2018 ASHS Annual Conference

Plants experiencing a phosphorus (P) deficiency commonly develop a red to purple coloration of the foliage. This pigmentation is typically attributed to foliar anthocyanins, and the relationship between P nutrition and anthocyanin accumulation is well known. Betacyanins are another red pigment produced in certain species that do not produce anthocyanins, but the relationship between P nutrition and betacyanin accumulation is not documented. We conducted this study to record the effects of P nutrition on the betacyanin concentration and subsequent foliar coloration of alternanthera [Alternanthera brasiliana (L.) Kuntze]. In an initial experiment, we grew ‘Purple Prince’ alternanthera with P concentrations of 0, 2.5, 5, 10, and 20 mg·L^-1 P. After four weeks, we restricted half of the plants from each non-zero concentration to 0 mg·L^-1 P, resulting in nine total treatments. In further experiments, we grew ‘Brazilian Red Hots’ and ‘Little Ruby’ alternanthera with the same treatments plus three additional fertilization treatments where plants initially grown with > 2.5 mg·L^-1 P were restricted to 2.5 mg·L^-1 P. Plants grown without P for the duration of the study were dark red or purple in coloration and had high concentrations of betacyanins. Alternanthera grown with high P concentrations for the duration of the study had the lowest betacyanin concentrations and exhibited less red and more green coloration as measured by a handheld colorimeter. This demonstrates that betacyanin accumulation is affected by P nutrition similarly to anthocyanin accumulation. Alternanthera grown with low or restricted P fertilization were stunted compared with those that were grown with sufficient P. Plants that were initially grown with 10 mg·L^-1 P but then restricted to 0 mg·L^-1 P also developed a dark red coloration and accumulated high concentrations of betacyanins, but were not stunted. This indicates that betacyanin accumulation may be enhanced without compromising growth. These findings may be used to improve fertilizer recommendations to enhance the foliar coloration and aesthetic appeal of horticultural species such as alternanthera.