LB 19-173 - Effects of different levels of potassium nitrate on seed germination rate and toxicity in Pinus radiata

Seed germination is known as the important initial stage of tree growth, it generally shows the environmental sensitivity to abiotic stresses with its performances against seedling growth (i.e., short-period development and courses without photosynthesis).Nitrate (NO3−) is a broadly and commonly used chemical substance for seed germination promotion in many plant species. Whereas investigation of NO3− toxicity from an excessive amount of that has been less explored in seed germination studies.Pinus radiata D. Don, regarded as a fast-growing conifer, plantations are abundant in New Zealand, Chile, Australia, Spain, and South Africa, covering over four million hectares.The seed germination test is an important study to check tree’s initial reactions against abiotic stresses or environmental harm, as well as a cost-effective bioassay to evaluate how radiata pine seeds react to the potential toxicity of dairy farm urine (i.e., nitrate-nitrogen) before evaluation of seedling and canopy scale study.Therefore, this study aims to confirm 1) whether a high concentration of nitrates negatively affects Pinus radiata seed germination rate (i.e., inhibition of seed germination) and velocity of that in response to different and abiotic stress (NO3− toxicity) tolerance; 2) to assess germination speed index (GSI), seedling vigour index (SVI) in response to different NO3− concentrations by time.Key findings of this study are as follows: 1) The concentration between 0 – 10,000 (i.e., 0, 1, 10, 50, 100, 300, 800, 1000, 5000, 8000, 10000) mg (KNO3) L–1 statistically showed a similar germination rate. However, between 10,000 – 20,000 mg (KNO3) L–1 every treatment showed significantly lower germinability (r2 = 0.74), germination speed index (r2 = 0.50) and seedling vigour index (r2 = 0.54) with an increase of each concentration. 2) In KNO3 treatments between 0 – 20,000, most of the germinability was over 51.7 % except for 20,000 mg (KNO3) L–1 (5%). 3) Seedling vigour index (SVI) showed different results in different pre-cold room and moisture treatments. In concentrations 10 and 5000 mg (KNO3) L–1, moisturizing seed treatment in the cold room induced a higher SVI than non-moisturizing seed treatment, but in the concentration of 50 and 300 mg (KNO3) L–1, non-moisturizing seed treatment at the cold room showed better SVI than that of moisturizing seed treatment. It is expected that different KNO3 concentrations might affect the different seed water potential and different water and moisture requirements. However, long-term monitoring is required to quantity specific factors to reveal more independent variables.