Epsilon Open Archive

Abstract

Even though the capacity of plants to absorb organic N compounds has been known since
the 1940.s it was not until recently that these N sources were recognized as a potentially
important source of N for plants. Thus, the classical paradigm that plants only use inorganic
N compounds and are forced to play a passive role acquiring N in excess of microbial demand
is today questioned. However, despite the accumulating amounts of studies suggesting
that plants have the capacity to absorb organic N at comparable rates to inorganic N the
quantitative importance of organic-N, as opposed to inorganic N, is still not understood. In
this thesis the focus has been to investigate the abundancy, uptake and growth of amino acids
in two economically important conifer species Scots pine (Pinus sylvestris L.) and Norway
spruce (Picea abies (L.) Karst.). Moreover, we also tried to examine to what extent amino
acids may contribute to the N budget of field grown Scotst pine seedlings. The results show
that Scots pine seedlings grown in a dry heath forest have acces to comparable or higher soil
solution concentration of free amino acids N compare to inorganic N sources. The seedlings
were also able to absorb amino acid N at the same or higher rates as inorganic N sources
both when these were supplied at higher concentration in greenhouse grown seedlings and at
lower more ecological relevant concentratons in field grown seedlings. Moreover, our growth
experiments suggested that amino acids are capable of supporting similar or even higher
growth in Scots pine seedlings compared to a commercial fertilizer based on NO₃⁻ and NH₄+.
The use of arginine as a source of N for growth of Scots pine seedling were also recorded to
give a much smaller N loss compared to the commercial fertilizer due to a strong adsorption
to the growth substrate. In all the results presented in this thesis strongly suggests that amino
acids is an important N source in the N economy of Scots pine and Norway spruce seedlings
and that these N sources may be a poteential alternative to inorganic N sources for comersial
seedling growth.