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Sour orange fine root distribution after seventeen years of atmospheric CO2 enrichment

Prior, S.A., Runion, G.B., Torbert, H.A., Idso, S.B., Kimball, B.A.
Agricultural and forest meteorology 2012 v.162-163 pp. 85
Citrus aurantium, biogeochemical cycles, carbon dioxide, crops, loam soils, long term effects, orchards, root water potential, rooting, roots, soil-plant interactions, trees, water supply, Arizona
Long-term (more than 15 years) effects of elevated CO₂ on belowground responses of trees have received limited attention in the literature. We report on a study in which sour orange trees (Citrus aurantium L.) grown in an Avondale loam in Phoenix, AZ, were exposed to ambient and elevated (ambient+300μmolmol⁻¹) levels of atmospheric CO₂ for 17 years. At study termination, soil cores were collected to determine how long-term CO₂ enrichment affected horizontal (0.5, 1.0, 1.5, and 2.0m from each tree) and vertical (0–105cm in 15cm increments) standing crop fine root dry weight and length. Overall, elevated CO₂ increased both root length (35.6%) and root dry weight (39.1%) densities. There was no effect of CO₂ concentration on horizontal root distribution patterns. However, significant CO₂ by depth interactions were noted for both root length and root dry weight densities with differences occurring only in the top two depths. Elevated CO₂ increased fine root length density by 64.5 and 57.2% at the 0–15 and 15–30cm depths. Respective increases for root dry weight were 80.3 and 82.8%. These large responses occurred under water and nutrient supplies typical of orchard conditions and suggest that long-term citrus productivity can be enhanced under future levels of atmospheric CO₂.