Root responses to different forms of nitrogen

In the boreal forest, the ecosystem is often limited by soil nitrogen availability, and forest fertilisation is one strategy to increase short-term forest production. But the nitrogen in the soil exists in several chemical forms, both organic and mineral, and behaves differently in the ecosystem. In the boreal forest soil, most of the nitrogen is found as immobile organic nitrogen. The more mobile mineral nitrogen on the other hand, makes up a smaller part of the soil nitrogen pool. 

Since the different chemical forms of nitrogen behave differently in the soil, we want to test the hypothesis that the plant roots' strategy to efficiently acquire nitrogen is different, depending on the nitrogen form available. 

Traditionally, fertilisation is done with mineral nitrogen. That means that the observed fertilisation effect could be because the nitrogen profile in the soil has transitioned from mainly organic nitrogen to mineral nitrogen. That is, the observed effect of fertilisation, with increased aboveground growth, might not only be the amount of nitrogen added, but also the form of nitrogen.