Carbon dioxide enrichment improves growth, water relations and survival of droughted honey mesquite (Prosopis glandulosa) seedlings

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Tree Physiology, 16:817–823

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Carbon dioxide enrichment improves growth, water relations and survival of droughted honey mesquite (Prosopis glandulosa) seedlings

H. Wayne Polley, Hyrum B. Johnson, Herman S. Mayeux, Charles R. Tischler and Daniel A. Brown

Grassland, Soil and Water Research Laboratory, USDA, Agricultural Research Service, Temple, Texas 76502, USA / Received April 4, 1996

Summary

Low water availability reduces the establishment of the invasive shrub Prosopis on some grasslands. Water deficit survival and traits that may contribute to the postponement or tolerance of plant dehydration were measured on seedlings of P. glandulosa Torr. var. glandulosa (honey mesquite) grown at CO₂ concentrations of 370 (ambient), 710, and 1050 µmol mol^–1. Because elevated CO₂ decreases stomatal conductance, the number of seedlings per container in the elevated CO₂ treatments was increased to ensure that soil water content was depleted at similar rates in all treatments. Seedlings grown at elevated CO₂ had a greater root biomass and a higher ratio of lateral root to total root biomass than those grown at ambient CO₂ concentration; however, these seedlings also shed more leaves and retained smaller leaves. These changes, together with a reduced transpiration/leaf area ratio at elevated CO₂, may have contributed to a slight increase in xylem pressure potentials of seedlings in the 1050 µmol mol^–1 CO₂ treatment during the first 37 days of growth (0.26 to 0.40 MPa). Osmotic potential was not affected by CO₂ treatment. Increasing the CO₂ concentration to 710 and 1050 µmol mol^–1 more than doubled the percentage survival of seedlings from which water was withheld for 65 days. Carbon dioxide enrichment significantly increased survival from 0% to about 40% among seedlings that experienced the lowest soil water content. By increasing seedling survival of drought, rising atmospheric CO₂ concentration may increase abundance of P. glandulosa on grasslands where low water availability limits its establishment.

Keywords: atmospheric CO₂, leaf shedding, osmotic potential, root biomass, water deficit, xylem pressure potential.