Transcription profiling of mycorrhized European beech (Fagus sylvatica L.) roots in response to fertilization with different forms of inorganic nitrogen. Transcription profiling of mycorrhized European beech (Fagus sylvatica L.) roots in response to fertilization with different forms of inorganic nitrogen

Young Fagus sylvatica trees (approximately 7 to 8 years) were collected from a natural regeneration beech forest. The trees were excavated with intact soil cores, roots and top organic layer. The trees were then kept outdoors at the Department of Forest Botany, Georg-August-Universität Göttingen. Plants were protected from rain, and light conditions were matched to those of the natural stand using a shading net; otherwise, plants were exposed to natural climatic conditions. The soil moisture was regularly measured; plants were watered with deionized water as needed to keep soil moisture close to the original conditions. Trees was randomly relocated on a weekly basis throughout the experiment to avoid biasses caused by location or light effects. After 21 weeks, a treatment was applied to understand the physiological mechanisms of inorganic nitrogen uptake and assimilation under conditions of an inorganic nitrogen saturated forest simulation: Plants were fertilized with either a 20 mM solution of KNO3, a 20 mM solution of NH4Cl, or demineralized water (control) for 2 days. On the third day, the trees were harvested. Root tips were immediately shock-frozen in liquid nitrogen and used for RNA extraction.