Elevated CO2 affects plant responses to variation in boron availability
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Effects of elevated CO2 on N relations are well studied, but effects on other nutrients, especially micronutrients, are not. We investigated effects of elevated CO2 on response to variation in boron (B) availability in three unrelated species: seed geranium (Pelargonium x hortorum), barley (Hordeum vulgare), and water fern (Azolla caroliniana).
Plants were grown at two levels of CO2 (370, 700 ppm) and low, medium, and high B. Treatment effects were measured on biomass, net photosynthesis (Pn) and related variables, tissue nutrient concentrations, and B transporter protein BOR1.
In geranium, there were interactive effects (P < 0.05) of B and CO2 on leaf, stem, and total plant mass, root:shoot ratio, leaf [B], B uptake rate, root [Zn], and Pn. Elevated CO2 stimulated growth at 45 μM B, but decreased it at 450 μM B and did not affect it at 4.5 μM B. Pn was stimulated by elevated CO2 only at 45 μM B and chlorophyll was enhanced only at 450 μM B. Soluble sugars increased with high CO2 only at 4.5 and 45 μM B. High CO2 decreased leaf [B] and B uptake rate, especially at 450 μM B. Though CO2 and B individually affected the concentration of several other nutrients, B x CO2 interactions were evident only for Zn in roots, wherein [Zn] decreased under elevated CO2. Interactive effects of B and CO2 on growth were confirmed in (1) barley grown at 0, 30, or 1,000 μM B, wherein growth at high CO2 was stimulated more at 30 μM B, and (2) Azolla grown at 0, 10, and 1,000 μM B, wherein growth at high CO2 was stimulated at 0 and 10 μM B.
Thus, low and high B both may limit growth stimulation under elevated vs. current [CO2], and B deficiency and toxicity, already common, may increase in the future.
KeywordsAzolla Barley Boron stress Boron transporter protein (BOR1) Geranium Nutrients Photosynthesis
This research was supported by the U.S. Department of Agriculture, Agricultural Research Service (SCA 58-3607-4-119 to J. Gray and S.A. Heckathorn). The authors thank Douglas Sturtz and Alycia Pittenger for nutrient analysis.
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