Relative growth rate of rich fen bryophytes
-a greenhouse experiment on common and rare species
Dagmar Kappel Andersen, Rasmus Ejrnæs & Tenna Riis
Background
Rich fens are among the most species rich habitats in the Northern hemisphere, and many rare
and endangered species are restricted to these habitats. During the past century European rich
fen- areas have decreased, and characteristic bryophyte species have become rare. The major
threats to the habitat type are changed hydrology and raised nutrient availability.
Aim: We study the effect of different nutrient levels and water type on the relative growth rate
and tissue nutrient content of two rare (Hamatocaulis vernicosus and Paludella squarrosa) and two
common (Calliergonella cuspidata and Bryum pseudotriquetrum) rich fen bryophytes.
Experiment
Results I
The four species, Bryum pseudotriquetrum (BP), Calliergonella
cuspidata (CC), Hamatocaulis vernicosus (HV) and Paludella
squarrosa (PS) were grown in mixture at three different levels
of nitrogen (addition of 0 mg N/L, 1 mg N/L or 3 mg N/L), three
different levels of phosphorus (addition of 0 mg P/L, 0.05 mg
P/L or 0.1 mg P/L) and two types of water (rain water or
groundwater). The experiment ran for 10 months in an
unheated greenhouse. Relative growth rate (RGR) was
calculated and tissue content of N and P was measured.
Results II
The figure shows the relative percentage
of explained variation (partial R2 ) of
relative growth rate in each species.
The species are very differently impacted
by treatment parameters .
B. pseudotriquetrum
0.81
Water type
5.20
13.15
4.59
N-level
Water type
N-level
36.67
41.19
6.61
P-level
Treatment interactions
Residuals
23.39
24.55
11.07
P. squarrosa
P-level
Treatment
interactions
Side effects
Side effects
Residuals
H. vernicosus
6.79
25.41
30.32
Water type
N-level
17.90
43.76
P-level
Treatment interactions
8.05
Side effects
12.59
Residuals
7.70
The relation between
C/N and C/P differs
between species.
The lower content of N
and P in C. cuspidata
may explain its ability
to maintain a higher
relative growth rate compared to the other species.
C. cuspidata
0.70
32.07
Irrespective of
treatment, C.
cuspidata had
the highest
relative growth
rate, whereas
the two rare
species, P.
squarrosa and H.
vernicosus , had
lowest relative growth rate, which correspond to the species
being restricted to very nutrient poor habitats.
21.51
16.82
6.68
2.47
Side effects include algae cover and total initial dry weight
E-mail: [email protected]
Conclusions
• The high RGR of Calliergonella cuspidata compared to the
other species in this experiment irrespective of nutrient
level offers an explanation to, why the species is much
more common.
• All species, but particularly P. squarrosa, had higher RGR in
ground water compared to rainwater.
• Effects of N and P are not unambiguous, but the two rare
species are most affected by N levels.