PhD Summary
Abstract
The Influence of Ion Accumulation on Growth and Development of Roses and Chrysanthemums in Solution Culture


Glenn L. Roberts                                                                                                                                        Supervisors:
University of Guelph, 2001                                                                                                                        M. A. Dixon & B. Grodzinski


The management of nutrition in recycling hydroponic systems requires close attention to a number of variables for quality and production to be sustained in greenhouse production.

Case studies of representative commercial systems over 2 years provided background and indicated specific ion accumulations which required further detailed study. Water from
ponds, culverts and ditches was sampled and analysed for nitrogen, phosphate, chloride and sodium. Three types of ponds were sampled, including, clear margin, semi-vegetated and vegetated ponds. Chloride and sodium were found to accumulate under certain conditions. These were subjected to detailed trials in the greenhouse. In addition, the ecological context of recycled solution management was found to influence the quality of the solution. Catchment ponds supporting diverse vegetation tended to maintain higher water quality than ponds with no marginal vegetation.
Chloride levels up to 1600 mgl-1 had no detrimental effects on yield of Rosa hybrida cv. Kardinal even though tissue concentration of chloride was 6477 mgkg-1 in the plants treat with 1600 mgl-1 chloride. Yield averaged 6 blooms per plant and 6.2 blooms per plant for controls and 1600 mgl-1 respectively. Vase life averaged 14.87 and 14.5 days for controls and 1600 mgl-1 respectively. Since no detrimental effects were seen form the potassium chloride source, further experiments were carried including sodium chloride and calcium chloride.

Similar rose plants were treated with potassium chloride, sodium chloride or calcium chloride at a rate of 1000 mgl-1 chloride in each case. Roses were grown for two crop cycles in a
model system. After the first crop cycle, no negative effects were observed on plants from any treatment. However, after the second crop cycle, symptoms became evident on plants from the sodium chloride treatment. Dry weights of both leaves and stems were significantly lower on plants treated with sodium chloride in the second crop cycle.

Chrysanthemum morifolium cv. Yellow Favour plants were treated with potassium chloride, sodium chloride or calcium chloride at a rate of 1000 mgl-1 chloride in each case. Damage was observed on plants treat with sodium chloride, but not on other treated plants, suggesting that it is the counter ion, sodium, that is having the most negative impact on plants. All salt treated plants had significantly more foliar chloride than the controls but levels of chloride in treated plants were similar to each other. Sodium, potassium and calcium were significantly higher in tissue of plants treated with the salt containing each particular cation.

Since it was apparent that sodium was having the major negative impact on plant growth, roses and chrysanthemums, both plants were treated with sodium salts including sodium chloride and sodium sulphate. Since these salts significantly increased the EC of the solution, standard nutrient solutions with EC's equivalent to the sodium salt solutions were included in the study. For both plant species, lowest fresh wieghts were observed on plants from the 30mMol sodium sulphate and the highest EC treatments. Plants from lower sodium sulphate concentrations and lower EC treatments showed an increase in fresh weight. Plants from the 30mMol sodium sulphate treatments showed no signs of chlorosis and were as green as controls.
Both chrysanthemums and roses were treated with various salts of sodium and chloride and placed in custom made
NCER chambers and exposed to increasing light levels. Plants exposed to the higher levels of sodium and sulphate showed maximum NCER above or equal to control plants. Light compensation points were similar for in all cases.