Effects of elevated CO2 and water stress on mineral concentration of cotton

Abstract

Projected increases in atmospheric CO2 concentrations may alter mineral and protein levels in plant tissues, systematically affecting growth, nutrient cycling and utilization, residue decomposition, and insect-plant interactions in the future. The free-air CO2 enrichment (FACE) system provided an opportunity to monitor seasonal trends in nutrient status and crude protein content of cotton (Gossypium hirsutum L. cv. Deltapine 77) grown in a natural field setting without the limitations often imposed by growth chambers or reduced rooting volumes. In 1990, plants were exposed to two levels of atmospheric CO2 (FACE, ≈ 550 μmol mol−1 and CONTROL, ≈ 370 μmol mol−1) and two irrigation regimes (100% and 75% replacement of evapotranspiration) beginning in early July. Cotton leaves, stem, and roots were sampled at different times during the season and analyzed for C, N, Ca, K, Mg, P, Cu, Fe, Mn, Zn, B, Mo, Si and protein. The N and protein concentrations of leaves, stems and roots were significantly lower in FACE plants than in CONTROL plants, but C:N ratios were higher for the FACE plants than the CONTROL plants. Some other elements were significantly affected by CO2 enrichment, but not for all dates and all plant tissues. There were no significant effects in any of the data because of the irrigation treatment or the irrigation—CO2 interaction. Reductions in tissue N and protein concentrations and the increases in the C:N with CO2 enrichment have important implications for agricultural and natural systems and demand additional research.