Root Growth of Winter Wheat under Elevated Carbon Dioxide and Drought

Abstract

With the atmospheric concentration of CO2 increasing, it is important to know how this will affect crop growth. The objective of this study was to determine the effect of enriched CO2 on root growth of winter wheat (Triticum aestivum L. ‘Newton’) under both wellwatered and dry conditions. The wheat was grown for 3 yr in 16 plastic chambers (121 by 92 by 168 cm) in the field under ambient CO2 (340 μL L−1) and elevated levels of CO2 (485, 660, and 825 μL L−1). Each chamber was placed over an underground box (77 by 37 cm at the top; 180 cm deep) containing a Muir silt loam (fine‐silly, mixed, mesic Cumulic Haplustoll). The boxes could be pulled out of the ground for observation of roots. Half of the boxes were maintained at field capacity (0.38 m−3 m−3) (well‐watered or not stressed plants) and half between 0.14 to 0.25 m3 m 3 (drought‐stressed plants). At harvest, root dry weights at different depths and stem dry weight were determined. Roots of plants grown under the three elevated levels of CO2 penetrated to the maximum depth of observation (176 cm) before roots of plants grown under the ambient level. At harvest, the difference in root growth between elevated and ambient levels of CO2 was most pronounced at the top level (0‐ to 10‐cm depth). Roots of drought‐stressed plants grown with 825 μL L−1 CO2 had a greater dry weight than roots of well‐watered plants grown with ambient CO2. The ratio of root to stem weight usually showed no trend (neither increase or decrease) with increasing CO2 concentration. Total dry weight at harvest of well‐watered root grown at ambient CO2 (3‐yr mean: 118 g m−2) was similar to that of drought‐stressed roots grown at the highest level of CO2 (3‐yr mean: 123 g m−2). The results indicated that high CO2 (825 μL L−1) can compensate for restrictions in root growth by drought.