Field horsetail (Equisetum arvense)—effects of potassium under different light and nitrogen conditions

Abstract

Field horsetail shoots were severed from the rhizomes and grown hydroponically with and without shade (40 and 190 μmol m–2s–1photosynthetic photon flux) under six different nutrient regimes, by using nutrient solutions with different amounts of nitrogen (N) and potassium (K) (6/42 mmol L–1N; 7/15/24 mmol L–1K). Nutrients were supplied daily with the same volumes for the six different nutrient solutions at exponentially increasing rates corresponding to a maximum relative growth rate (RGR) of 12.5% from days 0 to 31 and 6% from days 32 to 48. RGR was calculated for the highest N and K rate. Photosynthetic rate and stomatal conductance to water vapor were determined on day 48, then the plants were harvested. The fresh weight (FW) and dry weight (DW) of different plant components were determined. Shade completely inhibited growth of tubers and fertile shoots and drastically reduced RGR, average aerial shoot height, and DW of shoots and rhizomes. N supplied at the high rate to unshaded plants increased the growth of all parts or the plant except fertile shoots and tubers. No effects of K were detected at the low N rate, whereas at the high N rate, K significantly increased total DW and belowsurface DW. RGR never exceeded 10% d–1. In the unshaded treatments, the K concentration was higher in aerial shoots, 150 to 240 μmol g–1FW, than in belowsurface organs, 30 to 90 μmol g–1FW. Shoot growth was significantly reduced at shoot K concentrations below 150 to 210 μmol g–1FW, and root growth was significantly reduced at root K concentrations below 30 to 50 μmol g–1FW. K significantly increased maximum net photosynthetic rate, 10 μmol CO2m–2s–1, at light saturation, 1,300 μmol m–2s–1, in unshaded plants, whereas it reduced the light compensation point and respiratory losses of CO2in darkness. It is concluded that field horsetail is a typical sunny habitat species with a rather high K demand.