Nutrient solution concentration affects whole-plant CO2 exchange and growth of subirrigated pansy

To determine the effect of fertilizer concentration on plant growth and physiology, whole-plant C exchange rates of pansies (Viola x wittrockiana Gains.) subirrigated with one of four fertilizer concentrations were measured over 30 days. Plants were watered with fertilizer solutions with an electrical conductivity (EC) of 0.15, 1.0, 2.0, or 3.0 dS.m(-1) (N at 0, 135,290, or 440 mg.L-1, respectively). Plants watered with a fertilizer solution with an EC of 2 dS.m(-1) had the highest shoot dry weight (DW), shoot to root ratio, leaf area, leaf area ratio (LAR), and cumulative C gain at the end of the experiment compared to those watered with a solution with a higher or lower EC. Shoot tissue concentrations of N, P, K, S, Ca, Fe, Na, and Zn increased linearly with increasing fertilizer concentration. A close correlation between final DW of the plants and the measured cumulative C gain (CCG) (r(2) = 0.98) indicated that the C exchange rates were good indicators of plant growth. There were quadratic relationships between fertilizer EC and gross photosynthesis, net photosynthesis, and dark respiration, starting at 13, 12, and 6 days after transplanting, respectively. Although plants fertilized with a fertilizer solution with an EC of 2 dS.m(-1) had the highest C exchange rates, the final differences in shoot DW and CCG among ECs of 1.0, 2.0, and 3.0 dS.m(-1) were small and it appears that pansies can be grown successfully with a wide range of fertilizer concentrations. Plants with a high LAR also had higher DW, suggesting that increased growth was caused largely by increased light interception. A detrimental effect of high fertilizer concentrations was that it resulted in a decrease in root DW and a large increase in shoot to root ratio.