Interactive effects of elevated CO2 and potassium deficiency on photosynthesis, growth, and biomass partitioning of cotton

In modern cotton production systems, potassium (K) deficiency is one of the major factors limiting lint yield and affecting fiber quality. Although influence of K deficiency on cotton plant physiology and growth and lint yield responses to K fertilizer applications have received intensive studies, it is not clear whether elevated atmospheric CO2 concentration [CO2] affects plant requirements and sensitivity to K. An experiment was conducted in sunlit controlled-environment chambers to determine the interaction effects of elevated [CO2] and K deficiency during squaring and flowering on cotton plant growth, photosynthesis, and biomass accumulation and partitioning. The treatments included two levels of [CO2] (360 and 720 μL L−1) and five levels of K supply (optimum (control) and 40, 20, 5, and 0% of the control K) at each [CO2] level. Elevated [CO2] significantly increased photosynthesis, leaf area and biomass production of K sufficient plants, but did not affect leaf K concentration. Potassium deficiency not only reduced these growth variables but also changed biomass partitioning among plant tissues with the greatest decrease in fruit biomass. There were significant interactive effects of [CO2] × K on leaf area, canopy photosynthesis, and biomass accumulation and partitioning. The stimulation of the physiological and growth parameters observed due to elevated [CO2] was lost under severe K deficiency. Under ambient [CO2], leaf critical K level depended on growth variables measured and was 17 g kg−1 for leaf area expansion and 12 g kg−1 for canopy photosynthesis, stem elongation and biomass accumulation. Plants grown under elevated [CO2] were more sensitive to K deficiency with higher leaf critical K levels. The information from this study is useful for understanding the cotton K requirement in the present as well as in the future higher [CO2] environment and for recommendations of K application.