EFFECTS OF ELEVATED CO2 AND WATER-STRESS ON MINERAL CONCENTRATION OF COTTON

Projected increases in atmospheric CO2 concentrations may alter minera l 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) s ystem provided an opportunity to monitor seasonal trends in nutrient s tatus and crude protein content of cotton (Gossypium hirsutum L. cv. D eltapine 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, almost-equ al-to 550 mumol mol-1 and CONTROL, almost-equal-to 370 mumol mol-1) an d two irrigation regimes (100% and 75% replacement of evapotranspirati on) beginning in early July. Cotton leaves, stem, and roots were sampl ed 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 concen trations of leaves, stems and roots were significantly lower in FACE p lants 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 tissu es. There were no significant effects in any of the data because of th e irrigation treatment or the irrigation-CO2 interaction. Reductions i n tissue N and protein concentrations and the increases in the C:N wit h CO2 enrichment have important implications for agricultural and natu ral systems and demand additional research.