Effect of moss water content
The increase in the
D6S /D6R ratio from low
to high WT (Fig. 2A, 4A) revealed an increase in the
photorespiration/photosynthesis ratio, and thus reduction in net
photosynthesis at the high WT for both S. fuscum and S.
majus . A concomitant decrease inc c/c a from low to high WT
(Fig. 3B) suggests that the increase in the
photorespiration/photosynthesis ratio was driven by a decline inc c. In addition, the lowerc c/c a at high WT is
indicative of higher CO2 diffusion resistance, resulting
from the higher moss water content (Fig. S3). In this respect, our data
supports the hypothesis that the higher water content at high WT limits
CO2 diffusion and therefore C assimilation. This
hypothesis is also supported by earlier reports of reductions in net
photosynthesis with increases in water content (Titus et al .,
1983; Titus & Wagner, 1984; Schipperges & Rydin, 1998) and a negative
relationship between water content andc c/c a (Rice & Giles,
1996; Williams & Flanagan, 1996, 1998).