PARENT SESSION
Oral Session #10: Elevated CO₂.
Presiding: D. Hileman
Monday, August 5. 8:00 AM to 11:30 AM. Grand Ballroom East, Radisson.

Root nitrogen and water fluxes to the shoot are influenced by growth CO₂.

BASSIRIRAD, HORMOZ^*,1, SEHTIYA, HARBANS², ¹ UNIVERSITY OF ILLINOIS AT CHICAGO, CHICAGO, IL² HARYANA AGRICULTURAL UNIVERSITY RRS, KARNAL, IN

ABSTRACT- Fluxes of NH₄⁺ (J_NH4⁺ ), NO₃^- (J_NO3^- ) and amino acids (J_aa) through the root system are critical factors regulating N supply to the shoot. These fluxes are determined not only by the active loading of solutes into the xylem, but also by volume flow (J_v) which is governed by the gradient in pressure potential (P) and the hydraulic conductivity (L_P) of the root system. To evaluate the effects of elevated CO₂on various components of N transport to the shoot, we grew seven tree species from seeds under ambient (36) and double the ambient (72 Pa) CO₂ partial pressures. The species tested included four conifers and three broadleaf species. After 8 months of treatment, intact decapitated roots were placed inside a pressure chamber and pressurized to a P of 0.4 MPa to induce flow. L_P was calculated from the ratio of the J_v and the hydrostatic pressure gradient while N fluxes were calculated from the product of concentration and J_v. Overall, L_P was significantly lower in response to CO₂ enrichment, but this effect was significant in only three of the seven species. Elevated CO₂ did not affect J_NH4⁺ and J_NO3^- in broadleaf species, but reduced them in conifers to about 30% of those observed in ambient grown plants. Elevated CO₂ significantly increased J_aa to the shoot in conifers, but did not affect it in broadleaf species. The results have important implications for plant water and nutrient balances in responses to CO₂ enrichment.

KEY WORDS: Root hydraulic conductivity, Ammonium flux, Nitrate flux, Amino acid fluxes