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Elevated Carbon Dioxide and Solution Phosphorus in Soil with Vesicular-Arbuscular Mycorrhizal Western Wheatgrass

USDA-ARS, Great Plains Systems Res., 1701 Center Ave., Fort Collins, CO 80526

M. F. Allen

Dep. of Biology and Systems Ecology Res. Group, San Diego State Univ., San Diego, CA 92182

J. J. Jurinak and L. M. Dudley

Dep. of Soil Science and Biometeorology, Utah State Univ., Logan, UT 84322

*Corresponding author.

ABSTRACT

Plants infected by mycorrhizae may exhibit increased root/fungal respiration and elevated concentrations of CO₂ in the root zone. Carbon dioxide is a thermodynamically viable calcium phosphate weathering agent in calcareous soils. The weathering of phosphate minerals in soils releases P to the soil solution. This study was conducted to determine if differences in soil atmosphere CO₂, of consequence to plant P availability, may exist between mycorrhizal and nonmycorrhizal plants. Western wheatgrass (Agropyron smithii Rydb.) was inoculated with raw soil that contained propagules of Glomus spp. and grown in prefumigated soil columns in the greenhouse. Soil atmosphere CO₂ levels for inoculated plants averaged twice those of noninoculated plants in two separate experiments. The mean concentrations of CO₂ in the soil atmosphere, measured at discrete weekly intervals, ranged between 0.13 and 2.63 kPa for inoculated systems and was significantly higher in 10 of 19 sampling events than for noninoculated systems (range of 0.05 to 1.02 kPa). Total plant P uptake was also significantly higher for inoculated compared with noninoculated plants. Total solution P, measured monthly in saturation throughput from experimental columns, was significantly higher in three of seven sampling events for inoculated compared with noninoculated plant systems. In treatments where noninoculated plants were grown under an imposed soil CO₂ regime, total solution P was highly correlated with CO₂. In soil systems where P availability is governed by the solubility of Ca-phosphate minerals, mycorrhizae may contribute to the P nutrition of host plants via a CO₂-enhanced mineral weathering mechanism.

This work was supported in total by Grant BSR-8217358 from the Nat. Science Foundation.

Received for publication July 15, 1988.