Interplay between N-form and N-dose influences ecosystem effects of N addition to boreal forest

Per-Ola Hedwall,Takahide Ishida,Linda Gruffman,Torgny Näsholm,Annika Nordin,Tomas Lundmark,Fredrik From

doi:10.1007/s11104-017-3444-1

Per-Ola Hedwall, Takahide Ishida + Show 5 more

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https://doi.org/10.1007/s11104-017-3444-1

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Abstract

AimsNitrogen (N) addition effects on boreal forest ecosystem are influenced by an interplay between N-form and N-dose. We hypothesize that trees take up organic N more efficiently than inorganic N and that unwanted side-effects of organic N are smaller. We predicted that 1) the tree growth response to arginine (ARG) addition is larger than to ammonium-nitrate (AN) and, 2) understory vegetation and ectomycorrhizal (EcM) changes following ARG addition are smaller than following AN addition.MethodsWe investigated the effects of AN and ARG addition (50 and 150 kg N ha−1) during five years on tree growth, understory vegetation and EcM fungi in a Pinus sylvestris L. forest (c 50 years old) in northern Sweden.ResultsN addition increased tree growth and changed understory vegetation composition with few significant differences between AN and ARG. Differences in responses mainly occurred for the bryophyte Pleurozium schreberi which decreased more from ARG, and for EcM sporocarps, which sharply declined from AN, but not from ARG.ConclusionsWe found very few differences in responses between AN and ARG addition with the exception of EcM and bryophytes. These species groups have several key functions in boreal forests and the differences in responses merits further investigations.

Highlights

We investigated the effects of AN and ARG addition (50 and 150 kg N ha−1) during five years on tree growth, understory vegetation and EcM fungi in a Pinus sylvestris L. forest (c 50 years old) in northern Sweden
For more than a decade it has been known that conifer seedlings such as Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) can be cultivated efficiently with nitrogen (N) supplied in the form of the amino acid arginine (ARG). (Öhlund and Näsholm 2001, 2002; Gruffman et al 2012)
Independently of N-form or dose, elevated amounts of ammonium retained on the ion exchange capsules during the growth season in the year of N addition (2008) (Fig. 2)

Summary

Introduction

For more than a decade it has been known that conifer seedlings such as Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) can be cultivated efficiently with nitrogen (N) supplied in the form of the amino acid arginine (ARG). (Öhlund and Näsholm 2001, 2002; Gruffman et al 2012). It has been demonstrated that root uptake rates of ARG is substantially higher than that of ammonium or nitrate (Öhlund and Näsholm 2001; Gruffman et al 2013; Oyewole et al 2016). Numerous shortterm uptake studies have confirmed a high capacity of boreal forest plants (Näsholm et al 1998; Nordin et al 2001; Persson et al 2003) as well as temperate trees (Scott and Rothstein 2011) to take up different amino acids. Ammonium is the main inorganic N form in boreal forest soils and many boreal plant species prefer ammonium over nitrate (Wallander et al 1997; Marschner et al 1991; Nordin et al 2001). Nitrate uptake may even be inhibited by the addition of ammonium (Marschner et al 1991; Gruffman et al 2014), some understory species, like the grass Avenella flexuosa (L.) Drejer, have a high capacity for nitrate uptake (Nordin et al 2006)

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