: Oecologia 1991-11, Vol.88 (3), p.415-421
• Main Authors: Thomas, R.B, Richter, D.D, Ye, H, Heine, P.R, Strain, B.R
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Animal and plant ecology; Animal, plant and microbial ecology; Atmospherics; Autoecology; Biological and medical sciences; Biomass; Carbon dioxide; carbon dioxide enrichment; Fertilization; Fundamental and applied biological sciences. Psychology; Gliricidia sepium; growth; Leaves; Nitrogen; nitrogen fixation; nodulation; Nodules; Plant roots; Plants; Plants and fungi; Rhizobium; Seedlings
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00317587

Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO₂ and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO₂ partial pressures of 350 and 650 μbar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO₂ when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO₂ enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO₂ enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO₂. In seedlings supplied with soil N, elevated CO₂ increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf δ15N). While CO₂ enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO₂ partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO₂ will depend greatly on plant and soil nutrient status.