Document: RIC-3-34-42

Interactive effects of temperature and atmospheric CO₂ on nodulation and N₂ fixation of black locust (Robinia pseudoacacia) and red alder (Alnus rubra) seedlings.

THOMAS, R.B.*

West Virginia University, Morgantown, WV 26506, USA ¹

Abstract:
This study tested the hypothesis that elevated atmospheric CO₂ concentrations and elevated temperature would act synergistically to increase biomass production and net N uptake of black locust and red alder through increased rates of N₂ fixation. Seedlings of black locust, inoculated with Rhizobium spp., and red alder, inoculated with Frankia spp., were grown for 70 days in growth chambers with atmospheric CO₂ controlled at 350 or 700 mmol mol^-1 and air temperatures controlled at either 26/20 C (day/night) or 30/24 C. Plants were grown with a complete nutrient solution containing 1 mM N with a low level of ¹⁵N enrichment which was used to determine N source partitioning between N₂ fixation and inorganic N fertilizer uptake. High temperature stimulated nodule number, nodule mass and the specific rate of N₂ fixation of black locust as well as the specific rate of absorption of inorganic N by roots. Elevated CO₂ stimulated the specific rate of N₂ fixation of black locust seedlings but not nodule mass or nodule number. The specific rate of inorganic N uptake by roots was not affected by CO₂ enrichment. Elevated CO₂ stimulated biomass production of red alder but only at the low temperature. High temperature inhibited the growth of red alder seedlings and the capacity to fix N, including nodule mass and number and the specific rate of N₂ fixation. At low temperature, nodule mass of alder was stimulated by CO₂ enrichment but there was no CO₂ stimulation of specific N₂ fixation rate. This study suggests that CO₂ enrichment stimulates the capacity of symbiotic N₂-fixing plants to fix N either through increased nodule production or through increased specific N₂-fixing activity while the effects of increased temperature on N₂ fixation can be either stimulatory or inhibitory.

Keywords: CO₂ enrichment, N₂ fixation

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.