Biomass density, height increment and water content
For further assessment of possible morphological effects of observed
responses to increasing atmospheric CO2 on S.
fuscum , we measured its biomass density (total biomass dry weight per
volume) and height increment under all the test conditions (Fig. 3E, F).
No effect of atmospheric CO2 on biomass density was
observed, instead the variation in density (4.1 to 42.4 g
dm-3) was mostly explained by WT (45%,P< 0.001), light intensity (34%,P< 0.001) and the interaction between WT and light
(14%, P< 0.001, Table 1). Raising the WT decreased
biomass density by 41-71%, whereas light intensity increased it 2.1- to
3.5-fold at low WT and 1.6- to 2.6-fold at high WT (Fig. 3E).
Most of the variation in height increment (0.04-0.26 mm
d-1) was explained by temperature (51%,P< 0.001) and light intensity (24%,P< 0.001), while the interactions between light and WT
or CO2 as well as temperature and WT or
CO2 made minor contributions (each 2-3%,P <0.05, Table 1). Increasing the temperature increased
the height increment 2.4- to 4.5-fold (Fig. 3F), while increasing the
light intensity resulted in ~0.6- and
~0.35-fold reductions in the height increment at low and
high WT, respectively. Increasing
atmospheric CO2 significantly reduced height increment
by 0.19 to 0.35-fold only at the high temperature and low light
treatment, at low WT (Fig. 3F, Fig. S2).
S. fuscum ’s water content was consistently 4-9 % lower at the
high CO2 level, but CO2 only explained a
small amount of the total variation (6.6-23.4 g g-1)
in its water content (1%, P =0.006; Table S2, Fig. S3).
Most of the variation was
explained by WT (83%, P <0.001), temperature (5%,P <0.001), and the interactions between WT and
temperature (6%, P <0.001) and between WT and light
(3%, P <0.001, Table S2). At low WT, the water content
varied between 7.4 and 10.6 g g-1, within the reported
optimal range for photosynthesis (6-10 g g-1: Silvola
& Aaltonen, 1984; Schipperges & Rydin, 1998). At high WT, the water
content was between 15.4 and 22.3 g g-1, far outside
the optimal range for photosynthesis (Fig. S3).