Abstract
Endophytic nitrogen-fixing bacteria have been detected and isolated from the needles of conifer trees growing in North American boreal forests. Because boreal forests are nutrient-limited, these bacteria could provide an important source of nitrogen for tree species. This study aimed to determine their presence and activity in a Scandinavian boreal forest, using immunodetection of nitrogenase enzyme subunits and acetylene-reduction assays of native Scots pine (Pinus sylvestris L.) needles. The presence and rate of nitrogen fixation by endophytic bacteria were compared between control plots and fertilized plots in a nitrogen-addition experiment. In contrast to the expectation that nitrogen-fixation rates would decline in fertilized plots, as seen, for instance, with nitrogen-fixing bacteria associated with bryophytes, there was no difference in the presence or activity of nitrogen-fixing bacteria between the two treatments. The extrapolated calculated rate of nitrogen fixation relevant for the forest stand was 20 g N ha-1 year-1, which is rather low compared with Scots pine annual nitrogen use but could be important for the nitrogen-poor forest in the long term. In addition, of 13 colonies of potential nitrogen-fixing bacteria isolated from the needles on nitrogen-free media, 10 showed in vitro nitrogen fixation. In summary, 16S rRNA sequencing identified the species as belonging to the genera Bacillus, Variovorax, Novosphingobium, Sphingomonas, Microbacterium and Priestia, which was confirmed by Illumina whole-genome sequencing. Our results confirm the presence of endophytic nitrogen-fixing bacteria in Scots pine needles and suggest that they could be important for the long-term nitrogen budget of the Scandinavian boreal forest.
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Claims 5
Claim · model-written summary
Nitrogen addition did not change the presence of endophytic nitrogen-fixing bacteria in Scots pine needles.
- Taxon
- Scots pine
Pinus sylvestrise1 - Treatment
- fertilized plotse2
- Interactor
- nitrogen-fixing bacteriae0symbiont
- Outcome
- presence or activity of nitrogen-fixing bacteriae0
- Direction
- no differencee0
- Comparator
- control plotse2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there was no difference in the presence or activity of nitrogen-fixing bacteria between the two treatments”
e1“native Scots pine (Pinus sylvestris L.) needles”
e2“control plots and fertilized plots”
Claim · model-written summary
Nitrogen addition did not change activity of endophytic nitrogen-fixing bacteria in Scots pine needles.
- Taxon
- Scots pinePinus sylvestrise1
- Treatment
- fertilized plotse2
- Interactor
- nitrogen-fixing bacteriae0symbiont
- Outcome
- activity of nitrogen-fixing bacteriae0
- Direction
- no differencee0
- Comparator
- control plotse2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there was no difference in the presence or activity of nitrogen-fixing bacteria between the two treatments”
e1“native Scots pine (Pinus sylvestris L.) needles”
e2“control plots and fertilized plots”
Claim · model-written summary
The estimated forest stand nitrogen fixation rate was 20 g N ha-1 year-1.
- Taxon
- Scots pinePinus sylvestrise1
- Outcome
- rate of nitrogen fixation relevant for the forest stande0
- Value
- 20 g N ha-1 year-1e0
Not reportedInteractor
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The extrapolated calculated rate of nitrogen fixation relevant for the forest stand was 20 g N ha-1 year-1”
e1“native Scots pine (Pinus sylvestris L.) needles”
Claim · model-written summary
Ten of thirteen candidate bacterial colonies isolated from pine needles fixed nitrogen in vitro.
- Taxon
- Scots pinePinus sylvestrise1
- Interactor
- nitrogen-fixing bacteriae0symbiont
- Outcome
- in vitro nitrogen fixatione0
- Value
- 10e0
- Qualifier
- 13 coloniese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“of 13 colonies of potential nitrogen-fixing bacteria isolated from the needles on nitrogen-free media, 10 showed in vitro nitrogen fixation”
e1“native Scots pine (Pinus sylvestris L.) needles”
Claim · model-written summary
Sequencing identified bacterial isolates in six genera.
- Taxon
- Scots pinePinus sylvestrise1
- Interactor
- Bacilluse0symbiont
- Second interactor
- VariovoraxVariovoraxe0symbiont
- Outcome
- genera Bacillus, Variovorax, Novosphingobium, Sphingomonas, Microbacterium and Priestiae0
- Qualifier
- Novosphingobium, Sphingomonas, Microbacterium and Priestiae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“16S rRNA sequencing identified the species as belonging to the genera Bacillus, Variovorax, Novosphingobium, Sphingomonas, Microbacterium and Priestia, which was confirmed by Illumina whole-genome sequencing”
e1“native Scots pine (Pinus sylvestris L.) needles”