Effect of lateral far-red light supplementation on the growth and morphology of birch seedlings and its interaction with mineral nutrition

The effects of lateral far-red light (FR) and nutrient supply on the growth and nitrogen accumulation of silver birch (Betula pendula) seedlings were studied with the objective of testing the following hypotheses: (1) silver birch seedlings grow taller in response to increased FR irradiance received from the side; (2) this response is modulated by the nutritional status of the seedlings; and (3) an increase in lateral FR irradiance, and concomitant decrease in red to far-red photon ratio, affects the carbon and nitrogen economies of the seedlings. Two factorial experiments, each with two levels of mineral nutrient availability and two light treatments (background 'white' light with and without additional lateral FR simulating light reflected by neighbours in a sparse canopy) were done with small seedlings. The two experiments differed in PAR irradiance. The results of these experiments were that (1) stem elongation rate was increased by lateral FR addition, (2) there was no interaction between this effect and the nutritional status of the seedlings, and (3) neither whole plant accumulation of nitrogen nor dry weight increment was affected by lateral FR under either mineral nutrient supply regime.