Relationships between Plug Cell Size and Substrate Quality in the Bedding Pot Plant Impatiens wallerana (Hook. F.)

Abstract

In pot plant production, balancing the air and water content in the medium is one of the largest problems. The ‘root restriction’ effects of the plug cells on seedling growth during nursery could increase after transplant and thus limits pot plant productivity. Two plug cell size (limiting and non-limiting ones) and two growing media were tested. Different concentrations (0, 1.5 and 3.0 kg m-3) of the hydrophilic gel potassium acrylate (Stockosorb®, Evonik, Germany) were added at transplanting to create growing media with different container capacity. The aim of this work was to evaluate the physiological mechanisms involved when two different pre-transplant cell volumes (50- and 288- cells-plug tray-1) and two post-transplant growing media amended with different potassium acrylate concentrations (0, 1.5 and 3.0 Kg m-3) were used. The hypothesis tested was that the negative effects of combined abiotic stress sources (pre-transplant cell volume and growing medium quality) that reduced air-filled porosity and affect Impatiens wallerana growth and yield are mainly associated with a decrease in root size. Our results showed that the root restriction related to cell volume and growing medium quality reduced air-filled porosity but in different magnitude according to the growing medium tested. We found a decrease in the relative rate of leaf area expansion (RLAE), the relative growth rate (RGR), the net assimilation rate (NAR) and glucose content, and an increase in water-holding capacity. We also found positive relationships between the previous mentioned growth parameters and an increase in root dry weight. Since the responses to the different plug cell volume and growing medium to overcome the root restriction were the same as those found in other experiments in plants sprayed with exogenous cytokinins, we speculated that endogenous cytokinins are involved in plant growth.